Gerald - isn't that the purpose of attenuators? I'm not sure what
benefit is to be gained by mismatching RX antenna impedance, although I
agree it's not highly critical they be exactly matched.
I was thinking Merle might have a point - I'm trying to set up the
conditions where I saw the attenuation on a different band when
accidentally working cross-band, but I'm not able to replicate that
result at the moment. However, on 30m, where my G5RV Jr is definitely
non-resonant, 4.5 - 5:1 SWR, as a result of using the tuner, band noise
goes from S 3.5 to S5 (relative S-meter reading.) If the tuner is not in
the RX antenna path, how would this be explained (single VFO, simplex
operation)? Selecting a different band on the TX VFO causes the tuner to
turn off, but the S-meter still reads S 3.5. I'm on an original Orion
with 2.56 level firmware in case anyone else is also trying this. If I
had an RF signal generator, I could do better measurements, but I'll have
to live with noise level at the moment.
73, Duane
On Fri, 31 Mar 2006 21:55:10 -0600 "Dr. Gerald N. Johnson"
<geraldj@storm.weather.net> writes:
> On Fri, 2006-03-31 at 22:35 -0500, Carl Moreschi wrote:
> > Of course what you said is true, but it is still better to have a
> matched
> > antenna on receive. There is always the possibility of very low
> atmospheric
> > noise on a given night and the extra signal just might make the
> difference,
> > especially on 10 meters. Why do people insist on using a 9 to 1
> balun on
> > receive only beverage antennas?
> >
> > Carl Moreschi N4PY
> > 121 Little Bell Drive
> > Bell Mountain
> > Hays, NC 28635
>
> There are cases where a matched antenna is a benefit, where the
> receiver
> noise isn't so good. Most users of 10m antennas already build them
> pretty well matched, because matching at the transmitter end of the
> feedline makes the transmitter happy but doesn't guarantee the
> largest
> radiated signal, mostly because of the added losses of the
> transmission
> line with significant VSWR.
>
> And then there are situations were maximum signal to the receiver is
> the
> worst of conditions. Because it allows the local signals to
> overdrive
> the receiver obscuring the desired weak signal by clipping or by
> reciprocal mixing due to phase noise. Or there's a thunderstorm in
> the
> state or closer doing both of those. Something the NR and NB won't
> handle and the ringing Collins filters can't hack. Then its handy
> to
> reduce the power from the unwanted signals sacrificing the desired
> signal, hoping to remove the bad effects of the unwanted signals
> before
> loosing that weak desired signal.
>
> --
> 73, Jerry, K0CQ,
> All content copyright Dr. Gerald N. Johnson, electrical engineer
>
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>
--------------------------------------
Duane Calvin, AC5AA
Austin, Texas
http://home.austin.rr.com/ac5aa
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