Tuning CB Antennas/Better Reception

[Crimedog]

Roger Dodger, I know you like to play with CBs, and so do many others. I just bought a pair of whip style Diesel CB antennas. It has real basic tuning instructions on them, and all I get is static breaking in on voices, I can't get any clear voices. It says that these were made for big rigs, but can "easily" be tuned for pickup trucks. How do you properly tune a CB antenna?

Thanks

[Pickering Snow]

Crimedog

Going along way back in my thoughts i was looking and i still can find my old swr meter thats what i use to use to set my antennas up before they went to fixed non ajust, radio shack may even have one behind the counter and would come out and set it up for you they use to do it here.

I do know the standing wave has to be right be careful and get it done before you burn up your radio, Pelican may have some input on this too iam pretty sure he has spent time in otr trucks.

[Rooster]

Pickering is right, you need to adjust the SWR's. See if you can locate a CB shop, or stop by a truck stop, they used to be at a lot of locations.

Good luck.

Rick

[snowplowjay]

Originally posted by Rooster
See if you can locate a CB shop, or stop by a truck stop, they used to be at a lot of locations.

Good luck.

Rick


Try a TA Travel Center (those big truck stops). I remember going in one near Boston that had a huge CB and CB accesory department and im sure theres someone working that could help you.


Jay

[Pelican]

You need an SWR (Standing Wave Ratio) meter, they used to cost 20 to 25 dollars. It's been so long since I've seen them, I don't know what they'd cost now. SWR measures how much of your transmitted signal is reflected back to the radio. The ideal number is 1:1, but anything under 1.5:1 will give you a good working radio.

The way you adjust SWR is by changing the length of the antenna. You'll need to park your truck in an open area away from any trees, wires or buildings to get an accurate reading. The SWR meter goes in line between your CB and antenna with a small patch cord.

Check your SWR on Channel 40, and the again on Channel 1. If Channel 40's reading is higher than Channel 1's, you need to shorten the antenna. If 1 is higher than 40, you need to lengthen it. If you don't have an adjustable tip, you can't lengthen it, you shorten by trimming 1/4 inch at a time.

Take your adjustment measurements on Channel 19, this is the center of the frequency spread of CBs. Like I stated, make your adjustments 1/4 inch at a time, and check again on 1 and 40 after a couple adjustments to make sure you didn't pass optimum. If you get to 1.2, leave well enough alone, you will probably make it worse and if you've had to cut the antenna, your stuck.

Another tip: Do not coil up extra coax, this will cause SWR problems that you won't be able to overcome, spread out extra coax in a "S" shape.

Also make sure your antenna is grounded to the vehicle well. The high static condition you describe indicates a possible poor ground. If you have any other questions, don't be afraid to ask.

[Crimedog]

I actually bought them from a TA. The way I understand it, you tune them just to get longer reception, and the static could be the ground? They didn't have a very good drawing for how to attach them, so here is a pic of the way they are right now. I am thinking maybe there could be a bad ground. How should they be grounded, I mean what part of the antenna should?
Thanks

[phoenix827]

The base of the antenna should be grounded. I will bet thats your problem right there.
If you move the bracket to the top of the diamond plate and use a couple star washers, you might be all set. If not, you are going to have to run a ground wire from the mount to a good grounding point.

[phoenix827]

AHA! I just looked again and spotted the REAL problem!!!:D
You need to switch the 2 wachers you have on there!! The plastic one should go on the top to insulate the whip from the ground, and the star washer should be on the bottom side to lock the assy together.

[wyldman]

If your going to mount them there,then you need top loaded antenna's.The antenna will bounce to much off the truck mounted like that.

I forget the exact distance,but they should be a certain distance apart for best performance.I think it's like 104" or something.Those "dual trucker" type antennas are usally meant to be mounted on the outside top of the mirrors on a big rig.

[Crimedog]

Hmmm.... I switched them around, it helped a little. The weather station comes in clear, but I don't get a lot of reception, but I don't get constant static, either. I'll get ahold of a SWR meter, and go from there. Thanks guys.

[Adams Plowing]

out of curiousity what model cb are you running...

[Pickering Snow]

Crime dog if those dont work out see if they will trade you for some preset ones i carry a cb on my service truck but only throw the annt up when iam gonna be on the highway i bought mine from radio shack i didnt need to use a swr meter.

[phoenix827]

Another thing to remember is that CB's will ALWAYS have static. The newer radios filter it out a bit better, but if you turn the squelch down you will hear all the background noise out there.

[Crimedog]

I got my brother's Cobra from him. I had the antenna mounted the right way, and switched it to see if I could get a better ground (the way it is in pic). I then switched it back before I went to a friends house who had a SWR. Got there, turned on the radio, checked the SWR and it was 1.25 all around. So, it must have been a bad ground. It's working fine now :D :rolleyes:
Thanks for the input guys.

