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-   -   SWR meter. CB help. (http://www.wranglerforum.com/f282/swr-meter-cb-help-146391.html)

SteelBlue44 03-14-2012 05:43 PM

SWR meter. CB help.
 
This may sound like a stupid question, but im not at all familiar with CB radio's and how to set them up. I have Cobra 19DX IV, and 18' Firestik coax cable and Firestik "Firefly" 4 ft, 5/8 wave antenna with a tuneable tip. I thought that this was all i needed to setup my new CB, but i was told that i needed an SWR meter. HUHH? :eek:

Can someone explain to me what a SWR meter exactly is, and if it is necessary for me to hook up my new CB.:hide:

gmiller0737 03-14-2012 05:54 PM

SWR = "Standing Wave Ratio" (Power Reflected Back to the Transmitter) Ideal SWR is 1.1 to 1 (Almost impossible to attain) A reading of less than 2 is highly preffered lower is better,Readings of 3.1 to 1 & higher can damage the CB Transmitter's finals,Swr will also vairy from channel to channel,Meters are not that all expensive or if you have a local CB shop they should be able to check them for you,Also many Truck Stops will have a Cb store in or near them.

robbiecc 03-14-2012 06:51 PM

ebay or truck stop/cb shop should have cheap small ones-probably need a 2' jumper to put it in line. easy to use and handy to have if you change cb's, antenna, or vehicles.

SteelBlue44 03-14-2012 07:28 PM

Cool. Thanks for the info guys, but is the SWR meter something that tunes the radio outside the Jeep, or is it connected between the actual CB and the antenna?
Sorry for the ridiculous questions, im just looking for answers:hide:

Jerry Bransford 03-14-2012 07:50 PM

An SWR meter is used to tune the antenna so it puts out the most power possible. A CB antenna is tuned by adjusting its length.

A perfectly tuned antenna puts out (radiates) all of the CB transmitter's power. An untuned antenna doesn't put out all the CB's possible power. What an untuned antenna doesn't transmit, it reflects (like a mirror) right back to the CB transmitter. That reflected power can actually harm some CB transmitters though most have protective circuitry now to prevent damage from an untuned antenna.

So what an SWR meter does is measure that reflected power. The less reflected power the antenna is sending back through the SWR meter and back to the CB transmitter, the lower the SWR its meter will indicate and the more power the CB will be able to transmit with.

So what you do is adjust the antenna's length, a tiny bit at a time, to get the least amount of SWR (reflected power). A perfectly tuned antenna reflects back zero power, it radiates all of the CB's power out into space. So when it does that, it is transmitting everything that is sent to it by the CB transmitter.

For every watt being transmitted, a tuned antenna will radiate 1 watt. That gives the perfect 1:1 SWR ratio which is ideal. A mistuned antenna may only transmit half of what the transmitter is sending to the antenna and reflecting the other half back at the CB, like the mirror I mentioned above. That gives a 2:1 SWR... not good. A transmitter putting out 4 watts of power, the maxium legal power output for a CB, will only be radiating 2 watts if its antenna is mistuned so it has a 2:1 SWR ratio... the other two watts being reflected back to the transmitter by the mistuned antenna.

So basically, plug the CB transmitter into the SWR meter's CB jack and plug the antenna into the SWR meter's antenna jack. On the front of the SWR meter, you'll find a switch labeled FWD and REV for Foward and Reverse. Forward being what is being transmitted, Reverse being what is being reflected back by a mistuned antenna. Set the switch to FWD and hold the transmit key down on the CB's microphone and turn the Calibrate knob until the SWR meter's needle rests on the Cal (or Calibrate) mark on the meter. That is how you calibrate a SWR meter before using it. Release the microphone key.

Next, turn the SWR meter's switch to REF (Reflected) and press the transmit key on the microphone. What the meter is now indicating is the SWR of the antenna. The less the SWR meter's needle rises, the better. The lower the SWR indication, the better.

So now you will start to adjust the antenna's length bit by bit to get the SWR meter's needle indicator as low as possible. If the SWR goes up by lengthening the antenna, that means you need to go the other way... shorten the antenna. adjust the antenna's length in very small increments. Adjust its length until the SWR is at its lowest. Any SWR under 2:1 is sometimes called acceptable but I won't rest until the SWR is 1.5:1 or under... per the scale on the meter. WIth a little work, it's possible to get the antenna tuned well enough to where the SWR meter doesn't move up at all when you press on the transmit key... a 1:1 SWR ratio.

