[Skimmertalk] What causes audio images with QS1Rs?

Paul Higginson paul_group at greenrover.demon.co.uk
Sun Feb 24 10:20:58 EST 2013

Only other thing that came to mind while the dog and I were running just now, are these at a contest station. In other words are they Co sited with a transmitter ?


------- Original message -------
> From: Pete Smith N4ZR <n4zr at contesting.com>
> To: paul_group at greenrover.demon.co.uk
> Cc: K1TTT at ARRL.NET, RBN-OPS at yahoogroups.com, Skimmertalk at contesting.com
> Sent: 24.2.'13,  14:53
> Hi Paul.
> Yes, I'm in correspondence with the two - only two - QS1R-equipped Skimmers that showed this problem.  Both are savvy ops, and both use 2-amp or better supplies - in fact, one of them uses a 5V bench supply.  QS1Rs have been sold to users outside the US for some time with 2-amp, universal input voltage supplies.
> The bandwidth thing is interesting - worth asking.
> 73, Pete N4ZR
> Check out the Reverse Beacon Network at 
> http://reversebeacon.net, 
> blog at reversebeacon.blogspot.com.
> For spots, please go to your favorite 
> ARC V6 or VE7CC DX cluster node.
> On 2/24/2013 5:10 AM, Paul Higginson wrote:
>> I can't see anything external to the qs1r that could cause this, but willing to be convinced otherwise of course.
>> Do the Skimmer ops in question know of the issue? Has there been any change - do they use a different bandwidth during contests ? - I do.
>> Any changes made are sometimes good clues.
>> Substitute would be a very quick test
>> 73 de Paul   LA/GW8IZR
>> ------- Original message -------
>>> From: K1TTT <K1TTT at ARRL.NET>
>>> To: n4zr at contesting.com, RBN-OPS at yahoogroups.com, Skimmertalk at contesting.com
>>> Sent: 24.2.'13,  0:01
>>> Damaged qs1r's?   that was the final determination on mine, lightning damage
>>> did something to the sampling circuitry that caused some kind of distortion.
>>> Maybe phil would remember exactly, I sent it to him to see if it was worth
>>> repairing.  That was the same time I was trying to use the cwsl tee software
>>> and it seemed to be behaving badly, you could see the images and some other
>>> kind of intermittent noise when watching the bands using the hdsdr software
>>> on the tee data stream.  Since replacing the qs1r the cwst tee and hdsdr
>>> works perfectly, so that may be a way to test.  When I did a simple image
>>> test a couple weeks ago I could watch on the hdsdr on 10m and run a rather
>>> loud 10m signal from a radio up and down the band and not generate any
>>> image, when I did that with the damage there was an obvious image sweeping
>>> the opposite direction of my tx... basically if it is always the same
>>> distance on the opposite side of the mid range of the band it almost has to
>>> be inside the sampling circuitry, anything outside the sampler would most
>>> likely not be at the sampling image frequency but would be somewhere else
>>> and half the time would move along with the signal being decoded instead of
>>> opposite it... hopefully that makes sense, its kind of hard to visualize.
>>> David Robbins K1TTT
>>> e-mail: mailto:k1ttt at arrl.net
>>> web: http://wiki.k1ttt.net
>>> AR-Cluster node: 145.69MHz or telnet://k1ttt.net
>>> -----Original Message-----
>>> From: Pete Smith N4ZR [mailto:n4zr at contesting.com]
>>> Sent: Saturday, February 23, 2013 21:30
>>> To: RBN-OPS at yahoogroups.com; Skimmertalk at contesting.com
>>> Subject: [Skimmertalk] What causes audio images with QS1Rs?
>>> During the ARRL CW contest, we had two Skimmers using the QS1R/Skimmer
>>> Server combination that each produced many false spots, with the "signature"
>>> commonly associated with Skimmers using simple SDRs, ones which rely on a
>>> computer sound card for A/D conversion. That is, the two spots are spaced
>>> equidistant from the receiver's center frequency, one is significantly
>>> stronger than the other, and they arrive at the server typically within the
>>> same second.
>>> We're having no luck isolating what is different about those particular
>>> systems.  So far we've ruled out inadequate power supplies, and the idea of
>>> excessive gain before the receiver doesn't look promising.  Does anyone have
>>> any theories we can explore?  I'll be glad to provide the data in Excel
>>> format for anyone who wants it.
>>> Thanks in advance!

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