On Sat, 21 May 2005 16:32:14 -0400, C. J. Clegg
wrote:



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?


near, yes, but it will be a little short

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

Wes and I disagree, so you will have to toss a coin on this one. I
have built many of these multiband parallel dipoles over the years. I
still use them. Here is how I do mine.

I space the wires about 6-8 inches apart using the longest wire on top
and they get shorter as they go down. What I generally do is use a
long formula to set up the initial wires such as 495/f = length in
feet. Then I hang all the wires with the spacers. I trim the highest
frequency first and measure it out. I reverse the calculations to get
the X more accurately in the formula, X/f = L in Feet. I trim the
other two and I am done.

I have not tried this with an element so close in frequency as your
80/4.5 MHz elements, but I don't expect a problem. If you have an
antenna analyzer, you can see what the different elements are resonant
on and then calculate the reverse formula trimming only once per band.

The only real difference I see in the multiband parallel dipole is
that the bandwidth on 80 and 40 seem to be broader than on a single
dipole cut to frequency. I have read on some of these forums that
others are getting narrower bandwidth. I can't explain that.

FWIW

--
73 for now
Buck
N4PGW