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Re: [Amps] Testing a tuner

To: Rob & Terri Sherwood <rob@sherweng.com>
Subject: Re: [Amps] Testing a tuner
From: Tomm Aldridge <KD7QAE@ARRL.NET>
Date: Sun, 09 Jan 2005 21:34:27 +0000
List-post: <mailto:amps@contesting.com>
My balanced tuner is configured with the motorized roller inductors (26uH ea) in series mechanically with about a 2" separation. I have the capacitor split between 2 500pF Henry variables, one of which is almost always shunting the output of the 24 turn x 4" coax balun on the input of the tuner. This coupling has not caused me any grief to date. If you were to make a link coupler I would suggest opposed drives so the tank L increased or decreased symmetrically around the center where the link was located. The second motor would be simple enough to add.

Tomm, KD7QAE

Rob & Terri Sherwood wrote:

If the League is really only using resistive loads, then they could make the loads reactive with inductors or capacitors. This would be time consuming, but what other option do they have? The balanced L network tuners I have tried matched fine into resistors on 20 meters and above, but hooking them to a real antenna was another story.
On the balanced L network tuners, putting a 10 - 100 pF variable capacitor on the input solved virtually all my matching limitations. What does this imply? In every case the output Z was higher than 50 ohms because swapping the L network capacitor to the input always made the matching worse. So why did converting it to a Pi from an L make such an improvement? The balun was always on the transmitter side.
I am wondering if one could build a modern Matchbox with the following:
Two roller inductors in line mechanically and driven by a turns counter, and the link located in the middle between the two roller inductors.
Then of course we need a split stator and a dual differential capacitor.


Someone mentioned the issue of coupling between the balanced L network coils. If there is too much mutual coupling between the coils, what will happen?

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