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

[Josh Blum]

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
>    appropriately?

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.

yes

> 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.

-Josh