Hi Folks,
Today I had a chance to experiment with the use of a TOP HAT. I made it
real inexpensively. From three steel coat hangers bonded together at
the hook and each tilted 30 degrees from horizontal. Mounted it
12inches above the BB3 loading coil.
I operate 40m primarily so I compared the amount of coil normally used
on 40 meters with the resonant point after attaching the top-hat. I was
somewhat surprised at how much a difference it made regarding the
physical tap point on the coil. Normally it takes about 46 turns of coil
to resonant the BB3 w/63inch whip on 40m. With the top-hot the number
of turns on the coil dropped to 30 turns. That is almost a 1/3rd less
coil. Don't know what that equates to in inductance...
I presume less inductance means better efficiency.
Now a few questions:
o Did I just improve the efficiency of my mobile antenna?
o Can I start visualizing more current climbing up that 12 inches of
whip between the coil and
the top-hat?
o Is the claim of the screwdriver builders true -- that this little
top-hat is worth at least 1db
improvement?
o Is it true that the higher up the whip the top-hat is placed the
greater the effect?
o If the reduction of inductance does significantly improve effeciency
then is it reasonable to
presume that one could raise the power rating of the antenna?
HAVE FUN,
dave
WA3GIN
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