[TenTec] TT 238C will not tune

[Al Gulseth]

(Hope I'm understanding your question right, HI!!)

There is a "budget priced" lower power "clone" (to use the term very loosely!) 
of the 238 that might help you understand the concept of how the L network 
functions. It is made by another manufacturer located a little ways southwest 
of Sevierville in another "S" town: AKA the MFJ 16010T. Here's the manual:

http://www.mfjenterprises.com/pdffiles/MFJ-16010.pdf

The "executive summary" is that an L network is used to transform some low Z 
to some higher Z, or vice-versa if the network is reversed. To quote from the 
16010 manual:

"The connectors are labeled properly to match a transmitter to a higher
impedance. This is the normal connection.

To match impedances that are lower than your transmitter impedance (such as a
mobile whip), simply interchange the normal transmitter and antenna
connections to the MFJ-16010."

Simply put, when the cap is on the output side the transformation is L>H Z, 
and when the cap is on the input it's H>L Z. The 238 series accomplish this 
via the BYPASS switch, while the MFJ uses the less expensive and low-tech 
method of reversing the connections to the unit.

The direction of current flow is immaterial in this case. And yes, determining 
the actual zero inductance setting position would probably be beneficial in 
using the unit....

73, Al

On Sun July 28 2013 2:45:22 pm Richards wrote:
> Well, this is where I get corn-fused.
>
> The user manual states it is a REVERSIBLE L-NETWORK, whereby the fixed
> capacitors are either placed at the front of the circuit or at the end
> of the circuit using the BYPASS switch.   I presume the current always
> flows in the same direction through the circuit, including the inductor.
>   (Heck, I am still learning to read schematic diagrams.)
>
>  From some of the previous comments, it sounds as if there is some
> uncertainly as to the ZERO (0) inductor setting means the most or the
> least inductance.
>
> Is this not revealed in the schematic?  Or do we have to open the lid
> and look to determine the matter?  And, would it not be the same from
> unit to unit?   Some comments seem to suggest the Zero (0) setting could
> be different on some units.
>
> Sorry if I missed a point along the way.  It is still a mystery to me.
>
> ------------------- K8JHR  -----------------------