Re: [Discuss-gnuradio] DBSRx set gain code

[Matt Ettus]

Lee Patton wrote:
> I don't understand why the gain range returned by the DBSRx ranges from
> 0 to 104 when the PGA gives only 0 to 20 dB.  Obviously, the answer lies
> in db_dbs_rx.py, but I haven't a clue as to what the code is really
> doing.  Can anyone (Eric) explain?  I read about Registers 2/3 in the
> AD9862 data sheet, but I couldn't correlate that information with the
> code.
> 

There are 2 components to gain control in the RX daughterboards:

1>  The PGA gain, which ranges from 0-20 dB in 1 dB steps

2>  The gain control amplifiers on the daughterboard itself.

On the BasicRX there is no amplification, so you just get the PGA

On the dbsrx there are 2 variable gain amps.  One is controlled by an
analog signal from the low-speed DAC output.  The other is controlled
digitally over the I2C port.

On the TVRX there are separate IF and RF AGC amps, both are controlled
by the low-speed DACs

The FlexRF has a single AGC amp, again controlled by the low-speed DAC.

Matt