Author Topic: BG7TBL FA1 and FA2 frequency analyzers  (Read 8164 times)

0 Members and 2 Guests are viewing this topic.

Offline texaspyro

  • Super Contributor
  • ***
  • Posts: 1304
BG7TBL FA1 and FA2 frequency analyzers
« on: August 30, 2019, 08:21:06 pm »
The FA1 is a small, USB powered frequency counter.   You supply it with a 10 MHz reference and an input frequency of 1 .. 80 MHz.   It outputs a text string of the measured frequency every second.  They cost around $80 .. $120.

Apparently there is a PLL inside... the text string has a "PLL unlock" flag.  There is no info on how it works and I have not opened mine up.

I did a simple noise test on one where the input and ref clocks were from a Tbolt.  It looks like the measurement noise is around +/- 0.0002 Hz.

Lady Heather can now read it.  Attached is a screen capture of the noise test.
« Last Edit: September 29, 2019, 01:14:53 am by texaspyro »
 
The following users thanked this post: jpb, edavid, citizenrich

Offline ramon

  • Regular Contributor
  • *
  • Posts: 56
  • Country: tw
Re: BG7TBL FA1 frequency analyzer
« Reply #1 on: August 31, 2019, 09:58:44 am »
So how good is this device compared to others? I guess that it might be a very impressive number, otherwise you wouldn't had post this.
I can foresee a price increase on ebay of 200% due to eevblog effect.   

I have a 53131A, how do I need to configure Lady Heater to make this same test?
If I don't get a better noise ... I will be start looking the auction site to buy this new toy   :palm:  :-DD
 

Offline texaspyro

  • Super Contributor
  • ***
  • Posts: 1304
Re: BG7TBL FA1 frequency analyzer
« Reply #2 on: September 01, 2019, 05:28:04 am »
Ok, I opened it up...                                                                                       

Circuit uses:
a couple of 74LVÇ1G04 chips as input squarers.
Altera MAX-II EPM570T100CSN FPGA
Atmel Mega328 processor
FTDI USB interface
Analog Devices 8028AR dual op amp.
Some 10 pin chip with unreadable markings,
1117 voltage regulator
There are places for ISP and JTAG headers.
 

Offline jpb

  • Super Contributor
  • ***
  • Posts: 1622
  • Country: gb
Re: BG7TBL FA1 frequency analyzer
« Reply #3 on: September 01, 2019, 02:19:40 pm »
On the face of it, it would seem to be a relatively cheap means of getting ADEV plots. (Very cheap for the given accuracy.)

The PLL aspect worries me though. There is an established technique of getting accurate ADEV measurements by locking the oscillator under test to the reference and then tracking the Voltage needed to maintain lock.

http://www.ke5fx.com/tpll.htm

My guess is that it has a rational number type digital division in the PLL and maintains lock by changing the divisor or multiplier by a few bits up or down. It would be interesting to know how well it works with two separate sources - when doing a noise measurement with a split source it probably can maintain lock indefinitely but for two separate sources it may show steps or a bit of drift from time to time. For ADEV measurements the lock needs to be maintained but for a steady state measurement of frequency it will be less important.

The output indicates lost lock with an asterix (*) according to the ebay page I looked at. Texaspyro can you say how often in the output the stars appear? I suppose with a noise measurement where the same signal is applied to both terminals it should never lose lock.
 

Offline Yansi

  • Super Contributor
  • ***
  • Posts: 2677
  • Country: 00
  • STM32, STM8, AVR, 8051
Re: BG7TBL FA1 frequency analyzer
« Reply #4 on: September 01, 2019, 02:37:02 pm »
Interesting they could not implement it all within a 570 LE  FPGA and need an arduino to help.
 

Offline texaspyro

  • Super Contributor
  • ***
  • Posts: 1304
Re: BG7TBL FA1 frequency analyzer
« Reply #5 on: September 01, 2019, 06:25:21 pm »
I had it connected to an old Trak 8820 GPSDO that can output a programmable 1/5/10 MHz signal.  Switching between freqs caused 2 seconds of unlock messages.

The tight pll technique usually requires a DAC and ADC... there are none on the board.

As far as the FPGA vs Atmega chip...   I'm pretty sure there is floating point math and ASCII formatting going on in ATMEGA that would be a real pain in the FPGA.

Attached is a plot in measuring the Trak 8820.
 
The following users thanked this post: jpb

Offline texaspyro

  • Super Contributor
  • ***
  • Posts: 1304
Re: BG7TBL FA1 frequency analyzer
« Reply #6 on: September 07, 2019, 01:16:01 am »
I did a comparison of the performance of the TAPR-TICC/TADD2-Mini divider and the BG7TBL FA1 frequency analyzer performance.  The reference clock for both devices was a 5071A cesium.   The device being tested was a Nortel NTPX GPSDO 10 MHz output.  Attached are screen dumps of the two Lady Heather runs.

The noisy orange plot in the TICC run is the measured frequency offset from 10 MHz.   The noisy blue plot in the FA1 run is the measured frequency offset from 10 MHz.  (Note the scale factor differences)    Looking at the SPAN value (the difference between the max and min frequency measurements) shows that the FA1 noise level is around 4 times higher than the TICC.  The FA1 ADEV measurements are around 3 time higher.   The FA1 may be better than the TICC at lower (<50 second) tau,  but I have no way to verify that.  The FA1 screen dump includes a histogram of the frequency measurements.

One issue with the FA1 is that it seems to have an inherent frequency measurement bias of around -0.0002 Hz.  See the "avg#" value in the lower left corner of the plot.  I get nearly the same bias values when measuring 1, 5, and 10 MHz signals.   (I added a setting in Lady Heather to specify a measurment bias correction value).  It is interesting that the same -0.0002 Hz bias was present in the original BG7TBL GPSDO.

TAPR TICC pros:
high performance
lots of measurement and configuration options
open source design

TAPR TICC cons:
more expensive
requires external dividers to measure frequency (and a second power supply)
no case

FA1 pros:
inexpensive (around $100), decent bang for the buck
no frequency divider needed, 1 .. 80 MHz range
very simple operation (no configuration needed)
nice small unit with an extruded metal case.

FA1 cons:
only measures frequency (no way to test 1PPS signals)
around 3X-4x less performance than the TAPR TICC.
closed source "black box"
inherent minor frequency measurement offset

Lately BG7TBL has released the FA2.   This appears to be similar to the FA1, but it has some VERY nice features including a basic 1 Hz .. 200 MHz range plus a 30:1 pre-scaler allowing measurements to 6 GHz.  It as an LCD display, an internal (adjustable) OCXO and external freq ref input, reference output, selectable 0.1/1/10 second timebase.  Costs around $120 (with power supply)    If the FA2 measurement performance matches the FA1, it would be greatly preferable over the FA1.   I have an FA2 on the way.
 
The following users thanked this post: jpb, edavid, harha, 2N3055, Jacon, MegaVolt, syau

Offline edigi

  • Regular Contributor
  • *
  • Posts: 78
  • Country: hu
Re: BG7TBL FA1 frequency analyzer
« Reply #7 on: September 07, 2019, 08:36:32 am »
From where have you ordered the FA2?
I've ordered mine close to 2 weeks ago and I don't see anything shipped yet..

By based on the description it seems to have indeed nice features, although statistics does not seem to be very well worked out, at least I'd expect some ADEV value shown + statistics of significantly more measurements not just 4 or 5 that are shown on all of the pictures that I've seen.
« Last Edit: September 07, 2019, 09:27:22 am by edigi »
 
The following users thanked this post: harha

Offline texaspyro

  • Super Contributor
  • ***
  • Posts: 1304
Re: BG7TBL FA1 frequency analyzer
« Reply #8 on: September 08, 2019, 02:13:21 am »
I did a measurement of the arrival times of the freq measurement data....  around 1110 msecs... so it looks like the consecutive measurement cycles have around a 110 msec dead time between them.
 

Offline harha

  • Contributor
  • Posts: 15
  • Country: dk
Re: BG7TBL FA1 frequency analyzer
« Reply #9 on: September 10, 2019, 05:21:00 pm »
Hi
Are you sure the fa-2 will work with lady heather-timelab?
Anyway have ordered one --when you get yours please tell us how it works
Regards
Hardy
 

Offline edigi

  • Regular Contributor
  • *
  • Posts: 78
  • Country: hu
Re: BG7TBL FA1 frequency analyzer
« Reply #10 on: September 20, 2019, 12:50:36 pm »
It seems that FA2 units have started to ship this week (at least this has happened with what I've bought) so the lucky ones can maybe check it already next week (unfortunately shipping to my country is usually rather slow).

An interesting question to be answered would be that what the USB port at the back can be used for? None of the descriptions that I've found describe it...
 

Offline 2N3055

  • Super Contributor
  • ***
  • Posts: 2112
  • Country: hr
Re: BG7TBL FA1 frequency analyzer
« Reply #11 on: September 20, 2019, 01:39:18 pm »
Hi
Are you sure the fa-2 will work with lady heather-timelab?
Anyway have ordered one --when you get yours please tell us how it works
Regards
Hardy
Are you're talking to teksaspyro ?
If yes, then yes,he should know. He wrote Lady Heather .  :-DD
 
The following users thanked this post: harha

Offline texaspyro

  • Super Contributor
  • ***
  • Posts: 1304
Re: BG7TBL FA1 frequency analyzer
« Reply #12 on: September 20, 2019, 07:10:35 pm »
An interesting question to be answered would be that what the USB port at the back can be used for? None of the descriptions that I've found describe it...

If it's like the FA1, it outputs an ASCII stream of the freq measurements.

My status show "import customs clearance completed".
 

Offline Theboel

  • Regular Contributor
  • *
  • Posts: 223
  • Country: id
Re: BG7TBL FA1 frequency analyzer
« Reply #13 on: September 20, 2019, 10:45:35 pm »
its a very nice equipment I hope someday they will release a box that can measure phase noise with less than 150USD tag price  :-DD :-DD :-DD :-DD
« Last Edit: September 20, 2019, 11:38:56 pm by Theboel »
 

Offline Electro Fan

  • Super Contributor
  • ***
  • Posts: 1913
Re: BG7TBL FA1 frequency analyzer
« Reply #14 on: September 21, 2019, 09:29:01 pm »
its a very nice equipment I hope someday they will release a box that can measure phase noise with less than 150USD tag price  :-DD :-DD :-DD :-DD

Maybe BG7TBL will introduce such a product :)

In the meantime it will be interesting to hear from early users of the FA-2 about how it performs.
 

