[Skimmertalk] 160M Skimmer Observations

H Lawrence Serra hlserra at sbcglobal.net
Fri Dec 4 07:12:26 PST 2009


I have the same problem with the SDR-IQ on 160m and above 15 MHz (15m and 10m bands). With the Skimmer, it copies very few sigs. Skimmer and SDR-IQ work great on 40m and 20m. I sent the SDR-IQ back to Pieter after performing some diagnostics with him, he changed out the above-15 MHz filter ckt and relay, but it still shows the same insensitivity on the 15m and 10m bands with the Skimmer.

I use a 23 ft marine vertical with a motor-driven coil for the Skimmer/SDR-IQ combo. I just now tuned it to lowest SWR (1.4:1) for 160m for the contest this weekend. With the Skimmer on 160m all last night, it only copied about 20 calls. I will see if it is any more sensitive tonight with the ANT tuned best it can be for 160m. Since I am in San Diego right above the Pacific, if it is working right it should copy a lot of JAs and other PAC stations. You can log into its telnet spots at:

n6ncskimmer.ath.cx 7300

Could the lower sensitivity be an algorithm problem in Skimmer as opposed to an SDR-IQ sensitivity problem?

73, Larry N6NC (San Diego)

From: Rick Walker <rnwalker at bellsouth.net>
To: skimmertalk at contesting.com
Sent: Fri, December 4, 2009 5:04:37 AM
Subject: [Skimmertalk] 160M Skimmer Observations

Last night I hooked my 160M SDR-IQ/CW Skimmer combo to my main 160M receive
array (the combo is normally connected to a less capable but
omni-directional RX antenna).  I was listening to some EU stations on 160
and noticed that I could quite easily copy them on my K3 but that CW Skimmer
wasn't spotting them even though both the K3 and SDR-IQ receivers were using
the same RX antenna system.  I have long thought that CW Skimmer didn't "dig
signals out of the noise" as well as it could, but I thought that maybe in
this case the issue was the performance of the SDR-IQ versus the K3.  On a
whim, I took down the CW Skimmer application and started SpectraVue to
determine if the SDR-IQ was the bottleneck.  Interestingly, the signal in
question was clearly visible on the SpectraVue pan display and SpectraVue
demodulated the CW signal quite easily.  This little experiment caused me to
do more thinking about the problem than I had previously done.  Some
questions arise as a result:

1.  Is there some sort of "artifical squelch" within CW Skimmer?  
2,  How does Alex computes the noise floor used in the S/N calculation
produced by CW Skimmer?
3.  Anyone ever correlated the S/N value produced by their CW Skimmers with
any specific signal level parameter found by manually observing the same
signal with their station receivers?

I apologize if I bring up something that has been dealt with in the past.  I
searched on this subject but didn't find much.



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