[FARC] PSK Questions

[Bob Moroney]

Kirk,

I found a WinPSK user guide on the net at: 
ftp://det.bi.ehu.es/pub/ham/psk31/winpskuser11.pdf .  If you haven't 
looked at it, it may answer some of your questions.  It looks a bit 
dated, but it suggests that the "PPM" number has to do with the 
calibration of your individual sound card vs. an ideal value.  It 
doesn't seem to mention the IMD indication, which might have been added 
in a later version.  Another site has an explanation of IMD relative to 
PSK: http://www.psb-info.net/IMD-Measurement.html .  It confirms your 
suspicion that lower is better.  If you Google on "psk waterfall 
display", you'll find a good bit of information on what the display can 
reveal, plus its limitations.

Most of what I've seen on HF SSTV is folks' QSL cards or snapshots with 
the sending station's callsign added, and that's about it.  It's TV in 
the sense that it's transmitted video capture vs. fax or other scanned 
material, but it's definitely not full motion video.  As with any HF 
mode, "band conditions" (propagation+RFI+EMI+BCI+etc.) seldom combine to 
enhance signal quality, so what you get out of your speaker or on your 
display will almost always be less than perfect, sometimes way less...

73, Bob K9CMR

Kirk Talbott wrote:
> I have some questions about PSK31 and Slow Scan TV for the group.
>
> One:  Hams on PSK31 use a Morse code shortcut language.  For example, a 
> typical CQ looks something like this. "CQ CQ CQ de W4XXX W4XXX PSE k."  I 
> know what the "de" and "k" stands for but what does "PSE" mean?  Another 
> example is the signoff.  "KB3ONM de W4XXX W4XXX 73 sk sk sk."  What does the 
> "SK" mean?
>
> Two:  On my software, WinPSK, there are some numbers displayed at the bottom 
> of the screen below the waterfall window.  One is IMD the other PPM.  A read 
> a little about IMD and found that it stands for Inter-Modulation-Distortion. 
> Ok, but what does that mean?  My interpretation of the reading I've been 
> doing, a high numbered IMD means you're distorting and splattering all over 
> the place and low a number means you're getting close to a perfect signal. 
> It's kind of like mic gain in SSB phone. And like SSB phone, too low a mic 
> gain means you're not putting out enough "punch" in your signal. Does too 
> low an IMD number in PSK31 mean the same thing?  As for PPM, I have no idea 
> on what this means and can't find any info on it.
>
> Three:  I had one of my contacts give a signal report that went something 
> like this.  "Your RST is 599, and the waterfall display shows a near perfect 
> signal."  Ok, I understand what "599" is, but the reference to the waterfall 
> display and the near perfect signal has me baffled.  What are they looking 
> at in the waterfall that shows a near-perfect signal? My software, WinPSK, 
> is freeware and pretty limited.  So maybe it doesn't show what other more 
> sophisticated programs do.
>
> Four:  SSTV seems neat, but I can't seem to receive a signal strong enough 
> to get a decent picture.  The letters TV in SSTV seem a bit of a misnomer. 
> You can't really use video in slow scan TV....right?  What I see mostly on 
> SSTV are pictures that look like travel agency posters; beaches and palm 
> trees, mountains and lakes, etc. with call signs written on them. Is this 
> all there is to SSTV?
>
> Since June 26 I've had 38 PSK31 contacts.  I was going like gangbusters 
> there for a while.  July 4 and yesterday, I couldn't get one contact. On SSB 
> phone I didn't even hear one person on 20 or 10 meters, and I heard only 2 
> people on 40 meters.  Sometimes on PSK31 I can contact Texas on 15 watts 
> output, but then need 75 watts output to communicate with Florida.  HF is 
> really "fickle" isn't it.  Analogous to fishing.  Throw your line in the 
> water and sometimes they're biting and sometimes they're not.  F. Gump had 
> it right about a box of chocolates and it applies to HF. "You never know 
> what you're going to get."
>
> 73
> KB3ONM
> Kirk 
>