[TowerTalk] 40m Sloper system

Terry George g4amt@zetnet.co.uk
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 
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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