[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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 17:05:14 -0700
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv: Gecko/20100217 Shredder/3.0.3pre

The DDC can shift the IF signal in either direction. So yes, it must deal with negative frequencies and you should be able to pass the tune function a negative frequency in Hz.

Also, you can simulate the action of the ddc in grc with a complex sine source and a complex multiply. Watch the fft.


On 03/15/2010 04:32 PM, Marcus D. Leech wrote:
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

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 :-)

reply via email to

[Prev in Thread] Current Thread [Next in Thread]