Many CB questions, school me

[XJ Wheeler]

I've ran cb's for years on our trucks but always just took the easy route with a 3' steel magnet mount. Now i finally got one for my XJ and am realizing just how little i know.

I got a used Cobra 19 lV 40 channel off ebay and have used it with a magnet mount. It worked pretty good, so far no issues. But since its for my XJ i want something more permanent. What i'm looking for is something that will perform well, not too intrusive, and relatively easy on the ol wallet.

I plan on making a mount that bolts on to the tail light mounting area, but its not set in stone.

Also was thinking of maybe a 3' fiberglass antenna. Maybe Firestik? Is that easily removable? I cover my jeep up at night and don't want to deal with that all the time. Should i get one with a tunable tip, i probably won't have it tuned though.

Do i need a spring below the antenna? Is that just so it doesn't break the fiberglass if i hit something?

How would the antenna ground? Does it ground using the mount or a grounding strap?

What type of cord should i use, if there's a difference? What length would be best?

Assume that i am completely ignorant to all this, so think of me as a true beginner. Teach me of the infinite wisdom of xjtalk, i am here to learn from the masters. Grasshopper crave knowledge.

[Mudderoy]

I've ran cb's for years on our trucks but always just took the easy route with a 3' steel magnet mount. Now i finally got one for my XJ and am realizing just how little i know.

I got a used Cobra 19 lV 40 channel off ebay and have used it with a magnet mount. It worked pretty good, so far no issues. But since its for my XJ i want something more permanent. What i'm looking for is something that will perform well, not too intrusive, and relatively easy on the ol wallet.

I plan on making a mount that bolts on to the tail light mounting area, but its not set in stone.

Also was thinking of maybe a 3' fiberglass antenna. Maybe Firestik? Is that easily removable? I cover my jeep up at night and don't want to deal with that all the time. Should i get one with a tunable tip, i probably won't have it tuned though.

Do i need a spring below the antenna? Is that just so it doesn't break the fiberglass if i hit something?

How would the antenna ground? Does it ground using the mount or a grounding strap?

What type of cord should i use, if there's a difference? What length would be best?

Assume that i am completely ignorant to all this, so think of me as a true beginner. Teach me of the infinite wisdom of xjtalk, i am here to learn from the masters. Grasshopper crave knowledge.

One of the common mistakes newbies to radio make is the attention to reflected power, or SWR (standing wave ratio). The ratio of RF power going out to how much is coming back in.

One thing I learned by doing antenna stuff for multiple bands and bands that covered a much bigger frequency range that CB does, is that tuning a CB antenna is super easy.

For a 40 channel CB radio (they used to be 23) you just tune the antenna for about channel 20. Check it on 40 and 1. Anything 2.0:1 or less is fine.

I would recommend you basic inexpensive 3'(?) whip. Tuning shouldn't be necessary as long as you have a good RF ground and most of the antenna is away from the metal body. I would mount it on a mount that uses the bolts behind the passenger side rear brake/turn light. Also an easy way to run the coax inside the vehicle.

If you want to make it easy to remove the antenna check for a "quick disconnect" often used by HAMs so they can remove HUGE mobile antennas. It's just a twist on and off.

I can't remember right now but the length of your coax can affect your SWR, I think that if you get 20' RG-59(58 or 59 what ever the 50 ohm stuff is) you should be fine. If you have to loop the coax because it is too long make it a big loop, nothing tight. It can damage the coax and also change the electrical properties if the loop is too small.

[prerunner1982]

I believe the preferred coax length is 9' increments since 9' (108") is approx 1/4 wavelength in the 11 meter band. (102" whip with 6" spring= 108")

[XJ Wheeler]

One of the common mistakes newbies to radio make is the attention to reflected power, or SWR (standing wave ratio). The ratio of RF power going out to how much is coming back in.

One thing I learned by doing antenna stuff for multiple bands and bands that covered a much bigger frequency range that CB does, is that tuning a CB antenna is super easy.

For a 40 channel CB radio (they used to be 23) you just tune the antenna for about channel 20. Check it on 40 and 1. Anything 2.0:1 or less is fine.

I would recommend you basic inexpensive 3'(?) whip. Tuning shouldn't be necessary as long as you have a good RF ground and most of the antenna is away from the metal body. I would mount it on a mount that uses the bolts behind the passenger side rear brake/turn light. Also an easy way to run the coax inside the vehicle.

