[TowerTalk] 40m Sloper system
Mon, 16 Nov 1998 19:44:31 GMT
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
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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