[amsat-bb] Shack re-wiring: RTL-SDR options?

Greg D ko6th.greg at gmail.com
Thu Mar 2 22:46:11 UTC 2017

Hi folks,

Has anyone used an RTL-SDR dongle on the 10.7 MHz IF output from another
receiver?  Is that better than going direct?

My cable TV provider is forcing us to go all-digital.  With the new
"cable box" comes the opportunity to re-wire the shack and simplify the
many layers of cables, splitters, and lash-ups that have accumulated
over the years.  The proverbial camel is crying out for help.

What this has to do with Ham Radio is that part of the lash-up mess is
an old pre-CATV deep fringe TV antenna that I have in the attic, aimed
to the southern horizon.  We are well outside the range of any of the
digital OTA stations, and never one to leave a perfectly good piece of
RF equipment go to waste, I currently have it fed to an old Icom R-7000
scanning receiver (previously used as the AO-40 downlink IF) and to an
RTL-SDR dongle by way of a TV 2:1 splitter.  I've tried hooking the
dongle directly to my 2m ham antenna for satellite use, but for some
reason that was less than satisfactory.  Never really did hear much of
anything, and never could figure out why.  At least with the TV antenna,
I can copy some stuff with the dongle, though the Icom is generally
better.  But the Icom doesn't do the various digital modes that are
better suited for SDR.

Looking at the back of the Icom, I see that it has a 10.7 MHz IF output,
so the thought is that the SDR dongle might perform better hooked there
(with a DC bias block) instead of to the antenna itself through the
splitter.  Both receivers have similar frequency coverage, but perhaps
the Icom, while somewhat deaf by modern standards, might still make for
a better front-end to the dongle?

I think the down-side is that the Icom's IF bandpass is narrower than
the Dongle's, so I'd lose some flexibility there.  I would also lose the
ability to software-control the frequency of the receive chain, outside
of the IF bandpass.

What do you think?  Would this be a net win or loss for the RTL-SDR?


Greg  KO6TH

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