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Hi Graham,
following your advice I've now taken out the
SpecLab filter / noise blanker again. Not sure whether this will be for the
better... anyway I'm aiming for a fair comparison of our two
Opera reception methods.
Re DCF39: yes the space freq (139.17) is above the
mark (138.83 kHz). But the biggest problem is the unfiltered FSK
hardkeying, which (even at 325 km) produces annoying splatter down to about
136.6 kHz during each data telegram. That's almost 5 kHz occupied bandwidth
for a 200 baud FSK signal! Should be completely inacceptable by any
standard, but apparently fulfills specifications of their TRAM transmitter
:-(
Best 73,
Markus (DF6NM)
Sent: Friday, June 28, 2013 11:42 PM
Subject: Re: LF: VO1NA Op32 137.555 kHz
Ok Marcus ,
Needs must , I dont think the frequency
translation would be a problem, but any modification to
the envelope parameters will degrade performance ,
the low s/n sdr decodes , point to the
lack of 'ringing' in the filters , enabling much
lower levels , notably , using the £5 dongle in
direct-sample , I see the modulation is HF of
the carrier , where with any of the
conventional Rx's , there is a splash across
the band .
Strange that Iceland has not shown a decode ,
its about 1000 K north of the direct path
and half the range , expected ?
73 -G.
Sent: Friday, June 28, 2013 8:53 PM
Subject: Re: LF: VO1NA Op32 137.555 kHz
yes. I'm aware that Opera should nominally be
fed with straight full-band SSB. But going by the first results, the
preprocessing seemed to help a lot in the presence of our strong DCF
splatters, so I left it in. In any case I'd need SL as an audio mixer to
accomodate my fixed 135.5 kHz LO.
Best 73,
Markus
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