[VHFcontesting] Info/experience with TS790A and IC820H

Hoffman, Mark mhoffman at microwavedata.com
Thu Aug 14 11:27:55 EDT 2003


I'm actually with Dave on this one. In my station, all preamps 2-432 are
located in the shack, with feeder losses < 1dB on each. Until I'm ready for
EME, where I WILL be putting it on the tower - there's been no point at
which it's been useful to have one installed there. 

I DID have one up on the tower- but with the combination of sequencing,
extra control lines (130'), wx-proof enclosure, proper relays (to handle the
stooch) and the time/energy to install, I suspect it was useful all of 3X.
More often, when high-power local stations came on the air, it was relegated
to the OFF position. 

I have old transverters (MMT on 2,222), and a couple good ones(DEMI on 432)
and each has a preamp. More than anything, it's really just because I had
em, and it was easy to do. The NF of the transverter has been measured at
1.25dB (432) so it's totally unnecessary to use a preamp. On 2/222, where
the NF of the transverters is around 3dB, it DOES pay off a bit. In/Out
testing shows a qualitative improvement, that's for sure. But mostly so I
can set the resting S-meter to something just above 0. I like conversion

If you are in a quiet location, without other high-power locals in the
vicinity - it's probably OK to spend the extra time/effort to do it. Once
that local guy hits the air 15 miles away, you might wonder why you did it.

-Mark, K2AXX

-----Original Message-----
From: John Hawkinson [mailto:jhawk at MIT.EDU]
Sent: Thursday, August 14, 2003 10:05 AM
To: David Olean
Cc: Todd and Sandy Sprinkmann; vhfcontesting at contesting.com
Subject: Re: [VHFcontesting] Info/experience with TS790A and IC820H

David Olean <k1whs at worldpath.net> wrote on Thu, 14 Aug 2003
at 14:40:04 +0100 in <00d901c36269$92dcfc30$37c07f3f at DGL28221>:

> Comparing a modern version DEM transverter and good modern HF radio with a
> Yaesu 736 is like including Arnold Schwarzenegger and Pee Wee Herman in
> same class (humans).  Assuming that you are not a cheapskate, and get
> coax, there is no need to tower mount preamps on 144 or even 222 with a
> transverter. A preamp will just kill your overload capability. If you have
> to run more than 100 ft of coax, and it isn't 7/8" on the higher bands,
> maybe a low gain preamp could help. Shoot for 1 dB feeder loss. 3 dB loss
> starts to be real bad.

Our experience at W1XM, high up in RF noisy Boston (albiet with a
736R), is that a preamp on 2 meters is incredibily valuable, even with
an 80' run of heliax. However, it is necessary to front the preamp
with a cavity filter. Remember, you can always turn the preamp off...

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