[phoenix827]

NP, Glad to help.

[Roger Dodger]

Crimedog, sorry for showing up so late. If you had said something nasty about me, my ears would've burned and I would be searching the forums! (LOL)

Pretty much all the advice given thus far is spot on. Nice to see that my students are passing CB101... almost eliminating the need for me, a former Motorola technician. However, I'm flattered that I've been summoned.

Come closer Grasshopper and I will enlighten you further on the mystics of good reception:

Grounding is the absolute number 1 issue with effective communications. The two or three factory ground wires on the chassis are useless for radio waves. They work for the negative side of 12v but not for radio waves. Obtain some copper braid (like that in coax tv cable) and solder each end to a ring type solder terminal. Solder them, dont crimp since radio waves don't like mechanical connections! Make up about 6 of these approx. 6"- 8" long. Attach one to ground the bed to the frame, the frame to the motor, the motor to the front body, the hood to the body. Scuff the paint where they screw into the metal for good connectivity and do not apply any dielectric grease or paint over. This should eliminate ground loops and in effect present one huge ground (electrically speaking) for the antenna. The radio's negative wire should be at this "absolute" ground too. Since you have dual antennas, the coax harness should be cophased and of proper length (resonant wavelength that is)... not just two chunks of random length coax. You mention about static breaking in on voices... that could be a couple other problems too. If the SWR isn't where it should be, a good grounding throughout can dramatically improve things for you. If your SWR is within tolerance as recommended by the mfgr., check for interference generated by the ignition, charging system, or window & wiper motors. Disconnect antenna and if noise disappears with all motors running the interference or static is entering through the antenna setup. If it is there with antenna removed, it's getting through the power wires. The location of your antennas on the bed rails is not a very good one and receiving a fair amount of static is understandable from such. You may have your work cut out for you if you leave them there. The antenna is seeing a split ground plane... the low bed and the raised metal of the rooftop creating a lopsided signal pattern, even with 2 antennas at work.
One important test that many CBers skip is the field strength test. You can have the lowest SWR number and still have poor communications if the radiated signal just isn't emminating effectively. Many ham operators will "consider" SWR but rather tune for maximum signal field strength. Think of the SWR adjustment as static balancing of a wheel. Think of field strength adjustment as dynamic or spin balancing of the wheel... alot more accurate, right?
Lastly, the problem could stem from a mistuned or problem radio. Too often factory new radios can be tweeked to better performance, both on transmit & receive... sad but true. You could hook up the radio to someone's base station antenna and 12v and see if it behaves properly; if not it's the radio at fault then. I could get even more indepth here but we are approaching days end and I'd hate to see anyone miss their rides. Hope this info helps you and let us know how you make out. BTW, there will be a chapter test on Monday, so everyone please study and pay special attention to the section on comparisons of crystal and LC I.F. filters. Class dismissed. ;)

[Roger Dodger]

Originally posted by Crimedog
I had the antenna mounted the right way, and switched it to see if I could get a better ground (the way it is in pic). I then switched it back before I went to a friends house who had a SWR. Got there, turned on the radio, checked the SWR and it was 1.25 all around. So, it must have been a bad ground. It's working fine now

doh! This is what I get for skim reading and spending too much time in the cafeteria closet with Miss Pretty!:headwall

[Adams Plowing]

hey roger any suggestions on how to get rid of interferance im getting from my strobe becon? its coming through the antenna i have managed to filter it out of the power line and i know its out of there because when i disconnect the antenna it stops. i have isolated it to coming froim the becon because it only does it when its turned on. thanks for any help ya can give. oh btw im running a uniden pc-78 w/ weather and a "lil will" wilson antenna

[Roger Dodger]

I remember what gear you're running there!
You need to eliminate the interference at the very source... the strobe. I assume it's a solid state strobe or is it a motor operated revolving one? If it's a motor one, hop on down to Radio Shack and get a RFI interference filter, say around 10amps should do fine. If it's a solid state xenon lamped one, it would require a schematic diagram of the circuit design to further determine where extra filtering could be placed. Regardless of what kind of strobe you have, you could obtain a ferrite bead or torroidal loop (Rad Shack should have them or in your location LEVCO Communications/Parts Div. on E. 26th St.). They come in various sizes to fit whatever wire size you have and are nothing more than a powdered iron donut that you loop the both of the strobe's power wires through a 2-4 times. Just make sure the windings are wrapped sung and next to each other. You can experiment with the number of windings to get best results. Then perhaps wrap it in electrical tape to hold things in place. Very effective for reducing RFI (Radio Freq. Interference). One donut is cheaper than a dedicated filter module so perhaps try that first.

