[Amps] MOSFET amp filtering - was: auto-tune

[Catherine James]

I hear a lot of recommendations here for antennas that are flat across the band and very close to SWR of 1:1 to keep solid-state amps happy.  That is completely unrealistic on the low bands.

I have to re-tune my 160 meter dipole for even small excursions of a few tens of kHz.  A cage dipole would be broader-banded, but that is difficult to build and install, especially for a 270 foot long antenna that hangs in the trees.  I certainly couldn't put one up in the treetops where my current wire dipole lives, as it would get all tangled in the branches.

So much of discussion and recommendation around antennas seems to unconsciously assume that we are talking about the high bands.  I've lost count of the number of discussions where someone asked for a reco on an HF amp, and was told over and over, "don't start with an amp, improve your antenna system, put up a beam, etc."

At this point in the cycle, I am spending more and more time on 160, less on 20 and 40, and essentially none at all on 10 and 15. Few hams can put up a beam on the bands below 20.  The longer the wavelength, the wider a given band will be as a fraction of that wavelength, and the less broad-banded the antenna will be without tuning. Tuning is a fact of life, and amps are more important on bands where the ham cannot have a rotatable directional antenna.  

160 has been amazing lately.  10 doesn't appear to have opened at all for the contest last weekend, at least not here in New England. And 160 is where you really, really want an amp!

73,
Cathy
N5WVR

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On Mon, 12/12/16, Bill Turner <dezrat at outlook.com> wrote:
 
> Whatever "tuning" is needed is for the antenna, not the amplifier. If
> the antenna itself is broadbanded, no tuning is required at all.