BG7TBL FA1 and FA2 frequency analyzers

[Jarl]

apblog,

From my experience with my single sample of the FA-2 12 GHz version you should expect around +/- 0,02 Hz "single shot" accuracy at 0,1 sec gate time and about 10 times better accuracy at 1 sec gate time when measuring a 25 MHz source on CH 1. These figures are based on the FA-2 with a GPS disciplined Rubidium oscillator as the external 10 MHz reference. The accuracy improves with time when using the statistical mode and eventually reaches the value spacified in the manual of 0.001 Hz at 10 MHz and 0,1 sec gate time, equal to 0,0025 Hz at 25 MHz.

If you plan to use a BG7TBL GPSDO as external reference you may need to consider the accuracy of this device, including warm up effects and GPS induced jitter (if any). The FA-2 itself has no warm up time if used with an external reference - at least not at the level of accuracy you are considering in your question.

Your question about using the FA-2 for general purpose work is a bit difficult to answer - it depends on your requirements.

- If you wish to explore the accuracy of the FA-2 to its full extent you need to use an external reference with at least 10 x the same accuracy.

- You would probably not want to use the FA-2 below 100 kHz due to its internal limitations below that frequency.

- You will have to accept the inconvenience of the small screen of the instrument which is a nuisance especially in the very useful statistical mode.   

- Lacking a diagram of the FA-2 we do not know at this time how it is protected from overload at the CH1 and CH2 inputs - this could turn into a problem in its daily use as a service instrument since overloads inevitably do happen from time to time.

My personal conclusion: The FA-2 is an excellent low cost instrument with remarkable data for its intended purpose: frequency analysis on a hobbyist scale. If you are after something else you may perhaps better look for a second hand, professional counter with specifications according to your measurement needs.

Cheers

Jarl

[mankan]

Thanks Jarl, 100pF 0603 is on order now. Will update as soon I've mounted one.

[apblog]

Jarl,

Thanks for helping me understand how the specs translate into real-world units, and for the info on the limitations.

I was torn between buying used pro equipment that might not be reliable and that I can't verify, or buying new hobbyist grade equipment that I could count on (haha) to work.

On the whole though it sounds like this setup will help me understand the performance of my design.

[Diabolo]

Hello,

New frequency generator 1hZ at 15 GHz from BG7TBL called WB-SG1-OPT15G 1Hz at 15 GHz! The output level setting is adjustable compared to the 8 GHz model with the output level fixed.
https://www.ebay.com/itm/WB-SG1-OPT15G-1Hz-15GHz-Signal-Source-Signal-generator-Power-ADJ-OCXO-BG7TBL/233507852253
-----
Characteristic:
overview:1Hz-15GHz wide band output,10M-15GHz with amplifiler adjust,OCXO inside，
support extern connectfrequency stanard
CH1 frequency range：1Hz-200MHz
CH1 step:1Hz-19.999999MHz/1Hz,20MHz-200MHz/10Hz
CH1 output amplifiler:3.3Vpp
CH1 plug type:BNC
CH2 frequency range：10MHz-15GHz
CH2 step:10Hz
CH2 reference output power：+5DBM- -7dBm@1G
CH2 output impedance:50 OHM
CH2 plug type:SMA
inside frequency stadnard:10MHz
inside frequency stadnard type:OCXO
inside frequency stadnard ageing:0.5Hz/year
10M frequency output power:5dBm
extern frequency input range:0dBm to +20dBm
run mode:CH1 frequency mode,CH2 frequency mode,CH1 sweep mode,CH2 sweep mode
front panel:MODE,change mode
ENT:input data
<>^V:left/right/up/down key
CH1:channel 1 output
CH2:channel 2 output
rear panel:10M REF INPUT:extern 10M input
10M REF OUTPU:10M output
USB:USB port
STD ADJ:inside OCXO frequency adjust
power switch
dc plug
power :DC11.7-12.5V,star:less than 0.5A,stabilize:less than 0.25A
size:L*H*D=106*55*105mm
weight:350g
accessory: DC12V adapter 1pcs

Regards
Diabolo

[Lemonizer]

Wow ! I don't know much in terms of high frequency signal generator, but looking at it's bare specs, if it really act like what's on paper, how much a comparable device from regular known brands cost ? 285 USD for it seems quite acceptable !

I don't have the need for something like that, but I surely want to add it to the BG7TBL little collection :>

I was wondering : Is this a good device to test the maximum bandwith of counters or scopes ? For example I have a tds 540, which goes up to 500Mhz. My best waveform gen goes up to 30Mhz (60, if I find how to hack it), so I have no way to see how would look a signal at that frequency.

[mankan]

I took the 360pF one and measured channel 2 input sensitivity.

MHz	dBm
200	-21
1000	-29
3000	-28
4000	-25
5000	-15
6000	0

Then I added the 1000pF too, same results though. And I know now that I should have done these measurements before I started the whole thing. 

Still interested to hear about the original value.

Ok, mounted a generic cheap 100pF 0603 50V MLCC:

MHz	dBm
200	-20
1000	-28
3000	-27
4000	-25
5000	-14
6000	1

So a dB less sensitive now.

