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Re: [Discuss-gnuradio] Calling "tune" on BASIC_RX

From: Josh Blum
Subject: Re: [Discuss-gnuradio] Calling "tune" on BASIC_RX
Date: Mon, 15 Mar 2010 16:22:45 -0700
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv: Gecko/20100217 Shredder/3.0.3pre

On 03/15/2010 04:09 PM, Marcus D. Leech wrote:
Does the "tune" function actually do anything for the BASIC_RX? Does it
just set the DDC

Tune on the basic and lf rx only sets the ddc. In other words, the IF of the dboard is always 0 Hz in this case.

Because this tuning relies entirely on the ddc, you are really aliasing in frequencies above ddc_rate/2. Because of this, your RF frontend should need a bandpass filter so only the desired range can be aliased in.

The tune method should do the right thing.

For example, if I have a quadrature HF receiver, centered at let's say
20MHz, with 4MHz either
   side of 20MHz, can I use "tune" and setting the decimation to pick out
a particular chunk.


Let's say I wanted the 250KHz "chunk" that's +500KHz from the center
frequency, would I set
   the decimation to 256, and ask "tune" for 500KHz?

Assuming center_freq+500KHz is the center of the "chunk", that is center_freq+375khz to center_freq+625khz: you would do tune(center_freq+500KHz) and the tune method figures out what the ddc should be set to.


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