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Re: [TenTec] Palstar tuner

To: tentec@contesting.com
Subject: Re: [TenTec] Palstar tuner
From: "Dr. Gerald N. Johnson" <geraldj@storm.weather.net>
Reply-to: geraldj@storm.weather.net, Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Thu, 21 May 2009 21:34:39 -0600
List-post: <tentec@contesting.com">mailto:tentec@contesting.com>
On Thu, 2009-05-21 at 14:48 -0700, Arthur Trampler wrote:
> Isn't one of the key distinctions of the Ten Tec 238/B/C that these are 
> switched L networks, rather than T-networks, as I believe the Palstar is?
>  
> Some years back QST reviewed several external auto-tuners and with respect to 
> efficiency, the Ten Tec 253 came out far ahead of most competitors, as did 
> (surprising me) an MFJ tuner.  They both handily were measured as being far 
> more efficient than the Palstar especially on the lower bands matching low-Z 
> loads.
>  
> There is a common factor between the MFJ and the TT-253 (and 238), and that 
> is that it is also an L network.  Most Palstars are T-matches, right?
>  
> So forgetting the questions/comments about baluns, and whether the lowest SWR 
> is also the best match, and whether there may be multiple low-SWR tuning 
> points with a T-match...
>  
> Is an L-Match inherently less lossy than a T-match under most circumstances 
> (ceteris parabis)?
>  
Yes. Because it has only one possible loaded Q for any given impedance
ratio, the circulating current in the circuit is minimized. In a T or PI
the loaded Q can be higher resulting in more circulating current. In any
tuned circuit, the circulating current is higher than the external
current by the factor loaded Q. Typically Q is 12 for an amplifier
output network because that gives adequate harmonic reduction. But on
the higher bands, Q rises because the output device capacitance limits
the minimum Q. And efficiency suffers because of tank circuit (mostly
coil) losses from the higher current.

> Thanks,
> Art

73, Jerry, K0CQ

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