"C. J. Clegg" wrote in message
...

Good afternoon, all.

I would like to put up a dipole antenna for 80 and 40 meters, and a
frequency near 4.5 MHz (for non-amateur use), coax fed, without the
use of traps or a tuner.

I expect to use three dipoles (one for each band), all coming together
in the middle and fed with a single feedline through a 1:1 W2AU-type
balun.

For illustration purposes, let's say that the 80-meter dipole will run
east-west, the 4.5-MHz dipole will run northeast-southwest, and the
40-meter dipole will run north-south.

Questions...

Is the standard 468/F formula likely to be anywhere near accurate, or
will the three antennas interact with one another to throw the
calculations off?

In particular, is the 4.5-MHz frequency too near the 80-meter band
such that interaction will be greater than otherwise?

If the interactions are sufficient to throw the formula off, will my
antennas end up being longer or shorter than the formula length?

Thanks.... CJ


It should work just fine. I have an 18 MHz dipole, which also serves as the
support, and a 40 m inverted V hanging below that, fed through a current
balun. There will be interaction, so it would be a good idea to model it in
EZNEC first. You will want to trim the longest antennas first. Cut them a
little long to start with, and when you go to shorten one, don't cut off all
the extra wire, in case you have to go back. If the 4.5 is for receiving
only, it may not be worth the bother.

It took a lot of going back and forth, but I have an EZNEC simulation of a
75/80 m antenna that has an swr below 2.0 from 3.5 to 4.0. If you do put up
the 4.5 antenna, you can probably use that to extend the bandwidth of the 80
m antenna on the high side.

Tam/WB2TT