Offline harha

  • Contributor
  • Posts: 15
  • Country: dk
Re: BG7TBL FA1 frequency analyzer
« Reply #15 on: September 26, 2019, 11:51:01 pm »
Hi
Mine arrived at copenhagen airport--so maybe i can test it tomorrow :popcorn:
 

Offline texaspyro

  • Super Contributor
  • ***
  • Posts: 1304
Re: BG7TBL FA1 frequency analyzer
« Reply #16 on: September 27, 2019, 01:19:45 am »
Miy FA2 came in today.   A very quick test shows that it works.  It does not appear to have the -0.0002 Hz freq measurement bias that the FA1 has.

The 0.1 second gate time mode is useless... there appears to be  a 300 msec dead time between measurements in 0.1 (and 10 sec) gate time modes so you only get a new reading every 400 msecs.  10 second gate time produces a reading every 10300 msecs.  1 sec gate time outputs readings every 1100 msecs (like the FA1).

It auto-detects the presence of an external reference... no way to manually switch between internal and exterrnal references.  I have not done any testing on the internal ref or the high freq channel.

The screen shows a LPF setting and a 50 ohm setting... no idea if these are switchable.... there is no documentation. 

The screen shows the input signal level.
« Last Edit: September 27, 2019, 01:24:54 am by texaspyro »
 

Offline edigi

  • Regular Contributor
  • *
  • Posts: 78
  • Country: hu
Re: BG7TBL FA1 frequency analyzer
« Reply #17 on: September 27, 2019, 06:35:25 am »
The screen shows the input signal level.

Do you mean for the BNC input only or for the SMA input as well?
Even if it works only for the BNC (as I suspect), it's a nice addition...
 

Offline texaspyro

  • Super Contributor
  • ***
  • Posts: 1304
Re: BG7TBL FA1 frequency analyzer
« Reply #18 on: September 27, 2019, 06:40:54 am »
The screen shows the input signal level.

Do you mean for the BNC input only or for the SMA input as well?
Even if it works only for the BNC (as I suspect), it's a nice addition...

I don't know... I haven't tested the SMA high freq channel yet.  I've only tried 10 MHz in.  Another thing left to try is a 1PPS signal
 

Offline texaspyro

  • Super Contributor
  • ***
  • Posts: 1304
Re: BG7TBL FA1 frequency analyzer
« Reply #19 on: September 27, 2019, 06:54:59 am »
This helpful info from a Time Nuts user:

press and hold RST button, then MODE toggles LPF (low pass filter), GATE toggles input
impedence.
 
The following users thanked this post: citizenrich

Offline texaspyro

  • Super Contributor
  • ***
  • Posts: 1304
Re: BG7TBL FA1 frequency analyzer
« Reply #20 on: September 28, 2019, 04:03:44 am »
Attached is the FA2 noise floor test.  The FA2 was clocked by a HP-5071A 10 MHz output.  The FA2 frequency input was the FA2 reference output signal (which should be the 5071A output, maybe with some buffering distortion).   I didn't have the cables and T-adapter handy to split the 5071A output into the FA2 ref and signal input connectors.

The plot also shows the phase measurement of the input signal.

I am now looking at the FA2 internal oscillator performance.  Mine was shipped with it set 0.1 Hz high.  I used the tweak pot to get it within 0.003 Hz (with a little patience and twiddling you should be able to get it to +/- 0.001 Hz.   I am measuring the FA2 internal osc performance by running the FA2 with its internal osc as the reference and measuring the 5071A 10 MHz signal.
 
The following users thanked this post: citizenrich

Offline texaspyro

  • Super Contributor
  • ***
  • Posts: 1304
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #21 on: September 29, 2019, 01:29:34 am »
I did a test of the FA2 internal OCXO oscillator.  The FA2 uses this as the reference if you don't connect an external reference.  You can adjust the oscillator frequency with a small pot on the back panel.  As shipped the oscillator was 0.10 Hz off.  I adjusted to be within 0.003 Hz (I didn't try to fiddle it to be spot on).

I did the oscillator test by having it measure an HP-5071A cesium oscillator which is assumed to be (and is) spot on and very high quality.  Any deviations from the noise floor test that I did earlier are mostly due to the FA2 internal oscillator.

The wobbles in the frequency plot are due to air conditioning.  The oscillator changes freq by around 0.00025 Hz / degree C.  The oscillator drifted at the rate of 0.0065 Hz / day, but the drift rate is slowing down (it's now around 0.005 Hz / day).   It will be interesting to see how it ages in over the next few weeks.
 

Offline The Plumber

  • Contributor
  • Posts: 7
  • Country: ca
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #22 on: September 29, 2019, 02:18:55 pm »
Hi Tex,

Thanks for taking the time to do these measurements.  Cesium, eh? The more pedestrian among us have to settle for GPS!
Sadly I have no 10MHz output from my GPS, not without solder/surgery.
I took delivery of an FA-2 myself in the past week and noticed that I'm measuring a GPS's PPS at about 20ppb slow.
How much adjustment (turns clockwise or widdershins) did you need to apply in order to correct your OCXO?

I also notice a couple of hours before the OCXO seems to warm up to stability, speeding up  perhaps 3 ppb.
(I'm looking at ppb relative to the PPS measurements).  I'll set up some extended graphing once the garage door is fixed ;-)
 

Offline texaspyro

  • Super Contributor
  • ***
  • Posts: 1304
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #23 on: September 29, 2019, 07:04:46 pm »

How much adjustment (turns clockwise or widdershins) did you need to apply in order to correct your OCXO?


I don't really know.   The FA2 was in a bad place to get to and my screwdriver was not the right size, so I just started tweaking it while looking at my screen until the reading got close to 0.003 Hz off.  I could have got it closer to 0, but I figured that would be a waste of time until the unit settled in.   It was probably less than a turn.

I was unable to measure a Tbolt 1PPS with the FA2.   I would output intermittent 4 Hz readings, probably due to very narrow 1PPS pulse / low duty cycle.

This morning the FA2 oscillator drift is now around 0.001 Hz / day.  It's settling in faster than I expected.
 

Offline The Plumber

  • Contributor
  • Posts: 7
  • Country: ca
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #24 on: September 29, 2019, 07:39:12 pm »
I don't really know.   The FA2 was in a bad place to get to and my screwdriver was not the right size, so I just started tweaking it while looking at my screen until the reading got close to 0.003 Hz off.  I could have got it closer to 0, but I figured that would be a waste of time until the unit settled in.   It was probably less than a turn.

Thanks, I'll just have a go at making the adjustment.


I was unable to measure a Tbolt 1PPS with the FA2.   I would output intermittent 4 Hz readings, probably due to very narrow 1PPS pulse / low duty cycle.

Interesting. If your pulse is too narrow, maybe the "LPF" can actually help you.  The folks I bought the unit from claim that the magical key sequences are:
  • RST key: Restart test
  • RST+GATE:Enable / Disable CH1 LPF (150kHz low pass filter)
  • RST+MODE,CH1 select 50ohm/1Mohm

I actually tried out the LPF myself in order to try to get rid of an artifact I see when measuring PPS.  Once in a while, (<1% of measurements) measuring PPS with a gate of 10s, I see a jump of N*(1/22) Hz, that is, 0.0909..., 0.181818..., 0.363636... added to the measured frequency.   I'm assuming that this *must* be systemic, and must have something to do with the selection of events relative to the gating window.
« Last Edit: September 29, 2019, 08:05:00 pm by The Plumber »
 

Offline cncjerry

  • Supporter
  • ****
  • Posts: 946
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #25 on: September 30, 2019, 07:24:51 pm »
I wonder if that 300msec is related to the baud rate across the USB.  I thought it was sending 9,600 but I only used the arduino serial log and didn't see what it was set at, I thought 9,600. 
 

Offline texaspyro

  • Super Contributor
  • ***
  • Posts: 1304
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #26 on: September 30, 2019, 10:07:42 pm »
One big question is why the 1 Hz gate time has a dead time of 100 msec and the 0.1 Hz and 10 Hz gate times have a 300 msec dead time.
 

Offline cncjerry

  • Supporter
  • ****
  • Posts: 946
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #27 on: October 01, 2019, 03:04:48 am »
I hear there is a manual for the FA2.  Anyone have it?
 

Offline texaspyro

  • Super Contributor
  • ***
  • Posts: 1304
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #28 on: October 01, 2019, 03:07:30 am »
I hear there is a manual for the FA2.  Anyone have it?

Manual?  For a device from China?   :-DD

So, no manual for you!   But pretty much everything has been worked out.
 

Offline cncjerry

  • Supporter
  • ****
  • Posts: 946
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #29 on: October 01, 2019, 06:25:57 am »
Mark, my expectations for this device are not higher than any others but a time-nut said someone in eevblog was sent a manual so I thought I would try.  It was probably written in Chinese anyway...
 

Offline The Plumber

  • Contributor
  • Posts: 7
  • Country: ca
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #30 on: October 01, 2019, 10:40:45 pm »
Manuel
 

Offline The Plumber

  • Contributor
  • Posts: 7
  • Country: ca
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #31 on: October 01, 2019, 10:42:17 pm »
One big question is why the 1 Hz gate time has a dead time of 100 msec and the 0.1 Hz and 10 Hz gate times have a 300 msec dead time.

I wonder whether this is an attempt to fix the apparent (1/11)Hz bug I seem to have found...
 

Offline cncjerry

  • Supporter
  • ****
  • Posts: 946
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #32 on: October 04, 2019, 03:59:02 am »
what's this 1/11 hz bug?
 