If you want to make it easy to remove the antenna check for a "quick disconnect" often used by HAMs so they can remove HUGE mobile antennas. It's just a twist on and off.

I can't remember right now but the length of your coax can affect your SWR, I think that if you get 20' RG-59(58 or 59 what ever the 50 ohm stuff is) you should be fine. If you have to loop the coax because it is too long make it a big loop, nothing tight. It can damage the coax and also change the electrical properties if the loop is too small.

So, yes to the mount and 3' antenna. The cable needs to be 50 ohm? Is that pretty standard? Is that "quick disconnect" fairly standard as well?

Is the SWR basically the ratio of what is received compared what is put out, and by having a 2.0:1 SWR mean that you are essentially receiving 50% of what has been sent?

[XJ Wheeler]

I believe the preferred coax length is 9' increments since 9' (108") is approx 1/4 wavelength in the 11 meter band. (102" whip with 6" spring= 108")

Would that mean i would need 18' of cord plus antenna or 18' including antenna?

[EekGirl96]

from what ive experienced with my antenna, if you go with firestik(which I prefer over the whips or magnetic based antennas), you'll definately need a spring. My antenna has fallen off and broke many chords due to it hitting trees, moving back and forth, etc...the spring helps keep it on and keeps stuff in good shape lol.

[Mudderoy]

So, yes to the mount and 3' antenna. The cable needs to be 50 ohm? Is that pretty standard? Is that "quick disconnect" fairly standard as well?

Is the SWR basically the ratio of what is received compared what is put out, and by having a 2.0:1 SWR mean that you are essentially receiving 50% of what has been sent?

swr reading % of loss erp* watts available
1.0:1 0.0% 100.0% 100.00
1.1:1 0.2% 99.8% 99.8
1.2:1 0.8% 99.2% 99.2
1.3:1 1.7% 98.3% 98.3
1.4:1 2.8% 97.2% 97.2
1.5:1 4.0% 96.0% 96
1.6:1 5.3% 94.7% 94.7
1.7:1 6.7% 93.3% 93.3
1.8:1 8.2% 91.8% 91.8
2.0:1 11.1% 88.9% 88.9
2.2:1 14.1% 85.9% 85.9
2.4:1 17.0% 83.0% 83
2.6:1 19.8% 80.2% 80.2
3.0:1 25.0% 75.0% 75
4.0:1 36.0% 64.0% 64
5.0:1 44.4% 55.6% 55.6
6.0:1 51.0% 49.0% 49
7.0:1 56.3% 43.8% 43.8
8.0:1 60.5% 39.5% 39.5
9.0:1 64.0% 36.0% 36
10.0:1 66.9% 33.1% 33.1

:link: (http://www.wcerc.org/swrlosschart.asp)

So with 4 watts out, you would have a .44 watt power loss. Anything in the 3.0:1 range can damage your radio, but for short emergency transmissions it should be okay. Reflected power equals heat and heat is what causes the final transistor(s) to fail.

[XJ Wheeler]

swr reading % of loss erp* watts available
1.0:1 0.0% 100.0% 100.00
1.1:1 0.2% 99.8% 99.8
1.2:1 0.8% 99.2% 99.2
1.3:1 1.7% 98.3% 98.3
1.4:1 2.8% 97.2% 97.2
1.5:1 4.0% 96.0% 96
1.6:1 5.3% 94.7% 94.7
1.7:1 6.7% 93.3% 93.3
1.8:1 8.2% 91.8% 91.8
2.0:1 11.1% 88.9% 88.9
2.2:1 14.1% 85.9% 85.9
2.4:1 17.0% 83.0% 83
2.6:1 19.8% 80.2% 80.2
3.0:1 25.0% 75.0% 75
4.0:1 36.0% 64.0% 64
5.0:1 44.4% 55.6% 55.6
6.0:1 51.0% 49.0% 49
7.0:1 56.3% 43.8% 43.8
8.0:1 60.5% 39.5% 39.5
9.0:1 64.0% 36.0% 36
10.0:1 66.9% 33.1% 33.1

:link: (http://www.wcerc.org/swrlosschart.asp)

So with 4 watts out, you would have a .44 watt power loss. Anything in the 3.0:1 range can damage your radio, but for short emergency transmissions it should be okay. Reflected power equals heat and heat is what causes the final transistor(s) to fail.

