[UK-CONTEST] Data contest - apologies

[David]

Graham

I was not in the contest so no axe to grind but I do a lot of data
contesting.

PSK is a very poor mode for 80m during the winter/early spring evenings. The
reason is that 80m suffers form a lot of multipath propagation and Doppler
shift. The result of this is that the phase of any signal can change very
quickly in fact so fast that PSK31 becomes useless as it relies on the phase
on the incoming signal being reasonably stable over one bit time (32
milliseconds). I suspect this is what you were really suffering from.

You would have found that RTTY on the other hand is a different kettle of
fish. This relies on frequency shift rather than phase shift. Phase change
does not make a lot of difference to FSK. What destroys FSK using MMTTY is
multipath causing one of the tones to disappear (selective QSB) and this
does happen. It is a implementation failing of MMTTY as it is possible to
copy on just one tone. The other thing that rarely destroys FSK is multipath
with very long propagation delays causing the signal to be overlaid but
later. If this delay reaches about 10milliseconds or more and is about the
same strength as the main signal then it can and does confuse FSK decode. 

The sound card in your laptop unless it has gone faulty, which I very much
doubt, is perfect for these modes. There is no need to use an external one.
The only reason to use an interface box of some sort between your rig and
the FT1KMP is to reduce the amplitude of the audio out to the correct level
and if you have a problem remove hum loops by the use of small transformers.
However do not put small transformers near any power supplies especially
linear ones as the mains transformer magnetic field could make things
interesting.

I used to use a FT1KMP and I found that for RTTY the ideal mark tone
frequency was 990Hz when using the two 250Hz xtal filters on the SSB mode.
This was with the shift centred. Your optimum frequency may be slightly
different as it depends on the individual filters. PSK optimum was 900 to
910Hz. I found a lower frequency is useful as it makes tuning in by ear
easier. However do not overdrive the rig as on FSK you will create audio
harmonics with QRM to other band users. On PSK also get IMD products (make
sure the processor is off and no ALC indicated).

73 David G3YYD



-----Original Message-----
From: uk-contest-bounces at contesting.com
[mailto:uk-contest-bounces at contesting.com] On Behalf Of G4FNL
Sent: 06 March 2012 20:32
To: uk-contest at contesting.com
Subject: [UK-CONTEST] Data contest - apologies

I was active in the 80m RSGB contest last night. I had done a great deal of
pre-contest checks, over the past week or so,  to try and ensure that I had
everything working and properly operational in readiness. I am still new to
the data modes.  Before the contest, I was more confident with using the
software (N1MM), and also with using the radio and N1MM filtering more
effectively, along with shifting the IF pass-band to ensure that I could use
a narrower (400Hz) CW filter etc. So, I was very disappointed with the end
results. I ended up with just 52 Qs.

I believe that my TX signals were probably OK - but it possibly appears that
I was missing many stations calling me. If you were one, please forgive me
not responding back to you. I obviously lost out, and I apologise for
wasting your time. I am unsure of the cause of my inability to properly
receive on PSK - because it seems that it was working OK for some QSOs but
not for others.  I am suspicious that the problem could possibly be with my
in-built soundcard on the laptop PC.  I intend to try and replace my current
interface / soundcard set-up and borrow another for the next contest. So, if
I haven't been blacklisted on the data contest scene yet - please bear with
me and I'd be grateful if you would try and work me again next time. I would
like to know the size of the problem - and so, if you called me, and I
didn't respond - please tell me.

If anyone has any suggestions (that don't involve buying equipment) to
overcome the problems, I be grateful for the advice. I currently use an
FT1000MP, + ZLP DigiMaster ProPlus interface, an H-P laptop with built-in
soundcard, and generate PSK and RTTY with audio tones (AFSK). As I say, it
all seems to work OK for individual QSOs - but in the contest environment,
it's poor.

73 Graham G4FNL

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