[AMRadio] Baluns for Zepp Antenna


Barrie Smith barrie at centric.net
Wed Apr 19 21:49:18 EDT 2006


Balanced, swinging-link, dual-differential output tuners get rid of all the 
problems.  Build one.  I did.

Go to the Cebik site.

If I can do it, anyone can.

73, Barrie, W7ALW
----- Original Message ----- 
From: "Jim candela" <jcandela at prodigy.net>
To: "Discussion of AM Radio" <amradio at mailman.qth.net>
Sent: Wednesday, April 19, 2006 7:33 PM
Subject: RE: RE: [AMRadio] Baluns for Zepp Antenna


>
>
> 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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