[Electro Fan]

This my new 12.4GHz version looks to be more accurate than my old 6GHz version. With 10s gate time Avg is only 0.0015 mHz high.

Here are pictures when same 10 MHz signal is connected to EXT-REF and CH1. With 10s gate time Avg is about 0.02 mHz high and with 1s gate time 0.2 mHz high.

Hi EV, sorry for the late reply to this post but any chance you still have your 6GHz version to warm-up and try a similar test (same N samples with 10s gate and a similar DUT setup) so we can get a look at the results for comparison to your 12.4GHz version?  Thanks, EF

[Jarl]

Hi Electrofan

I happen to have ADEV recordings available that may answer your request.

Annexed you will find direct comparison of ADEV measurements of the FA-2, 6 GHz and 12 GHz versions. All tests are made on CH 1 with a stable 10 MHz external reference.

One set of recordings show the ADEV self test with 1 sec. gate time and the corresponding test measuring ADEV on an independent LPRO 101 Rb-standard which has been switched on and left to itself for many months.

The other set of recordings show the ADEV self test with 10 sec gate time.

It is worth noting that all the ADEV  measurements of the 12 GHz version are slightly worse compared to the corresponding measurements on the 6 GHz version. I guess that this is due to the wider CH1 bandwidth of the 12 GHz FA-2 (300 MHz vs. 200 MHz).

Cheers / Jarl

[EV]

I don't have this 6 GHz version anymore.

This my new 12.4GHz version looks to be more accurate than my old 6GHz version. With 10s gate time Avg is only 0.0015 mHz high.

Here are pictures when same 10 MHz signal is connected to EXT-REF and CH1. With 10s gate time Avg is about 0.02 mHz high and with 1s gate time 0.2 mHz high.

Hi EV, sorry for the late reply to this post but any chance you still have your 6GHz version to warm-up and try a similar test (same N samples with 10s gate and a similar DUT setup) so we can get a look at the results for comparison to your 12.4GHz version?  Thanks, EF

[Electro Fan]

Hi Electrofan

I happen to have ADEV recordings available that may answer your request.

Annexed you will find direct comparison of ADEV measurements of the FA-2, 6 GHz and 12 GHz versions. All tests are made on CH 1 with a stable 10 MHz external reference.

One set of recordings show the ADEV self test with 1 sec. gate time and the corresponding test measuring ADEV on an independent LPRO 101 Rb-standard which has been switched on and left to itself for many months.

The other set of recordings show the ADEV self test with 10 sec gate time.

It is worth noting that all the ADEV  measurements of the 12 GHz version are slightly worse compared to the corresponding measurements on the 6 GHz version. I guess that this is due to the wider CH1 bandwidth of the 12 GHz FA-2 (300 MHz vs. 200 MHz).

Cheers / Jarl

Hi Jarl,

Thanks for the data collection, graphing, and sharing.  Nice work!

I found the results different than what I expected given the impressive results EV showed with his 12 GHz FA-2 - but given your good testing maybe the explanation is that EV simply had a better DUT than what I've been using in my tests.   Assuming the 6 GHz FA-2 counter performs as well or better than the 12 GHz FA-2 counter the only other explanation beside a better DUT I guess could be that EV's 10 MHz reference was better than the GPSDOs I've been using, but it seems the more likely explanation would be that his DUT had better performance.  Thoughts?  Thx again

EV - if you happen see this, what DUT and 10 MHz reference were you using?  Thx

[Jarl]

Electro Fan

Thanks for your kind words.

I would like to add, that when making a simple self test on CH 1 on my FA-2 6 GHz and 12 GHz versions using the statistics mode I have noted that resetting the counter - take say 100 or 1000 readings - reset once again - repeat the measurement - show different offset results from one test run to the next run. My 12 GHz version is better in this respect compared to the 6 GHz version but in any case the offset is there and in my case it is quite unpredictable.

What annoys me is, that I cannot just make a self test and subtract the offset from the result of the following test on a independent source since I do not know the real internal offset value when I reset the counter to make a new measurement.

This problem do not show itself on the ADEV measurements since any initial offset do not enter into the ADEV calculations.

When using the FA-2 for precision measurements on independent sources one should take account of the accuracy and stability of the external time base of the counter. I suggest  the time base should have a precision and stability 10 times better than the object you are measuring in order to avoid influencing the result too much.

Since you get a lot of numbers from the FA-2 following the comma you may have to disregard some of the numbers since in reality they just reflect inaccuracies of the time base.

When using a simple GPS based reference you may need to extend the measurement period in order to even out the GPS reference's minor, slow variations in frequency. 

/ Jarl

[EV]

I am using ZYT QPSDO with Trimble unit as 10 MHz reference. What DUT means?

...
EV - if you happen see this, what DUT and 10 MHz reference were you using?  Thx

[jpb]

DUT = Device Under Test (in this case the oscillator being measured)

[EV]

Here is picture of the DUT attached. WB-SG1 is connected to FA-2. Both of them have ZYT GPSDO as reference connected from Extron distribution amplifier at right of them.

