[Elecraft] Auto balanced tuner

[Ron D'Eau Claire]

I'm rather astonished they get away with such tiny relays, even if it is
never "hot switched". 

At high impedances there can be thousands of volts of RF in there, even at
the moderate power levels it's specified for. In my experience that sort of
voltage easily produces coronas that would put a smile on Tesla's face. I'm
used to seeing several inches of ceramic insulation or air space between
conductors at those power levels. (Most of us O.T.s raised with vacuum tubes
have pulled inches long arcs off of the high-impedance tank circuit of our
rigs at far less than 200 watts.) 

At very low impedances the currents can run into correspondingly huge
amounts, with substantial ohmic losses in the inductor wires and relay
contacts. I'm used to seeing tubing or at least large gage wire used for
inductors to minimize that problem. Sometimes the wires are silver plated. 

Even heavy-duty commercial automatic tuners, such as those used on ships for
the HF rigs, have very specific combinations of minimum length of antenna
and minimum frequency they can handle because it's an electrically-short
antenna that produces the highest voltages. 

Since Stewart found that losses escalate at impedance extremes, maybe they
aren't getting away with using those tiny relays or the little inductors. 


Ron AC7AC

 


-----Original Message-----
I made a carbon copy of this ATU. It works pretty well, however at 
impedance extremes it was a bit lossy.

Stewart G3RXQ
>>
> Here's a really nice one:
>
> <http://www.hamware.de/hardware/tuner502/descr-at502-e.pdf>
>
> Get ready to sell your car and mortgage your home, however.