Tower mounting preamps can get you into trouble. At low freqs, (below
432 usually) they can be avoided.
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 the
same class (humans). Assuming that you are not a cheapskate, and get decent
coax, there is no need to tower mount preamps on 144 or even 222 with a DEM
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.
I start using preamps on 432 and above. My background noise on the
horizon is so high on 144, that any thought of a preamp with the DEM
transverter strikes me as a waste of time. (Feedline is 365 ft of 1 5/8")
Loss is just under 1 dB. The background sky temperature your antenna sees
on the horizon is about 600-1000 degrees K at 144. Occasionally it may get
down to 300. Another 20-50 degrees does not do much. I remember lowering my
EME array to the horizon and seeing the noise level increase as I started to
see tree fioliage in the antenna pattern. I had to do this when the sky
background was 180 degrees K behind the trees. It was a good experiment, and
shows how noisy 144 MHz is when pointed at the horizon.
Sam Harris W1BU, once said: " If your feedline is over 1 dB, FIX IT!"
Save ur money on tower mtd preamps, and put the $$ into some good coax.
Dave K1WHS
----- Original Message -----
From: "Tree" <tree@kkn.net>
To: "Kenneth E. Harker" <kharker@cs.utexas.edu>
Cc: "Todd and Sandy Sprinkmann" <sprinkies@excel.net>; "VHF Contesting"
<vhfcontesting@contesting.com>
Sent: Wednesday, August 13, 2003 7:11 PM
Subject: Re: [VHFcontesting] Info/experience with TS790A and IC820H
>
> > Some Yaesu FT736R rigs have been
> > improved with a Mutek front end mod, which basically replaces several
boards
> > in the radio, but these are relatively expensive and rare.
>
> I have been using the FT736R for 144, 222 and 432 work for a few years
now.
>
> While a common complaint is that they are deaf, I must say that a large
part
> of this is just that the front end gain is pretty low. The noise figures
> don't seem to be too bad. I now have preamps on the tower for 144 and
432,
> and will for 222 as well. There is an increase in the S/N ratio using the
> preamp, but it isn't much more than the coax loss.
>
> In other words, if you crank the AF gain on a 736R, it isn't as bad of a
RX
> as it sounds initially when you look at the s-meter.
>
> > My favorite VHF/UHF setups have been Kenwood TS-850SATs with Downeast
Microwave
> > transverters. You might also consider an Elecraft K2 plus Elecraft XV
> > transverters. You'd have to build it, but you could get on your first
VHF/UHF
> > band for ~$1000 and add bands ($350 each) as you need them, and have one
of
> > the best ham receivers ever made. You wouldn't be ready for this
September,
> > though.
>
> These are great choices and I would use DEMI as my next choice. However,
> even with them, on frequencies above 100 MHz, I would argue that you would
> want a preamp at the antenna eventually in order to crank every db out of
> your system - therefore, it becomes a wash with the 736R.
>
> So far, my 736R has been very reliable - and I would dare say that just by
> the number of cables necessary necessary to hook up transverters, you will
> have plenty of issues.
>
> Tree
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> VHFcontesting@contesting.com
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>
>
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