Hello again,
For all those who wrote asking about the vertical wire zepps, here are the
dimensions for two that I have built and been very happy with. Please give
them a try and post your results!
HF wire j-poles for 10m/28.4 MHz & 20m/14.175 MHz (end fed 1/2 wave
verticals):
* Radiators are made from #14 or #18 stranded copper (electrical 1/2
waves):
10m length - 198"/16.5' note: 95% velocity factor
20m length - 396"/33'
* Matching stubs are made from 450 ohm window line that has #18 copperweld
conductors. They are shorted together at the bottom:
10m length - 93.5"/7'-9.5" note: 90% velocity factor
20m length - 188"/15'-8.5"
* Choke baluns and feedpoint were made with a single section of rg-58 coax,
formed into a coil of 5 turns @ 4" diameter, just below the bottom of the
stub. The portion of the coax between the coil and up to the feedpoint is
cable-tied to the stub. I soldered on an SO-238 connector just below the
coil to attach a 50 ohm feedline.
10m length - start with approximately 73" of rg-58
20m length - start with approximately 76" of rg-58
* Feed points are soldered on to the stub conductors (shield & center at
the same height) above the bottom, shorted end of the stub. The shield was
connected to the same side of the stub that was connected to the radiator
(long side of 'J'):
10m feed point height - 6"
20m feed point height - 9"
I was able to achieve an SWR of 1.1 to 1 at the SO-238 connector as
measured on my MFJ-259 analyzer. It also looked great in the shack through
50' of rg-8x feedline - no tuner required, unless trying to tune them
on the next lower HF band.
Experiment with the feed point tap height if you don't get an excellent
match.
I Will try modelling these soon using NECWIN-BASIC to find out what the
angle of radiation is. I had them both suspended in trees such that the
upper end of the radiator was up about 65'
Here is an ASCI art illustration:
R=Radiator
M=Matching stub
S=Shield conductor of coax
C=Center conductor of coax
B=Balun coil
T=Coax Tail with connector
R
R
R
R
R
R
R
R
R
R
M M
M M
M M
M M
M M
S C
M M
M-M
B B
B B
B B
T
T
Hope you have as much fun with this as I have.
Mark, N1LO, Gloucester, VA
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