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

[Kenneth G. Gordon]

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