[Tazz]

Comparing Hgl and Diabolo boards picture posts, the PCBs of the counter and generator are common/the sames.
This is anyway clearly indicated on the pcb: F-CNT&F-SSG
Did someone see a counter with the 2019-10-20 PCB date ? (6Ghz Diabolo Gen).
Is the 15Ghz Gen version have new main PC Rev date ?

Very interesting devices, it already have a lot of history with all theses evolutions/variations. This is sad that it does not have official published schematics with revision history and binary firmware updates (at least).

[texaspyro]

I've had a BG7TBL FA2 measuring an HP 5071A cesium beam unit since September.  After a couple of months of initial warmup and aging, I adjusted the internal oscillator of the FA2 to get the reading to 10.000000000 MHz.  Six months later the reading had drifted around 0.009 Hz.   Over the last month the drift rate was less than 0.0002 Hz/month.

[mino-fm]

It would be nice though to have some sort of clue as to the theory of operation/circuit so we could understand its limitations or at least to satisfy our curiosity.

Reading the datasheet you get 8 digits/s for 1 Hz signals. I suppose it is a reciprocal counter with Fref between 100 - 200 MHz. User 'hgl' observed that Fin <= 0,6 Hz reduces the update rate to 10 s and at < 0,3 Hz display shows 0 Hz.
For higher input frequencies as 1 MHz linear regession promises three more digits, so 11 digits/s are possible. Because of CPLD's max. frequency of 200 MHz it could be possible to achieve >= 12 digits/s at this input frequency.
So far theory.

Today I'm sure FA-2 works just that way.
CPLD is able to add and multiply each single pulse up to some 10 MHz. Size of variables should be 80 or 96 bits integer to avoid overflow errors. At the end of gate time the µC has to perform math calculations with 64 bit double precision. Gaps between two samples are 0.1 - 0.3 s which is enough for a slow µC like ATmega328 to do this.
Finally you get 11 - 12 digits/s for 10 MHz signal without any magic.

Using a fast µC (STM32H750) combined with TDC7200 results in 10 digits/s. Double (64 bit) calculations are very fast, so several 10000 time stamps/s are possible, which will give further two digits/s. At last I was succesful using linear regression. Let me add one picture and a .xls-file to show results of some minutes with 1s gate time (gapless).

[vk3alb]

What am I missing? I have a FA-2 and LH windows version 6.14 beta. I've searched all over looking for a way to get LH to recognise the counter. The counter works and is sending stuff to a comport, I can select the comport / baudrate but LH is not picking up the counter. Is there a /rx to choose the FA-2?

[texaspyro]

What am I missing? I have a FA-2 and LH windows version 6.14 beta.

I have FA1/FA2 support in the next version of Heather.  Unfortunately the code is on a computer that is in a locked down building on a university campus.

[notfaded1]

I have FA1/FA2 support in the next version of Heather.  Unfortunately the code is on a computer that is in a locked down building on a university campus.

Awe bit by the plague virus again!!!  What kind of cesium do you have @texaspyro?

[bingo600]

I've had a BG7TBL FA2 measuring an HP 5071A cesium beam unit since September.

[Ringmodulator]

Tip for newbees like me:

TimeLab from KE5FX works wth the FA-2. No special configuration required.

Choose the Aquire menu: Aquire from counter in Talk-only Mode...
Choose comport
Start Measurement

(yes, kinda obvious for TimLab users)

http://www.ke5fx.com/timelab/readme.htm

Chris

[notfaded1]

Tip for newbees like me:

TimeLab from KE5FX works wth the FA-2. No special configuration required.

Choose the Aquire menu: Aquire from counter in Talk-only Mode...
Choose comport
Start Measurement

(yes, kinda obvious for TimLab users)

http://www.ke5fx.com/timelab/readme.htm

Chris

Thanks for the info!  I have an FA-2 and didn't realize timelab would recognize in talk only mode.  The 5071 Cs is a really nice design... must be for it to make it through 4 companies.

[Ringmodulator]

I was curious about a detail, that was not described in the maual:

What comes out of the 10Mhz output, when an external 10MHz signal is fed to the external 10MHz input?
Might be the 10MHz from the internal OCXO, or the external fed 10MHz, or nothig...

It turns out, that it is the external fed 10MHz, that is been sent to the extenal input. So If you feed in an external reference, you can dasychain this signal to another device without a spltter or distributor. At least worth a try.

[DM4DS]

... No special configuration required.

Choose the Aquire menu: Aquire from counter in Talk-only Mode...
Choose comport
Start Measurement
.
Chris

Any idea why this doesn´t work for me?

hterm is working.

I see :
F-CH1:0024999999.999956054
F-CH1:0024999999.999980506
F-CH1:0024999999.999990234
in the monitor.

Line Terminator 10 or 13 makes no difference, What am I missing?

Hardware is the 12Ghz version saying 20200705 at startup.

Timelab shows only: Initializing acquisition on the right side , but not Acquired etc shown.

I am the only one?