Author Topic: BG7TBL FA1 and FA2 frequency analyzers (Read 83865 times)

cncjerry · « **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.

texaspyro · « **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.

cncjerry · « **Reply #27 on:** October 01, 2019, 03:04:48 am »

I hear there is a manual for the FA2. Anyone have it?

texaspyro · « **Reply #28 on:** October 01, 2019, 03:07:30 am »

Quote from: cncjerry on October 01, 2019, 03:04:48 am

I hear there is a manual for the FA2. Anyone have it?

Manual? For a device from China?

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

cncjerry · « **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...

The Plumber · « **Reply #30 on:** October 01, 2019, 10:40:45 pm »

Manuel

The Plumber · « **Reply #31 on:** October 01, 2019, 10:42:17 pm »

Quote from: texaspyro 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.

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

cncjerry · « **Reply #32 on:** October 04, 2019, 03:59:02 am »

what's this 1/11 hz bug?

texaspyro · « **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

FransW · « **Reply #34 on:** October 05, 2019, 10:10:08 am »

Any internal pictures available of the FA-2, indicating used components?

Thanks,

Frans

The Plumber · « **Reply #35 on:** October 05, 2019, 04:15:14 pm »

Quote from: cncjerry on October 04, 2019, 03:59:02 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.:

[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

texaspyro · « **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

texaspyro · « **Reply #37 on:** October 06, 2019, 04:31:16 am »

Quote from: The Plumber on October 05, 2019, 04:15:14 pm

Quote from: cncjerry on October 04, 2019, 03:59:02 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.

The Plumber · « **Reply #38 on:** October 06, 2019, 05:53:52 pm »

Quote from: texaspyro on October 06, 2019, 04:31:16 am

Quote from: The Plumber on October 05, 2019, 04:15:14 pm
Quote from: cncjerry on October 04, 2019, 03:59:02 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.

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.

The Plumber · « **Reply #39 on:** October 06, 2019, 06:33:35 pm »

Quote from: texaspyro 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".

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 :-)

cncjerry · « **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

harha · « **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

texaspyro · « **Reply #42 on:** October 08, 2019, 02:43:56 am »

Quote from: harha on October 07, 2019, 12:39:35 pm

Where can i download Ladyheather supporting the fa-2?

I hope to get a new version out in a week or two...

edigi · « **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?

edigi · « **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.

harha · « **Reply #45 on:** October 09, 2019, 07:36:01 am »

No
I have the same signal--but the measured input impedances are ok.
Hardy

edigi · « **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.

Electro Fan · « **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.

harha · « **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

edigi · « **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.


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Author Topic: BG7TBL FA1 and FA2 frequency analyzers (Read 83865 times)

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