[TenTec] OT: Openwire Balanced Antenna Tuners (QST Test)

[Jim Brown]

On 2/18/2013 9:22 PM, Rick - DJ0IP / NJ0IP wrote:
> Is that really comparing apples to apples?

Sure. Efficiency is efficiency.  Power is dissipated by current flow 
through resistors. The greater the power applied, the more we must be 
concerned with it, and the heating produced.  The W3NQN designs are 
conservatively rated for 200W. Power is dissipated in the capacitors 
(represented by their equivalent series resistance) and in the inductors 
(wire and core loss). Any design that includes inductors must take their 
stray capacitance into account, which affects how much wire you need to 
provide a given inductance, the loss coupled to the wire from the core, 
and the resistance of the wire. Both stray C and resistance increase 
with more turns, and with more closely spaced turns. Inductance also 
increases as turns are more closely spaced.

As part of his design to provide higher power rating and greater 
tolerance of mismatch, 5B4AGN uses VERY high grade capacitors that have 
extremely low ESR. W3NQN does the same thing, using a different vendor.

If you look inside the new Elecraft high power auto tuner, you will find 
a lot of inductors, capacitors, relays to switch them, and logic 
circuitry to control the relays. The inductors are wound on toroidal 
cores. I know nothing about the design, but I do know that Elecraft 
extensively studied (using infrared cameras) dissipation in every part 
of the tuner, and both components and the design were tweaked to 
minimize it. There is, for example, some dissipation on the circuit 
traces and in the relays. The entire tuner is about 1.5 inches high and 
has the same footprint as the K3. There are no air openings to provide 
ventilation.

The tuner is rated for legal limit on the HF bands with VSWR of 3:1 or 
less, and for about 700W for a much wider range of VSWR. I'm running two 
KAT500s with a pair of Titans at the legal limit. My neighbor, K6XX, a 
world class contester, is also running them at legal limit.

73, Jim K9YC