[pskmail] Re: Test Alpha Fldigi version for FM (VHF/UHF) links
- From: John Douyere <vk2eta@xxxxxxxxx>
- To: pskmail@xxxxxxxxxxxxx
- Date: Wed, 21 Mar 2012 21:59:00 +1100
Some extra information regarding the usage of the new modes in FM.
In my test I have noticed that it is easy to overload the TX audio and
start loosing decoding accuracy on the other side.
Since the ALC level is not related to the audio level in FM, the indicator
I use is the Modulation level (FT-8x7 series).
As an example I found that having the modulation indication at about 1/3 of
the maximum for a single carrier PSK is about right, giving a reasonable
audio level but no visible distortion.
The multi-carrier modes can be a trap since the average level is lower than
a single PSK carrier modulation but the peaks are the same. So it sound
lower but the level must not be increased to compensate, otherwise the
peaks get truncated and the decoding suffer too.
In SSB, the multi carrier PSK modulations will result in an average power
well below that of the single carrier PSK, but again we should not try to
compensate for it.
Under these modulations, if you push the TX audio level ALC too high you
actually may well be getting only 20% of the max RIG power at the output,
with the ALC way up.
Hope this helps,
73, John
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