[AMRadio] Baluns for Zepp Antenna


Jim candela jcandela at prodigy.net
Wed Apr 19 21:33:29 EDT 2006



Don,

   You are of course correct about having a balanced tuner with split stator
capacitor, center tapped inductor, swinging link, and series capacitor with
the link, and other variations that have been around since radio's were
powered by steam. You leave out one important thing though that gets picked
up by those who market tuners, and that is for every dollar spent on a
commercial amplifier, you need to spend half of that for a tuner suitable
for the job. There are tuners out there for more than a thousand bucks that
still put the balun on the load side of the tuner. This does not have to be,
and one solution dreamed up by folks wanting higher profit margins, is to
take a flawed design, and keep scaling it up until it works. This is kind of
like building a 10KW tuner for a 1 KW job.

   Maybe I am exaggerating a little, but not really that much. There are
tuners that put the balun on the input side of the tuner where when the
conjugate match is obtained, the balun only sees a resistive load at 50
ohms. These can use a conventional "universal transmatch" design with the
ground return floating (common to one side of balanced input, and one side
of the balanced output). I made a tuner like this, and used it for years. It
worked great on 160-20 meters, but the compromise design starts to show
imbalance above 20 meters. I am pretty sure MFJ, and a few others do have a
few tuners designed this way.

   It is also refreshing to see MFJ marketing a line of tuners that are
somewhat similar to a Viking Matchbox.

I still think that those kilo-buck + tuners with a big balun on the output
are often used in ways that are not very efficient when the load is highly
reactive, and these will act exactly like Ron described below.

Regards,
Jim Candela
WD5JKO

-----Original Message-----
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net]On Behalf Of w6om at cox.net
Sent: Wednesday, April 19, 2006 11:54 AM
To: Discussion of AM Radio; amradio at mailman.qth.net
Subject: Re: RE: [AMRadio] Baluns for Zepp Antenna



Thanks Don

You make a good point everyone should consider. I have noticed a
teeker-totter effect with Toroids and un blanaced reactive feeders like 450
ohm ladder line. Get the SWR nulled out and in one minute it starts to climb
again as a toroid saturates, null it out again and it happens again.

Your tuner suggestion is obviously the best but a few of us like to see if
we can noodle it out with home brew stuff.

Thanks again for your comments

Ron
From: "Donald Chester" <k4kyv at hotmail.com>
Date: 2006/04/19 Wed PM 12:43:25 EDT
To: amradio at mailman.qth.net
Subject: RE: [AMRadio] Baluns for Zepp Antenna


>From: <w6om at cox.net>
>
>
>Simple Coax Balun
>
>www.southgatearc.org/techtips/coax_balun.htm
>
>Toroid Balun
>
>www.rason.org/Projects/balun/balun.htm
>
>Romex and PVC under $3.00 Balun
>
>www.bloomington.in.us/~wh2t/balun.html
>


All those baluns operate on the assumption that the balanced load is
primarily resistive.  If the load is highly reactive, as is often the case
with open wire resonant feeders, the balun may not function properly,
especially the toroidal types at high power.

I still prefer an honest-to-god balanced tuner, with split stator capacitor
and symmetrical balanced coil.

Don k4kyv


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Ron Weaver - W6OM

Web Site:  www.qsl.net/w6om

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