Hello Terry,
I think that you must have what we call a "Lazy Vee" array out here in cattle
country. I put one of these up about 5 years ago. It was my first directive
array for 40 meters and it worked great. I later made one for 75 and another
for 160. They were all good performers. My friend Bob, W7LR, wrote it up for
an article that appeared in February 1994 QST Technical Correspondence I
believe.
As I recall Terry, I went around the pole and tuned each antenna independently
by plugging the cable into an antenna analyzer and tuning to the middle of my
operating band. You may have to go around all the dipoles a couple times until
it converges. I left the unused antennas connected just as they would be in
real operation through the switch box.
73/Mike, N7ML
Terry George wrote:
> Has anyone on towertalk any experience of correctly tuning / matching
> a 4 element 40m sloper system.
>
> I have used two of these systems but never felt that they have been
> at optimum performance.
>
> The arrangement I have at present has four dipoles suspended from a
> 40 foot mast - about 4 feet apart at the top - sloping down at about
> 45 degrees, with the bottom ends variously tucked in to fit into the garden.
>
> Each dipole is fed with 36 feet of 50 ohm co-ax per ARRL Antenna
> Handbook, and the switchbox selects one dipole, leaving the other
> three `floating`.
>
> Because they are so close together, there is obviously a large amount
> of mutual coupling so what`s the best way to tune it ?
>
> Should I put up one dipole ; adjust for best swr, then cut the other
> three to identical length (this puts the apparent resonance of the
> system about 350 kc/s below the single dipole fr)....or should I
> attempt to adjust each dipole for best swr `in situ` in the array ?
>
> In the latter case , it seems very difficult to get the swr below
> 2:1......but am I dealing with a matching impedence problem hiding
> the true resonant frequency ???
>
> I have also had some interesting results driving (paralleling) any
> adjacent two dipoles.
>
> This is an extremely cheap way to obtain an instantaneously switched
> beam , and `front to back` can be pretty good...it would be nice to
> get it `right`
>
> Any comments / advice much appreciated - please reply direct.
>
> Many thanks, Terry
>
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