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

Scott scott23192 at gmail.com
Fri Mar 3 05:09:19 UTC 2017

I don't know what your budget is, but an SDRPlay would work fine at those 
frequencies and is a higher performing SDR as well.

-Scott,  K4KDR


-----Original Message----- 
From: Mac A. Cody
Sent: Friday, March 03, 2017 12:03 AM
To: amsat-bb at amsat.org
Subject: Re: [amsat-bb] Shack re-wiring: RTL-SDR options?


There are modified versions of the RTLSDR dongle that support
direct sampling.  That is to say, a signal is fed directly into the
RTL2832 chip, bypassing the tuner/down-converter chip.  This
enables reception of signals from 0 to 14.4 MHz (half the
28.8 Msps sampling rate of the analog-to-digital converter).
Perhaps you could make use of one of these. Search for them
on Ebay or through Google in general.  You may need to
attenuate the 10.7 MHz IF signal prior to feeding into the
dongle, as too strong a signal will damage it.  Hope this helps.


Mac / AE5PH

On 03/02/2017 10:40 PM, Greg D wrote:
> Doh!
> Well, that answers that question.  Thanks, Jim.  You are correct!  24.00
> is the minimum Gqrx will let it go.
> Greg  KO6TH
> Jim Jerzycke wrote:
>> I don't think an RTL dongle will tune down that low.
>> Jim  KQ6EA
>> On 03/02/2017 10:46 PM, Greg D wrote:
>>> 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?
>>> Thanks,
>>> Greg  KO6TH 

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