C. J. Clegg wrote:
On Tue, 21 Nov 2006 23:24:59 +0000, Dave Platt wrote:

2. How do I determine the minimum power rating for the terminating
resistor for an antenna that will be driven by 100 watts maximum?
Ummm... I'd say that you'd need a resistor capable of dissipating 100
watts, continuous, when used under ambient-free-air conditions in the
highest operating temperature you'll encounter. I'd probably de-rate
it by at least 50% (200 watt resistor) just to be sure, especially if
you're going to be operating RTTY or any other high-duty-cycle mode.

One of the unfortunate things about a T2FD is that there are going to
be frequencies where most of your power warms up the feet of the birds
perching on the termination resistor :-(

Yeah, this is exactly what I'm trying to avoid, by careful choice of
design parameters like length, resistor value, balun type. Feeding the
antenna with 100 watts and having all 100 of those watts dissipated in the
resistor, at any frequency within my range of 4 to 9, isn't going to work.
If I can't keep the efficiency above 50 percent across the range, then it
probably isn't going to be worth doing.



Narrowing the frequency range isn't going to help much with the design.
I'm no expert, but if I read my signs correctly, the T2FD has the same
ups and downs in SWR as does most other multiband antennas. IOW, it
relies on frequency harmonic relationships.

Cebik has a good web page at:

http://www.cebik.com/wire/t2fd.html