I know this thread is ancient, but since it's been dragged up, I thought I'd try to clean up some of the really, really bad information that 's been presented here as fact.

I'm an RF (radio frequency) engineer. Radio stuff is what I do for a living. I've also installed well over a thousand cellular phones (back when they were installed in cars) and business-class radios in everything from ghetto beaters to Rolls Royces to multi-million dollar yachts. I just might know something on the subject.

So let's dive in:


Bad move.

Exactly. 75 ohm cable should NEVER be used in a radio application. Matching impedance is what it;s all about, and if you start with mismatched cable, you have nowhere to go but down.


Fiberglass vs. Stainless steel has nothing to do with it. Nothing. Antenna design is what matters. Anybody who tells you things like that is simply revealing that he knows nothing about the subject.


Wow. Just wow. Putting an attenuator on an antenna to compensate for mismatched cable is probably the worst thing you can do. You just masked the problem. Yes, your SWR reading is good. That's because you have attenuated the signal below where the meter can read the reflected power.

Bad, bad, bad move.


There is no such thing as "too much ground plane". The more the better.

The best place to mount your antenna is the dead center of the roof, to take full advantage of the limited ground plane that you have.

Any other location is a compromise. You might need to do that for various reasons, but you are giving up radio performance.



That can happen. It's likely that some atmospheric conditions played a part in that, but yes, this is very believable, and the explanation that was given is accurate.

Yes, you can think of the ground plane as your signal bouncing off part of your vehicle. That's not exactly accurate, but it's a reasonable approximation of what's happening.



That's a good explanation. Not strictly accurate, but a good way to understand it without getting into the details of the physics.

Agreed.


No, and no. You want 50 ohm cable, unless your antenna and radio both specify 75 ohm. I've never heard of that iin 31 years in the business, but I suppose it could happen. The radio world runs on 50 ohms. The cable TV world runs on 75.

As far as separation, you really want as much as you can practically get. Depending on your setup, the distance may need to be carefully calculated. It's not a simple thing.


Yes indeed!




Its not "wire", it's coaxial cable. Not the same thing.

And no, you don't have to have 18 feet. Sometimes yes, sometimes no. Depends on a number of factors.

But whatever you have, DO NOT PINCH OR KINK YOUR COAX!! Treat it very carefully, and don't make sharp bends around corners.


They are illegal, but those rules are mostly unenforced. However, when you add an amplifier, you run the risk of causing interference to somebody, and that will likely get you a visit from some nice men from the FCC, who will do some nice paperwork with your name on it, and you will be losing some serous cash out of your bank account.


No, you'll just have crappy reception. It might be necessary to put up with the loss of performance, but don't fool yourself that you are going to get better this way or that way.



Hmmm. Might be. Cellphones use 50ohm cable, so that part is probably good. Power for your CB is another matter. I'm not sure you're going to have sufficient current available if it was sized for a cellphone. A CB will typically take more juice. Not a lot more, though, so maybe....

Post some pictures of the setup and maybe I can help you figure it out. It's worth looking into it.

 

*the photos are of the "cable" that I have that fits into the cable for telephone that would plug into the box under the rear seat*
The first photo is the end the cable that can plug into the cable already present for the phone in my jeep. I checked and it fits.
The second photo is the other end of the cable that connects to the telephone cable. I don't know what it could be used for, but my dad said it's a typical kind of plug found in older printers, but I'm sure there is something else this can plug into. Knowing that there is already a cable (forgot what you called it in your post) for the antenna and the plug that goes to the phone (the cable that fits the one in the first photo), is there anything I can do with those? I'll take pictures of the telephone cord connection, model numbers and the box I mentioned tomorrow. I'll also see if I can find out the specs for the box (it's Motorola so hopefully I can use the model number to find out the performance specs on it).

 

Interesting. That's a standard AMPS cable used for the original analog phones. It connected the transceiver (the box) to the control head (the phone looking part).


BTW, your Dad is right - that connection was used for older printers, and a lot of other stuff that transferred data of one kind or another.

Is this cable still in the vehicle? Is there a box under the seat still? And if so, can you get a picture of it?

That cable's not going to do you any good for a CB. I was thinking you still have the coaxial cable in there going up to where the antenna was mounted. That could be useful if it's still in good shape.

If the coax is there, it should have either a TNC or a mini-uhf connector (used only by Motorola) on the end. Like this:




Or this:








You may also have a power cable that went to the box. See anything like that? Can you get a picture of where the box was/is?

