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

[Marcus D. Leech]

On 03/15/2010 07:22 PM, Josh Blum wrote:
> 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.
Well, the front-end converts everything to complex baseband, so in this
case, do I just hand "tune"
  the offset frequency?  That is, does it "deal" with negative frequencies?

We'll go back to the example.  Complex quadrature direct-conversion
receiver, giving "I" and "Q"
  from DC-4MHz to DC+4MHz.    That is, it converts everything to
baseband.  Do I tune
  frequencies below DC, using negative values to the tune function?

I know this seems rather rudimentary, but please have patience for me :-)

-- 
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org