ORIGINAL MESSAGE:

On Mon, 04 Sep 2006 19:40:35 GMT, Cecil Moore
wrote:

For those of us who don't have the 2004 ARRL Handbook,
could you describe the theory? If it is based on the
old wives' tale that the current through a loading coil
is constant, it is all wet.

------------ REPLY FOLLOWS ------------

No, this is not that type of circuit. This uses a simple vertical whip
without any loading coil. At the base of the whip there is a variable
coil and variable capacitor in parallel with each other and connected
to ground. From the junction of the whip and coil/cap there is another
capacitor which goes to the input of a 4:1 unun which steps up the
resultant 12.5 ohm impedance to 50 ohms, which goes to the
transceiver.

For 3.5 MHz, the values in his example are 44 uH for the coil and 11.9
pH for the cap which feeds the unun. The value of the variable cap in
parallel with the coil is not specified. He states that exact values
of all components are highly dependent on coil Q.

I see two major advantages to this network:

1. The whip itself is as simple as it can be; no loading coil at all.

2. The value of the coil at the base is smaller that a conventional
loading coil would be.

One drawback, although the author does not state it, is both
capacitors must see a LOT of voltage, and vacuum variables would
probably be necessary. At the 100 watt level, I'd guess the voltage
there is on the order of 2-4 kV, possible more.

If anyone is interested, email me at my qrz.com address and I'll send
a screenshot of the circuit and the text of the article.


--
Bill, W6WRT