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Re: [Discuss-gnuradio] FW: Questions about USRP TV RX agc setting
From: |
Eric Blossom |
Subject: |
Re: [Discuss-gnuradio] FW: Questions about USRP TV RX agc setting |
Date: |
Thu, 18 Aug 2005 12:30:29 -0700 |
User-agent: |
Mutt/1.5.6i |
On Wed, Aug 17, 2005 at 12:34:18PM +0800, address@hidden wrote:
> Hi, all
> When I traced the tv_rx.py code, I found that in order to adjust the RF
> AGC/IF AGC
> the AUX DAC inside the AD9862 must be used. But I had several questions about
> this.
>
> 1). the AUX DAC bit width: in the code segment below, there is a magic number
> 4096
> (2e12), but the bit width of AUX DAC is only 8 bits width(2e8=256).What is
> the relationship
> between the 8-bit and 4096?
2e12 == 2,000,000,000,000. I think you mean 2**12 ;)
The interface is specified with a 12-bit value to allow us to possibly
update to higher res aux dacs in the the future. The library current
just shifts the argument 4 bits right.
> 2). the gain/voltage formula:
> Are there two formula approximation from the tuner datasheet ?
See http://comsec.com/usrp/microtune/NF_tutorial.pdf
To get the best noise figure, you max out the RF gain prior to ramping
the IF gain.
> 3). TV RX daughterboard
> In the schematics, it is necessary to have two signals: AUX_DAC_A, and
> io_rx_00
> to control the IF AGC setting. What is the use of io_rx_00 signal?
Per the schematic R11 and R13 are not loaded. io_rx_00 and io_rx_01
are not used on the TVRX board.
Eric