BG7TBL FA1 and FA2 frequency analyzers

[texaspyro]

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?   

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.

[Electro Fan]

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

[Electro Fan]

Happiness is test equipment where frequencies, amplitudes, and phases all read pretty closely across the gear.   

[texaspyro]

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.

[edigi]

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?).

[texaspyro]

You power cycled it...   could cause oscillator retrace error.

[neil]

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.

[Diabolo]

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

[Jarl]

Thanks for the hint, Diabolo - I ordered my FA-2 from the seller you indicated. The instrument has now arrived and seems to work fine except for the missing 50 ohms resistor in the CH2 input which should be easy to fix.

As the proud owner of a few BNC T-adapters and some  pieces of coax I initially set up a noise floor test at 10 MHz. With assistance from TimeLab I recorded the ADEV at 1 and 10 sec gate time as shown in the attached file below. I find the result quite remarkable even compared to professional equipment.

I also attach my edited version of the User Manual. The chinese language has been left out in order to make reading easyer for non-chinese readers.

I now look forward to see further documentation from BG7TBL, i.e. block diagram, circuit schematic etc.

[hgl]

Probable measurement principle of the FA-2.
A VCO (SI5351A) converts the 10Mz to 100Mhz. Resolution is further increased by delay elements (MAX II LCELL) and flip-flops. Principle like the FPGA solutions.
The delays probably calibrated and stored in the EEPROM. The question is: are the devices individually calibrated during production or was a single characteristic recorded once for all?

How the delay chain works for MAX II CPLD, see here: https://iopscience.iop.org/article/10.1088/1742-659

[Vojtech]

Hello Hgl, Your link doesn't work.

[hgl]

Seems to be a temporary link ...

Search IOP for "Design of High-Precision Frequency Measure System Based
on CPLD Time Delay Unit" and use the first hit.

[Jarl]

You are probably right in your analysis of the circuit topology inside the FA-2, hgl.
 
I can add that it seems that the FA-2 has a small stationary offset of approx 0,1 mHz at 10 MHz. The offset varies with the shape of the external clock input and with the test frequency -  among probably other factors.

But just to illustrate the merits of the FA-2 in connection with ADEV tests I attach a collection of ADEV noise floor tests at 10 MHz with 1 sec gate time and external clock. In the tests I compare the SR620 counter, the TAPR TICC with 10MHz to 1 pps prescaler and the FA-2, all with the same setup and using the same external clock input. As only one laptop was available for the test, the testing was done sequentially.

[hgl]

I've done some reengineering and that's the result. As expected, the cpld increases the resolution, makes the switching of the reference sources and is used as a level converter. The first picture shows the I2C communication between MCU and SI5351 VCO.

[hgl]

When used with a terminal program FA-2 shows on Power up:
FREQ COUNTER
BG7TBL
V20190922
READ EEPROM!

Version 2.0 22.sept.2019 ?

I have also made some measurements
Noise internal ref
Noise external Rb ref
Measurement Rb with internal ref




 

[hgl]

This is a more detailed circuit. What is still missing ? power supply U1 and U3,
prescaler, relay and impedance switching, voltage reference U2 for the ocxo trimming pot,  TLC3702 dual comparator U7 where I dont know what he is good for and the chicken feed.

[Jarl]

I am very impressed by your results so far, hgl.

If possible, be specific with the exact design of the circuit of the connections into and out of the counter, since no information is available about their sensitivity to overload in the "manual".

In short:  are all input and output connections protected in any way and if so, how well protected ?

[hgl]

The BNC inputs are AC coupled and have protective resistors and diodes. The reference output is also protected. At 6 GHz input, I can't see any protection. I can see right now there are two versions and the CH1 input is different.

[hgl]

The board posted by edigi ends with 190823 and mine with 190920. Bottom right in the CH1 input area are differences.

[FransW]

These differences are not very obvious.
Except for the board numbers.
Can you please indicate what they are?

Thanks, Frans

[hgl]

The 190823 board has a 6 pin IC and the other board did not have it.

[FransW]

Spotted,
Thanks

[bnz]

For me, the noise floor by looping back the internal reference is noticeable better than the noise floor with an external reference. For the external reference I tried various setups (T-adapter, two buffered outputs) and oscillators, they give similar results.

Could that be due noise of the reference input circuity?

[hgl]

I have also observed and the external reference should have 50% duty cycle. For example, 30/70 does not work.

[bnz]

The oscillator I used with the T-adapter had sine output, the other slightly deformed sine.