rohre@arlut.utexas.edu writes:
<< The Omni VI is well documented in ARRL tests in QST magazine, and in the
advertising over several years, as having a lower noise floor than Yaecomwood
transceivers. It is therefore more sensitive to RF. It is also INCORRECT
with modern radios, to run all the time with maximum RF gain setting, for as
you correctly state, that would amplify noise as well as signal, and you may
well introduce overloading of early stages and intermodulation products with
excessive gain. >>
<<and other "explanations">>
I have discovered this "noise problem" on my second hand Omni VI. When I
posted question to the reflector, I got similar answers (wishy-washy). One
reflectoree described the source of the problem to me. Procedure to verify
this is: turn your LP and DSP off, disconnect the antenna, trun your RF gain
full up: you will hear high pitched hiss from audio. As he properly
identified, the noise is caused by IF stages after the crystal filters and
detected and amplified. On my Omni VI+ this happens when I turn my RF gain
past 3 o'clock. This is what it is. Has nothing to do with sensitivity, front
end, quieter radio, TenTec superiority. It looks like unsolved design problem
in the IF stages. The remedy is to use LP or DSP on CW, on SSB use outboard
filter or keep the RF gain just below the point where it starts hissing. If
the signals and noise from the antenna is loud, this problem is masked. Looks
like some type of filtering or adjustment of IF stages could solve the
problem. I have not had the chance to look at it yet.
One nice thing about Omni is that S meter's needle zero position doesn't go
up with reduced RF gain.
73 Yuri, K3BU
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