Bill Cromwell wrote:
> meters). One of the problems with high levels of electrical noise is
> overloading of the front end and blocking of the receiver. Therefore
> noise that is not actually on or very nearly on your operating frequency
> jams you up. I am also investigating some of the loop antennas to use
I don't see how noise overload of the receiver front end can
be an issue. You can simply add front end attenuation such
that the external noise just overcomes the receiver's internal
noise. It would only be an issue if somehow there was much more
noise just outside the 160 meter ham band than there was inside
the 160 meter ham band. How would that ever happen?
> along with the high level mixers (NO rf amp and none needed on 160
> through 20 meters). That Xtal filter used ahead of such a receiver and
> possibly with one of those antennas that can null out some (or all) of
> the noise should get Anton happily on the air.
>
The loop I described in the National Contest Journal is fairly
sensitive and certainly doesn't require an external RF amp.
It may or may not need to have the transceiver's internal RF amp
enabled. If you build the 40 foot circumference version, you get
about another 9 dB of signal output.
There seems to be a notion here that xtal filters are somehow
a bulletproof front end fix. However, the third order intercept
of the filters is not necessarily all that high. Although
they are "passive", that doesn't mean they are linear when
driven hard. This topic was covered extensively in "Technical
Topics" in RSGB Radio Communication (I don't have specific
citations). The reason why crystals are non linear is that the
extremely high Q results in tremendous acceleration effects on
the quartz even for 1 mW drive. It is not unusual to see
hundreds of thousands of G's of acceleration.
Rick N6RK
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