[Elecraft] PSK31 -- ghost image:

Fri Feb 14 08:32:03 2003

Some of this "ghost image" stuff seems to be a quirk of the computer sound card.
Or even possibly some distortion in the receiver's audio system causing accentuation
of the harmonics of the audio signal.
I have noticed this even when a VERY clean CW signal is generated and it's spectrum
is
watched carefully.  The "ghost signals" appear on the spectrum display in exact
multiples
of the fundamental audio tone, even if the audio level into the sound card is
carefully
adjusted until it "just appears" on the display.

Usually when the transmitted PSK signal is being overdriven, "sidebands" appear on
either side of the "railroad track" signal.  I have also seen wide bands of spurious
signals that
appear over the portion of the spectrum being monitored at times.  This is also
sometimes accompanied with harsh sounding signal or a "hissing" note.

Must PSK operators are unaware of this unless you TELL THEM that their signal is
"dirty", but I hasten to add, that the "ghost signal" images you are viewing are not
usually
the fault of the transmitted signal, but flaws in the actual receiving
setup/software/hardware.
I was somewhat alarmed in first seeing this until I ran some tests and discovered
what I
have conveyed above!  I would be curious to find out what happens to the audio signal
while it is being processed in the sound card!  To date, I am not brave enough to go
probing around in the audio card with an oscilloscope!
73,
Sandy W5TVW
----- Original Message -----
From: "Gregg R. Lengling" <[email protected]>
To: <[email protected]>; <[email protected]>
Sent: Friday, February 14, 2003 6:00 AM
Subject: Re: [Elecraft] PSK31 -- ghost image:

| No there is nothing wrong...what you found was a poorly setup transmitting
| station.  If you were to watch his IMD when he idles with no characters sent
| you would have seen a very poor IMD figure....chances are his signal was
| very wide on the waterfall also.  He is overdriving his radio and causing
| such a wide signal and distortion that he is actually splattering.  I've
| helped out a couple hams that didn't realize they were doing this.....a good
| clean PSK31 signal on the waterfall should be clean and less than 50 Hz
| wide...anymore and they defeat the purpose of the mode.
|
| Gregg R. Lengling, W9DHI
| PSYCHOLOGY:  The science of inventing words for things that do not exist.
|
| ----- Original Message -----
| From: "Martin AC6RM" <[email protected]>
| To: <[email protected]>
| Sent: Thursday, February 13, 2003 11:11 PM
| Subject: [Elecraft] PSK31 -- ghost image:
|
|
| > I've just started playing with PSK31 with the K2 and a rigblaster Nomic.
| > I noticed something strange today.  A station appeared strongly just above
| > 14071 kHz, but the station also appeared almost 2kHz higher in the band as
| > well.  I'm using digipan 1.6 which allows you to watch two QSOs at the
| > same time.  They were both the same station -- character-for-character.
| > Is there something wrong with the way that I have set up my equipment?
| >
| > Tks in advance, and 73,
| >
| > Martin AC6RM K2#3021
| >
| >
| >
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