[VHFcontesting] Info/experience with TS790A and IC820H

Jim Worsham wa4kxy at bellsouth.net
Fri Aug 15 13:43:39 EDT 2003


I have to agree with Dave.  In my experience IF you have a good low loss
feedline and IF you have a good receiver (transverter/HF rig combo) and IF
you are not trying to do something like EME with a really low background
noise floor then preamps cause more harm than good.  Spend the money on
hardline and a good transverter (DEMI).

73
Jim W4KXY

----- Original Message ----- 
From: "David Olean" <k1whs at worldpath.net>
To: <vhfcontesting at contesting.com>
Cc: "Todd and Sandy Sprinkmann" <sprinkies at excel.net>; "VHF Contesting"
<vhfcontesting at contesting.com>
Sent: Thursday, August 14, 2003 9:40 AM
Subject: Re: [VHFcontesting] Info/experience with TS790A and IC820H


>     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 at kkn.net>
> To: "Kenneth E. Harker" <kharker at cs.utexas.edu>
> Cc: "Todd and Sandy Sprinkmann" <sprinkies at excel.net>; "VHF Contesting"
> <vhfcontesting at 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 at contesting.com
> > http://lists.contesting.com/mailman/listinfo/vhfcontesting
> >
> >
>
>
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