Looking for some shunt feed wisdom from the list. Trying to shunt feed 25G
tower ( 8-10ft sticks, 8ft flat top, base 18" out of the ground = total tower
89.5 ft) has a F12 C31XR just above the thrust bearing (@90ft) with 6ft 2" mast
above the tribander with a F12 D140 dipole (@96ft). Based on various archive
reading I can't get a good sense of how much top loading I may have (some say
only the boom, others say much more). That said I've first tried a cage wire (
four 14ga wires spaced 6" apart) all the way at the top of the tower spaced
about 2ft out. Trying to dip this with an Autek RF-1 yielded about 1.15 Mhz
which didn't seem right. Cage was taken down and tried just a single wire at a
lower tap height of 60ft. Strangely enough I get about the same frequency but
the Z dropped. Moving farther down to 50ft again about the same frequency but
again Z dropped. I'm assuming the frequency readings are completely off and I'm
getting overload from nearby AM broadcast as I am surrounded by them. I'm
unsure now if I should continue trying tap points farther down the tower just
looking for the best Z or use some other approach. If anyone has experience
with how much top loading a C31XR could represent I could use the graphs in
ON4UNs book to perhaps get close, but I'm unsure what the loading looks
like and found no real answers searching the archives. Any help appreciated to
help eliminate many more trips on the tower looking for the nearest 50 ohm
spot. Tnx 73's Bob - N4PQX
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