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

From: Marcus D. Leech
Subject: Re: [Discuss-gnuradio] Calling "tune" on BASIC_RX
Date: Mon, 15 Mar 2010 19:32:00 -0400
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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

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