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Re: [Discuss-gnuradio] DBSRx set gain code
From: |
Matt Ettus |
Subject: |
Re: [Discuss-gnuradio] DBSRx set gain code |
Date: |
Wed, 21 Dec 2005 23:02:57 -0800 |
User-agent: |
Mozilla Thunderbird 1.0.7-1.1.fc4 (X11/20050929) |
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