From seeing the pic of your truck, that Wilson ss whip is very close to the strobe so, you are creating a situation ripe for interference. If none of my suggestions work, simply wrap the entire strobe assembly in a couple layers of thick aluminum foil. That will stop interference dead in it's tracks. Then all you have to do is have someone ride along with you and blink a flashlight at the foil!!!
:eek: :rolleyes: :rolleyes:

[Adams Plowing]

ive moved the becon to one side of the top of the truck and the antenna to the oppisite side now the becon doesnt have a motor its an eccho brand strobe or something like that does it matter where in the line that donut gets placed? does it have to be right next to the light or just anywhere in the line? thanks for the info..

[Roger Dodger]

Good point - that crossed my mind but I forgot to mention in previous post. Place the RF choke close as possible to the strobe. You can also place one at the rear of your radio, wrapping it's power leads as well for extra measure!

[Pelican]

Roger, how about remote strobes with power paks? Do you place the filter at the power input to the controller?

[chtucker]

On a funny note about tuning antennas and how an untuned antenna can cause problems.

I just completed the reprogramming of 150 mobiles and handhelds for an entire county (pd, sheriff, ems, fire, streets etc.) and I got a phone call.

"Hey what the F*** did you do to my car?"

"Whats wrong?"

"Everytime I try to talk on the radio the wig-wags go on and the rear wiper starts moving!"

"I really don't think that is something I did....but bring it by my house right now and I will take a look"

"Fine!"

Sheriff's deputy gets to my house, I swap antennas to a new one and all the problems go away. His antenna was about 8" to short from going through the drive through a few too many times.

The radio energy was being reflected back towards the radio where the strobe/wig wag controls were too.

I had it fixed in under 60 seconds.

Howard

[Adams Plowing]

well i got some of those ferrite things and they seemed to do the trick but i will be able to tell for sure when i have my next event and have the radio going for some hours... seeing as i couldnt get 1 that was big enough to loop it through due to the size of the cord on the strobe i just put 2 on there right next to each other right where the cord comes out of the light... and ialso through one on the power cord at the back of the radio just for the hell of it... either way i think it may have solved my problem thanks... ofcourse the guy at radio shack had no clue what i was talking about when i asked him for em... we ended us searching the store till i found them...

[Crimedog]

Roger-What are some ways to turn up the power on a CB? I mean, get it to transfer from farther away?

If this is Monday's lesson, can I get it in advance? I don't think I will be in on Monday ... cough ... cough ... sniffle;)

[Got Grass]

Well now that ya guys got me thinking at 6am, I'm wondering what I can do to improve my CB.

In my truck I have a pretty basic Cobra radio w/ a Radio Shack mag mount antenna. Reason for the mag mount is so I can just rip it off when I gotta get in my garage, hit the wash, etc...
I have the antenna cable running the passanger side to avoid some of all that other eletrical junk on the drivers side. It's just screwed into the radio & the radio power is ground to some metal up in there & the hot goes to an accessory fuse.
Antenna is centered on the roof behind my rotor light bar, mag mount as well.
Any tips to get better preformance outta it?

#2
I have a couple other radios sitting arround & want to install one on our motorhome, It's a decent Cobra w/ the sidebands & all that fun stuff.
I know the mirror option is prolly the best, the mirros are attached to the doors so the cables would be moving arround & flexing quite a bit, plus they would really annoy me.
Odviously I cant stick somethig big on the roof unless I want it ripped off lol...
Any cheep antenna's out there that would work decent & placement?

[Roger Dodger]

Originally posted by Pelican
Roger, how about remote strobes with power paks? Do you place the filter at the power input to the controller?
Generally, it's always best to reduce the noise/interference at or as close to the source of it. As an extra measure, a person can also place another filter at the radio or device that is being affected by the noise. That way you are filtering both at the source and at the end of the line.

Just remember to try that little trick I mentioned during "Friday's lesson" where you should determine first if the interference is entering through the power cord or from the antenna. It makes a difference so you know which solution to use.

[Roger Dodger]

Seth -
Try this item from Radio Short (Shack): snap-together torroid core (http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&category%5Fname=CTLG%5F011%5F002%5F009%5F000&product%5Fid=273%2D104)
It should be alot easier to wrap those windings and snap it closed afterwards. BTW, ever notice that large "knobby thingie" at the end of computer monitor VGA cables? That's a ferrite core with the wires passing through it to reduce interference. Computers make use of them throughout the PC itself and the peripherals. As for getting knowledgeable help from a Radio Shack clerk, that's impossible. I think they hire off-season snowplowers just trying to pay their bills!;)

Originally posted by Crimedog
Roger-What are some ways to turn up the power on a CB? I mean, get it to transfer from farther away?

