[SFDXA] K4FK antenna party results

[Ed Callaway]

Kai,

Thanks - I'd appreciate that.  The specific problem I had was that EZNEC wouldn't tolerate more than two wires connected to the source, requiring a single wire segment to be used at the (split) source, then branching out to the two dipoles.  Simultaneously, however, the wire segment had to be longer than 0.02 wavelength, plus some other restrictions, and when all the requirements were met simultaneously the geometric arrangement ended up being a single dipole again.  Very clever, these simulators . . . .

Ed.

From: Kai Siwiak [mailto:k.siwiak at ieee.org]
Sent: Tuesday, January 17, 2012 8:43 AM
To: Ed Callaway
Cc: SFDXA at mailman.qth.net
Subject: Re: [SFDXA] K4FK antenna party results

Hi Ed,
Nice that the dipoles are ok now. When I get back I can do a NEC analysis (I use Arie Voor's 4NEC2 - free, and very nice interface).
Alternatively try a purely analytical mutual coupling analysis, but for straight dipoles rather than Vee.

I should be back within a few days, and would like to help with the 80/160 dipoles.

73
Kai, KE4PT/3



Ed Callaway wrote:

Pete, N8PR, and I got the 40/30m dipoles re-strung Saturday, using fresh wire and UV-resistant Dacron rope.  The most interesting thing to note of the experience was that the calculated lengths were off by a foot for the two dipoles - too short on 30m, too long on 40m.  Corrections were made, and everything now tunes up where it should.



Pete and I aren't sure why the resonances were so far off, and in opposite directions.  I was expecting some interaction, and a move upward in resonance as the wires were moved from straight dipole to their inverted-vee configuration, but this surprised me.  I had spent a few hours the night before on EZNEC trying to model crossed dipoles, but for a novice at EZNEC it turns out to be hard to simulate that.  Comments welcome.



Regarding 80/160m, the north sides of both dipoles have broken from the center point and are lying on the roof, while the south sides of both dipoles and the feedline are still in their proper place on the tower.  Another antenna party, this one involving actual tower-climbing, will be required to correct the problem.



Ed N4II.



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