[TenTec] Optimizing 238 settings?

[Jim Brown K9YC]

On Sat, 26 Dec 2009 10:39:12 -0500, Joel R. Hallas wrote:

>Rule 1 is use the minimum inductance. With an L-network there really should
>only be one match, or all apparent matches should be very close to the same
>settings. 

Hi Barry,

I own five of these tuners to use with my wire antennas. For most antennas 
and most operating frequencies, there is, as Joel notes, a single setting 
that provides a match, and it tends to work over a fairly wide part of the 
band. There are, however, a few conditions where the impedance transformation 
is close to unity, and I'll get a match in both the first left and right  
settings of the fixed capacitor switch. When that happens, I study how 
broadband the match is for each switch position, and choose the one that 
matches over the widest range. Usually that range is broad enough to cover 
the part of a band I'm working in a contest. 

BTW -- there are a few fixed caps in this tuner that will overheat and fry 
with high power for a while into certain values of load. Be prepared to 
replace them. Note also that these caps have a negative temperature 
coefficient. I don't know if that is an attempt to match temp drift of other 
components or if it is simply a matter of what HV, high current caps can be 
bought cheap. :)  That's easy to do out here in Silicon Valley, where there's 
still at least one good electronic surplus store where we can browse bins. 

73,

Jim K9YC