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Re: Pre-amp question



At 10:14 AM 03/18/1999 -0800, Jordan wrote:

>I agree with the DCI filter usage... I wouldn't be without them on 2
>,222 and 432... they increase loss by around .8dB , but they drop the
>noise floor by 4 or 5 dB... well worth the loss... gets rid of all the
>intermod and TV spurs ,computer spurs and noise... 73 de Jordan...

Amen.  I have a fairly short run of coax--40 feet of 9913.  I found that
here in RF-intensive Seattle, I got better results on 2 meters using  the
"brick" amp's preamp in the shack--*after* a DCI helical filter--rather
than a Landwehr preamp near the antenna.

We've discussed this on the amsat-bb before, and several AMSAT lumiaries
from from the "underpopulated" wilds of California mentioned similar
experiences.  The best noise figure in the world is worth little if your
receiver or preamp is overloading on ambient RF crud.

The DCI filter creates one little problem.  My Yaesu 736R's transmitter
does not like the 2m DCI filter.  The 736's SWR protection circuitry "sees"
the filter as a mismatch, and reduces output to almost nothing.  However,
an SWR bridge shows no significant increase in SWR over the antenna alone.
If I turn on the "brick" amp, it's quite happy to transmit.

I left message on Yaesu tech support's phone line about this, and they
never replied.  I tried several lengths of coax between the "barefoot"
Yaesu and the DCI, to no avail.  So now I always use the amp and sequencer
when operating 2m, turning the power down appropriately.

It's more of a minor annoyance than a problem, but I've always wondered why
the 736's transmitter doesn't like the DCI.  Any ideas?

73 from KD7MW,

--- Peter
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