[ARC5] Hello Smart People: Output Network "L"

[mac]

On Apr 14, 2012, at 12:12 PM, Kenneth G. Gordon wrote:

> On 14 Apr 2012 at 12:45, David Stinson wrote:
>
>> But in AM I was seeing 100 mills into those two 807s.
>> That's 55 watts in for 12 out unmodded carrier... hmm.
>
> Not good.
>
>> So, for the dozens of you smarter than me,
>> here's the question:
>>                              Why?
>
> Simple: impedance mismatch.
>
> You, yourself, in your series of e-mails and at least one article on  
> the ARC-5
> transmitter covered that aspect pretty well yourself.
>
> You might try removing that short, then adding a 2:1 un-un at the  
> output. I'll
> bet that would fix most of it.
>
> By shorting a turn of the tank coil, you are changing the impedance  
> in the
> final output circuit (raising it?), and therefore it is, perhaps, no  
> longer set up
> to match to 100 ohms, but to something closer to the 50 ohm load,  
> thereby
> increasing the efficiency.
>
> I say "raising" the impedance at the plate since by shorting a turn  
> in the
> inductor, you're essentially increasing both the "Q" of the coil,  
> and the ratio of
> capacitance to inductance.
>
> There are undoubtedly other factors involved here, since shorted  
> turns tend
> to cause other problems.
>
> Ken W7EKB
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