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CB/AM/FM Antenna question

Help with installing an Antenna, or just choosing the right antenna to go with your radio, or your mobile.

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MightyMo
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CB/AM/FM Antenna question

Post by MightyMo » Saturday, 04 March 2017, 1:46 AM

I need a new AM/FM (broadcast) antenna and mount for the family van. This gives me an in to get a CB set up on it without the wife knowing what's going on until it's too late. 8) My first thought was a to put a Wilson Flex antenna (I THINK the flex is thinner than normal disguising it as a regular antenna) in place of the stock antenna with an AM/FM/CB splitter. However, much Googling has revealed that the splitter doesn't work.

Next idea/question. If I run the same setup without the splitter., will it damage the CB or car radio to be on the same coax line? I realize a CB antenna is not tuned for the FM broadcast band. But right now, we have NO ANTENNA and get some stations. Any antenna is better than no antenna. Right?


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Re: CB/AM/FM Antenna question

Post by sonoma » Saturday, 04 March 2017, 7:42 AM

I never had any luck with a splitter on a regular car antenna. I have used a antenna made for this purpose and it came with a splitter and it worked fine, even had low swr. I could only talk about 5 to 7 miles with it but that is the nature of the beast using a short antenna. ran one in the early 80's on a 76 mercury bobcat I had and it was just fine. in the early 80's I worked for General Motors assembly plant and we sold cars with this setup also and it worked fine in those cars also. a splitter stuck on a regular car antenna does not work to good. I built truck boxes for drivers with a splitter in the box so they could run a cb antenna on the truck and the splitter would adapt the cb antenna so you could run a am fm sterio radio off the cb antenna with a cb hooked to it.

just type in cb antenna splitter and you should get samples to come up. i just did and all are from sellers so can not post them.
Last edited by sonoma on Saturday, 04 March 2017, 22:21 PM, edited 1 time in total.

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Re: CB/AM/FM Antenna question

Post by MightyMo » Saturday, 04 March 2017, 21:33 PM

Thanks for the response.

Maybe I wasn't clear. I want to get rid of the vehicle antenna and use that spot for a CB antenna. So the AM/FM and CB will use the CB antenna. I've seen ham guys have duplexers (not sure what they are exactly). I don't know enough technical info to figure out if I could get one to work for me.

Sonoma, you said you've built boxes with splitters to do this? What do you mean by boxes? Amps? Also, what do you mean by splitters? Was it a simple "T" like a splitter you use for dual antenna or did it have electronics in it to create band/frequency filters?

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Re: CB/AM/FM Antenna question

Post by sonoma » Saturday, 04 March 2017, 22:16 PM

you mentioned the am,fm,cb splitter. I thought you knew what it was. it is an adater that will let you hook a cb radio to the same antenna with the am,fm radio. the box mentioned is called a slip seater for truck drivers to carry all the radio items inside a suit case and have all the hook ups on the case. you just have to find a antenna that will work on your vehicle and most when you buy that type of set up comes with the splitter to hook the cb and sterio radio to the antenna.

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Re: CB/AM/FM Antenna question

Post by Radar-DLDN » Sunday, 05 March 2017, 7:30 AM

A duplexer is a set of bandpass filters that allow you to use a single coax to run multiple radios of different frequencies. This is one option that could do what you are looking for. If you were just monitoring you could just use a simple T-junction, but the second you key up on that you can kiss your car radio goodbye. You need filtering or a switch to prevent your transmitted power from going to the radio. If filtering then it will need to allow the MF frequencies of AM through, as well as the VHF FM frequencies while blocking the HF CB transmission.

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Re: CB/AM/FM Antenna question

Post by MightyMo » Sunday, 05 March 2017, 17:47 PM

sonoma wrote:you mentioned the am,fm,cb splitter. I thought you knew what it was. it is an adater that will let you hook a cb radio to the same antenna with the am,fm radio. the box mentioned is called a slip seater for truck drivers to carry all the radio items inside a suit case and have all the hook ups on the case. you just have to find a antenna that will work on your vehicle and most when you buy that type of set up comes with the splitter to hook the cb and sterio radio to the antenna.
I've seen the splitters you are talking about. I thought you may have made your own because other posts on this forum have said they don't work. You've been able to use the premade AM/FM/CB splitter with good results? I've only seen two brands. Firestick and Procom. But the Firestick version seems to be discontinued. Do you know what brand(s) you used?

