Jim Lux wrote in
:

Owen Duffy wrote:
"998cc" wrote in
et:



The good thing is that your 5WL Yagi will have a good deal of
selectivity whereas it is certainly lacking in the '706IIG and in
many of the lower cost preamps (no money wasted on filtering).

I suspect the preamp makers would portray this as providing more
system engineering flexibility, letting you, the system builder,
decide how much filter selectivity (and corresponding loss/degradation
of NF) you want.

After all, if you were doing EME with a big array pointed up into the
sky, selectivity might not be such a big deal, but absolute lowest
system noise figure might be.

Hi Jim,

I suspect that was a bit tounge in cheek! I guess the manufacturers have
done us a bigger favour with hand helds in making them lighter by
minimising filtering.

If you want to fix an IC706IIG's front end selectivity here in Oz, one of
those Canadian filters for about $250 + $300 shipping is just the go.
Wait a minute, $550 to fix a $1000 radio's performance, and on just one
band... I don't think so.

I wrote an article on the performance of a modestly priced kit 144MHz
amplifier in the real world (as opposed to in a shielded room). I have
devised a test configuration that asseses what I term the 'realisable
sensitivity' which may be quite different to the specs derived in a
shielded room. The article is at http://www.vk1od.net/gt/144LNA/index.htm
..

The article also looks at the G/T improvements expected from other
configuration changes like a higher gain antenna and low loss coax, and
whether the preamp is located at the masthead or transceiver. Of course,
it all depends on one's own configuration, but the tools are there to
model a specific configuration.

Owen