Flexrf AGC sensitive to noise?

Hi All,

I am trying to get some experience of flexrf1800. I am receiving a CW of
1766MHz (from a signal generator) and transmitting a wavefrom at a
different
frequency. Now, changing the frequency of the outgoing signal from
1800MHz
to 1900MHz changes the estimated amplitude of ingoing signal by 0.5dB!
(yes,
they shouldn’t have anything to do with each other, and yes, the SNR is
high).

Could it be that the level of the AGC control signal (of the AD8347) is
affected by the the TX circuitry ? Can the AGC be switched off entirely
?

By the way:
I am using my own C++ driver for the flexrf1800 that I contribute if
somebody wants it. However, it is out of context with the gnu-radio
framework, not properly tested, and is not object oriented.

BR/
Per

Per Z. wrote:

Hi All,

I am trying to get some experience of flexrf1800. I am receiving a CW of
1766MHz (from a signal generator) and transmitting a wavefrom at a different
frequency. Now, changing the frequency of the outgoing signal from 1800MHz
to 1900MHz changes the estimated amplitude of ingoing signal by 0.5dB! (yes,
they shouldn’t have anything to do with each other, and yes, the SNR is
high).

You will get leakage from the transmitter into the receiver. When you
bring the TX frequency closer to the RX, more of it will get through and
will change the amplitude estimates. The RFX boards can do full duplex,
but there are limitations to how close you can have the TX and RX.

Could it be that the level of the AGC control signal (of the AD8347) is
affected by the the TX circuitry ?

Not likely.

Can the AGC be switched off entirely ?

No, you need to have some voltage going to the variable gain
amplifiers. It is not automatically controlled however, unless you make
it so.

Matt

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