On Sun, 22 May 2005 17:41:22 -0400, "Tam/WB2TT"
wrote:

I ran an EZNEC simulation on a pair of crossed dipoles at 3.7 and 4.5 MHz,
with a 7.2 MHz inverted V below the 3.7. Not good. The 7.2 works OK, but the
4.5 really messes up the 3.7. Among other things the impedance at 3.7 and
4.5 MHz is about 115 Ohms. I ran the simulation at 50 feet above average
ground. If the 4.5 is for receive only, I would forget about it, and take
the 10:1 SWR that the 80 meter dipole gives you.

Good evening, Tam.

Thanks for running the simulation for me. Your results don't surprise
me much.

(I'm going to have to get that EZNEC program and play with it for a
while ... thanks to all for mentioning it.)

The 4.5-MHz antenna will be used for transmitting as well as
receiving, and so I need to get the SWR down to something reasonable.

I guess there's no reason why I can't just put up a separate dipole
for 4.5 MHz and the crossed dipoles, fed with a single coax, for 80
and 40.

I could also (and I might...) just put up an 80-meter dipole fed with
ladder line and use a tuner, though I was trying to avoid the tuner.

Thanks (to you and to all) for saving me a bunch of work. :-)

CJ