Transmit Frequencies

GNU Radio
1

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.

Thank You,
Scott Meuleners

2

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

3

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.

Scott,

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.

Tom