 

Sorry. Been a long weekend. And the coaxial cable is still there and looks to be in good shape because it's not bent around a corner or anything. It looks like the one in the second pic. I'll send pics soon. And I still have the box but it's not in the jeep at the moment. Took it out for room to put tools in.

 

Totally forgot I did in fact take a photo of the box!Attachment 278511

 

My turn to be sorry to be so long getting back.

After thinking about his a bit more, I don't think that coax is going to do much good, unless you plan to install the CB under the back seat where the cellphone transceiver was.

And maybe not then! Most CBs use a UHF connector, and yours is a mini-UHF. You'd have to find an adapter, and then you probably still have the same problem on the antenna end, even if that coax goes to where you want to go.

Unless there's a roof antenna mount already in your roof, it probably ends near the back of one of the rear side windows, where it was connected to a glass-mounted antenna. That would be a typical installation for a Cherokee if the owner didn't want to drill a hole in his roof. That's not going to help with a CB antenna.

And then there's the problem of the length. It's probably not going to work out right for a CB.

Sorry about that!

BTW, I can't see that attachment for some reason...

 

Nice post but you forgot the most important thing... All CB radios suck coming straight out of the box. FCC regulations (Which are like 30-40 years old) limit CB radios to a 5 watt output. Spending more on one won't help because these regulations apply to all CBs. So you will be dead keying 3 watts and swinging to 5 and your modulation is gonna kinda suck too. Take it to any decent CB shop (Most truck stops have one somewhere on the property) and the tech there can make a few minor adjustments and you can easily get 30-40 watts out of a decent quality radio and increase the modulation also.

 

well this is the setup that I've taken forever to post pics of! It is a 3w box but you was mentioned that if I take it to a truck shop they can get more out of it with some adjustments? I contacted Motorola today and they had no idea what specific model my phone setup was. But why would there be two coaxial cord inputs in that box though?

 

And I have a RF Modulator that's hanging around and I was wondering if that would help in any way? I know it's mainly meant for TV's and stuff like that but maybe I can just use it for the audio part? I'm not experienced at all in this stuff so asking random questions about it help give me the general idea of the Do's and Don'ts

 

Nope. Not useful for anything CB related.

 

I have a cobra 29 classic and 4' firestik on my truck at work. I tuned it via the cobra website. it works well enough to transmit clearly about 4 miles on flat ground. the ground and tuning is very important.

edit: mine is mounted on the slide bar on the back of the cab. these trucks came with antennas on the mirror, but they don't work very well.

2nd edit: I didn't modify the radio or antenna. no spring. just a solid mount. I've received from as far as 13 miles away.

 

There is an interesting hypocrisy about this regulation. It also regulates those using this band to 5 watts even if they have a Ham license. Hammers are the first to track down and police Ham bands, but in turn tend to be "Above the law" and broadcast at 1500 to 2000 watts or more on Citizens Band frequencies. Legally they are also not supposed to broadcast over 5 watts in this band either. It's a double standard.

 

This has many downsides besides being illegal the first is the power limit on the CB band of 5w AM and 12W pep SSB. That said when you let some jack leg do this to your radio it also affects the modulation beyond design capacity of a CB, very poor sound quality with distortion and high heat in the finals. In the end you get very little gain over stock wattage in real world results, just do a proper install with a good antenna mounted properly,


This is a very solid answer and what could be expected from a good install.


I was an early CB'er in the mid 70's to early 80's before I became a ham and operated very carelessly then as for power and antenna wise a 60' tower with a 6 element beam way to much power base and mobile. The FCC located an operator a short distance from me and he was also illegal they took all of his gear thousands of dollars worth and fined him $25,000. I shut mine down the next day as I think it was me they were looking for.


Many yrs later got a ham license and went through all three class's and hold an Extra class license now. A well installed CB is good for a short distance in the mountains on trails or like said above more on level ground but good for traveling with a group.


If you want to cover longer distances with higher powered radios get a ham license a Tech license is easy to get (I have 7-8 yr olds get them in my FCC testing sessions) and you can use 10/6/2/440m FM radios with 50w mobiles.

 

Exactly right, Fred. Well said.

Most of that jacking of power is an attempt to overcome the deficiencies of a lousy installation.

 

I am a truck driver, but I have no interest in having an abnormally strong radio. I'll adjust the gain and squelch depending on my location as it receives very well. and 99.9% of radio traffic is nonsense anyway. I use it at our terminals frequently and rarely on the road unless it pertains to safety or lights on a truck not working etc. I replaced everything but the radio when I started here and I think I had about $40 in it. the radio prob sells for $80 or so new.