[Skimmertalk] Monitored Frequencies vs. Displayed Frequencies

[Pete Smith]

Hi Jeff - good to hear from you. and particularly to hear about your PJ2T 
experience.  I'm doing a presentation at Dayton on "Skimmer - the First 
Year" and it is always nice to have good news.

Regarding your questions, I've interspersed a couple of comments below, and 
have copied Alex, so he can correct me as necessary.

73, Pete

At 07:29 AM 2/2/2009, Jeff Maass wrote:

>I am constantly annoyed by the inability to look at sections of the band 
>away from the
>"Tune at Frequency".
>
>I'd like to be able to check visually the activity across the monitored 
>bandwidth without
>changing the "Tune at Frequency. The green "bumper stops" as I drag the 
>visual display to
>change frequencies displayed are my least favorite "feature" of CW Skimmer.
>
>Let me see if all my assumptions are correct.
>
>My assumptions:
>
>0. I use SDR-IQ receivers with CW Skimmer. I have
>     them set for "96 KHz" sampling rate.


Me too


>1. This is going to sample a bit less than 96 KHz
>     of the band;

Well, it samples 96 KHz, but the two KHz or so at each end of the range are 
apt to be cluttered with artifacts.  For this reason, and because of 
concern about a DC spur in the output of the SDR-IQ, the connection between 
the SDR-IQ and Skimmer was set up so that you should set the Tune At 
frequency to 36 KHz above the lower band edge.  This drops the bottom end 
artifacts below the band edge, but still covers up to ~7092 or so (for 
example) with good quality.

It is also recommended that you set the decoder only to decode in the CW 
band segment, and adjust the bandplan limits (and the bandplan you select) 
so that it covers the minimum range necessary to achieve your coverage 
goal.  To see why, try this on 40M some night with your center frequency at 
7036 and a bandplan that covers the entire band up to 7150.  You'll see the 
program quickly spawn over 1000 decoders as it attempts to make sense out 
of SSB signals and broadcasters.  Help your computer up off its knees and 
then limit the range. and things get much more reasonable.


>2. The *center* of the sampled band segment is set
>      in CW Skimmer by setting the "Tune at
>      Frequency".


Yes


>3. The "Tune at Frequency" also sets the point at
>     which I can listen to a CW signal on the band.
>     If I click on another signal displayed in the
>     ~11 KHz displayed on my screen (may vary with
>     screen resolution), it changes the "Tune at
>     Frequency" to that frequency, and so changes
>     the center of the monitored band segment.

Yes, this is correct.  You can also click on any callsign in the callsign list.


>I would like be able to set the center frequency independent of the 
>frequency range I am
>viewing or the frequency I am listening to.
>
>Is this possible? Has anyone proposed this to Alex, or am I just 
>completely off-base in my
>understanding of CW Skimmer and the SDR-IQ receiver?


Here's the rub (Alex, do I have this right?).  Every time you change the 
Tune At frequency, the decoding by *all* of the decoders currently active 
is upset for a second or two.  If you actively tune the band, you can 
significantly degrade Skimmer's ability to decode and spot all the signals 
on the band that you're *not* listening to.


>BTW, CW Skimmer was **invaluable** at PJ2T during the CQWW 160 CW Contest! 
>Our DSL crashed
>on the first night, and Skimmer (connected to our switchable receive 
>antennas system)
>provided us with several "pop-up multipliers" that we might have otherwise 
>missed. We will
>(likely) be in 3rd Place Multi-op Worldwide (after Africans CN3A and CT9M) 
>when all the
>dust settles.
>
>
>73,  Jeff  K8ND
>