[TowerTalk] Fan dipole

[Jim Brown]

Hello Vytenis,

First, I have two 80/40 fan dipoles up about 41M.  They are at right 
angles to each other, one broadside to you and VK/ZL, the other 
broadside to JA and South America.  They are two wires, one for 80, one 
for 40. The 80M is bigger copper to better support the weight. The wires 
are spaced about 10 inches.  I have not tried a 3-wire for 80/75/40, but 
I'm quite pleased with how my antennas work. They have been my 80/40 
antennas since I moved here in 2006.

You said your antenna would be low so that you can work better locally. 
Be careful about that.  Study

http://k9yc.com/VertOrHorizontal-Slides.pdf  , which shows that the 
ideal height of a horizontal antenna for short distance work is a 
quarter wave, and you give up only 3 dB at high angles by going to 3/8 
wave high.  Look at the graph on page 19 for 80M Those numbers work out 
to be 67 ft and 100 ft on 80/75, and half that on 40M.  I lose about 10 
dB at high angles with my high dipoles on 80M; but I'm a lot louder at 
angles below about 45 degrees.  AND -- because I'm much closer to the 
high angle stations, there's less loss to inverse square law (beam 
spreading with distance), so I have no trouble working locals.

If you really want to optimize both bands, for short distance, I'd go 
with two antennas.

73, Jim K9YC

On Thu,3/26/2015 12:12 PM, LY2KZ wrote:
> Hello gentlemen,
>
> I'm considering one antenna for domestic - continental contacts. I'm 
> curious about all pros and cons of this construction and possible 
> pitfalls. That is a fan dipole having three wires. Something like here 
> http://www.hamuniverse.com/multidipole.html One wire is for 7100kHz, 
> another for about 3800kHz and third for 3550kHz. My idea is to have 
> two bands covered in full. Is there anyone who has had experience with 
> fan dipoles? What should I keep in mind before starting to build? Yes, 
> tuning perhaps will not be very simple, but hopefully I will manage.
> How far apart wires should be? 10in OK?
> Should all center conductor legs go to the same side or vary left - 
> right - left
>
> This will be low hanging antenna 10-15m. For DX contacts there will be 
> another antenna.
>
> Thank you
> Vytenis LY5T
>
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