[Antennaware] Space between antennas

[K9AY]

I have also recently heard stories of big interaction problems with the new 
XM240, worse than the older 40-2CD. The only other commercial antenna I know 
about is the old KLM 2- and 3-element 40M beams, which  have a small effect 
on 15M, but are quite usable.

Perhaps someone can develop a modification for the Cushcraft beam.

It is not difficult to design a "shorty forty" for low 15M interaction. The 
distance from boom to loading coils is a key parameter. My homebrew 52-foot 
element 40M beam has loading coils about 6 foot out from the boom (outer 
elements are #14 wire inside 20-ft. fiberglass fishing poles). Resonances 
are near 26 and 48 MHz. I detect no changes on my X9's performance with or 
without the 40M beam. I might note that these resonances changed very little 
when the driven element was used alone as a rotatable dipole, and after the 
refelector was added.

73, Gary
K9AY



> Unfortunately, the Cushcraft 40 will detune the TH7DXX on 15m at any
> spacing you can manage on the
> same mast.
>
> There have been numerous instances locally of "pulling" any 15 meter
> antenna's tuning by co-masted
> Cushcraft 40's. It also modifies the pattern at 15m.
>
> This happens because without modification a 40 antenna is also resonant at
> three times the
> frequency.  Some 40m beams are specifically designed to be placed in
> proximity to tribanders, etc.
>
> The Force 12  x40N antennas are linearly loaded, and their secondary
> resonance is around 18 MHz
> instead of 21. Also their Delta x40 antennas were specifically designed to
> eliminate secondary
> resonance in 21 MHz band.
>
> There may be other commercial 40m antennas that are non-resonant at 21
> MHz, but I don't know of any.
>
> 73, Guy.
>
>
> | Hello,
> |
> | I will put a Hy-Gain TH7DXX and a Cushcraft 2 elem. 40 mts Yagi in the
> | same mast on top of a tower.
> |
> | Will apreciate any recomendation about will antenna must be at top and
> | the space between both antennas for not interaction.
> |
> | Thanks in advance
> |
> | 73,
> | Jorge
> | CX6VM
> |