Offline texaspyro

  • Super Contributor
  • ***
  • Posts: 1304
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #33 on: October 04, 2019, 04:26:52 am »
I did a test of the FA2 internal OCXO warm up time.  I powered mine down for 4 fours and then powered it up and measured the frequency as it warmed up.  It looks like it takes 45 minutes to stabilize close to its ultimate value. 

Note that it took a week of constant power for the oscillator drift rate to settle down.  The drift on mine seems to be around 0.00025 Hz/day.  I need to do a longer test to better weed out temperature sensitivity.

BG7TBL internal oscillator warm up time:

Minutes   Freq error
0         221 Hz
1         17 HZ
2         0.2760 Hz
3         0.0500 Hz
4         0.0350 Hz
5         0.0240 Hz
10        0.0130 Hz
15        0.0080 Hz
20        0.0060 Hz
25        0.0050 Hz
30        0.0042 Hz
35        0.0040 Hz
40        0.0034 Hz
45        0.0021 Hz <--- stable
50        0.0025 Hz
55        0.0022 Hz
60        0.0020 Hz
 

Online FransW

  • Regular Contributor
  • *
  • Posts: 65
  • Country: nl
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #34 on: October 05, 2019, 10:10:08 am »
Any internal pictures available of the FA-2, indicating used components?

Thanks,

Frans
 

Offline The Plumber

  • Contributor
  • Posts: 7
  • Country: ca
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #35 on: October 05, 2019, 04:15:14 pm »
what's this 1/11 hz bug?

When measuring a GPS-referred PPS on CH1, I see intermittent measurements that appear to be small integer multiples of 1/11Hz above the actual frequency, e.g.:

[2019-10-04 22:23:46]    F:0000000001.181818179
[2019-10-04 22:25:10]    F:0000000001.090909087
[2019-10-04 23:17:22]    F:0000000001.090909088
[2019-10-04 23:17:58]    F:0000000001.181818178
[2019-10-05 00:18:58]    F:0000000001.090909088
[2019-10-05 00:22:10]    F:0000000001.090909087


 

Offline texaspyro

  • Super Contributor
  • ***
  • Posts: 1304
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #36 on: October 06, 2019, 04:26:30 am »
The first time that I tried to set the FA2 internal oscillator frequency I tilted the case so that the screen was facing down and the adjustment screw was facing up.  I got it on frequency, but when I placed the unit with the bottom of the case facing down the oscillator was 0.032 Hz off.  So I did some more testing with the case in various orientations.  It looks like the frequency is fairly insensitive to orientation except for tilt in the front-back axis where it is around +/-1 milliHertz per 3 degrees of tilt (which seems rather high to me).  If you are using the FA2 in a mobile application and using the internal oscillator  pay close attention to the front/back tilt of the case.  Oscillator sensitivity to orientation is a well known "feature".

   F:0010000000.001619430  bottom down
   F:0010000000.001687723
   F:0010000000.001946380
   F:0010000000.001902348
   F:0010000000.001692710
   F:0010000000.001663366
   F:0010000000.001712156
   F:0010000000.001760899
   F:0010000000.001590295
   F:0010000000.001648737

   F:0010000000.001922004 bottum up
   F:0010000000.002214679
   F:0010000000.002209653
   F:0010000000.002063463
   F:0010000000.001912133
   F:0010000000.002556087
   F:0010000000.002775519
   F:0010000000.002053697
   F:0010000000.002014587
   F:0010000000.001570725

   F:0010000000.033927950 screen down
   F:0010000000.033435257
   F:0010000000.032562128
   F:0010000000.032625399
   F:0010000000.032098574
   F:0010000000.032225335
   F:0010000000.032391257
   F:0010000000.032571790
   F:0010000000.032922928

   F:0009999999.971298357  screen up
   F:0009999999.967820455
   F:0009999999.967859533
   F:0009999999.967986393
   F:0009999999.967800925
   F:0009999999.967947314
   F:0009999999.968327835
   F:0009999999.968252960
   F:0009999999.968030373

   F:0009999999.998658455  left edge down
   F:0009999999.998985308
   F:0010000000.000419484
   F:0010000000.002063510
   F:0010000000.003292634
   F:0010000000.003956045

   F:0010000000.002448722  left edge up
   F:0010000000.002029197
   F:0010000000.001917045
   F:0010000000.001985357
   F:0010000000.002012571
   F:0010000000.001980588
 

Offline texaspyro

  • Super Contributor
  • ***
  • Posts: 1304
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #37 on: October 06, 2019, 04:31:16 am »
what's this 1/11 hz bug?

When measuring a GPS-referred PPS on CH1, I see intermittent measurements that appear to be small integer multiples of 1/11Hz above the actual frequency, e.g.:


Most PPS signals have a very skewed duty cycle which can screw up a lot of counters.   I you can, try a PPS with a 50% duty cycle.  Also, try enabling the Low Pass Filter.    My Thunderbolt PPS shows up as intermittent 4 Hz readings.
 

Offline The Plumber

  • Contributor
  • Posts: 7
  • Country: ca
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #38 on: October 06, 2019, 05:53:52 pm »
what's this 1/11 hz bug?
When measuring a GPS-referred PPS on CH1, I see intermittent measurements that appear to be small integer multiples of 1/11Hz above the actual frequency, e.g.:
Most PPS signals have a very skewed duty cycle which can screw up a lot of counters.   I you can, try a PPS with a 50% duty cycle.  Also, try enabling the Low Pass Filter.    My Thunderbolt PPS shows up as intermittent 4 Hz readings.

The vendor also suggested the LPF.  I've been running for a few days with LPF off and just switched it on a few hours ago.  I still see a couple of 1.090909...-type measurements, but time will tell whether they are less frequent.  I'll put the PPS on the scope, too.  I'd be very surprised if it were anything like square.

Intermittent 4Hz is also pretty weird, though.
 

Offline The Plumber

  • Contributor
  • Posts: 7
  • Country: ca
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #39 on: October 06, 2019, 06:33:35 pm »
The first time that I tried to set the FA2 internal oscillator frequency I tilted the case so that the screen was facing down and the adjustment screw was facing up.  I got it on frequency, but when I placed the unit with the bottom of the case facing down the oscillator was 0.032 Hz off.  So I did some more testing with the case in various orientations.  It looks like the frequency is fairly insensitive to orientation except for tilt in the front-back axis where it is around +/-1 milliHertz per 3 degrees of tilt (which seems rather high to me).  If you are using the FA2 in a mobile application and using the internal oscillator  pay close attention to the front/back tilt of the case.  Oscillator sensitivity to orientation is a well known "feature".

It's amazing that you can observe this effect using a little mail-oder counter of O(100) USD.
You'd probably need to spin a smartphone in a centrifuge for days before being to be certain of observing the same effect.
If ~1mHz works out to 0.1ppb, then yeah, that does seem rather high.  Applications under lots of acceleration need to account for this one way or another.  Speaking of which, if you're planning to corner aggressively in your FA2 mobile application, you'll suffer from a bit of offset there too.  Be sure to keep an ongoing acceleration profile if any of this matters to you :-)
 

Offline cncjerry

  • Supporter
  • ****
  • Posts: 946
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #40 on: October 07, 2019, 07:42:28 am »
As I reported on time-nuts, measuring the 1pps from my 5061b resulted in a 3hz count until I put an attenuator on/through it.  Then it dropped to 1hz.  I know the 5061b 1PPS is hot so that has something to do with it.  I also noticed that the power measured by the device didnt correlate with the before and after expected by the attenuator.  Probably something to do with the spikes.  l have to look at that 5061b signal again.  I bought a bunch of those SMA inline attenuators a while back and they work ok for this stuff.

Anybody know who BG7TBL actually is?  Have an  email?  If he/she (heard it was the latter) can do the FA2 for so cheap I can think of some other equipment for this person to make...like a DMTD comes to mind.

Jerry
 

Offline harha

  • Contributor
  • Posts: 15
  • Country: dk
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #41 on: October 07, 2019, 12:39:35 pm »
Hi
I got mine fa-2,seems to work great--upper limit with -20dBm at 7.6Ghz--Wutong Elektronics seems to be the name for the company???.
Where can i download Ladyheather supporting the fa-2?
Regards
Hardy
 

Offline texaspyro

  • Super Contributor
  • ***
  • Posts: 1304
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #42 on: October 08, 2019, 02:43:56 am »
Where can i download Ladyheather supporting the fa-2?

I hope to get a new version out in a week or two...
 
The following users thanked this post: harha, citizenrich, Marck

Offline edigi

  • Regular Contributor
  • *
  • Posts: 78
  • Country: hu
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #43 on: October 08, 2019, 05:17:30 pm »
Finally I've also received FA2 and hardly even starting the testing I've found immediately something strange.

The input impedance of the CH1 seems to be fixed to 50 Ohm (actually pretty precisely around 100 MHz checked with NanoVNA)  and the input impedance of the CH2 seems to be fixed to high impedance.
With pressing RST+MODE I can change what is shown on the display that is 50R or 1MR (50 Ohm or 1 MOhm) both for CH1 and CH2 (not supposed to be changeable for CH2, in fact by default it's not shown only after RST+MODE) but nothing is actually changed in the input impedance.
(The CH1 I've used with a BNC-SMA converter that has no 50 Ohm termination, double checked that),

This is actually pretty much the opposite how I'd expect the input impedance to be by default and that it cannot be changed is really annoying.
If CH1 would be fixed to 1MOHm and CH2 would be fixed to 50Ohm that would be still a better setup even if cannot be changed...

Can someone cross check this?
 

Offline edigi

  • Regular Contributor
  • *
  • Posts: 78
  • Country: hu
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #44 on: October 09, 2019, 06:52:13 am »
Actually the first clue that something is not right with the impedance of FA2 was that CH2 is showing a frequency even without anything connected. I've checked this even with a 50 Ohm termination and it's still showing some frequency that is actually not even varying too much (I'm far from anything to cause such interference).
Is this issue present only with my copy?

