Can anyone help a newbie installing a J-Pole antenna.

Antenna: Copper Pipe Dual Band 2M/70CM. Bottom of long leg is tee. lower leg
of tee goes 14" w/ 1/2" copper then transitions to 1" x 36". This is clamped
to two tv mast mounts, anchored to a wooden chimney chase.

When I built the antenna, it displayed a relatively flat SWR across both
bands, using an MFJ-269. Antenna was free standing in yard, away from
anything to affect it.

After mounting, the SWR seems to vary from as measured (1:1.2) to off the
map. Thought it was maybe bad coax (LMR-400) but as I checked it, the SWR
came back into line. Someone told me to ground the lower end of the j-pole,
as if it were clamped to a tower. I did this and the SWR goes off the map.

Should a J-pole be grounded? if not, how do you protect it or the structure
from a lightning strike?

Thanks

Paul P

On Mon, 09 Jan 2006 00:34:45 GMT, "Paul Proefrock"
wrote:

Should a J-pole be grounded? if not, how do you protect it or the structure
from a lightning strike?

A j-pole should be insulated from a conductive mast and a choke type
balun use on the transmission lines. Not so much for matching but to
keep the maximum signal towards the horizon and not shoot up at high
angles. Unless you want to talk to airplanes.

Danny, K6MHE

email: k6mheatarrldotnet
http://www.k6mhe.com/

Hello Paul,

You do not need to ground the J-Pole antenna because it is a half-wave
dipole feeded with a quarter-wave length.
That's why the total antenna lentgh = (1/2 + 1/4) x lambda

I have built several 2m J-Pole antennae (with copper pipes) without any
problems. The last one was clipped to the TV mast (as yours). The only
problem I have experienced was with a dual band (2m/70cm) J-Pole (your
case). It was solved by ajusting some of the dimensions.

If it is your first J-Pole, I suggest you to built first a mono-band (2m).
You will succed because this is the most easier antenna I have ever built!!!
Then you will be able to handle a dual band J-Pole.

Do not vanish!!!.... This is a very nice antenna. It's main benefit is the
very low angle of its radiation over the horizon (between 3 and 4 degrees).
I did a contact with Marocco from my location (IN88HR) with 10 watts!!! OK
!!! It was a sporadic .... ;-)))

Good luck. Contact me if you want more details.

Best regards

Jean-Marc
F4DRH
www.barbaxoops.com







"
Antenna: Copper Pipe Dual Band 2M/70CM. Bottom of long leg is tee. lower
leg of tee goes 14" w/ 1/2" copper then transitions to 1" x 36". This is
clamped to two tv mast mounts, anchored to a wooden chimney chase.

When I built the antenna, it displayed a relatively flat SWR across both
bands, using an MFJ-269. Antenna was free standing in yard, away from
anything to affect it.

After mounting, the SWR seems to vary from as measured (1:1.2) to off the
map. Thought it was maybe bad coax (LMR-400) but as I checked it, the SWR
came back into line. Someone told me to ground the lower end of the
j-pole, as if it were clamped to a tower. I did this and the SWR goes off
the map.

Should a J-pole be grounded? if not, how do you protect it or the
structure from a lightning strike?

Thanks

Paul P