On 12/10/2013 10:41 AM, Nemanja Savic wrote:
hi,
thank you Ralph.
It looks like I should have known about not packing two receivers in
the same band in the sme box, but anyway, rf parts are not in the same
box, and I intended to keep them at the distance of arround 5 to 10
meters. Antenna of 434MHz in is more or less conected directly do the
pin, there just matching cuircuit between. The 10.7 MHz out will be
with 5 - 10 meters long cable connected with USRP. Power supply of
external frontend runs through twisted pair of a UTP CAT 2 cable,
which is kind of shielded, and I have a few capacitors on the other
end for filtering supply line. As for the LP filter on the 10.7 MHz, i
think that LFRX itself has cuoff frequency of arround 50 MHz or so.
Will it help a bit if I put some alu plates over WBX board?
--
Nemanja Savić
The problem is that even with 50dB LO suppression in the TX mixer, there
will still be some LO energy leaking out the antenna port.
But something you *can* do is use offset-tuning on the TX side to move
the LO off to the side. It'll still be there, but outside of your RX
passband.
In "built for a specific purpose" radios, it's often the case that the
last conversion stage uses a fixed LO that is offset from the final
frequency, and
there's a deep notch filter on the output of the final mixer. That
strategy isn't possible in designs like these that aren't "for a
specific purpose", since
there's only a single conversion stage, with variable LO--you'd have
to put in a notch yourself.
--
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org
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