I need the help from one of the Guru's here on the group....
I need to know how to match the 160 meter vertical ground plane here. It
worked fine for years until I removed 80 meter 4-square from the tower. I
have no modeling capabilities here.
The set-up is this:
A 200 foot Rohn 25 tower, with insulators at the 60 foot level.
Three elevated radials at the 60 foot level; sloping down to about 10 feet
off the ground at the far ends. They are c. 110 electrical degrees long.
The vertical radiator is c. 140 feet long.
There is a large 1:1 balun at the feed point.
The feed line is 450 feet of 7/8 helix to the ham shack.
The reading on the 259B at the feed point is c. 3:1 VSWR, with a slight dip
to 2.7:1 at 2.45 mhz.
I am at my wits end here; several trips up the tower produced no good
results. There are many systems on Google and YouTube, but the matching
systems are for antennas shorter that 1/4 wave length.
The old matching system when the 80 m 4-square was co-located was a 600 pf
series capacitor from the center of the coax to the base of the vertical
element. The three radials are joined together at the feed point, and
connected to the coax shield.
The VSWR back then was 1.25:1 @ 1835 khz. , and was a "killer" antenna on
160!
Any help will be greatly appreciated; my old knees have about two more
climbs left in them!
Thanks in advance.
(((73)))
Phil, K5PC
_______________________________________________
UR RST IS ... ... ..9 QSB QSB - hw? BK
|