I've also made a longer (overnight) and a shorter measurement of it's own reference (OCXO is still in an early phase of aging). Results attached.
« Last Edit: October 09, 2019, 07:01:49 am by edigi »
 

Offline harha

  • Contributor
  • Posts: 15
  • Country: dk
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #45 on: October 09, 2019, 07:36:01 am »
No
I have the same signal--but the measured input impedances are ok.
Hardy
 

Offline edigi

  • Regular Contributor
  • *
  • Posts: 78
  • Country: hu
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #46 on: October 09, 2019, 09:19:35 am »
Strange. Do you mean that both CH1 and CH2 have the correct impedance and CH1 is switchable and CH2 is fixed to 50 Ohm?

It's quite easy to explain why one channel does not have the correct impedance (some manufacturing error) but it's increasingly hard to find an explanation why both channels are not OK like in my case.
 

Offline Electro Fan

  • Super Contributor
  • ***
  • Posts: 1913
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #47 on: October 09, 2019, 02:51:45 pm »
Probably/maybe not Wi-Fi but that frequency seems to be pretty close to the center frequency for Channel 108 on 5 GHz.
« Last Edit: October 09, 2019, 02:59:15 pm by Electro Fan »
 

Offline harha

  • Contributor
  • Posts: 15
  • Country: dk
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #48 on: October 09, 2019, 06:02:33 pm »
Yes mine have  a fixed 50 ohm input for ch 2.works ok
Channel 1  have 50/1M ohm-- very usefull for lf.
Hardy
« Last Edit: October 10, 2019, 05:51:26 am by harha »
 

Offline edigi

  • Regular Contributor
  • *
  • Posts: 78
  • Country: hu
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #49 on: October 10, 2019, 06:34:29 am »
I've disassembled FA2 to see what's inside and what can be the reason for wrong impedance.
The prescaler is on a separate PCB and does not seem to have on the input side any resistor so I'm not surprised. The BNC side has some kind of switch but with so many connection points that it probably has some extra function as well.

I've made lots of high res photos (none of the components have the type scratched off, they seem to be well above that level) and I must say that I'm impressed. The whole thing is very neat and tidy and there are are lots of good quality components inside (BOM cost must be huge compared to the price). it's visible that quite much attention is paid into details (despite it seems they were in a rush to push this out).

I don't have time now to process the photos but I still attach some.
« Last Edit: October 10, 2019, 07:06:37 am by edigi »
 
The following users thanked this post: FransW, wolfp

Offline cncjerry

  • Supporter
  • ****
  • Posts: 946
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #50 on: October 13, 2019, 07:36:06 am »
In addition to the FA2 I'm looking at the FSA3011 frequency stability analyzer.  But then I ran across this thing:

https://www.ebay.com/itm/DC5V-0-2A-1M-100M-simple-phase-noise-tester-noise-tester/122376396168?hash=item1c7e339d88:g:RbwAAOSw3v5YtmXN&redirect=mobile

This is listed as a "simple phase noise tester".  It has an input and output sma and is used with a spectrum analyzer.   I doubt very much it is really a phase noise tester.  I've used John's PN.exe with my spectrum analyzer but that is very limited to the SA noise floor unlike real PN test sets that go down to -170dBm.  So what is this thing doing?

Thanks,

Jerry
 

Offline jpb

  • Super Contributor
  • ***
  • Posts: 1622
  • Country: gb
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #51 on: October 13, 2019, 01:46:40 pm »
In addition to the FA2 I'm looking at the FSA3011 frequency stability analyzer.  But then I ran across this thing:

https://www.ebay.com/itm/DC5V-0-2A-1M-100M-simple-phase-noise-tester-noise-tester/122376396168?hash=item1c7e339d88:g:RbwAAOSw3v5YtmXN&redirect=mobile

This is listed as a "simple phase noise tester".  It has an input and output sma and is used with a spectrum analyzer.   I doubt very much it is really a phase noise tester.  I've used John's PN.exe with my spectrum analyzer but that is very limited to the SA noise floor unlike real PN test sets that go down to -170dBm.  So what is this thing doing?

Thanks,

Jerry
That has been around a while and has been discussed on this forum before, though I now can't find the relevant post. It is a frequency multiplier (with corresponding phase noise multiplication) so you can view the phase noise of say a 10MHz oscillator up at 2.6GHz.
Unfortunately it is very hard to get any details from the seller. I tried sending the seller a message and got no response.

I'm interested in the FSA3011 but it is rather pricey so it would be good to know if it works as well as advertised. If it was around half the price I might take a punt on it but at £400 plus import duty I'd prefer to spend money on a good quality USB audio interface and put together my own system. I'm a bit frustrated at present because my current setup with a good counter and using a DDS as a local oscillator is a bit too noise at around 10^-11 at 1s.
 

Offline cncjerry

  • Supporter
  • ****
  • Posts: 946
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #52 on: October 13, 2019, 08:07:10 pm »
I think I am going to have to just bite the bullet and purchase a phase noise test set of some type.  I'll have all the stability test equipment I need shortly as I have another board coming.  But I also have a Cs, about 10 Rb units and two GPSDOs so stability-wise I'm covered. But I wish there was a way to measure close-in phase noise, like from 0 to 10Khz (but out to 100Khz) within the HF spectrum for less than $500.  Every time I look for a test set they are mucho $$$$.  I have used John's PN tool with my spectrum analyzers but they don't compare to the oscillators used today.  This all started when I built the N2PK VNA and I started a second one using a better oscillator.  But I couldn't measure the improvement other than a slightly better noise floor.

Not to get off topic, but if someone has an idea on how to inexpensively measure close in PN for less than $500, I would appreciate a PM.  I looked at a filter method where you used the signal in test (or another oscillator) out of phase to cancel the primary leaving just the noise.  I cant remember the challenges around that system.

By the way, I thought TVB and Corby on time-nuts tested the FSA3011.  I think the comments were inline with those here that it was a little expensive by 2x and he couldn't get it to meet the specs but I thought that was an early comment.  I would have to go back and see if there were other notes.

The FA2 is a great unit for the money.  Not good for 1pps measuring or comparison a/b of low frequencies unless there are hidden features.

Jerry
 
The following users thanked this post: jpb

Offline jpb

  • Super Contributor
  • ***
  • Posts: 1622
  • Country: gb
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #53 on: October 13, 2019, 09:22:03 pm »
Re the FSA3011
Thank you for the reference to time nuts - I found this :
https://lists.febo.com/pipermail/time-nuts_lists.febo.com/2019-August/097304.html
I don't know if there is any further info later than August.

Going back a bit earlier the main one is in July:
https://www.mail-archive.com/time-nuts@lists.febo.com/msg04082.html

It does look as if it is over-priced for the claimed results. Also, if it doesn't live up to the specs then there is a danger that it fails to be good enough so it is a lot of money to  spend on something that may not be able to measure because the noise floor is too high.
« Last Edit: October 13, 2019, 09:29:21 pm by jpb »
 

Offline bnz

  • Newbie
  • Posts: 4
  • Country: de
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #54 on: October 14, 2019, 06:02:21 am »
Some info on the FSA3011 can be found at:
www.leapsecond.com/pages/FSA3011
 
The following users thanked this post: jpb

Offline edigi

  • Regular Contributor
  • *
  • Posts: 78
  • Country: hu
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #55 on: October 15, 2019, 05:34:42 pm »
Some more photos and measurement of own reference with 10s gate time.
I've noticed that OCXO is very sensitive to any vibration or movement but if it's kept stable it's pretty good.
« Last Edit: October 15, 2019, 05:41:23 pm by edigi »
 
The following users thanked this post: harha, FransW, wolfp

Offline Electro Fan

  • Super Contributor
  • ***
  • Posts: 1913
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #56 on: October 15, 2019, 08:15:35 pm »
Those displayed numbers look pretty good.

On a related note, not sure that the info is reliable or even that it matters but fwiw, I asked an eBay seller (who sells/sold both the FA-2 and a 2018-06-05 BG7TBL GPSDO) which provides greater accuracy for a 10 MHz signal - and the answer was the BG7TBL GPSDO. 

I'm pretty happy with the BG7TBL GPSDO and I'm going to try the FA-2 using the BG7TBL GPSDO to provide the FA-2 with a 10 MHz reference and then see what the FA-2 displays for various frequencies fed from other source devices and compare those results to a couple other counters also taking the 10 MHz ref signal from the BG7TBL GPSDO and the other same source devices. Kinda hard to know what causes what but maybe it will be possible to isolate a few variables and learn something. When TEA syndrome strikes it can be hard to shake. 
« Last Edit: October 15, 2019, 08:18:17 pm by Electro Fan »
 

Offline Diabolo

  • Regular Contributor
  • *
  • Posts: 101
  • Country: fr
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #57 on: October 16, 2019, 01:00:13 pm »
Hello,


On the PCB front, we notice that D1 to D6 are not in place, and that the board has the location of 3 unassembled switches.

What can these missing elements serve?

Datasheet OCXO CTS 196xxxx : http://www.xtal.cc/UploadFiles/Product/20161101163222_40783.pdf


Cdlt,
Diabolo
« Last Edit: October 16, 2019, 01:17:13 pm by Diabolo »
 

Offline picburner

  • Regular Contributor
  • *
  • Posts: 204
  • Country: it
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #58 on: October 16, 2019, 07:29:47 pm »
@ edigi: the buzzer will be very weak with the protective label still attached.
 

Online mark03

  • Frequent Contributor
  • **
  • Posts: 562
  • Country: us
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #59 on: October 17, 2019, 05:37:18 pm »
I think I am going to have to just bite the bullet and purchase a phase noise test set of some type.  I'll have all the stability test equipment I need shortly as I have another board coming.  But I also have a Cs, about 10 Rb units and two GPSDOs so stability-wise I'm covered. But I wish there was a way to measure close-in phase noise, like from 0 to 10Khz (but out to 100Khz) within the HF spectrum for less than $500.  Every time I look for a test set they are mucho $$$$.

Something like this, perhaps?  http://www.wenzel.com/documents/measuringphasenoise.htm
 

Offline edigi

  • Regular Contributor
  • *
  • Posts: 78
  • Country: hu
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #60 on: October 18, 2019, 07:38:56 am »
Buzzer is my least concern (btw. it's loud enough even with protective seal on, unless you work in very noisy environment that is not too healthy).

