raised by myself:
I can't see that it makes much
difference, but is there any deference which way the coax is
connected to a J pole antenna. Is it better to have the centre of
the coax connected to the main element or the stub?
I notice that most if not all J pole designs on the net have the
centre of the coax connected to the main element, however when I
refer to a 1977 ARRL antenna book it has it connected the other way.
Is there any difference?
I would explain more, but it's 3:15 AM here in Missouri.
Do a search for J-pole in the qrz.com forums. You'll find that it
works, but it has a feedline radiation problem.
Look at patterns at the bottom of
See exert below:
You'll see the feedline or mast
grounds directly to what everyone assumes is a "zero
voltage" point. This is the electrical equivalent of any J-pole
with the coax connected in series with the feedpoint, and the
shorter leg connected to the shield. The shield can be connected to
any supporting mast with any change in results. Here is the
Shorter leg to shield:
Longer leg to shield:
Notice the low-angle gain dropped about
5dB with just a simple reverse of feedline connections! If I didn't
model the feedline, the model would never show this problem. In ALL
cases, the SWR stays near 1:1, yet gain at low angles changes 5dB!