Cobra 75 range
Thread Starter
JK Enthusiast
Joined: Aug 2007
Posts: 149
Likes: 0
From: Jacksonville, FL
Cobra 75 range
I just installed the Cobra 75 w/ 3' Wilson flex on spare tire mount and have excellent SWR readings. I can pick up signals off I-95 sometimes 7 miles+, but I can't get a radio check to save my life. I don't know anyone yet w/ a cb so have tried testing transmit on the highway w/lots of radio traffic a few dozen times and get no response. I'm going to have to find someone w/a cb I guess because I'm starting to think I can't transmit for some reason.
But anyway... what kind of transmit range are you guys getting on your similar setups? On the highway? On the trail? I know there's lots of different variables, but on AVERAGE what should I expect?
But anyway... what kind of transmit range are you guys getting on your similar setups? On the highway? On the trail? I know there's lots of different variables, but on AVERAGE what should I expect?
JK Freak
Joined: May 2008
Posts: 744
Likes: 1
From: Escondido, CA
Element,
A CB radio's transmission is Line of Sight (LOS), which means that, if there is any physical obstacle or structure in the LOS to the distant radio, the signal will be physically stopped or deflected. There is a real dichotomy here, however, because if you are on the top of a mountain and can see (LOS) an other mountain top 30 miles away, you could talk to a fellow CB'er on the distant mountain top because there are no obstructions in the way. That being said, if you are in hill country or wheeling in canyons, you may not be able to talk to a fellow CB'er who may only be 500 yards away because there is a hill or canyon wall stopping your transmission.
Here is another factor. Your antenna doesn't radiate the same distance on all directions, that is called the antenna pattern. Generally speaking, a CB installation on a Jeep, with the antenna mounted on the tailgate, will transmit further to the rear of the vehicle than it will to the front. This is especially true if you have a hard top. For best all around results, the antenna should be installed in the center of a steel roof, which ain't going to happen with a JK.
There are other factors such as antenna wave length and construction, which I am not going into here.
Bottom line, if your SWR reading is under 2 (while you have the engine running) and you have 2/3'rds of your antenna above your roof line, which is very important, you can expect to have a average transmission distance of about one mile, give or take, depending on the terrain. You will find this more than adequate for running trails with your friends. "But, but, I can hear truckers more that ten miles away." That you can, because most of them use illegal linear amplifiers with power out from 100 to 1000 watts which is much higher that the 4 watts your CB puts out. You need to fine a fellow JK'er and do some CB testing of your own.
KI6VBQ
A CB radio's transmission is Line of Sight (LOS), which means that, if there is any physical obstacle or structure in the LOS to the distant radio, the signal will be physically stopped or deflected. There is a real dichotomy here, however, because if you are on the top of a mountain and can see (LOS) an other mountain top 30 miles away, you could talk to a fellow CB'er on the distant mountain top because there are no obstructions in the way. That being said, if you are in hill country or wheeling in canyons, you may not be able to talk to a fellow CB'er who may only be 500 yards away because there is a hill or canyon wall stopping your transmission.
Here is another factor. Your antenna doesn't radiate the same distance on all directions, that is called the antenna pattern. Generally speaking, a CB installation on a Jeep, with the antenna mounted on the tailgate, will transmit further to the rear of the vehicle than it will to the front. This is especially true if you have a hard top. For best all around results, the antenna should be installed in the center of a steel roof, which ain't going to happen with a JK.
There are other factors such as antenna wave length and construction, which I am not going into here.
Bottom line, if your SWR reading is under 2 (while you have the engine running) and you have 2/3'rds of your antenna above your roof line, which is very important, you can expect to have a average transmission distance of about one mile, give or take, depending on the terrain. You will find this more than adequate for running trails with your friends. "But, but, I can hear truckers more that ten miles away." That you can, because most of them use illegal linear amplifiers with power out from 100 to 1000 watts which is much higher that the 4 watts your CB puts out. You need to fine a fellow JK'er and do some CB testing of your own.
KI6VBQ
JK Jedi
Joined: Aug 2007
Posts: 5,813
Likes: 0
From: Kenai Peninsula, Alaska
[QUOTE=Desert Fox;1123720]Element,
A CB radio's transmission is Line of Sight
Well..........yes and no. The "line of site" term is usually used more as you get up into the VHF/UHF bands, because HF signals actually do "bend". What you are referring to as "LOS" is really called "ground wave". And for the most part, and at this time in the solar cycle, weak signal CB is mostly ground wave. But at the right time 11 meters (cb band) is just as condusive to atmostpheric propagation (skip) as any other of the HF bands. This will be quite noticeable as the solar cycle picks up. Soon there will be so many strong CB signals coming down into your little radios from bouncing off the atmostphere/s, that you will barely be able to get a signal out across the street. I'm exaggerating of course, but believe me, it will seem like that before too long. You guys that are just now getting into CB are experiencing a very low time in the solar cycle. In the next few years things will start to change dramatically.
A CB radio's transmission is Line of Sight
Well..........yes and no. The "line of site" term is usually used more as you get up into the VHF/UHF bands, because HF signals actually do "bend". What you are referring to as "LOS" is really called "ground wave". And for the most part, and at this time in the solar cycle, weak signal CB is mostly ground wave. But at the right time 11 meters (cb band) is just as condusive to atmostpheric propagation (skip) as any other of the HF bands. This will be quite noticeable as the solar cycle picks up. Soon there will be so many strong CB signals coming down into your little radios from bouncing off the atmostphere/s, that you will barely be able to get a signal out across the street. I'm exaggerating of course, but believe me, it will seem like that before too long. You guys that are just now getting into CB are experiencing a very low time in the solar cycle. In the next few years things will start to change dramatically.
Last edited by AK4Dave; May 14, 2009 at 07:27 PM.