The CH2 input impedance can be fixed with a 56 Ohm through hole resistor (we need through hole here to have some inductance that cancels it out on higher frequencies as the chip used for prescaler has 50 Ohm input impedance there; I've used a 1/8W version with short leads but I could not check the exact crossover point). While this fixes the input impedance of CH2, there is still some frequency shown for CH2 even nothing connected. In the prescaler output there should be a schmitt trigger but it's either not doing correctly its job or its something else and while driving the divided down signal connected to the main PCB it picks up noise from the prescaler.
Note: If you've checked my photos the meter is very well shielded (including front and back side PCB) so the signal that is measured cannot originate outside of the box (I've tested it even in the cellar, where even my mobile has trouble picking up any signal).
The prescaler is a /256 one (checked with DSO as I could not identify the chip). 6 wires are connecting the prescaler with the main PCB, 2 for power, 1 for the divided signal and 3 I can guess only. 2 probably is used to control division ratio (typically this kind of control is used with high divide ratio chips; probably not used here) and 1 wire that has a very strange, long burst of pulses like PWM. I suspect this has something to do with the shown frequency and probably this is what picked up by the prescaler chip. Otherwise I don't know the purpose.

The input impedance of CH2 was easy to fix (although requires some soldering experience) but I don't know what to do with CH1 without schematic or any kind  of documentation. CH1 is actually more problematic from this perspective as worst case I can swap the prescaler for CH2 (I have PCB that goes up to 11 GHz and probably even more from HMC chip series so I could even gain in the upper range with this kind of swap).
CH1 can handle quite low level signal till 270 MHz (even if frequency cannot be measured power is shown thanks to the AD8307) and a bit more if signal level is increased with sensitivity for frequency measurement dropping quite sharp from 280 MHz upwards.

Note: I've updated this post to reflect correct information based on what is learned from the standalone BG7TBL prescaler (see later posts).
« Last Edit: October 31, 2019, 09:00:55 am by edigi »
 

Offline cncjerry

  • Supporter
  • ****
  • Posts: 946
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #61 on: October 19, 2019, 08:33:23 pm »
I think I am going to have to just bite the bullet and purchase a phase noise test set of some type.  I'll have all the stability test equipment I need shortly as I have another board coming.  But I also have a Cs, about 10 Rb units and two GPSDOs so stability-wise I'm covered. But I wish there was a way to measure close-in phase noise, like from 0 to 10Khz (but out to 100Khz) within the HF spectrum for less than $500.  Every time I look for a test set they are mucho $$$$.

Something like this, perhaps?  http://www.wenzel.com/documents/measuringphasenoise.htm


The challenge with this and others is that you need a reference source VCO that is as good as or better than the DUT or OUT, ha.  I've played with these as they are easy to wire up on a breadboard.  Really easy to test 10Mhz as I have a bunch of decent, better than average, HP 10811's plus the one in my Cs beam for a reference.  Then you just need two switch the PLL loop constants to test 1hz, 10, 1K, 10K, etc. and using an external sound card adapter, you can get out to 100k using Spectrum Lab.

There is another version that uses a Johnson counter or quadrature hybrid (twisted wire quad hybrid by Breed et al, if IIRC) and then you get the I/Q advantages and you only need the source.  Now that one I haven't wired up but was thinking about it lately.

I guess what I'm looking for is some type of external board, already put together with high quality, high-speed ADCs, all the transformers and mixers architected like the one you suggested or the one I mentioned, for less than $500.  I can put it all together but the drawings are way over simplified because you should condition the input (those circuits are available) and I don't know if you need zero crossing for this or not.

Thanks

 

Offline jpb

  • Super Contributor
  • ***
  • Posts: 1622
  • Country: gb
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #62 on: October 20, 2019, 08:21:26 pm »
you should condition the input (those circuits are available) and I don't know if you need zero crossing for this or not.

For my experiments I've been conditioning the inputs using LTC6957 demo boards. They are expensive relative to the core chips but you get nice sma inputs/outputs.
https://www.digikey.com/product-detail/en/linear-technology-analog-devices/DC1766A-A/DC1766A-A-ND/3973495
 

Offline edigi

  • Regular Contributor
  • *
  • Posts: 78
  • Country: hu
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #63 on: October 22, 2019, 04:39:04 pm »
I could get my hands on second copy of FA2 and naturally I've immediately started to check the input impedance.
1) CH2 is not 50 Ohm but some higher impedance so it's the same (but this is easy to fix)
2) The impedance displayed for CH2 cannot be changed with RST+MODE
3) The impedance displayed for CH1 can be changed with RST+MODE, clicking can be heard (which I could not hear earlier) and indeed the impedance is changed

Based on this it seem that my copy has some SW issue (has probably earlier wrong SW).
Is anyone aware of SW update possibility for FA2? Was it ever possible for FA1?
I fear the whole SW is closed and not even binary is available...
It seems that I have bad luck.

I've attached pictures of my wrong FA2 variant showing impedance for CH2.
« Last Edit: October 22, 2019, 06:36:11 pm by edigi »
 

Offline cncjerry

  • Supporter
  • ****
  • Posts: 946
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #64 on: October 23, 2019, 11:01:03 pm »
you should condition the input (those circuits are available) and I don't know if you need zero crossing for this or not.

For my experiments I've been conditioning the inputs using LTC6957 demo boards. They are expensive relative to the core chips but you get nice sma inputs/outputs.
https://www.digikey.com/product-detail/en/linear-technology-analog-devices/DC1766A-A/DC1766A-A-ND/3973495

Looking at those boards, are there two inputs outputs?  It looked like from the data sheet it was an in+ and in- with corresponding outputs.

thanks - a little pricey.
 

Offline jpb

  • Super Contributor
  • ***
  • Posts: 1622
  • Country: gb
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #65 on: October 24, 2019, 03:18:19 pm »
you should condition the input (those circuits are available) and I don't know if you need zero crossing for this or not.

For my experiments I've been conditioning the inputs using LTC6957 demo boards. They are expensive relative to the core chips but you get nice sma inputs/outputs.
https://www.digikey.com/product-detail/en/linear-technology-analog-devices/DC1766A-A/DC1766A-A-ND/3973495

Looking at those boards, are there two inputs outputs?  It looked like from the data sheet it was an in+ and in- with corresponding outputs.

thanks - a little pricey.

Yes the inputs are + and - (so only one of them). I put a 50 ohm termination on the one I don't use. They are pricey (sadly) - it would be much cheaper to do your own pcb for the chips - I wanted to have something to go quickly. I was only planning to use one of them but then later I decided I needed a second (for source and reference).
There are two outputs (for the CMOS version I have) so you can supply two instruments or get a noise floor for the ref/dut inputs.
 

Offline wolfp

  • Contributor
  • Posts: 35
  • Country: de
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #66 on: October 26, 2019, 08:55:09 am »
My FA2 arrived yesterday. The first thing I did was translating the manual into understandable language.
Then I connected the FA2 to a Leo Bodnar GPSDO waited an hour and started measurements at 100MHz on CH1. The deviation was 1.4Hz - not bad for such a cheap device. The test is still running to observe the stability.
The next I will do is to compare the power-measurement of CH1 to a precision-generator.

BTW: The display of my FA2 seems only to be illuminated after warm-up of the VCOCXO.

Wolfgang
 

Offline edigi

  • Regular Contributor
  • *
  • Posts: 78
  • Country: hu
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #67 on: October 27, 2019, 06:46:46 am »
BTW: The display of my FA2 seems only to be illuminated after warm-up of the VCOCXO.

That's yet another (3rd variant) then.

Btw. The aging of the internal OCXO in the first week is around 50-100mHz (in the first days above 10mHz/day) thus precise measurement can be done only with external reference.
I didn't even bother to set the compensation in the first 2 weeks (partly because the hole at the back is not perfectly aligned with the adjustment potentiometer that makes harder to use the flat type of screwdriver).
With aging the frequency of the internal reference tends to decrease.
 

Offline Diabolo

  • Regular Contributor
  • *
  • Posts: 101
  • Country: fr
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #68 on: October 29, 2019, 02:28:42 pm »
Actually the first clue that something is not right with the impedance of FA2 was that CH2 is showing a frequency even without anything connected. I've checked this even with a 50 Ohm termination and it's still showing some frequency that is actually not even varying too much (I'm far from anything to cause such interference).
Is this issue present only with my copy?

I've also made a longer (overnight) and a shorter measurement of it's own reference (OCXO is still in an early phase of aging). Results attached.

Hello,

I received an FA-2. Channel 2 also gives me the frequency 56xx mhz. If I shunt the CH2 input this frequency is always displayed. I think of an internal phenomenon of radiation captured when CH2 has no signal at the entrance. Maybe a shield is needed on some of the electronics. Overall this FA2 works very well and suits me.

Cdlt,
Diabolo
 

Offline wolfp

  • Contributor
  • Posts: 35
  • Country: de
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #69 on: October 29, 2019, 05:26:14 pm »
Imho it is not unusual that these prescalers oscillate near the upper frequency if no signal is connected. I observed this also with other devices.
 

Offline wolfp

  • Contributor
  • Posts: 35
  • Country: de
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #70 on: October 29, 2019, 05:30:05 pm »
Concerning the illumination of the display: Its not a feature but a bug. There seems to be a bad connection to the display.
 

Offline edigi

  • Regular Contributor
  • *
  • Posts: 78
  • Country: hu
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #71 on: October 29, 2019, 06:20:55 pm »
It's pretty much common with FA2 that it displays something using CH2, maybe it's possible to get rid via connecting some small capacitor to the input of the next chip.
I have however many Fuji and Hittite prescalers and all of them work without any such phenomenon.

I've managed to make progress with the help of the seller in the wrong impedance of CH1 (which is more an issue than what signal is shown when nothing is connected).
Most probably I have a faulty relay switch. It does not switch no matter if it gets 5V (in case of 50R) or 0V (in case of 1MR).
Maybe the package had a harsh shipping or the relay switch was faulty already when it was built in and went unnoticed as even if someone checks if the unit works, it requires a bit more check if input impedance is correct or not...

