Forum: GNU Radio LFRX as IF stage questions

Aaa0fc4458ead49e4f9317634a32ae92?d=identicon&s=25 Nemanja Savic (Guest)
on 2013-08-09 11:26
(Received via mailing list)
Hi all guys,

I have designed a small board based on Ti's CC1000 transciever, which I
want to use as my RF front end. The board provides 10.7 MHz IF signal at
one of the pins. After connecting everything I come to the point where I
don't understand what's going on after LFTX.
In the "documentation" about LFTX on ettus website it is written that it
can be used for one complex baseband rx channel or two real valued rx
chains. I which way i can get only real valued signal from RX-A (taking
only the real part from the signal coming from usrp source?)
I suppose that signal is downconverted to baseband using DDCs. Do they
make
quadrature signal from the input and make complex baseband at the end?

Is there any stable clk signal at the board with frequency between 10
MHz
and 14 MHz that I can use as clock reference for my board?

Cheers,
3596cfe1d579c65b9babd35e8787977c?d=identicon&s=25 Matt Ettus (Guest)
on 2013-08-14 01:26
(Received via mailing list)
The LFRX has 2 inputs.  For your application you only need to use one of
them, since you have a real IF and not complex IQ baseband.  The signal
will then be downconverted from 10 MHz by the DDCs, and you will have a
complex baseband signal.

The LFRX has a clock output pin.  You will need to explicitly turn that
pin
on and set the divider to 10 in order to get a 10 MHz reference output
for
your system.

Matt
3596cfe1d579c65b9babd35e8787977c?d=identicon&s=25 Matt Ettus (Guest)
on 2013-08-14 01:48
(Received via mailing list)
I just realized the LFRX does not have the clock pin.  The BasicRX does,
and should also work the same way for your application.  So if you need
the
clock output, the BasicRX is a better choice.

Matt
558c40b97bd1af8d912424757714bda9?d=identicon&s=25 Marcus D. Leech (Guest)
on 2013-08-14 01:57
(Received via mailing list)
On 08/13/2013 07:47 PM, Matt Ettus wrote:
>
> I just realized the LFRX does not have the clock pin.  The BasicRX
> does, and should also work the same way for your application.  So if
> you need the clock output, the BasicRX is a better choice.
>
> Matt
And, as a follow-up, you might need to muck with the appropriate UHD
driver to get it to enable those clock pins,and drive them at a suitable
rate.

You will likely have to "crib" from the drivers for cards that require a
refclock--like, well, all of them *except* for BASIC_* and LF_*.

In fact, it might be reasonable to suggest that there be an option in
the standard drivers to enable those pins at a default rate of 10Mhz or
something
   for the BASIC_* cards.  Or some easily-usable API frob to do so.



--
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org
Aaa0fc4458ead49e4f9317634a32ae92?d=identicon&s=25 Nemanja Savic (Guest)
on 2013-08-15 14:06
(Received via mailing list)
I can't use basix_rx, cause i can't get it. the problem is i want to use
ti's cc1000 as rf frontend. it has if output at 10.7 MHz.
The problem is i can't make pll of cc1000 to lock, and I assume that the
problem is mayne in not accurate quartz reference
due to bad loading capacitors.

Yes I agree it would be great to be able to enable some clock for lf
boards.

Nemanja
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