Hi Ian,
>That's the key question, because you have been talking all the time
>about 3rd order IMD, which is close to and underneath the speech signal
>itself.
Does a transmitter with poor 3rd order IMD therefore have any noticeable
distortion in the voice quality due to the speech intermod products within
the audio bandwidth?
>A 3rd-order IMD figure on its own is no guide to what the amplifier
>sounds like further out.
If the system/amplifier is IMD'ing in the audio frequencies, then
intuitively, the problem causing that IMD is probably also causing splatter
products outside the audio bandwidth too.
>All these complexities mean that when someone talks about "IMD" without
>going into very specific detail, it's likely to be incomplete or
>meaningless. We all do it, but we also need to be aware of it.
That is the point I was trying to get to, what really constitutes a
meaningful lab test for splatter?
>Ironically, the most meaningful test of IMD performance for SSB is also
>the simplest - just tune away from the signal, using a good receiver
>that isn't being overloaded, and notice how far away you have to go
>before the splatter dies away into the noise.
Using the (meaningful) receiver method, I have heard terrible, very wide,
signals transmitted from "high end" transceivers, and excellent, no
splatter, signals from the so called "cheap" transceivers!
--
Zyg AF4MP
Roswell GA USA
|