[TenTec] Palstar tuner

[Dr. Gerald N. Johnson]

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