[TowerTalk] Multi-band dipoles

[Tom Osborne]

Hi Jim

I just put up a 15/17 meter fan dipole.

Separately, they work fine.  When hooked together, the 17 meter dipole works 
fine, but the SWR goes way up on 15.  If I unhook the 17 meter dipole, the 
15 meter goes back to a low SWR again.

Are 15 and 17 too close together to have 2 antennas on the same feedline. 
The lengths of wire are pretty close to the same. 73
Tom


> On 4/20/2011 7:03 PM, K8RI on TT wrote:
>> It's been mentioned that with fan dipoles the lowest frequency band has
>> it's band width increased
>
> Correction -- In a fan dipole made from parallel wires, the lowest
> frequency band has the full SWR bandwidth as if no other antenna were in
> the fan. The higher frequency band(s)  have their SWR bandwidth reduced
> by roughly one half. This works out just fine when the lowest frequency
> is 75/80M, because the higher bands are a relatively low percentage
> bandwidth.
>
> Another VERY important point -- coax, especially BIG coax, has VERY
> little loss on 160M, and only a bit more on 75/80M, so moderately high
> SWR (up to 5:1, for example) that might be present far off frequency
> still doesn't add much loss.  You WILL need a decent antenna tuner to
> work at the band limits. I use Ten Tec 229 and 238 tuners, which have
> better than average efficiency and, because of their design, once they
> are tuned, they tend to maintain a match over a much wider bandwidth
> than T-section tuners.
>
> 73, Jim Brown K9YC
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