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RE: [Discuss-gnuradio] Transmit Frequencies

From: Tom Rondeau
Subject: RE: [Discuss-gnuradio] Transmit Frequencies
Date: Sat, 2 Dec 2006 18:08:35 -0500

> -----Original Message-----
> Thomas Schmid
> Sent: Friday, December 01, 2006 1:48 PM
> To: Scott Meuleners
> Cc: discuss-gnuradio
> Subject: Re: [Discuss-gnuradio] Transmit Frequencies
> >From Ettus Inc.'s FAQ you can read that the BasicTX goes only up to
> about 50MHz because the DACs in the USRP run at 128MS/s. You would
> need some other hardware to upsample your output to 70MHz.
> Thomas
> On 12/1/06, Scott Meuleners <address@hidden> wrote:
> >
> > I am working on a project for a class, and we have been using the FM
> > transmit functions included with the examples, and we've run into a
> problem
> > where we are unable to transmit on frequencies from about 40 to 80 MHz,
> the
> > problem is that we would like to transmit at 72MHz.  The errors amount
> to
> > something like "cannot tune frequency", etc...  Does anyone have any
> > suggestions as to how we might get this to work?  We are using the USRP
> with
> > the Basic TX daughterboard.
> >


Thomas' email is correct, using the BasicTX boards, you can only transmit up
to 44 MHz and because of the 128 Msps DAC, you can only get up to 64 MHz
from a comms. perspective. However, you can cheat (sort of) by using the
sampling process of the system. When you sample the original frequency, you
get images around the sampling frequencies, in this case 128 Msps. Out of
the BasicTX, you get three fairly strong signals: one at the specified
center frequency (fc), one at 128 MHz + fc, and one at 128 MHz - fc.

You won't be able to hit your target of 72 MHz this way, though (128 - 44 =
84 MHz), but I point it out in case it helps.


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