Once the antenna is tuned, you can remove the SWR meter and plug the tuned antenna directly into the CB.

Hope that helps.

By the way, you can find an SWR meter for under $20 at places like Fry's Electronics and close to that at places like Radio Shack or a CB shop. Incidentally, any new SWR meter will come with complete instructions for how to do what I just described above. :)

dcstewart 03-14-2012 07:53 PM

x2

siafu 03-14-2012 07:55 PM

I got mine for $15 shipped on Amazon. I was going to try without it and decided it was cheap enough to just get one. Even came with a little jumper cable.

SteelBlue44 03-14-2012 08:00 PM

WOW! i really appreciate you taking the time to explain that to me, thanks. :)
Thanks for solving a fellow Jeeper's problems once again Jerry. :thumb:

SteelBlue44 03-25-2012 06:03 PM

So i finally got my CB hooked up and tuned properly. I just have one problem, i don't seem to be getting a signal even when around tractor trailers. All that shows up on my CB is the channel number.

DaK 03-25-2012 06:16 PM

Not being a smart butt here but you don't have the squelch all the way up do you? If so, back it off till you hear static, then increase till the static/chatter goes away. Now only signals close enough or better put, strong enough will be heard when they break the squelch threshold.

lindel 03-25-2012 08:46 PM

What channel are you using? Most truckers use channel 19 when on the road, but you should be able to pick up some chatter on every channel but 9.

Here's a somewhat decent FAQ on CB radios.

FAQ: CB (Citizen's Band) Radio Answers

AC0QR 03-26-2012 11:18 AM

It's worth noting that the usual anenna mounting spots on Jeeps are not good from a transmit standpoint. Metal objects near an antenna will change its characteristics and cause high SWR.

You want to avoid metal objects parallel to and above the base of the antenna within 9 feet for CB frequency (1.6 feet for 2M ham).

Mounting on a tail light is not the best spot - body & roll bars are parallel and above. Slightly better but not great is on the spare tire carrier.

The roof is an ideal spot for most vehicles, as no metal is parallel nor above an antenna on the roof, and there is an excellent flat metal ground plane (the roof) right below it. But Jeeps don't have a metal roof. The best spot I've found for my 2M whip antenna is on the drivers side front fender. I was able to tune it to get 1.2:1 SWR.

However, for most practical purposes, an SWR of 3:1 or lower will be "OK".

lindel 03-26-2012 01:56 PM

I've got an antenna mount on the driver's side windshield hinge. Not sure who made it, but I'll grab a pic tonight after work. Granted, not the best of spots, but Wranglers are a little lacking in good antenna mounting locations.

Jerry Bransford 03-26-2012 03:16 PM

Quote:

Originally Posted by AC0QR (Post 2183367)
It's worth noting that the usual anenna mounting spots on Jeeps are not good from a transmit standpoint. Metal objects near an antenna will change its characteristics and cause high SWR.

You want to avoid metal objects parallel to and above the base of the antenna within 9 feet for CB frequency (1.6 feet for 2M ham).

Mounting on a tail light is not the best spot - body & roll bars are parallel and above. Slightly better but not great is on the spare tire carrier.

The roof is an ideal spot for most vehicles, as no metal is parallel nor above an antenna on the roof, and there is an excellent flat metal ground plane (the roof) right below it. But Jeeps don't have a metal roof. The best spot I've found for my 2M whip antenna is on the drivers side front fender. I was able to tune it to get 1.2:1 SWR.

However, for most practical purposes, an SWR of 3:1 or lower will be "OK".

From 40+ years working with commercial, military, and amateur 2-way radios, I'd never consider 3:1 acceptable... the max SWR I'd ever accept is 2:1 and even that wouldn't be good enough to stop me from working to get it well below that. I've yet to see a tunable CB antenna mounted at various locations on a Wrangler I couldn't get tuned to 1.5:1 or below.

