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[TowerTalk] Tuner Loss - Do Not Panic

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Subject: [TowerTalk] Tuner Loss - Do Not Panic
From: (Michael Tope)
Date: Wed, 17 Nov 1999 07:54:49 -0800

First of all, a quarter dB of loss in the tuner would be 50
watts of dissipation when running 900 watts total output, so
it doesn't take much loss to produce noticeable heating. As
far as the length of the feedline adding to loss (heat) in the
tuner, the two aren't directly related. The longer feedline will
be more lossy than a shorter feedline of the same type of coax, but
this loss manifests itself as heat dissipated along the length of
the coax, and not in the tuner. Aside from impedance interactions
(different lengths of feedline may present different impedances to
tuner which can be matched more efficiently), the two sources of
loss (tuner and feedline) are independent.

If your Amp is happy with the 1.5:1 VSWR from the Force 12,
I wouldn't bother with the tuner. The PI network in the Amp is
designed to match a range of impedance's centered around 50 ohms.
A 1.5:1 VSWR should be close enough to 50 ohms that you can tune
the amp up with no loss in efficiency. In fact, think of it this
way, the amp and the tuner probably both use PI networks for matching.
Why cascade two PI networks one right after the other. The only reason
to do this is if the range of the first PI network (the one in
the amp) isn't large enough to match the impedance presented
by the antenna. For low VSWRs (<2.0:1) the tuner shouldn't be needed.

The one place where the tuner would be useful, is the case where
you are switching between two antennas on the same band (without time
to retune the amp in between). If the impedance's of the two antennas
differ greatly, you will only be able to optimize your amp tuning for
one of the antennas, the other will be a compromise. The external tuner
can make the second antenna look like the first so that the amp sees 
approximately the same load impedance from both antennas. In this case the 
extra 0.1 - 0.2 dB loss will be well worth it.

Hope this is helpful.

73 de Mike, W4EF.............

From:   WA9ALS - John[]
Sent:   Tuesday, November 16, 1999 8:01 PM
To:     Towertalk Reflector
Subject:        Re: [TowerTalk] Tuner Loss - Do Not Panic

Following this thread with interest for 2 reasons:

1)  I have recently used a couple of different tuners in several
configurations with "long dipoles" (several combinations of open wire,
outside baluns, etc and had some fun with 160M.)  I finally ended up
using the Radioworks full size Carolina Windom 160 and the MB-V-A
tuner - works great with power on 160 and has been dynamite on the other
bands, of course!

2)  Now my question:  I recently completed my first tower/yagi project,
ending up with a Force 12 tribander.  The SWR is below 1.5:1 everywhere
I'm interested in, if not the whole band of interest.  However, I
elected to run the feedline through the MB-V-A to make it "perfect" for
my amp.  During this past weekend's WAE RTTY contest, after a couple
hours of running about 900W, I noticed significant heat when I put my
hand on the tuner case.  It wouldn't peel paint or burn your hand, but
it was quite warm.  I had never noticed this when using the tuner with
power to the windom, although I don't think I was ever specifically
looking for it.  Both antennas have good "tuner-less" SWR - The main
thing that is different is the feedline length - over 600 ft for the
yagi, mostly LMR-600DB.  Is this the source of the heat (?loss) in the
tuner?  Gotta get a wattmeter out there!  Should I bypass the tuner
altogether if within the amp's specs?  Tnx!

WA9ALS - John

----- Original Message -----
From: Ward Silver <>
To: Towertalk Reflector <>
Sent: Tuesday, November 16, 1999 6:04 PM
Subject: [TowerTalk] Tuner Loss - Do Not Panic

> > > I have a friend who peeled the paint on one of the Dentron tuners
a few
> > > years ago,

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