I understand there is numbers and decimals on that chart but more than that hurts my brain. Sorry, i am trying to understand.

[prerunner1982]

So, yes to the mount and 3' antenna. The cable needs to be 50 ohm? Is that pretty standard? Is that "quick disconnect" fairly standard as well?

Is the SWR basically the ratio of what is received compared what is put out, and by having a 2.0:1 SWR mean that you are essentially receiving 50% of what has been sent?

I would say that 50 ohm coax is pretty standard however the quick disconnects are not at least not in the CB world. Can be easily found though.


Would that mean i would need 18' of cord plus antenna or 18' including antenna?

My understanding is that any combination of 9' segments is fine. I would use the least amount possible. You aren't going to need 27' of coax in the XJ though depending on where you mount the radio you may need 18' with some left over coiled up.

I am by far no expert... and have read posts by people that say the length of the coax is not an issue. The reasoning doesn't sound bad to me though.

[prerunner1982]

I understand there is numbers and decimals on that chart but more than that hurts my brain. Sorry, i am trying to understand.

What is all adds upto is that with a 2.0:1 SWR you aren't losing 50% as you had suggested, only just above 10% of the watts. 4 watts output, .44 watt loss, which isn't bad.

[EekGirl96]

I would say that 50 ohm coax is pretty standard however the quick disconnects are not at least not in the CB world. Can be easily found though.



My understanding is that any combination of 9' segments is fine. I would use the least amount possible. You aren't going to need 27' of coax in the XJ though depending on where you mount the radio you may need 18' with some left over coiled up.

I am by far no expert... and have read posts by people that say the length of the coax is not an issue. The reasoning doesn't sound bad to me though.

Uhm, I thought you werent supposed to have your cable "coiled up", its supposed to stay relatively straight...from what I've heard

[Carves]

X 2 on a spring base if you get a stiff/no flex, fibreglass antennae.

Firestik do a Q.D. like Mudderoy described .... http://www.rightchannelradios.com/firestik-cb-antenna-quick-disconnect.html

Different mounting locations and addons like the Q.D. etc., .... affect both transmission direction and SWR numbers .... so always do a SWR test after an antennae instal or mounting relocation .... for best results.

[Mudderoy]

Uhm, I thought you werent supposed to have your cable "coiled up", its supposed to stay relatively straight...from what I've heard

That's why I was saying NOT to coil it tightly. It can act as an inductor and change the value of the cable. No coil at all is my preference, but sometimes that is impossible to do.

[EekGirl96]

That's why I was saying NOT to coil it tightly. It can act as an inductor and change the value of the cable. No coil at all is my preference, but sometimes that is impossible to do.

Maybe I shouldve read the post more carefully lol. Yeah, thats how I've done it, no coil in the cable and mount the antenna up high(even though mine is on the side of my rear bumper)

[prerunner1982]

Uhm, I thought you werent supposed to have your cable "coiled up", its supposed to stay relatively straight...from what I've heard


Generally a large coil is ok, just not tightly wound. But yes straight is best.

Nevermind, Tony beat me to it.

[XJ Wheeler]

Ok, let me make sure i got this. A 2.0:1 SWR on a 4 watt system (is that what mine would be?) is essentially an 11.1% or 0.44 watt loss. Anything higher would heat up and damage the transistor. Good? Is the 2.0:1 SWR max a general range for all CBs?

I take it i would either need a meter of some sort to make sure of the SWR or have someone check it?

Use a spring if i want to keep the antenna nice and in one piece.

Keep the cord straight if possible, if not the larger the coil the better.

Thanks Carves for that link, that will be way easy to deal with.

[prerunner1982]

Legal watts on a CB is 4, though yours will probably have less. Mine only puts out about 2 watts.

You will need a SWR meter to check, the Cobra 19 does not have one built in. They aren't too expensive, some of the better ones have a built in Watt meter as well.

Yes spring is recommended...darn near required if you off road.

[Mudderoy]

Ok, let me make sure i got this. A 2.0:1 SWR on a 4 watt system (is that what mine would be?) is essentially an 11.1% or 0.44 watt loss. Anything higher would heat up and damage the transistor. Good? Is the 2.0:1 SWR max a general range for all CBs?

I take it i would either need a meter of some sort to make sure of the SWR or have someone check it?

Use a spring if i want to keep the antenna nice and in one piece.

Keep the cord straight if possible, if not the larger the coil the better.