Radar-DLDN wrote:A duplexer is a set of bandpass filters that allow you to use a single coax to run multiple radios of different frequencies. This is one option that could do what you are looking for. If you were just monitoring you could just use a simple T-junction, but the second you key up on that you can kiss your car radio goodbye.
Awesome. That the info I was looking for. Would my car radio receive better on a CB antenna WITH a duplexer then WITHOUT the duplexer (on the same CB antenna)?
Radar-DLDN wrote:You need filtering or a switch to prevent your transmitted power from going to the radio. If filtering then it will need to allow the MF frequencies of AM through, as well as the VHF FM frequencies while blocking the HF CB transmission.


So I need a device that will allow RX for both car radio and CB radio but will filter CB TX from entering my car radio. Can I get a Ham duplexer that will do that? Any idea on price?

Also, I think CB is considered HF and broadcast frequencies are in the VHF range. Is that right?

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Re: CB/AM/FM Antenna question

Post by Radar-DLDN » Sunday, 05 March 2017, 18:05 PM

Something like the Comet CF-706 would do it, though you will lose your AM radio receive. Looks to run about $75, dunno if any sponsors carry it but if not you can search Google for it.

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Re: CB/AM/FM Antenna question

Post by sonoma » Sunday, 05 March 2017, 20:59 PM

that is not what he really wants. he needs the regular splitter that has been used for years. I have not built a box for about 7 or 8 years now. not sure what brand would be the best now days. but I saw them when I did my search the other night for about 25.00 shipped from most places. it has the place for the am fm radio hookup and cb hookup and the main antenna lead. it has a couple antenna tuners inside the box to adjust the nswr with.

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Re: CB/AM/FM Antenna question

Post by MightyMo » Sunday, 05 March 2017, 22:00 PM

Guys, thank you so much for your input on this. I'm going to get a splitter first and see how that does. If it doesn't do what I want or doesn't give me the range I want, I'll start looking into something else.

Last question: The Procom splitter seems most available on various websites. But, it specifically says "No tuning required". Should I do some more digging and get one that is tunable?

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Re: CB/AM/FM Antenna question

Post by sonoma » Monday, 06 March 2017, 0:19 AM

not sure which I would use, it all depends on your setup. the procom is for using a cb antenna and then just hook up the radio. this is the type I used for truck boxes since the driver used a regular cb antenna. not sure what antenna you plan to use. the uverse brand or what ever it is called may be more what you want. like I said depends on how you plan to do the antenna.

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Re: CB/AM/FM Antenna question

Post by MightyMo » Monday, 06 March 2017, 11:21 AM

Ok. Thanks again for the help.

I'll look to see what I can find. It may take a couple of weeks, but I'll try to get pictures up when I get it done.

I'm planning on using a Cobra 19 for the radio. I realized I have a 3 ft Procom antenna (with tuning rings) laying around. I'll try that first. If I get bad SWR with that antenna, I'll try another that I know will have low SWR.

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Re: CB/AM/FM Antenna question

Post by MDYoungblood » Monday, 06 March 2017, 12:23 PM

I installed one of the retracting AM/FM/CB antennas on my father's van back in the 70's, it extended when the AM/FM radio was turned on, only down point, it raised to well over 3ft and works as it was suppose to for a short time, (until it got dirty). After that I installed a regular CB antenna and ever since. I've spent many a day in the dog house but the wife usually got over it.

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Re: CB/AM/FM Antenna question

Post by MightyMo » Saturday, 27 May 2017, 22:47 PM

Sorry it's taken me 2 months but I finally got it all installed and it works. Here is how it went down.(I'll post pictures a little later)
I used the ProComm antenna splitter, 3 ft ProComm antenna with tuning rings, 18 ft wilson coax.
I modified the vehicles antenna mount to hold the antenna and stud mount. The problem is my 08 Chrysler Town and Country radio does not use the typical antenna jack. I tried to find an adapter but couldn't. (Most car audio installs involve aftermarket radios connecting to factory antennas. They have adapters for that. Not aftermarket antennas connecting to factor radios). So I got an adapter that conect ed to the ProComm antenna splitter and cut the othe end and made my own adapter.

Factory broadcast radio sounds great. No issues there. I got it all buttoned up and tried to tune my antenna but had crazy high swr. Seemed no matter what I did nothing helped.

