[TowerTalk] 80m 4-square materials

[Jim Lux]

At 06:15 PM 12/16/2006, john at kk9a.com wrote:
>I don't know that Array Solutions still carries the 80m vertical.  ZeroFive
>Antennas  http://www.zerofive-antennas.com sells one that looks very
>similar to the Array Solutions freestanding vertical for $2200.  I built a
>54' freestanding vertical at P40A for considerably less.   For K1TTT's
>installation, I would consider using 3" diameter aluminum tubing guyed at
>two levels.  The larger top sections will improve the bandwidth and I think
>it's a strong antenna than can be built for a reasonable price.  I believe
>that K4JA built his 80m 9 circle vertical array this way.


In an array, the effect of narrow band elements (skinny) is probably 
less than the fact that the spacing and phasing will be wrong with 
significant frequency shifts. (at least for F/B.. forward gain 
doesn't change much with pretty significant misphasings).

Consider that a 5% change in frequency (Say, from 3500 up to 3725) 
will be a misphasing by 18 degrees, just from the spacing being 
"wrong", aside from any reactive impedance effects.  That's enough to 
get a perfect F/B to around 13 dB.

And, on top of that, the mutual impedance changes pretty fast with 
elements spaced less than 1/2 wavelength apart.




>John KK9A