Re: What's the Dealio with the J-pole?
- From: "John KD5YI" <groups2_dot_jocjo@xxxxxxxx>
- Date: Sat, 30 May 2009 17:37:54 GMT
"Jim Lux" <james.p.lux@xxxxxxxxxxxx> wrote in message news:gvp0bo$lo9$2@xxxxxxxxxxxxxxxxxxxx
John KD5YI wrote:"JB" <nospam@xxxxxxxxxxxx> wrote in message news:clSTl.1516$9L2.889@xxxxxxxxxxxxxxxxxxxxxxx
The 1/4 wave ground plane has a useless pattern. Main lobe at about 30
degrees above horizon, but broad enough to be usable and simple to build.
The quarter-wave antenna's height above ground has much more to do with the elevation angle than the fact that the antenna is a quarter-wave ground plane. Using EZNEC, I see that a quarter wave antenna situated 3 wavelengths above real/high accuracy ground of medium characteristics has a main lobe 4 degrees above the horizon. At that angle, the gain is 5.1 dBi. You can confirm this if you have a copy of EZNEC.
John
If you're just looking for a portable vertical antenna, just a wire on the end of the coax, and hanging it up, works pretty well. The shield of the coax (outside surface) serves as the other half of the dipole. Heck, it will have a bizarre pattern, and couple RF everywhere, but you're talking about an antenna you're hanging out of a hotel window or something.. You're not doing earth-venus-earth radar tests... you're just getting the antenna away from where you are sitting to "outside"..
Bob D. -
Please don't take my comments as being negative about a J-Pole. I happen to like them for other reasons. They can be made very rugged. The few I made started out as a 30-foot mast. 3/4 wavelengths down from the top I mounted a horizontal metal bracket. To that I mounted a vertical 1/4 wave tube. I then used automotive hose clamps to connect a 1/2 wavelength piece of coax near the bottom just above the horizontal bracket. I adjusted the connection point of the coax to find the lowest SWR point and then replaced the 1/2 wave piece of coax with my longer lead-in. I put some weatherproofing on the coax.
I ran 10 gauge wire from my nearby ground rod over to the bottom of the mast. What I like about this arrangement is that the entire assembly is grounded. I once had a nearby lightning strike cause my IC2AT to block signals for several seconds while I was listening to a local repeater with a home-made ground plane. Charge buildup, I guess. That never happened with my J-Pole. That thing worked flawlessly for several years until I replaced it with a commercial dual-band (expensive) antenna.
Have fun.
73,
John
.
- References:
- Re: What's the Dealio with the J-pole?
- From: John KD5YI
- Re: What's the Dealio with the J-pole?
- From: Jim Lux
- Re: What's the Dealio with the J-pole?
- Prev by Date: Re: Sun Spots
- Next by Date: Re: Sun Spots
- Previous by thread: Re: What's the Dealio with the J-pole?
- Next by thread: Re: What's the Dealio with the J-pole?
- Index(es):
Relevant Pages
|
Loading