For the vast majority of us running our CB antennas on the rear corners of the tub like on tail light mounts, our CB and ham antennas work just fine there. It won't be perfect due to the rollbar but that's where the vast majority of Wrangler owners mount them and they work fine there. Few will want to run their antennas on the roof and with a Wrangler, which this forum is all about, that's nearly impossible unless you want to cut a hole in the soft top or fiberglass hard top, or run with no top.

I tune antennas mounted most commonly on the rear corners but sometimes on the bumpers, near the hood, etc. and so far, I've never had one that was over perhaps 1.5:1.

dcstewart 03-26-2012 03:19 PM

I have read that 1.5:1 is what you should shoot for also.

SteelBlue44 03-26-2012 03:19 PM

Got everything in working order! Finally!:thumb:

C.L. 03-26-2012 04:11 PM

Seems to be alot of helpful information being passed around here. Could someone weigh in on the following? (Not in the linked FAQ)

1.) Coax length importance: Would trimming a 20' foot cable down to ~8ft for cleaner routing affect the tune? Likewise, would tuning it with the added length of the meter-to-radio jumper in the loop be optimal once the jumper length is removed?

2.) Antenna length vs. position: Which takes priority? Lets say one wants to fit through a garage door, limiting the maximum elevation of the antenna TIP. Would it be preferable to install a 4'-5' antenna down on a rear bumper corner (length advantage, but with half the antenna parallel to metal tub/roll bar), or a 2'-3' antenna up on a metal tire carrier (no metal above the base, but shorter overall length)? Assume proper grounding for both.

lindel 03-26-2012 04:24 PM

The effect of trimming the cable would be negligable. Unless you're experienced with installing connectors you might do more harm than good to the connector/cable. As long as you have the proper cable, then length shouldn't be much of an issue.

On the other, as long as the antenna is properly loaded, meaning the antenna has an impeadance matching network (like the balun or transformer used on the old style tv antennas), then length shouldn't be a big issue. Placement of the antenna will have more to do with performance assuming the antenna is tuned correctly.

lindel 03-26-2012 04:30 PM

This might be of some use.

CB Radio Articles: Selection | Installation | Troubleshooting

Jerry Bransford 03-26-2012 04:36 PM

Quote:

Originally Posted by lindel (Post 2184412)
The effect of trimming the cable would be negligable. Unless you're experienced with installing connectors you might do more harm than good to the connector/cable. As long as you have the proper cable, then length shouldn't be much of an issue.

On the other, as long as the antenna is properly loaded, meaning the antenna has an impeadance matching network (like the balun or transformer used on the old style tv antennas), then length shouldn't be a big issue. Placement of the antenna will have more to do with performance assuming the antenna is tuned correctly.

X2, with added emphasis on the length of cable having no effect on CB performance, within reason. Run whatever length gets the antenna connected to the CB and you're good. That said, I always leave several extra spare feet to allow for rerouting, replacing the connnector, etc.

2002TJ 03-27-2012 02:05 AM

Well, maybe, and maybe not.....Odds are you came here because you are having trouble reaching an acceptably low SWR (below 2.1), so I'll NOT tell you to shorten your coax, or anything other than this:

First try ALL the published-tried n true rules, including starting with 18' of QUALITY coax of the right type.

There's lots of 'little' details concerning CB install and maintenance that if ignored will add up to high SWR, so first play by ALL the rules then once you get really good SWR, try to break the ones you would like to, and see if it has any negitive effect by measuring SWR with each change....And remember this; what works on my Jeep may not work on yours cause each radio/coax/antenna combination is as unique SWR-Wise as we peoples are in other ways.

One little detail many folks don't know is to NEVER loop your extra coax like you would any other wire....When I installed my fender mount antenna, I took the extra 7' of coax and first looped it in a coil and stuffed it up under the dash...My SWR meter showed over 3 across all channels.....

So I uncoiled it and carefully ran it up high behind the dash all the way across to the passenger side and then back to my radio....Then tie wrapped it well out of sight and the way of pedals and steering shaft. I'm now getting 1 to 1.25 with a 3" Firestik mounted on driver side front fender.

I also used factory assembled/moulded Firestik Fire Ring coax and to install the radio end connector very carefully.

When I mounted the Firestik antenna mount to the fender, I made sure to dremmel off paint to bare metal under the mount, PLUS ran a braided ground strap from mount to inner fender bolt.....I then seal the mount to the fender to prevent corrosion.

