"Buck" wrote in message
...
An earlier discussion brought to mind the question of the 3/2 wl
antennas such as using a 40 meter dipole to operate on 15 meters. I
just modeled one using the following stats:

1 wire, 66 feet high, 68.8286 feet long. I then pulled an SWR reading
from it from 3.5 to 30 MHz using .1 increments. The result was, of
course, two dips, one at 7.0 MHz and one at 21.1. By playing with the
alternative impedance, I found that 94 ohms matched both frequencies
at about 1.15:1.

Here are some observations about it.

at 7.0 MHz, the shows:

50 ohms -- 1.65:1
72 ohms -- 1.14:1
75 ohms -- 1.09:1
94 ohms -- 1.14:1

at 21.1 MHz, I get the following:
50 ohms -- 2.16:1
72 ohms -- 1.5:1
75 ohms -- 1.44:1
94 ohms -- 1.15:1


The above are the lowest SWR readings (which is why 21.1 instead of 21
MHz)

so, how does one make a 94 ohm match?


--
73 for now
Buck
N4PGW

You might try this, connect a 50 Ohm feedline to the antenna through an
electrical 1/4 wave section of 75 Ohm coax. That should help the SWR on 21,
without much effect on 7.

BTW, Roy mentioned bending the elements to form a V. That is what is done on
some VHF TV antennas. They work on fundamental mode on channels 2 -6 and 3/2
mode on channels 7 - 13. If you didn't bend the elements, channels 7 - 13
would not come in from the same direction as 2 - 6.

Tam/WB2TT