I hope that the seller comes up with some reasonable solution, as even if I could replace the relay switch (probably as I have desoldering station) maybe it's not so cheap and easy to get 1 of such relay switch.
« Last Edit: October 31, 2019, 08:56:57 am by edigi »
 

Offline edigi

  • Regular Contributor
  • *
  • Posts: 78
  • Country: hu
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #72 on: October 29, 2019, 07:08:22 pm »
Actually for the record if someone faces a similar issue later on I attach a picture of the PCB and a short description that contains a significant amount of guessing.
 
Both the low and the high side of the  relay switch is controlled (the 0 volt is actually zero, if you add some load as otherwise it's more like floating). The low side control comes via R76 and Q3 (this is certain).  The high side control comes from Q1 and that ugly long line. D6 is probably for reverse current protection (the relay switch has coil).
The AD8307 measuring the power is connected together with the 50 Ohm load so it's not independent. My guess is that D9 switches the LPF.
I was wrong earlier that the relay switch has also some other purpose. No, its sole purpose is switching on the AD8307 together with the 50 Ohm input load.
U11 is probably for input signal amplification (could be easily checked with scope but sorry I was lazy).
 


Offline edigi

  • Regular Contributor
  • *
  • Posts: 78
  • Country: hu
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #74 on: October 30, 2019, 01:24:16 pm »
Thanks. I've already bought a replacement in the local shop that I regularly use (+ more spares of them in Ebay, as it's cheaper but it takes weeks til it arrives). Local shop was more expensive, I've got 2 for around the same price as in your link for 5.
We'll see during the evening, as what still troubles me why is it possible change the impedance shown on the LCD for SMA input in my case?  :-//
That's why I actually didn't want to post an update till I know more.
Btw. I never know what's available in these local shops as they are so old school that they don't even have a web page.
When I was looking for a 0603 SMD resistor they looked on me like I'm from the moon. This time when I've presented my need for this relay switch I've got it like when a roll is requested in the bakery shop...
 

Offline Diabolo

  • Regular Contributor
  • *
  • Posts: 101
  • Country: fr
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #75 on: October 30, 2019, 02:15:40 pm »
Hello,

With the FA-2 I received, on CH2 I can not change the impedance and LPF because these 2 options are not displayed on the display in CH2 mode. So, if I press RST + Mode and RST + Gate are not enabled on CH2 with my FA-2.
-----
On the board of the facade, there are 3 switches, but the board is provided for 6 switches, what can serve the 3 switches (+6 diodes D1 to D6) uncabled, and what function would they have had if they had been wired ?


Diabolo
 

Offline Diabolo

  • Regular Contributor
  • *
  • Posts: 101
  • Country: fr
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #76 on: October 30, 2019, 03:34:11 pm »
« Last Edit: October 30, 2019, 05:04:43 pm by Diabolo »
 
The following users thanked this post: edigi

Offline Diabolo

  • Regular Contributor
  • *
  • Posts: 101
  • Country: fr
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #77 on: October 30, 2019, 05:42:10 pm »
@Edigi

On your prescaler card, your resistance R35 is not Ok, you must have 10K, that is marking 103.
Look at my prescaler card in attached photo.




Diabolo
 

Offline edigi

  • Regular Contributor
  • *
  • Posts: 78
  • Country: hu
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #78 on: October 30, 2019, 08:12:29 pm »
I've managed to fix the wrong non-switchable CH1 impedance problem.

The culprit was indeed the relay switch but it was not faulty.

After removing the switch you can see that the PCB has absolutely clear marking about the orientation.
Naturally someone totally unqualified for this kind of job managed to solder it with the wrong orientation (it makes me wonder how many percentage of the units has this mistake...)

I've attached a picture with the correct orientation (sorry for the shade, this was after the second re-solder and I could hardly wait to finish it). If you check back my earlier photo it's just the opposite way on them.

Diabolo
I don't have more time to check the prescaler now, it works at least . Based on the schematic that you've linked the chips seem to be pin compatible, but to me those don't appear as genuine ADI chips based on the marking and this prescaler seems to me a heavily simplified version (or one that is engineered down to cost).
Based both on product description and PCB the LPF and impedance change works only for CH1. I don't know why but I can still change what is displayed for both of those even for CH2 but it does not mean that it works or can be expected to work.
So far I haven't made any hacking, I've just tried to fix the product that I've received to meet its spec.
« Last Edit: October 31, 2019, 06:12:19 am by edigi »
 

Offline edigi

  • Regular Contributor
  • *
  • Posts: 78
  • Country: hu
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #79 on: October 31, 2019, 07:28:31 am »
Topic to read, and download the PDF prescaler BG7TBL for general information, it may help.
- https://www.eevblog.com/forum/rf-microwave/bg7tbl-6-ghz-rf-prescaler/

When  you mentioned yesterday that prescaler it occurred to me that probably I have some variant of that prescaler (actually the /1000 version), although I've never bothered to check what's inside the box.
And yes I have it.
It's clearly a more complete version with genuine ADI chip.

In the FS2 prescaler the resistor you've mentioned is indeed 1k not 10k, but probably it does not matter much as it sets the charge pump current and in these prescalers only the scaled RF is used in the muxout output.
This explains also the extra 3 wires from the PCB. It's the SPI interface. The long pulse that I saw is the clock, the other is the data (I don't know why I did not see it) and the 3rd one is the LE.
The prescaler part is pretty clear now I think. They've re-used some of their older design but made it significantly simpler and cheaper.
« Last Edit: October 31, 2019, 07:32:54 am by edigi »
 
The following users thanked this post: FransW

Online FransW

  • Regular Contributor
  • *
  • Posts: 65
  • Country: nl
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #80 on: October 31, 2019, 10:48:45 am »
Edigi & Diabolo,

A question:
did you check these experiences with either BG7TBL or the seller?

I am also wondering how your comments propagate to other buyers experiences.

Thanks,
Frans
 

Offline edigi

  • Regular Contributor
  • *
  • Posts: 78
  • Country: hu
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #81 on: October 31, 2019, 12:33:31 pm »
I've contacted the seller with the relay switch issue (wrong/non-switchable CH1 impedance). He was helpful but at the end I had to find it myself. He offered a discount (but nothing concrete) if I buy next time in his shop.
I have no idea how to contact BG7TBL.
Also as no input protection was mentioned in the spec, we can't complain about that and after all CH2 input impedance is also 50 Ohm but just around 6GHz...

Btw. I've tried to fix it again using the new information I've learned here (also updated the original post not to mislead people; through-hole resistor is used to have some inductance that cancels it out where the chips starts to have the correct input impedance). A photo attached. I know it's not the nicest job, but I did not want to stretch this anymore after several solders (first starting with SMD).
Note: If someone has access to 6GHz VNA or 6GHz SA + directional coupler + FA2 (not a too likely combination I know) I'd not mind knowing what is the correct lead length for proper crossover...

However if the question is if am I planning to directly complain, the answer is no. In fact if you are happy with relatively precise frequency measurements this device is great deal (especially if you get one that doesn't need too many fixes).
At this price point it's probably hard to find a better package for hobbiest use. It's also possible to build one, but it's even more time (I've calibrated FA2 with my own developed GPSDO so I'm quite aware of many challenges already, actually I'm still in search of an OCXO that has good phase noise despite I have already some double oven, SC cut and Japan made you name it version).

Sure, if you're willing to spend the money (or your job depends on that), there is no question that one has to settle a branded device (even if it cost significantly more) that meets its spec out of the box and you can have a proof of calibration (another cost factor that hobbiest are not necessarily willing to take).
Btw. talking about double oven, when using this device unboxed for a while I've noticed that its reference has shown a 10mHz offset (probably due to better airflow). Thus its temperature sensitivity would be another lengthy exploration...
« Last Edit: October 31, 2019, 12:36:18 pm by edigi »
 
The following users thanked this post: FransW

Offline Diabolo

  • Regular Contributor
  • *
  • Posts: 101
  • Country: fr
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #82 on: October 31, 2019, 05:27:26 pm »
In the FS2 prescaler the resistor #35 you've mentioned is indeed 1k not 10k
Hello,

A marked resistance 103 is 10K. The 3rd digit indicates the number of zero, either 10 + 3 zero, or 10 000 ohms, or 10K. A resistance of 1K will be marked 102.
 ̶T̶h̶e̶ ̶r̶e̶s̶i̶s̶t̶a̶n̶c̶e̶ ̶#̶ ̶3̶5̶ ̶m̶a̶r̶k̶e̶d̶ ̶0̶1̶0̶ ̶t̶h̶a̶t̶ ̶y̶o̶u̶ ̶h̶a̶v̶e̶ ̶o̶n̶ ̶y̶o̶u̶r̶ ̶p̶r̶e̶s̶c̶a̶l̶e̶r̶ ̶i̶s̶ ̶w̶o̶r̶t̶h̶ ̶1̶ ̶o̶h̶m̶.̶
Update : I searched for resistance marked 01C. I had seen 010 on Edigi blurry picture. This resistance 01C would be a 10K, because 01C equals: 100 x 100 = 10 kOhms, so it is R35 compliant with a value of 10 kOhms marked 103.
------
I'm waiting the HSMS8202 diodes to install 1 and see how the CH2 input behaves.
------
My FA-2 works very well, but the ocxo installed seems to be an ocxo that has already been used. BG7TBL using only used ocxo in all its devices, a new ocxo costing more than the devices sold by BG7TBL. .
------
For contact BG7TBL : Email: BG7TBL@GMAIL.COM/BG7TBL@QQ.COM/BG7TBL@126.COM
------
FA-2 Service Manual: https://www.eevblog.com/forum/metrology/bg7tbl-fa1-frequency-analyzer/?action=dlattach;attach=846500


Diabolo
« Last Edit: November 02, 2019, 03:17:56 pm by Diabolo »
 

Offline Kean

  • Supporter
  • ****
  • Posts: 916
  • Country: au
  • Embedded systems & IT consultant
    • Kean Electronics
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #83 on: October 31, 2019, 07:03:14 pm »
The resistance # 35 marked 010 that you have on your prescaler is worth 1 ohm.

