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Gregg, W6IZT wrote:
I am in the process of planning my antennas for a new qth. There is a 55
ft crank-up already in place with a Force12 C31 xr at 60 ft. I am hoping
to shunt feed this tower for 160 and 80.
I'm sure this has been done before, but I am concerned about feeding the
tower and the potential for less than perfect electrical continuity. As
an alternative I have considered running a parallel conductor from the
top of the tower and grounding it at the base.
==========
When I was W5RTQ in Houston in 1968 to 1975, I shunt fed my telescoping
three-section crank-up 69' tower with a TH6DXX at 70' on both 160m and
80m. The tower performed extremely well for DX on both 160m and 80m.
I attached the shunt wire for 160m at the top of the tower and the shunt
wire for 80m at the top of the center section at about 45 feet.
Fortunately, by adjusting the shunt wire spacing, these points were close
to 50 ohms for the real part of the impedance on the two bands, so only a
single "gamma" capacitor was needed on each shunt feed to tune out the
inductive reactance.
Standoffs for the shunt wires were used only at the tops of the three
sections, with another standoff at the base of the bottom section. This
enabled me to crank down the tower during high wind periods with no
problem. The shunt wires would just droop when the tower was cranked
down.
The coax for the tribander and the rotator cable came down inside the
tower to ground level, just hanging loosely inside the tower, so they
also presented no problem when cranking down the tower.
If you don't wish to attach the shunt wires to the same points, the only
alternative is to attach both the 160m and 80m shunt wires to the top of
the bottom section of tower and use an omega match system to tune the
shunt feeds. Then the only thing you will have to watch when you crank
down the tower is the Force 12 coax and rotator cable.
I took no precautions to electrically bond the three sections of tower
together and I had no problems in that respect, either. If you're queasy
about this, you can make some metal straps to slide against the tower
legs on each section assuring electrical continuity.
The W5RTQ tower is described in all of the latest editions of the ARRL
Antenna Book.
73, de Earl, K6SE
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<DIV>Gregg, W6IZT wrote:</DIV>
<DIV> </DIV>
<DIV><FONT face=3DArial size=3D2>I am in the process of planning my =
antennas for a=20
new qth. There is a 55 ft crank-up already in place with a Force12 C31 xr =
at 60=20
ft. I am hoping to shunt feed this tower for 160 and 80. <BR><BR>I'm sure =
this=20
has been done before, but I am concerned about feeding the tower and the=20
potential for less than perfect electrical continuity. As an alternative I =
have=20
considered running a parallel conductor from the top of the tower and =
grounding=20
it at the base. </FONT><BR>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D</DIV>
<DIV>When I was W5RTQ in Houston in 1968 to 1975, I shunt fed my =
telescoping=20
three-section crank-up 69' tower with a TH6DXX at 70' on both 160m and=
=20
80m. The tower performed extremely well for DX on both 160m and 80m.<=
/DIV>
<DIV> </DIV>
<DIV>I attached the shunt wire for 160m at the top of the tower =
and=20
the shunt wire for 80m at the top of the center section at about 45 feet.&=
nbsp;=20
Fortunately, by adjusting the shunt wire spacing, these points were =
close=20
to 50 ohms for the real part of the impedance on the two bands, so =
only a=20
single "gamma" capacitor was needed on each shunt feed to tune out the=
=20
inductive reactance.</DIV>
<DIV> </DIV>
<DIV>Standoffs for the shunt wires were used only at the tops of the three=
=20
sections, with another standoff at the base of the bottom section. =
This=20
enabled me to crank down the tower during high wind periods with no=20
problem. The shunt wires would just droop when the tower was cranked=
=20
down.</DIV>
<DIV> </DIV>
<DIV>The coax for the tribander and the rotator cable came down inside the =
tower=20
to ground level, just hanging loosely inside the tower, so they=20
also presented no problem when cranking down the tower.</DIV>
<DIV> </DIV>
<DIV>If you don't wish to attach the shunt wires to the same points, the =
only=20
alternative is to attach both the 160m and 80m shunt wires to the top of =
the=20
bottom section of tower and use an omega match system to tune the shunt=20
feeds. Then the only thing you will have to watch when you crank=
down=20
the tower is the Force 12 coax and rotator cable.</DIV>
<DIV> </DIV>
<DIV>I took no precautions to electrically bond the three sections of tower=
=20
together and I had no problems in that respect, either. If you're =
queasy=20
about this, you can make some metal straps to slide against the tower legs =
on=20
each section assuring electrical continuity.</DIV>
<DIV> </DIV>
<DIV>The W5RTQ tower is described in all of the latest editions of the ARRL=
=20
Antenna Book.</DIV>
<DIV> </DIV>
<DIV>73, de Earl, K6SE</DIV>
<DIV> </DIV></BODY></HTML>
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