On Apr 25, 2010, at 7:10 AM, Wayne Rogers wrote:
Obviously a 40' gamma match is easier to implement
than a full height (90' in my case) shunt feed. Is there any benefit to
going all the way to the top?
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I shunt feed my tower at the top of the bottom section, which is at 22 ft. The
rod is 3/8 inch aluminum, 15 inches from the tower leg. I then use an omega
match which obviates the need to search for the vertical sweet spot. My shunt
feed works on 160 and 80 using latching relays to switch capacitors to change
bands. This 22 ft feed point causes very high RF voltage across the omega
capacitors which requires them to be vacuum variables. In addition to the
voltage breakdown, the vacuum variables verniers make tuning very easy and
precise compared to air variables. Attach point and distance from the tower leg
will affect the values of the capacitors required, the RF voltage breakdown and
the bandwidth vs SWR.
It works. 173 DXCC on Top Band in 10 years from a very small West Coast USA
city lot.
YMWV.
GL & 73 - Steve WB6RSE
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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