Nope, I believe it is actually the correct value.
It is marked "01C" which is the EIA-96 marking code for a 10k 1% SMD resistor
http://kiloohm.info/eia96-resistor/96C

 

Offline edigi

  • Regular Contributor
  • *
  • Posts: 78
  • Country: hu
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #84 on: October 31, 2019, 08:04:41 pm »
The resistance # 35 marked 010 that you have on your prescaler is worth 1 ohm.

I've used the device in the attached photo to measure (for good reasons). Since it was showing 1k and I did not solder the resistor out, it can be higher value but cannot be lower.

but the ocxo installed seems to be an ocxo that has already been used.

Unlikely, as a used OCXO has a different aging characteristics, but cannot be totally excluded. True for GPSDO modules.
 

Offline Electro Fan

  • Super Contributor
  • ***
  • Posts: 1913
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #85 on: November 01, 2019, 02:07:59 am »
Received an FA-2.

At first I thought the FA-2 had some problems but after about an hour of playing around with it (after not having read the specs closely or the manual at all) I found that the FA-2 is a very nifty device.  The ability to see the dBm power reading on the 50 Ohm setting on Channel 1 is very instructional - mostly I purchased the FA-2 to look at frequencies but I think the power reading feature might be my favorite feature. :)  The LPF feature on Channel 1 is something I’m still trying to get a grip on – I think the specs say 150 kHz but I haven’t figured out how to get it to perform in predicable manner – might be operator error.

I don't have any good way to check the FA-2's accuracy but it seems to show values that are consistent with what other users here have published, and the values seem consistent with what my generator and other counters indicate.  So when I say "the device seems to work ok" that just means I can't measure with the accuracy needed to confirm the exact displayed measurements.  (There are a lot of digits displayed to the right of the decimal point on the FA-2; accuracy and resolution are two different things, of course.)

The device seems to work ok with an external 10 MHz reference signal or the internal oscillator, and it seems to output a 10 MHz reference signal ok.  I'm not sure if the 10 MHz reference output is derived from the internal oscillator or the external reference signal but it outputs the 10 MHz reference signal both when the device is attached to an external reference and when it is operating with the internal oscillator.

Channel 1 toggles between 50 Ohms and 1 MOhm.  Initially I couldn't figure out why Channel 2 seemed to show a 10 MHz input signal is about 21 MHz but I figured out that Channel 2 doesn't operate below 20 MHz. (Duh.)  When fed a signal of 20 MHz or greater it seems to operate ok (even though the spec says it only starts at 30 MHz).  Channel 2 doesn't appear to offer the ability to toggle the impedance or the LPF on and off - as per the other posts here I guess that is by design.  Also, as others have reported, with nothing attached to Channel 2 it shows a frequency - on my unit about 3.95 MHz - maybe not ideal but I can live with it.

Overall, it seems like another good and fun product offering a lot of value from BG7TBL.
 
The following users thanked this post: FransW

Offline Diabolo

  • Regular Contributor
  • *
  • Posts: 101
  • Country: fr
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #86 on: November 01, 2019, 04:32:01 pm »
Hello,

I searched for resistance marked 01C. I had seen 010 on Edigi blurry picture. This resistance 01C would be a 10K, because 01C equals: 100 x 100 = 10 kOhms, so it is R35 compliant with a value of 10 kOhms marked 103.
-----
It's not easy with all these kinds of SMD markings, because BG7TBL uses 2 kinds of SMD markings in its resistances.

Sorry
Diabolo
 

Offline Electro Fan

  • Super Contributor
  • ***
  • Posts: 1913
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #87 on: November 04, 2019, 02:17:05 am »
Just checking to see if any FA-2 users might be up for comparing the dBm power readout on Channel 1 at 50 Ohms to see how it compares with respect to accuracy on any known power measurement devices you might have?  I've tried to account for my short cable and connectors but I'm getting lower readings on the FA-2 than I would expect.  Might have fed it a tad too much power...?  :palm:

Edit:

Or maybe I've got my red apples (dBm) confused with my green apples (dB).

The cable I'm using is a Tektronix 012-0117-00 which I think is RG223.  The spec on RG-223 indicates that the loss on the 2.5 foot cable at 20 MHz should be 0.1 dB (according to the Times Microwave calculator but let's say maybe 0.2 dB total with the two BNC connectors).

https://www.timesmicrowave.com/Calculator?Product=RG-223&RunLength=2.5&Frequency=20

So that's ~0.2 dB of cable plus connectors loss, but the the FA-2 and my generator both specify dBm (dB's relative to a milliwatt).  So if the generator says it's set for 3.0 dBm (while outputting a 20 MHz signal - on the 50 Ohm setting) and the FA-2 says it is seeing 1.9 dBm (while reading 20 MHz - on the 50 Ohm setting), is it possible that the loss of 1.1 dBm between the generator and the FA-2 is roughly equivalent to (ie, caused by) ~0.2 dB of cable and connector loss?  If I understand correctly, 1.0 dBm at 50 Ohms is 1.25 mW.  Is it possible that 2.5 feet of RG223 absorbs approximately 1.25 milliwatts?  Seems plausible but I think I need some help understanding the calculations even if that's where the 1.1 dBm went missing. 

|O

Thanks
 
« Last Edit: November 04, 2019, 03:29:57 am by Electro Fan »
 

Online FransW

  • Regular Contributor
  • *
  • Posts: 65
  • Country: nl
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #88 on: November 04, 2019, 02:59:15 pm »
Hi,

Also the connectors play a role:
theoretical representation of a matched impedance connection (50 ohms) and VSWR < 1.35:1.  Under these circumstances, approximately 97.7% of incident power will be delivered to the load, thus resulting in minimal reflected power.

VSWR
The voltage standing wave ratio (VSWR) is a measure of the effective impedance of the mated connector. The higher the VSWR, the more power is reflected from the connector due to impedance mismatches. Note that VSWR is a function of frequency, and connector VSWR values should only be compared at the same frequency.

The attachment shows the max power for connectors as a function of frequency.
I could not unearth the loss per connector table. Sorry.
Anyway, the connector contributes to the total loss.

Frans
« Last Edit: November 04, 2019, 03:06:08 pm by FransW »
 

Online FransW

  • Regular Contributor
  • *
  • Posts: 65
  • Country: nl
 

Offline edigi

  • Regular Contributor
  • *
  • Posts: 78
  • Country: hu
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #90 on: November 04, 2019, 03:43:28 pm »
The CH1 input impedance of FA2 is very well matched in 50 Ohm mode except at the edges of its range (lower edge: capacitive -a higher DC blocking capacitor would do good here-, upper edge: inductive; no surprises). The reflected power is at least 30dB below of the incident power in most of the range (definitely so in 20MHz) or at least with my copy. Thus impedance mismatch cannot be the source for the lower power shown.
The source for the lower power shown is either the generator (I don't know what kind of generator you've used) or the FA2 interpretation of the ADC value (AD8307 output value converted).
So far I didn't bother to check at all if it's precise at this level or not as for power measurements I have significantly better tools (that also work for a wider frequency range).

Note: For 20 MHz, the connector is of negligible significance.
« Last Edit: November 04, 2019, 03:45:12 pm by edigi »
 

Offline Electro Fan

  • Super Contributor
  • ***
  • Posts: 1913
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #91 on: November 04, 2019, 04:42:11 pm »
Frans, thanks for the charts.  I think they show the impact of the connectors and even any VSWR is likely to be relatively small.
I'm guessing it's something in the FA-2.
EF
 

Offline Electro Fan

  • Super Contributor
  • ***
  • Posts: 1913
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #92 on: November 04, 2019, 04:46:42 pm »
The CH1 input impedance of FA2 is very well matched in 50 Ohm mode except at the edges of its range (lower edge: capacitive -a higher DC blocking capacitor would do good here-, upper edge: inductive; no surprises). The reflected power is at least 30dB below of the incident power in most of the range (definitely so in 20MHz) or at least with my copy. Thus impedance mismatch cannot be the source for the lower power shown.
The source for the lower power shown is either the generator (I don't know what kind of generator you've used) or the FA2 interpretation of the ADC value (AD8307 output value converted).
So far I didn't bother to check at all if it's precise at this level or not as for power measurements I have significantly better tools (that also work for a wider frequency range).

Note: For 20 MHz, the connector is of negligible significance.

edigi,

Thanks.  The generator is an Agilent 33522B and it produces signals with measurements that are consistent with an Agilent 8648C, so I'm thinking the discrepancy is in the FA-2 - but I might have fed it too much power when using it.  I'm hoping someone here can compare the FA-2 dBm readings from a generator to some other dBm measuring device.
 

Offline edigi

  • Regular Contributor
  • *
  • Posts: 78
  • Country: hu
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #93 on: November 04, 2019, 07:31:21 pm »
I've made a quick check and in case of my FA2 copy the power level indicated for CH1 is just the opposite way, that is, it's quite consistently 1.1 dB or so above the real value.
I've checked it using 2 different methods thus changing the generator output level and using SMA attenuators (that I trust) with the same level.

It would be interesting to know if this is consistently off (depending on the FA2 version; remember my FA2 copy can change both the impedance and LPF even for CH2 even though it does nothing else just the display is changed so it has its own SW issues as well) or there is a varying level of error in the displayed value depending the actual FA2 (showing the lack of any calibration).
The best would be though if the SW allowed some compensation (not just for this but also for the frequency; the current potentiometer based solution is far from ideal).

Somewhat related: There is a pretty good material related to precision frequency standards (without any math and with simple and clear terms so well understandable by anyone not even deeply technical) that I'd recommend almost to anyone (OK excepts for experts of this topic) to read in order to know what to expect from FA2 or similar precision frequency meters (using OCXO or external reference).

https://apps.dtic.mil/dtic/tr/fulltext/u2/a248503.pdf
 
The following users thanked this post: Electro Fan, MegaVolt, wolfp

Offline Electro Fan

  • Super Contributor
  • ***
  • Posts: 1913
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #94 on: November 04, 2019, 08:13:46 pm »
I've made a quick check and in case of my FA2 copy the power level indicated for CH1 is just the opposite way, that is, it's quite consistently 1.1 dB or so above the real value.
I've checked it using 2 different methods thus changing the generator output level and using SMA attenuators (that I trust) with the same level.

