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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 
> 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.


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