[SFDXA] K4FK antenna party results

[Kai Siwiak]

Oh, they are tied in parallel!!??!!??   There is more to that problem, 
then,  if you used a source in NEC loaded with a 50 ohm source 
impedance.  That is not necessarily what happens across two bands.  When 
you operated on 30, for example, the 40m dipole "sees" a complex 
reactance (not a 50 ohm load) since the transmitter output impedance is 
not resistive, not even on the operating frequency. 

Hmmmm  time to put on the thimking hat.
Kai


Ed Callaway wrote:
>
> 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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