It would be interesting to know if this is consistently off (depending on the FA2 version; remember my FA2 copy can change both the impedance and LPF even for CH2 even though it does nothing else just the display is changed so it has its own SW issues as well) or there is a varying level of error in the displayed value depending the actual FA2 (showing the lack of any calibration).
The best would be though if the SW allowed some compensation (not just for this but also for the frequency; the current potentiometer based solution is far from ideal).

Somewhat related: There is a pretty good material related to precision frequency standards (without any math and with simple and clear terms so well understandable by anyone not even deeply technical) that I'd recommend almost to anyone (OK excepts for experts of this topic) to read in order to know what to expect from FA2 or similar precision frequency meters (using OCXO or external reference).

https://apps.dtic.mil/dtic/tr/fulltext/u2/a248503.pdf

edigi, thanks for the measurement and the link.

So based on a very small sample size (2) it looks like the dBm power reading is about +/- 1.1 dBm of actual :)
 

Offline texaspyro

  • Super Contributor
  • ***
  • Posts: 1304
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #95 on: November 04, 2019, 09:24:18 pm »
I know a guy that tested a FA2 with a very accurate generator and was very happy with the results. 

Also, the FA2 has two commands for calibrating the power meter:

select CH1=50R,input 10M 0dBm
$E4040*   

select CH1=50R,input 10M -20dBm
$E4141*

 

Offline Electro Fan

  • Super Contributor
  • ***
  • Posts: 1913
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #96 on: November 04, 2019, 09:46:06 pm »
I know a guy that tested a FA2 with a very accurate generator and was very happy with the results. 

Also, the FA2 has two commands for calibrating the power meter:

select CH1=50R,input 10M 0dBm
$E4040*   

select CH1=50R,input 10M -20dBm
$E4141*

That's cool!  Thanks for command info texaspyro.
 

Offline Electro Fan

  • Super Contributor
  • ***
  • Posts: 1913
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #97 on: November 05, 2019, 12:22:49 am »
So looking at the manual and the commands:

select CH1=50R,input 10M 0dBm
$E4040*   

select CH1=50R,input 10M -20dBm
$E4141*

Just guessing but the process is to run the $E4040* command while the FA-2 is powered up and connected on Ch1 at 50 Ohms to a reliable generator outputting 10 MHz at 0 dBm?  Then save and exit?  Then repeat with $E4141*while the generator is running at -20 dBm?  Then save and exit? 

Save and exit might be $E2020* ?

Thanks
 

Offline texaspyro

  • Super Contributor
  • ***
  • Posts: 1304
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #98 on: November 05, 2019, 02:13:04 am »
So looking at the manual and the commands:

select CH1=50R,input 10M 0dBm
$E4040*   

select CH1=50R,input 10M -20dBm
$E4141*

Just guessing but the process is to run the $E4040* command while the FA-2 is powered up and connected on Ch1 at 50 Ohms to a reliable generator outputting 10 MHz at 0 dBm?  Then save and exit?  Then repeat with $E4141*while the generator is running at -20 dBm?  Then save and exit? 

Save and exit might be $E2020* ?

Thanks

Not quite... the $Exxxx commands do the work and save the results.  So just connect the proper signal and issue the appropriate $Exxxx command.
 

Offline Electro Fan

  • Super Contributor
  • ***
  • Posts: 1913
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #99 on: November 05, 2019, 03:49:16 am »
So looking at the manual and the commands:

select CH1=50R,input 10M 0dBm
$E4040*   

select CH1=50R,input 10M -20dBm
$E4141*

Just guessing but the process is to run the $E4040* command while the FA-2 is powered up and connected on Ch1 at 50 Ohms to a reliable generator outputting 10 MHz at 0 dBm?  Then save and exit?  Then repeat with $E4141*while the generator is running at -20 dBm?  Then save and exit? 

Save and exit might be $E2020* ?

Thanks

Not quite... the $Exxxx commands do the work and save the results.  So just connect the proper signal and issue the appropriate $Exxxx command.

So I can see all the 10 MHz counter readings scroll by in terminal mode on the PC (via USB connection).  I've turned off the FA-2 and entered the $E4040* command while the generator is outputting 10 MHz at 50 Ohms on Ch1 and then turned the FA-2 on but that didn't work.  What's the process for uploading the commands from the PC to the FA-2?  Thx
 

Offline texaspyro

  • Super Contributor
  • ***
  • Posts: 1304
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #100 on: November 05, 2019, 04:00:54 am »
So I can see all the 10 MHz counter readings scroll by in terminal mode on the PC (via USB connection).  I've turned off the FA-2 and entered the $E4040* command while the generator is outputting 10 MHz at 50 Ohms on Ch1 and then turned the FA-2 on but that didn't work.  What's the process for uploading the commands from the PC to the FA-2?  Thx

WTF?   How can one possibly expect it to accept commands or do anything when  it is powered off?    :palm:

You enter the $Exxxx commands while the counter is powered on and spewing measurement data.  Yes, the terminal display will look like confusing crap,  but the FA2 doesn't care.
 

Offline Electro Fan

  • Super Contributor
  • ***
  • Posts: 1913
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #101 on: November 05, 2019, 04:09:11 am »
So looking at the manual and the commands:

select CH1=50R,input 10M 0dBm
$E4040*   

select CH1=50R,input 10M -20dBm
$E4141*

Just guessing but the process is to run the $E4040* command while the FA-2 is powered up and connected on Ch1 at 50 Ohms to a reliable generator outputting 10 MHz at 0 dBm?  Then save and exit?  Then repeat with $E4141*while the generator is running at -20 dBm?  Then save and exit? 

Save and exit might be $E2020* ?

Thanks

Not quite... the $Exxxx commands do the work and save the results.  So just connect the proper signal and issue the appropriate $Exxxx command.

So I can see all the 10 MHz counter readings scroll by in terminal mode on the PC (via USB connection).  I've turned off the FA-2 and entered the $E4040* command while the generator is outputting 10 MHz at 50 Ohms on Ch1 and then turned the FA-2 on but that didn't work.  What's the process for uploading the commands from the PC to the FA-2?  Thx

Edit:

Figured it out.... Seems to be working!  Thanks!!

Looks to now be within 0.1 dBm; fluctuates between 0.0 and 0.1 dBm of mirroring the generator settings for both 0 dBm and - 20 dBm.

On a scale of 1 to 10 that is about a 10. :)

For anyone else trying the process, a few details.

Connect the FA-2 on Ch1 at 50 Ohms to your generator outputting 10 MHz at 50 Ohms at 0 dBm.
Connect the FA-2 via a USB port.
Open a terminal program on your PC.
If it's working on the right com port you will see the 10 MHz counter readings scroll by.
Open MS Word and enter $E4040*
Save the file as a .txt file named E4040 (or some acceptable characters).
In the terminal program use the "send a text file" command to upload the E4040 text file.
You will see an acknowledgement of the calibration text file going by among the scrolling counter info in the terminal program.
Notice that the dBM reading on the FA-2 is now very close to 0 dBm.

Repeat the process at -20 dBm.

You should be good to go with not only pretty accurate frequency counting on the FA-2 but also pretty accurate dBm power readings.

BG7TBL Rocks!  and texasypro too!

EF
« Last Edit: November 05, 2019, 04:30:15 am by Electro Fan »
 
The following users thanked this post: sab

Offline Electro Fan

  • Super Contributor
  • ***
  • Posts: 1913
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #102 on: November 05, 2019, 04:40:15 am »
Happiness is test equipment where frequencies, amplitudes, and phases all read pretty closely across the gear.   :)
 

Offline texaspyro

  • Super Contributor
  • ***
  • Posts: 1304
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #103 on: November 05, 2019, 09:11:07 pm »
There is no need to send the $Exxxx commands from a text file.   You can enter them from the keyboard while the FA2 is spewing frequency readings.  Yes, it looks horrible and confusing but works just fine.

The next version of Lady Heather supports the FA2.  It has keyboard commands (in the "P" menu) for changing most of the device configuration options,  but I did not include the calibration commands (to minimize the chance of somebody accidentally screwing up their calibration).   But you can use the !u keyboard command that sends command strings to the FA2 in order to send the $Exxxx cal commands.
 

Offline edigi

  • Regular Contributor
  • *
  • Posts: 78
  • Country: hu
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #104 on: November 06, 2019, 09:22:21 am »
My FA2 copy has probably some kind of beta SW as when I did the power measurement calibration it did not take any effect until a power cycle (btw. I was using Putty and right clicking sent the text to FA2 that I've copied earlier to clipboard; text is not echoed back though).

What was even stranger that at the end of the power measurement calibration I've noticed a huge change in its reference frequency (~120mHz; even retrace around the time when I replaced the relay switch was only a fraction of this), so I had to calibrate the frequency of the reference again. I simply don't have an explanation for this jump (maybe I've slightly knocked the box during the power measurement calibration or is this calibration also impacting the compensation voltage of the OCXO?).
 

Offline texaspyro

  • Super Contributor
  • ***
  • Posts: 1304
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #105 on: November 06, 2019, 04:25:13 pm »
You power cycled it...   could cause oscillator retrace error.
 

Offline neil

  • Contributor
  • Posts: 47
  • Country: us
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #106 on: November 06, 2019, 08:00:54 pm »
Ebay has a bunch of different sellers with what appear to be the same FA2 device (photo's of some show a date code printed on the front panel after the BG7TBL name, others don't - significant?). And AliExpress and probably other sources also offer the device.

I'd like to get one, and so I'd appreciate vendor recommendations.  At this price point I'm not too concerned over the small price differences of the various sources, but more interested in quality and latest version.
 

Offline Diabolo

  • Regular Contributor
  • *
  • Posts: 101
  • Country: fr
Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #107 on: November 08, 2019, 01:00:23 pm »
Hello,

I bought my FA-2 from this seller. Quick expedition. The received FA-2 operates without defects or problems. I asked PSU EU version.
- https://fr.aliexpress.com/item/4000120075382.html?spm=a2g0s.9042311.0.0.1ec66c378LS7JX

Regards.
Diabolo
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf