[TenTec] 4229 Tuner Balun Replacement?

[Dr. Gerald N. Johnson]

Sometimes we want to FORCE that voltage balance, sometimes we just want 
to limit feed line shield current on the outside of the line. A home 
built tuner need not have the secondary capacitors or coil center tap 
grounded. Sometimes we need that ground to keep from having the tuner 
capacitors arcing to ground from static pickup on the antenna when 
charged clouds pass.

73, Jerry, K0CQ

On 11/14/2010 11:13 AM, Steve Hunt wrote:
> Of course, the Johnson Matchbox has its secondary capacitors
> "centre-tapped" to ground; that makes it a "stiff" voltage source. In
> other words it's a VOLTAGE balun, just like the 4:1 Ruthroff found as
> standard in many tuners. But usually we want to balance the currents in
> the TL, not the voltages on each leg.
>
> That referenced 1:1 balun from Balun Designs is a good choice -
> particularly for the lower-frequency bands.
>
> 73,
> Steve G3TXQ
>
> On 14/11/2010 03:59, Ken Brown wrote:
>>> Question: How does the internal balun in a link coupled tuner
>>> compare with the a 'tri-filer' balun such as used in the
>>> Nye-Viking MB-V-A?
>>>
>> A link coupled tuner IS a balun. It is not a tuner WITH a balun. It is
>> essentially a tunable air core transformer. Usually (perhaps always) a
>> link coil of just a few turns is the primary of the transformer, fed by
>> the UNbalanced transmission line (coax) from the source (transmitter).
>> The secondary generally has a many turns, perhaps tapped for band
>> switching (as in the case of a Johnsom Matchbox) and is connected to the
>> BALanced transmission line to the load (antenna). The transformer
>> windings have variable capacitors connected to them to make it tunable.
>> In the Johnson Matchbox only the secondary has tuning capacitors. Other
>> variations may also have a tunable primary. In the Johnson Matchbox the
>> secondary is actually two coils, with the primary link in the middle of
>> them.  Or perhaps you could say it is one big center tapped coil, with
>> bandswitching taps at both ends.
>>
>> My labeling of primary and secondary assumes that you are transmitting.
>> Turn the labels around for receiving.
>>
>> DE N6KB
>>
>> _______________________________________________
>> TenTec mailing list
>> TenTec at contesting.com
>> http://lists.contesting.com/mailman/listinfo/tentec
>>
>>
> _______________________________________________
> TenTec mailing list
> TenTec at contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec
>