wrote:
Is this OCF dipole a single band antenna or a multiband antenna?
- 'Doc

It is alleged to be a multi-band antenna. Assuming that
the standing-wave current is 90 degrees out of phase
with the standing wave voltage, one can actually calculate
an approximation for the feedpoint impedance by dividing
the standing-wave voltage by the standing-wave current at
the feedpoint. With an OCF, the feedpoint impedance will
always be lower than Vmax/Imin and always higher than
Vmin/Imax and thus provide a reasonable SWR for 450 ohm
ladder-line.

The free demo version of EZNEC available from
http://www.eznec.com
will provide a reasonable guess at the feedpoint impedance.

Here are what EZNEC 4.0 says about the
feedpoint impedance of the following:

------------83'----------FP-----47'--------

3.8 MHz, 85.5+j98.5 ohms, SWR(300)= 3.9, SWR(450)= 5.5
7.2 MHz, 177-j181 ohms, SWR(300)= 2.5, SWR(450)= 3
10.125 MHz, 3569-j102 ohms, SWR(300)= 12, SWR(450)= 7.9
14.2 MHz, 96-j357 ohms, SWR(300)= 7.7, SWR(450)= 7.7
18.14 MHz, 797-j911 ohms, SWR(300)= 6.3, SWR(450)= 4.4
21.3 MHz, 933-j1239 ohms, SWR(300)= 8.8, SWR(450)= 6
24.95 MHz, 218-j652 ohms, SWR(300)= 8.5, SWR(450)= 6.7
28.4 MHz, 757+j1019 ohms, SWR(300)= 7.4, SWR(450)= 5.1

As you can see, the myth that this antenna has a 300
ohm feedpoint impedance is just an old wives' tale but
it does have reasonable SWRs when fed with 450 ohm
ladder-line.
--
73, Cecil http://www.w5dxp.com
"According to the general theory of relativity,
space without ether is unthinkable." Albert Einstein