On 4/20/2011 10:53 AM, Mike Fatchett W0MU wrote:
> This might also be called a Fan dipole.
>
> Can you run 160 and 80 on the same feedline with decent swr? I have
> tried to model this and have not been very successful.
>
The short answer is yes, sort-of. In general, the longer antenna will
show the same SWR bandwdith as it would without the higher one, and the
higher one will have it's SWR bandwidth reduced by about half. My
experience is with 80/40 fans, and with 20/15/10 fans, and these
characteristics show up both in the NEC models and in measurements of
real antennas.
This is exactly the opposite of what happens with the loaded multi-band
dipoles like those sold by Hy Power Antenna Company -- the higher band
antenna retains full SWR bandwidth, and the lower frequency (loaded)
band has reduced SWR bandwidth. I've also modeled those antennas, and
like them a lot. In boht cases, the reduced SWR bandwidth can be
compensated with a tuner and losses minimized by using low loss feedlines.
For more detail, see my applications notes on Antennas for Limited
Space. There are two that compliment each other -- one is text, the
other a power point presentation.
http://audiosystemsgroup.com/publish.htm
73, Jim K9YC
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