>
>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.
>
Apparently as rare as the dodo bird. .
......
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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