Peter:
Whether you feed a vertical of a given length as a folded unipole, or as a
regular undipole witha gamma or omega match, does not make any difference
to the radiation resistance of the antenne, at least not the radiation
resistance we use for calculating the radiation losses of antennas.
Thinking that folded elments increase the radiation resistance if one of
the many fairy tales we hear regularly on the band and on the verious
reflectors. There is nothing like a free lunch!
73
John, ON4UN
At 10:28 8/14/97 +0100, you wrote:
>> I have very good success with a grounded tower fed as a folded
>> unipole. It has the advantage that the radiation resistance goes up,
>> minimising ground losses.I use a crank up at 60 feet, top loaded with
>> a 5 ele for 20, and interlaced 4 eles for 10 and 15 at 68 feet. I feed
>> it with 3 parallel wires spaced about 10 inches from each other, and
>> bond all the coax outers for the beams top and bottom. An L match
>> requires no readjustment over the band on 160, although on 80, it's
>> very sharp tuning and runs lots of volts. Adding radials gave no
>> change in input impedance ( <1%) and no measurable current in them
>> with 400watts and a 250mA thermo ammeter in the radial. This suggest
>> that the ground currents are low. The subsoil is heavy wet clay, and
>> the grounding is three 4 foot ground rods. It works - VK0IR 2nd call
>> on 160, 1st call 80 SSB. I spent a long time trying gamma and omega
>> matches until going to the folded unipole approach.
>>
>> 73
>>
>> Peter G3RZP
>>
>
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* John Devoldere, ON4UN, AA4OI, OT7T *
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