> Yes. I believe it may be due to the IMDDR3 performance not
> creating internal distortion products within the passband. Whatever
> the reason, it was noticeably different than my experience with the MP
> in the same contest, same band, the previous 4 years.
I'm a little puzzled by that. Most of the IM we hear is from transmitters,
not generated in receivers.
The typical SSB transmitter IM3 is in the -25 to-30dB (below one tone of two
equal tones). A typical receiver like the 1000MP is about mid 80's for IM3.
The Orion measures mid-90's or so. At higher orders, transmitters are even
further worse than receivers.
The exception is when the NB gain is up (even with the NB off) in the MP. In
that case a mix in the NB amplifier, even with the NB control OFF, decreases
IM performance of the MP. But it is still better than transmitters.
What I notice is far more flexibility in setting selectivity and skirts. I
can use a 1.8kHz roofing filter and use the DSP to keep good audio allowing
closer work to strong signals, but I haven't seen a reduction in adjacent
channel splatter that is really splatter nor have I seen a difference when
BW's are the same when viewed on an audio spectrum analyzer program.
It's not that I don't see a difference, my Orion is clearly better on SSB
than my other radios. I just think it is all in the selectivity, mostly the
ability to use a narrow roofing filter and correct sound with the DSP
system.
I just don't see how that difference ties into IM3 performance. In order to
improve IM3 performance, we'd have to fix the transmitters first wouldn't
we? Or am I missing something?? What roofing filter do you use Bill?
73 Tom
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