Used a multimeter to check continuity. Ground was good. But I did not have continuity from the antenna element to center pin on my coax going to my radio. That would explain high swr. I took it apart and varied all the cables were good. The disconect must be in the box. I was planning on taking the antenna spitted box apart and check all the connections but didn't have time.

Fast forward to today. I got an antenna analizer a week ago or so. I decided to hook it up to this antenna and see what it had to say. Sure enough 27.185 MHz had high swr. But I noticed as I swept the frequencies it did have a point where the swr dropped. With 2 min of moving the tuning rings I got the swr down to 1.2-1.3 on 27.185. I haven't rechecked for continuity but it worked great!

I don't think I have lots of range. But I have enough for going down the highway and summer road trips with the in laws who have a cb also.

I'm really suprised how well this worked out. I'll post some pictures when I get a chance. I will say for only being a 3 ft antenna, it is REALLY flexable. Going down the freeway it bends quite a lot in the wind. Like I said, it's only 3ft. Anything longer made of the same material would probably make the antenna unusable while moving.

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Re: CB/AM/FM Antenna question

Post by Scipio Kid » Sunday, 28 May 2017, 11:16 AM

I'm glad its working for you, Mo. I did a couple of those back in the day and they worked pretty well. Since getting back into it I've just run a CB antenna and let the stock one do for am & fm. I've got my CB antenna on the mirror on my truck only a foot or so from the stock antenna, some say that causes problems with both but I don't have any trouble. I'm not really listening to the radio when I'm talking on the CB and my SWR is near perfect and I get out like crazy on the CB ... and the install was fast and easy, other than mounting the radio. I decided I'd rather have it on the ceiling than the dash and that was a project, but worth it. I really like having my mobiles up high rather than down low, easier to hear and see (in my book). Yeah, on the dash would be easier but I grew up with the CB on top and I guess you can't teach an old dog ... anything!
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Re: CB/AM/FM Antenna question

Post by 443 Arizona » Monday, 29 May 2017, 5:32 AM

i recently found an am/fm/cb splitter as was so popular back in the 70's. was in a bucket of junk at a garage sale. needless to say it is in my pile now. did not test it. sort of looks like it was possibly a radioshak /Archer brand.

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Re: CB/AM/FM Antenna question

Post by MDYoungblood » Monday, 29 May 2017, 15:29 PM

I wouldn't trust one of those adapters with today's radios.

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Re: CB/AM/FM Antenna question

Post by Scipio Kid » Monday, 29 May 2017, 17:42 PM

Why or why not? The biggest problem I see is lack of performance (provided the adapter works right). Now if yo mean you wouldn't trust a 35 year old piece of equipment found in a bucket of junk not to ruin your new radio, well I'd have to agree I'd be very skeptical. But I'd give it a shot just to see if it'd work. Now I don't need a single antenna so it doesn't apply to me but If, for some reason, as Mo apparently has, I needed to have only one antenna, why this might be the solution. With the setup I had years ago, I was able to make the centerload CB antenna the common antenna and got rid of the stock one. So I had real good performance, great SWR and no apparent loss of TX or RX. My worry would be that using the stock antenna, the 'matcher' would be able to get you SWR right but your performance, RX and DX would take a hit because the usable mast would be diminished. It's like the Big radio shack Walkie Talkies I had years ago. With the telescoping antenna extended all the way, they got out pretty well but those 4' long antennas were always at risk of getting bent or broke so the radios weren't very versatile. Then I bought the little (still a foot long) rubber whip antennas for them. What a great idea, now I could move through the trees and underbrush without wrecking the antennas. Only problem was the range was cut so much we could yell farther than we could transmit. A lot of guys say the same thing about those little 12" or 18" whips you can get nowadays. squishing an 11 meter wave down to 12 inches means there'll be some trade offs. So Mo, how is your performance so far? I didn't make it up your way today or maybe we could have tested it back and forth. Let us know how it works.
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Re: CB/AM/FM Antenna question

Post by Scipio Kid » Monday, 29 May 2017, 18:03 PM

You know, MD and all the pro's here have told us time and again, your antenna is the most important part of your radio. If it's not working, nothing is. But as long as you don't fry your radio (and get the SWR right) and only need to talk to your buddy in the truck behind you, sometimes you don't need the biggest and best antenna as long as you understand the trade offs.

It's sometimes sad, however when you see someone with a junk antenna and an expensive radio and amp that don't perform as well as some guy with a Radio Shack TRC-422 and a mag mount antenna on the hood of his old Impala. It's worse if you're the guy with the big radio.
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