In article , Vinnie S.
wrote:
Thanks for all the responses, but I seem to be more confused because it
seemed I
got differing opinions. As I said, I am a beginner at antenna theory. The
frequencies I am trying to make an antenna for, are centered at 3.875, 7.225,
and 14.250. Those are the center for the phone frequencies on the US bands. I
wanted to shorten the 80 meter band antenna. I would have kept the 40
and 20 at
the specified lengths. I guess I will buy the ARRL book. But they also make a
long wire classic book. I might get that instead. .

Vinnie-

One thing isn't clear. How short do you need the total length to be?

I think everyone is in agreement that a trap dipole is shorter on the
lower band than a simple dipole would be for that band. The trap acts
like an inductor below its resonant frequency, so the part of the antenna
beyond the trap is electrically lengthened on the lower band(s).

Therefore, the 20 Meter traps would be at the proper places, around 16
feet each side of center. However, the 40 Meter traps would be closer to
the center than for a simple dipole, due to the inductive effect of the 20
Meter traps. Similarly, the added wire for 80 Meters is less than for a
simple dipole due to both the 20 and 40 Meter traps' inductance.

You may find that the resulting length of a dipole with both 20 and 40
Meter traps, is short enough for your needs.

73, Fred, K4DII