[Lowfer] Re: Amplifiers for 136k

[John Andrews]

Bill,

> (BTW the filter is very close to Lyle's
> Simple Transmitter's output stage)

Actually, it's the same, I think! I alluded to my theft in the original
posting of the schematic.

> 1. The filter adds a good degree of harmonic suppression at the loop over
my
> filterless stage.

Probably overkill at 1 watt, but it'll be a good practice at 20 dB over
that. As you and I have observed, harmonics up in the AM broadcast band
don't seem to be much of a problem. Analysis above that would be pretty
rough, as others have suggested.

> 3. The output impedance of the stage, in spite of the filter, is close to
0
> ohms, and hence, makes a poor match for a coax line (take notice Mike).

As Johan mentioned, transmitter PAs are designed to work into a specified
impedance, not to present it. This particular circuit seems to work into a
wide variety of load impedances, based on what I saw on the bench before
putting it outside.

> This all leads back to my original thoughts last week on the simplicity of
> using a two transistor switching PA out in the woods at the base of the
loop
> for the 136k, 100w application. Adding a core with four or five turns and
a
> mica cap is no burden at all!

Not sure that I follow that description. Add some words please!

John A.