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40M dipole--antenna pattern on 15M?

Aug 10th 2011, 18:27

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
A member asks:

Recently I was using a 40 M dipole up at 37' to work PSK 31 on the 15M band. The dipole is cut for the low (CW) portion of the 40 M band, and the 15M PSK portion falls within the 3rd harmonic.

Results were excellent, and it raises the question: Is there any gain associated with using the longer 40M dipole over using a dipole cut specifically for 15M? And, does the radiation pattern differ from a normal dipole pattern when working 15M on the 40M dipole?

Yes, you get about 0.67 dB of gain with the longer dipole, as well as a slightly lower angle of radiation. Yes, the pattern is considerably different, with six lobes, compared to just two for a normal dipole.

You can look at pattern plots for your dipole. I’d suggest the free EZNEC demo program, which you can download from www.eznec.com or from here

Zack Lau W1VT
ARRL Senior Lab Engineer

Aug 11th 2011, 05:33

W0BTU

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Here's a file for a 40 meter dipole 37' high that should work with the demo version of EZNEC. (Ideally, it should have 31 segments, but the pattern with only 20 --the limitation of the demo version-- looks similar enough.)

http://www.w0btu.com/files/antenna/EZNEC/40M_dipole_37ft-h_21.175_MHz.EZ

Overall, the pattern is not bad at all. There's some wasted high-angle radiation and nulls in certain directions, but I wouldn't let that stop me from trying it on 15.

73 Mike
http://www.w0btu.com

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