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Re: [TenTec] OT Antenna Tuners

To: tentec@contesting.com
Subject: Re: [TenTec] OT Antenna Tuners
From: "Dr. Gerald N. Johnson" <geraldj@storm.weather.net>
Reply-to: geraldj@storm.weather.net, Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Mon, 21 Jul 2008 08:50:18 -0600
List-post: <tentec@contesting.com">mailto:tentec@contesting.com>
On Mon, 2008-07-21 at 03:41 -0700, Jim WA9YSD wrote:
> Only up to 21 MHZ, is because of too much inductance.
> Unun must be acting like a old fashion link coil with out the link.  
> I did something like that with a single coil and had 3 pairs of taps.  
> One pair of taps for input, one for caps and one for the roller inductors.
> I did not know that any one made a 4:1 unun balun.

Unun is simply a transformer. Can't call it an unun balun. Probably made
with two windings series connected like a 1:4 voltage balun but
connected to the world differently. Where the 1:4 voltage balun would
have the center tap grounded, and feed one winding with the balanced
load on the ends, the transformer (or unun) would ground one end, feed
the center with the low Z and put the high Z load on the free end.
> You took and installed a 1:4 unun on the input.  That should be 200 Ohms to 
> the L- match and 50 ohm out to the coax line of the antenna.  Do I have that 
> right or is it a 1:4 then 4:1 making it a unun on the input, then to the 
> L-Match?
That's right. 1:4 unun at the input.

> You got more band width out of the tuner.  Now why is that?  L- Match is 
> rather narrow.

L-match is always the lowest possible loaded Q so should be wider than
any PI or T match. Q in the L-match is a function of the impedance
ratio. Q*Q + 1 = impedance ratio.
> Making up a 1:4:1 unun is easily done Just on the input side of the tuner 
> with out taking the tuner a part.
> You must have float the ground on the tuner?  Did you ground one side of the 
> unun on the 4 side rather than the 1 side?
No. Everything is still unbalanced in and out of the tuner. With the
unun both the input and the output are grounded, same winding and wire.

But if the load was balanced and high impedance, the input could be a
1:4 voltage balun and give the same reduction in L-match Q while feeding
the balanced load with an unbalanced match circuit.

>  Keep The Faith, Jim K9TF/WA9YSD
73, Jerry, K0CQ

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