>
Thanks Andy - any volunteer among the SpecLab users who already realized
this with the colour palette editor ?
If so, I'd like to add it in the next release so others can try it out
too ;-)
73, Wolf DL4YHF .
Dear Wolf, Andy, LF Group,
Funnily enough, I tried something very similar with Spectrum Lab a while
ago - the palette up_down.pal attached is more or less what Andy described.
But I found the effect to be rather counter-intuitive, with strong signals
"punching holes" in the waterfall display. I settled on having a progression
blue-red-yellow-light green-white, as in the attachment jim.pal, which I
have been happy with ever since.
As far as RX bandwidth goes, I find quite a wide bandwidth is best with
SpecLab. The dynamic range of sound card ADCs seems to be pretty good, and
the limiting factor on strong interfering signals is what the receiver IF
and audio channels can cope with. So as long as the IF/Audio/soundcard gains
can be set so that nothing is driven into overload, there is no AGC action,
and the noise level is still lower than the signals, QRM much stronger than
the wanted signal can be present at the RX audio output without problems,
and all filtering can be provided by the spectrogram program. With the
RA1792 RX I usually use the 300Hz or 1000Hz bandwidths; it has a 150Hz
filter too, but this worsens the effects of QRN. When a QRN impulse occurs,
the RX is bound to be driven into limiting at some point, but with a wider
filter, the duration of the overload is shorter, and has less effect on
narrow-band signals displayed. This effect is even worse with the W&G SPM-19
level meter with 25Hz bandwidth - barely audible QRN seems to get magnified
into great streaks on the spectrogram. I suppose it depends a lot on the
impulse response of the individual filter.
Most of the "visual modes" reception I am doing currently uses a "sound card
RX", converting 135.7 -137.8kHz down to 10.7 - 12.8 kHz, and feeding this
output directly into the sound card. All tuning is done by adjusting the
Spectrum Lab frequency axis on the PC, and the audio bandwidth is fixed at
about 3kHz, so the whole band is being fed into the sound card input all the
time. It seems to work at least as well as a "proper" RX for tranatlantic
reception, etc. The circuit is the one in the new edition of the RSGB radio
communication handbook.
Cheers, Jim Moritz
73 de M0BMU
jim.PAL
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up_down.pal
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