View Single Post
Old 05-27-2009, 06:52 PM   #68
Scooby Newbie
Member#: 202982
Join Date: Feb 2009
Location: GROBARR

Ty, the Cobra WX75ST I'm using has performed flawlessly and RF-wise works quite well for being a handheld unit. The RF portion is deatched from the control head and has never given me any problems. I'm able to talk to anything withing range (when using my NMO27B), so I wouldn't paint all the handheld units with the same hatebrush.

The antennas "used in industry" alluded to by DeathStar are more properly called "No Ground-Plane Antennas". All this means is that they have been creatively designed to have a low SWR even when they're not attached to a large metal sheet to act as the RF ground plane. For instance, you have to use a No Ground Plane Antenna to put an antenna on top of your fiberglass motor coach. What these antennas do is to use the outer braid of the coax for a specific length to act as the "other half" of the antenna. In this usage, the bit of feedline that's radiating as the "other half" of the antenna is usually called a counterpoise. The presence of the designed-in counterpoise gives the antenna enough of a RF ground to reduce the SWR to the point that the radio can operate at full power without hurting itself. The drawback is that these No Ground Plane antennas are hugely inefficient and will always perform worse than an antenna above a proper ground plane.
I was trying to stay non-techy with my explaination, but since we "went there" here comes more techy stuff.

Ty is right, the no-ground plane 1/2 wave antennas frankly suck compared to a properly-installed antenna with a ground plane, but sometimes there is no choice as the antenna is mounted on a vehicle that has no metal. CB antennas are a 1/4 wave design, meaning the physical antenna length is 1/4 the total electrical this case, the proper 1/4 wave antenna would be 108 inches tall. I doubt most of you would use a ball mount with a 108" whip on the side of your Subaru

The antenna that Ty and I use for CB, the Larsen NMO27B, is a base-loaded 1/4 wave, meaning there is a coil of wire in the tall back base electrically makes up for the missing ~60 inches of antenna. The radio still sees the correct antenna electrically, but it's only 49" long. The FireStik antenna does that as well, which is readily visible by the looking at the thin wire that wraps up around the inner fiberglass whip. Same concept.

Bottom line is without a proper antenna on a good groundplane, your comms gear (CB or otherwise) will work for crap.
* Registered users of the site do not see these ads.

Last edited by DeathSStar; 05-27-2009 at 07:08 PM.
DeathSStar is offline   Reply With Quote