[Elecraft] High power tuner

[Joe Subich, W4TV]

On 11/26/2011 6:00 PM, Vic K2VCO wrote:
> The balanced output is not referenced to the case. So the balun is
> functional when feeding a balanced line, not shorted as you suggest.

You are correct, that the balun is not shorted when feeding a balanced
antenna.  However, in that configuration it will *only* function as a
common mode choke (if it is not constructed as a voltage balun).

Any antenna connected to the "balanced" terminals will still not be
truly "balanced" as it is not possible to generate a balanced output
at the output of an unbalanced network by forcing balance at the input
of that network.  It is quite likely that a "balun" at the input of
an unbalanced network will only increase circulating currents (and
losses) in the network.

73,

    ... Joe, W4TV


On 11/26/2011 6:00 PM, Vic K2VCO wrote:
> The balanced output is not referenced to the case. So the balun is functional when feeding
> a balanced line, not shorted as you suggest. However, you are correct that it will not
> serve as a common mode choke with unbalanced output. And Paul's comments about the
> placement of the balun are correct. I was surprised to see this from Alpha, whom I would
> have expected to know better.
>
> I suppose I'll have to wait for the KAT1500 (no, no such product has been announced or
> hinted at as far as I know!)
>
> On 11/26/2011 8:55 AM, Joe Subich, W4TV wrote:
>>
>>> The new RF Concepts tuner would not work well for me. It's an
>>> unbalanced C-L-C design with a CM choke input, similar in design
>>> with several Palstar tuners, only with much more rugged components
>>> than what Palstar provides. W9CF, W7EL, and W8JI have analyzed a
>>> current choke placed at the input to a C-L-C tuner and have concluded
>>> that placement at the input is not as effective for maintaining line
>>> balance as a balun placed at the tuner's output.
>> The common mode choke in the Alpha tuner will be completely ineffective
>> with any of the coaxial fed antenna outputs in any case!  Since it is
>> *inside* a metal box and the input as well as output connectors are all
>> connected to the case, any common mode current will simply bypass the
>> the choke on the case!
>>
>> The *only way* to make a common mode choke effective with an unbalanced
>> tuner is to connect the case of the tuner to a low impedance "ground"
>> and place the choke in the feedline between the rig/amplifier and the
>> tuner - external to the tuner.
>>
>> 73,
>>
>>       ... Joe, W4TV
>>
>>
>