Laurence,
Dennis, LF,
Good
discussion has emerged since my first observation. I have had many constructive
comments from various LF authors on here.
Laurence
has stated just what I have been thinking to myself that it is only now with
the introduction of the wideband Softrock SDR & the software (SpecLab) that
it has come to my attention visually & caused me to question what I previously
had overlooked or taken for granted. I believe I am more inquisitive now than
my early days in the hobby.
Thank
you Dennis & Laurence for your input.
73
Gary –
G4WGT.
This was a very good write up -
thanks -
With the advent on "spectrum analyers" and panaraomic displays with
the new SDR radios they provide a very telling visual fade pattern on even
narrow FSK modes on HF - as you said you could actually visualize the antiphase
moving up and down in freq and having the affect on each tone.
I dont know but 500 seems to have some of the worse fade characteristics, not
too slow and not too fast - just plain difficult for the info rate for some
modes (:-) Funny but I never remembered the fading as much when I was at sea on
CW/MCW...
As Alan has pointed out the phase/antiphase cancellation on multiple iono paths
can ruin hours worth of listening on 137kHz and relatively small changes in
location (a few Kms) can show diverse signal reception levels on some nights.
Long haul pretty good at the moment - DCF39 some 45-50dBs above my neons and
other restaurant Christmas tree flashers on peak - the normal about 15-20 min
fade pattern.
Laurence BY3A-KL1X Tanggu OM89UA
ps Scott VE7TIL made it here on 40m WSPR last night :-) on the probe
> Date: Tue, 30 Dec 2008 01:11:19 +0100
> From: [email protected]
> To: [email protected]
> Subject: Re: LF: 500KHz QSB
>
>
> Hi Gary!
>
> Yes fading seems to be very selective.
>
> Have you ever been listening to a distant AM radio station? Give it a try
:)
> There it is often audible, that a "fading notch" travels through
one sideband down to lower modulation frequencies, then there is a moment of
often terribly distorted audio due to the notched out carrier (the remaining
sidebands "virtually much overmodulated"), then the "notch"
goes further through the second sideband (if this also passes your filter).
>
> The fading is fast on shortwave, where almost all the time different
skywaves "are fighting each other" , medium fast on medium wave, and
in the case of longwave transmitters sometimes very slow (may take minutes).
>
> Here in Berlin this longwave radio QSB appears very nicely at dusk to the
204km away "Polskie Radio I" 225kHz transmitter. The skywave becomes
stronger and seems to equal the value of the groundwave, so constructive and
destructive interference takes place.
>
> Have a nice evening :)
> Dennis
> DL6NVC
>
>
> --
> Psssst! Schon vom neuen GMX MultiMessenger gehört? Der kann`s mit allen:
http://www.gmx.net/de/go/multimessenger
>
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