Peter says:
>Finally a question, when talking IMD, enlighten a mere mortal as to
>where this distorsion is to be heard. Is it within the passband, outside of
>the passband or maybe both.
Peter,
Generally, if the distortion is bad enough to be noticed on the signal, it's
tearing up the band for a long way either side. I've been consistently
surprised in tests just how bad IMD has to be before it's really noticeable
on the signal itself. I suppose it shouldn't be that surprising because how
good a signal to noise ratio does one get on the HF bands? I guess on 10m
you can get 30 to 40dB on a real strong signal. But most receivers do not
have very good Signal to Noise Improvement Ratio figures, which will mask
things.
The real test is 5kHz away! ITU requirements ( Recommendation. SM.329) don't
actually call for emissions to be 43 + 10logP dB down (not exceeding 50dB
for amateurs) (P is the PEP in Watts) until you are about 6.25KHz away from
the assigned frequency - which is 1400Hz away from the carrier for SSB.
For being reasonably popular, you need to be rather better than that.
> Can we hear a difference of 15 db IMD with our ears on the bands or is it
>academic ?
It depends on how strong you are.
You may well have a DAF that is linear with speech, but if so, it does
appear to be a rare bird.
73
Peter G3RZP
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|