[Elecraft] ATU efficiency and the Elecraft T1

[wayne burdick]

Jay wrote:

> All tuners will eat up some percentage of your RF output power.
> The ones with toroid or smaller inductors may eat up more power.

Jay, John, etc.:

The physical size of the inductors would only be a factor if they were 
also inefficient (dissipating a lot of heat). In all of our tuners, 
including the T1, we use high-Q toroidal inductors with core and wire 
sizes appropriate for the intended RF current. In addition, we use 
high-Q capacitors (NP0/C0G ceramic or in some cases silver mica).

In lab tests of the T1, I used loads from 3 to 1000 ohms, calculating 
the power into and out of the L-network. The T1's efficiency was on a 
par with other tuners of this type, including those with much larger 
toroids. For typical matches, losses range from 0.1 to 1 dB. A tuner 
using very large air-wound inductors and air-variable capacitors might 
cut these values in half, and would have an advantage at very high or 
low impedances. But such a unit would also not be very portable, so 
it's a tradeoff.

A much bigger factor in most antenna installations is ground loss, 
which usually dwarfs any L-network losses. This is especially true of 
portable antennas. If your goal is to radiate the best possible signal, 
you can reduce ground losses by using *lots* of radials, or consider a 
dipole or inverted V with its feedpoint as high off the ground as 
possible.

When I'm in casual operating mode I simply toss a wire in a tree, lay 
out one radial, use no feedline at all, and accept the inevitable 
ground loss. If I'm "serious," I string a wire between two trees such 
that the center is 20 to 30 feet high, feed it with 300-ohm low-loss 
twinlead, and use a low-loss balun between the feedline and the tuner 
(the Elecraft BL1 is quite small and works well in this application). 
In this cases I use a wire that's at least 1/2-wavelength long on the 
lowest band of operation.

The T1 finds a low-SWR match on most or all HF bands with either 
"casual" or "serious" antennas  :)

73,
Wayne
N6KR