[TenTec] TT 238C will not tune

[Richards]

Hey... I had one of those once ... during my SWL days.
I thought it might improve my long (i.e., random) wire receiver antenna, 
but I could never see any improvement no matter how I set it.

OK, so if that is a simplified version, I would take it Zero (0) on the 
inductor scale means zero (0) inductance.   Although it could be maximum 
inductance if it was installed the other way around.

Comparing the schematic for each, it would appear the low side of the 
inductor faces the radio input, and the high side faces the output - but 
that does not indicate, for sure, which way the inductor is physically 
oriented in the cabinet, and vis-a-vis the front dial.

Or does it?

And the MFJ 16010 description makes it sound like the whole circuit gets 
reversed - which would reverse the direction of the inductor relative to 
the current flow - rather than just alter the location of the fixed 
capacitors relative to the same circuit/inductor direction.
On point, but I am still corn-fused.

Someone on the list talked me into getting an L/C meter but I have yet 
to learn how to use it !  So much to learn, so little time.

---------------------- K8JHR  ----------------------

On 7/28/2013 5:15 PM, Al Gulseth wrote:
> (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  -----------------------
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