Jerry Bransford 03-27-2012 09:04 AM

Quote:

Originally Posted by 2002TJ (Post 2186553)
First try ALL the published-tried n true rules, including starting with 18' of QUALITY coax of the right type.

For the unbalanced type of antenna we use with our CB radios, there is no need to use any specific length of cable. Only certain types of antennas, typically balanced antenna systems, require a specific feedline length... but not the type of antenna we use for our Jeeps.

There are many articles that explain why the 18' length is still pushed by a few is a myth, here are a couple.

Exposing the 18' CB Coax Myth
The Ultimate Guide to 11 Meter CB Antennas

KidRock171 03-27-2012 10:16 AM

Quote:

Originally Posted by Jerry Bransford
An SWR meter is used to tune the antenna so it puts out the most power possible. A CB antenna is tuned by adjusting its length.

A perfectly tuned antenna puts out (radiates) all of the CB transmitter's power. An untuned antenna doesn't put out all the CB's possible power. What an untuned antenna doesn't transmit, it reflects (like a mirror) right back to the CB transmitter. That reflected power can actually harm some CB transmitters though most have protective circuitry now to prevent damage from an untuned antenna.

So what an SWR meter does is measure that reflected power. The less reflected power the antenna is sending back through the SWR meter and back to the CB transmitter, the lower the SWR its meter will indicate and the more power the CB will be able to transmit with.

So what you do is adjust the antenna's length, a tiny bit at a time, to get the least amount of SWR (reflected power). A perfectly tuned antenna reflects back zero power, it radiates all of the CB's power out into space. So when it does that, it is transmitting everything that is sent to it by the CB transmitter.

For every watt being transmitted, a tuned antenna will radiate 1 watt. That gives the perfect 1:1 SWR ratio which is ideal. A mistuned antenna may only transmit half of what the transmitter is sending to the antenna and reflecting the other half back at the CB, like the mirror I mentioned above. That gives a 2:1 SWR... not good. A transmitter putting out 4 watts of power, the maxium legal power output for a CB, will only be radiating 2 watts if its antenna is mistuned so it has a 2:1 SWR ratio... the other two watts being reflected back to the transmitter by the mistuned antenna.

So basically, plug the CB transmitter into the SWR meter's CB jack and plug the antenna into the SWR meter's antenna jack. On the front of the SWR meter, you'll find a switch labeled FWD and REV for Foward and Reverse. Forward being what is being transmitted, Reverse being what is being reflected back by a mistuned antenna. Set the switch to FWD and hold the transmit key down on the CB's microphone and turn the Calibrate knob until the SWR meter's needle rests on the Cal (or Calibrate) mark on the meter. That is how you calibrate a SWR meter before using it. Release the microphone key.

Next, turn the SWR meter's switch to REF (Reflected) and press the transmit key on the microphone. What the meter is now indicating is the SWR of the antenna. The less the SWR meter's needle rises, the better. The lower the SWR indication, the better.

So now you will start to adjust the antenna's length bit by bit to get the SWR meter's needle indicator as low as possible. If the SWR goes up by lengthening the antenna, that means you need to go the other way... shorten the antenna. adjust the antenna's length in very small increments. Adjust its length until the SWR is at its lowest. Any SWR under 2:1 is sometimes called acceptable but I won't rest until the SWR is 1.5:1 or under... per the scale on the meter. WIth a little work, it's possible to get the antenna tuned well enough to where the SWR meter doesn't move up at all when you press on the transmit key... a 1:1 SWR ratio.

Once the antenna is tuned, you can remove the SWR meter and plug the tuned antenna directly into the CB.

Hope that helps.

By the way, you can find an SWR meter for under $20 at places like Fry's Electronics and close to that at places like Radio Shack or a CB shop. Incidentally, any new SWR meter will come with complete instructions for how to do what I just described above. :)

Great "write up" can't wait to get my new antenna and give this a whirl.

Would leaving the SWR meter inline during daily operation have any negative effect?

KidRock171 03-27-2012 10:35 AM

I'm also wanting a firestick. Is there any preference to the KW FS or FL models?

