[Skimmertalk] What causes audio images with QS1Rs?

[Pete Smith N4ZR]

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!
>>
>