Re: [Discuss-gnuradio] Flexrf AGC sensitive to noise ?

[Matt Ettus]

Per Zetterberg 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