Thanks Carves for that link, that will be way easy to deal with.

A SWR of 2.0 would be a 11.1% loss, so if you are REALLY getting 4 watts to the antenna (remember there are losses in the cable) then your output would be 3.666 watts, and your reflected power (back into your radio) would be 0.444 watts.

As a rule of thumb 3.0:1 I wouldn't transmit very long, just a few seconds at a time, and FIX the problem A.S.A.P. I do NOT think a 2.0:1 would cause you any problems, but a 1.0:1 would be best.

A spring is fine, however a spring means it can move closer and further away from the metal of the body. This will change the SWR and the radiation pattern. With that said, if you are talking to people with in a few miles of your location you'll never notice the changes. Personally I'd just have a spare 3' whip and no spring. The spring changes the length of the antenna and therefore it's resonant frequency. If the 3' whip is designed to work with a spring, then you'll need one.

[Mudderoy]

Something not covered her is power source. I always recommend running positive and negative all the way to the battery. If you want to have it auto power off with the key, then wire in a 30 amp relay with the trigger from the ACC switch on the ignition. Personally I just remember to turn it off. :smiley-whacky119:

[EekGirl96]

Yes spring is recommended...darn near required if you off road.

Amen

[XJ Wheeler]

Something not covered her is power source. I always recommend running positive and negative all the way to the battery. If you want to have it auto power off with the key, then wire in a 30 amp relay with the trigger from the ACC switch on the ignition. Personally I just remember to turn it off. :smiley-whacky119:

I had wired on a 12 volt plug for the lighter plug, that's ok right?

Ok, I've got the SWR meaning now but have forgotten something. How would i change the SWR if it was too high? Is that where a tunable tip would come into play?

What about grounding the antenna?

[Mudderoy]

Legal watts on a CB is 4, though yours will probably have less. Mine only puts out about 2 watts.

You will need a SWR meter to check, the Cobra 19 does not have one built in. They aren't too expensive, some of the better ones have a built in Watt meter as well.

Yes spring is recommended...darn near required if you off road.

Just to reenforce, the spring makes the antenna longer, so it changes the resonant frequency, therefore it changes the SWR. If the length of the antenna is NOT adjustable then you'll need a antenna designed to have a spring. All the 3' fiberglass whips may be designed to use a spring, I don't know.

[Carves]

I had wired on a 12 volt plug for the lighter plug, that's ok right?

It'll do ... but I prefer to do the same as Mudderoy suggested.


Ok, I've got the SWR meaning now but have forgotten something. How would i change the SWR if it was too high? Is that where a tunable tip would come into play?

Tunable tip saves fiddly cutting ... but if the lockscrew vibrates loose ... you may not have a tuned tip ;)


What about grounding the antenna?

It should ground through the mount ... some springbases have a braid strap for a better earth connection.


btw .... If you do your own plug fittings on the coax cable ... use a multimeter to make sure theres no shorting between the inner core wire and the braid/outer sheath.

[olds-cool]

A SWR meter will run you ~$20. I've got one similar to this (http://www.google.com/products/catalog?q=swr+meter&hl=en&safe=active&rls=com.microsoft:en-us:IE-SearchBox&prmd=imvns&bav=on.2,or.r_gc.r_pw.r_qf.,cf.osb&biw=1235&bih=692&wrapid=tlif133460927407010&um=1&ie=UTF-8&tbm=shop&cid=6523484195862632823&sa=X&ei=fYWMT-7WI4X10gGIrN27CQ&ved=0CHMQ8wIwAQ#)

http://lh5.googleusercontent.com/public/LLEsAupmerSV027NHUNYdrQ5_7FyAahOoVc8Vk2HWE1pcIF8_6 JZ2BxllBkP4AC3qwzg_gv7pFASwPot16KHcJGr6jsBoxGTi2xp UVHRGTRTr5AA-QsEz_AVlL6SCaNGe8EVDleYk-zw8TMH__BO1ULpOqWzpZxsFlPD5c-L84k-OTPbiLwFYhuH1ZJV8lLet4Hb-GrHDPJ_vCyqW2uDWdPPm4XKFHgz7ON7rMjjMJin6tRp5q8zuPw aUBTKf8bjGQlPXqLYgMz54BPSyeGkQaJcqhMm-4hsDQMHKRRk-J0

Almost forgot, you'll need a small cable, like2' to go between the radio and the meter while you are testing.