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Offset on S21 below -15dB


METRA FLORENT 2021/04/27 10:00

Hi everybody,

i have an issue with my SAA-2N.
I wanted to measure an attenuator of -30dB, and i found -28dB on my SAA-2N. I checked the attenuator on a R&S ZNB, and the measure was -30dB!
So, i measured a step attenuator from 0dB to -50dB on the SAA-2N and on the ZNB at 350MHz on both.

Look at the curve, below -15dB, there is an offset of around 2dB. It is the same issue without any calibration, and it is not dependent to the frequency.

Do you have an idea ? Is it a bug software or an hardware issue ?

Thanks for your help,

Best 73's Florent, F4CWN.

DiSlord 2021/04/27 21:18

Update fw
==============
or set output power STIMULUS->CFG SWEEP-> ADF4350 TX POWER to 0 and save to 0 slot
after device on switch back to need value

METRA FLORENT 2021/04/28 13:26

I updated the firmware, same problem. If I set output power to 0, the problem appears between -5 and -6dB.

It look like the gain control of the baseband amplifier changed

Florent


DiSlord 2021/04/28 06:40

You can check Config->DMSG
See bbgain3 value, should be ~-20dB (on error you see ~-18.5dB)

https://nanorfe.com/downloads/20201124-experimental/

Or you can try my variant:
https://groups.io/g/NanoVNAV2/message/1371
Unpack archive,and instal correct version

METRA FLORENT 2021/04/28 08:28

BBGAIN3 is -17.94

Is it normal ? What is BBGAIN ? Is there any documentation about this parameter ?

I will try the experimental file ...

Thanks

Florent

DiSlord 2021/04/28 10:57

В среду, 28 апреля 2021 г., в 08:28, МЕТРА ФЛОРЕНТ пишет:

>
> BBGAIN3 -17,94

No, this mean overflow on calibration internal attenuator (should be near -20dB) and you see this 2dB shift near 18dB.
Fixed in last fw or reduce output power at startup (save in 0 slot settings vs 0 ADF output).

METRA FLORENT 2021/04/28 13:31

When is done the calibration on internal attenuator ? At startup ?

I tried this firmware ( https://nanorfe.com/downloads/20201124-experimental/ ) but BBGain was also -18 dB,

i also tried Dislord Firmware ( https://groups.io/g/NanoVNAV2/message/1371 ) , and this firmware fixed the problem !!

I tried also with last firmware ( nanovna-v2-20201013-v2_74.bin ) work also !!

At the beginning i used a firmware from a tutorial of a french guy, i don't understant because it look like the same as nanovna-v2-20201013-v2_74.bin, but not working !(bbgain -18dB !)

Shame on me not using original files on official website !

Thanks all for your great help !

Best 73's Florent, F4CWN

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