AC0QR 03-27-2012 11:53 AM

Quote:

Originally Posted by Jerry Bransford
From 40+ years working with commercial, military, and amateur 2-way radios, I'd never consider 3:1 acceptable
Agreed. Buddy of mine got 3.5:1 on his 2m/70cm spare carrier mount dual band and called it good. I guess "good" can mean anything from "perfect" to "I can almost hit the repeater 5 mi away"

G.I. Joe 04-03-2012 09:48 AM

So quick question. I am also a very big newbie with cb's.

I have a cobra 19 III i dont remember the exact code but thats it in jist. I got it used off CL for 40 bucks and came with a 9 ft whip antenna. Will this antenna be fine with the cb and i was planning on mounting on the rear bumper. any help would be great. Also came with a PA horn and do not know how to wire the cb, or the pa and would need very basic instructions please. I know the pa needs a mono plug but I dont know what size.

Thanks

Chunks 04-05-2012 03:18 PM

Quote:

Originally Posted by G.I. Joe (Post 2214174)
So quick question. I am also a very big newbie with cb's.

I have a cobra 19 III i dont remember the exact code but thats it in jist. I got it used off CL for 40 bucks and came with a 9 ft whip antenna. Will this antenna be fine with the cb and i was planning on mounting on the rear bumper. any help would be great. Also came with a PA horn and do not know how to wire the cb, or the pa and would need very basic instructions please. I know the pa needs a mono plug but I dont know what size.

Thanks

Should work out just fine. That antenna's length is a 1/4 wavelength on channel 19. Should match well with a good ground connection and will perform better than any shortened loaded whip antennas.

Enjoy!:)

Regards,
Jim

Jerry Bransford 04-05-2012 04:10 PM

Quote:

Originally Posted by G.I. Joe (Post 2214174)
and came with a 9 ft whip antenna. Will this antenna be fine with the cb and i was planning on mounting on the rear bumper. any help would be great.

That antenna will of course work but it's not a good choice for offroading since it sways so much. Most organized 4x4 clubs and 4x4 offroad events have banned antennas longer than about 50" or so due to longer antennas being a hazard on the trail. Attaching the tip to the forward part of the Jeep won't get you past most 4x4 event safety inspections because they have a habit of breaking free.

Chunks 04-05-2012 06:50 PM

Quote:

Originally Posted by 2002TJ (Post 2186553)
Well, maybe, and maybe not.....Odds are you came here because you are having trouble reaching an acceptably low SWR (below 2.1), so I'll NOT tell you to shorten your coax, or anything other than this:

First try ALL the published-tried n true rules, including starting with 18' of QUALITY coax of the right type.

There's lots of 'little' details concerning CB install and maintenance that if ignored will add up to high SWR, so first play by ALL the rules then once you get really good SWR, try to break the ones you would like to, and see if it has any negitive effect by measuring SWR with each change....And remember this; what works on my Jeep may not work on yours cause each radio/coax/antenna combination is as unique SWR-Wise as we peoples are in other ways.

One little detail many folks don't know is to NEVER loop your extra coax like you would any other wire....When I installed my fender mount antenna, I took the extra 7' of coax and first looped it in a coil and stuffed it up under the dash...My SWR meter showed over 3 across all channels.....

So I uncoiled it and carefully ran it up high behind the dash all the way across to the passenger side and then back to my radio....Then tie wrapped it well out of sight and the way of pedals and steering shaft. I'm now getting 1 to 1.25 with a 3" Firestik mounted on driver side front fender.

I also used factory assembled/moulded Firestik Fire Ring coax and to install the radio end connector very carefully.

When I mounted the Firestik antenna mount to the fender, I made sure to dremmel off paint to bare metal under the mount, PLUS ran a braided ground strap from mount to inner fender bolt.....I then seal the mount to the fender to prevent corrosion.

I'd be more concerned about antenna resonance rather trying to achieve the lowest SWR but that's just me. Also, if the antenna is properly matched, it shouldn't matter how long the feedline is. If adding extra cable does change the resonance of the antenna, there's other issues with the installation and the extra cable is just masking the problem.

Regards,
Jim N9WW

2004_Silver_Sport 04-20-2012 03:41 PM

Does the SWR meter need to be level? I noticed that if I barely moved the SWR meter the reading would change.


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