The product detector mod I mentioned is applicable to the Omni-V and Omni-VI.
I have no idea if it might be relevant to any other TT radio., probably not
at least for most folk.
Product detector performance was carefully researched in UK using an Omni-VI.
The authors found that the standard detector exhibited relatively poor strong
adjacent signal performance. I have to say that this applied under UK
conditions where the levels of adjacent channel and BC crud, mostly from
Europe, are often truly humongous. If you do not have such QRM problems -
and many certainly do not have, then any improvement will not be noticed.
But with my 40m inverted V high on a hilltop, strong European QRM (coming in
at high angles) is almost always there. And I can hear distortion products in
the form of spurious signals. Using my Elecraft K2 on the same antenna, the
same distortion products are not there, period...
There are at least two other solutions to this strong signal distortion
problem, aside from getting an Orion. Firstly, using the K2 is not the anwer
because (a) 10 watts does not really drive my TT linear very well, and more
significantly (b) the skirt selectivity of my ancient K2 is not as good as
that given by the cascaded filters in the Omni. The INRAD filters do show
excellent skirt selectivity.
Secondly, you can try to eliminate, or at least reduce high angle signals, by
using a something like a groundplane instead of an inverted V. Now that does
work, but at this city location it has problems The noise level goes up and
there are substantial buildings in some directions. But it paid off big time
once when I could not copy BS7H on the inverted V because of BC birdies on
7005. I swapped to a Cushcraft R7 I had temporarily rigged for testing on a
post in the yard and there was BS7H, a solid 579. One call and BS7 was in the
log.
At that time I did not have the INRAD 7mHz roofing filter that goes ahead of
the Omni, directly in series with the antenna input and ahead of all internal
filters (Just don't transmit thru it !!) That filter does eliminate the 7005
BC birdy, but not of course distortion products due to strong signals inside
its 15 kHz passband.
John G3JAG
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