BG7TBL FA1 and FA2 frequency analyzers

[Diabolo]

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.
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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

[Diabolo]

If one refers to the BG7TBL 6 ghz prescalator, there should be a HSMS8102 ? (HSMS8202 is ok) clipping diode on the CH2 input stage. The front panel has the slot (D7), but HSMS8202 SOT-23 is missing.


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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/

Datasheet HSMS8102, HSMS8202 :
- http://www.farnell.com/datasheets/47811.pdf
- https://pdf1.alldatasheet.vn/datasheet-pdf/view/527215/AVAGO/HSMS-8102.html

Purchase HSMS 8202 :
- https://www.ebay.com/itm/10PCS-Diode-AVAGO-AGILENT-SOT-23-HSMS-8202-HSMS-8202-TR1-HSMS-8202-BLK-2R-2RX/162776443991?_trkparms=aid%3D1110001%26algo%3DSPLICE.SIM%26ao%3D1%26asc%3D60668%26meid%3D595ca2b77d7140cebd6f3d93df63cae5%26pid%3D100010%26rk%3D1%26rkt%3D12%26sd%3D183851485844%26itm%3D162776443991%26pmt%3D0%26noa%3D1%26pg%3D2047675&_trksid=p2047675.c100010.m2109


Diabolo

[Diabolo]

@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

[edigi]

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.

[edigi]

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.

[FransW]

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

[edigi]

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...

[Diabolo]

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.
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I'm waiting the HSMS8202 diodes to install 1 and see how the CH2 input behaves.
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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. .
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For contact BG7TBL : Email: BG7TBL@GMAIL.COM/BG7TBL@QQ.COM/BG7TBL@126.COM
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FA-2 Service Manual: https://www.eevblog.com/forum/metrology/bg7tbl-fa1-frequency-analyzer/?action=dlattach;attach=846500


Diabolo

[Kean]

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

[edigi]

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.

[Electro Fan]

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.

[Diabolo]

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.
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It's not easy with all these kinds of SMD markings, because BG7TBL uses 2 kinds of SMD markings in its resistances.

Sorry
Diabolo

[Electro Fan]

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...? 

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. 



Thanks
 

[FransW]

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

[FransW]

Found something:
https://www.digikey.com/en/articles/techzone/2018/jun/how-to-select-use-maintain-coaxial-connectors-rf-applications

[edigi]

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.

[Electro Fan]

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

[Electro Fan]

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.

[edigi]

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

[Electro Fan]

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

[texaspyro]

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*

[Electro Fan]

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.

[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

[texaspyro]

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.

[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