If this is Monday's lesson, can I get it in advance? I don't think I will be in on Monday ... cough ... cough ... sniffle;)
First, it's illegal to be fiddling with a radio's transmitter section without being officially licensed by the FCC, as chtucker will likely agree with me on this. BTW, it's good to have another radio tech aboard! However what you do behind closed doors is none of my business. Just had to type that legal disclaimer should you tweek things and set off every RELCO light in town! There are plenty of websites that provide CB mods. Type CB modidfcations and start scrolling. Look up your radio's model and follow the recommendations. If you aren't electronically inclined, a good CB shop or TA truck stop may be able to improve things. Don't expect them to do illegal tweeks though. Read below on how to improve things legally.

- Got Grass
In my truck I have a pretty basic Cobra radio w/ a Radio Shack mag mount antenna.
...I have a couple other radios sitting arround & want to install one on our motorhome
The antenna is equavalent to a stereo's speakers. Even crummy receiver can sound decent wired to great speakers. A thousand dollar receiver sounds crappy wired to $hitty speakers. Same logic with antennas. Spend the money on the antenna and microphone rather than the radio and echo mics/toys. You can't go wrong with a Wilson, K-40, Antenna Specialists, FireStick antennas. As for mics. almost all factory mics are curses from hell. Rely on the brands like Turner, Astatic, Road King/RF Limited, Telex. They alone will make a radio "talk" without all this "tweeking" stuff. Locate the antenna in the best possible spot you can live with and tune it accordingly. Assure you have electrically solid, multiple ground straps throughout the vehicle to improve both reception & transmission. I caution against using power amps and tweeking the radios for max power. You can end up having signals enter the ABS system and computer modules as well, causing further problems. My radio pumps out a measley 2.5 watts on a dead key (legal max is 4 watts input), but with an Astatic noise cancelling mic at 100% modulation, it swings to a peak of 27.5 watts!!! On sideband it's closer to 40 watts. No amps needed, see! Power mics are not wise in a mobile environment. Many folks are misled to believe they will boost transmissions. Far from the truth as they amplify all surrounding noise as well and that's awful for the listener to have to decipher. Get a quality noise cancelling one and only your voice will be transmitted and with a good punch too. No batteries to corrode or replace either. As for tweeking a radio, many tweekers end up cutting components out or turning up adjuctments to the point that the signal is actually worse. Sure the signal is more powerful but the modulation is typically distorted (even without a power mic and worse yet with one), and other parameters of the radio suffer. When you hear a loud trucker or whomever, chances are they aren't running a power amp. They have a properly tuned radio and are using a high quality mic/antenna setup. A well setup mobile cb should yield approx. 5 miles and well beyond that in range, reliably. I can avg. between 9-12mi on mine and I'm meaning - reliably. So throw away those Rad Shack antennas, Cobra High Gear power mics, and other toys and get with the program! (lol)

As for motorhomes, Camper's World sells cb antennas for fiberglass RVs. Same deal as with mounting on boats: antennas that work without the need for a ground plane. Side view mirrors are a fine location as well.

chtucker any comments to add or is this enough for one day's lesson?

[Roger Dodger]

Correction on mylast posting:

should be Camping World (http://www.campingworld.com/browse/skus/index.cfm?skunum=13608&src=SRCH&tcode=37) not camper's world.
They seem to have dropped the number of antennas they carried in favor for the thru-glass type. Easy to work with but not as much a performer as other dedicated no-plane types. FireSticks usually shine in performance for mirror mounts. Easy to tune too.

[Adams Plowing]

what i got (http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&category%5Fname=CTLG%5F011%5F002%5F009%5F000&product%5Fid=273%2D105) thats what i ended up getting it was just the right size for the wire from the strobe to go through 1 time thats why i just used 2 of them in a row... it seems to be working though...although there was enought room in that one to make a loop on the power wire going into the radio... the cased wire coming out of hte strobe is about 3/16th of an in which made those perfect size for the wire to go through 1 time...

[Roger Dodger]

No, no, no - get the one I listed. The wires have to be wrapped more than once to be effective and the Rad Shack # 273-104 will let you do that, or similar sized types. They come in many sizes and you might have to try MCM Electronics (mail order outfit) (http://www.mcmelectronics.com) for a variety of them The kind you bought is for passing wire(s) straight through as used in PC monitors. BTW, don't ever pass an antenna wire through one of those! Talk about reducing a signal!

[chtucker]

My general feelings are:

If you need communications for Busiiness use nextel, FRS or one of the iternant business channels.

If you want to communcate with friends or have techinical interests then get ham radio license. I

Talk to space shuttle, talk to MIR, talk around the world, talk on repeaters, lots of hi tech equipment out there.

I think CBs are from the stone age.

Howard

[digger242j]

Well, I'm from the stone age too, so I don't feel stupid having to ask what happened to my CB the other day.

It's a Cobra, I don't remember what model it is, but it wasn't real expensive, and it's probably 10 years old. It's got the NOAA weather radio frequencies in there too, but only 3 of them.

Anyway, Friday afternoon, without anything at all being done to it, it just got real quiet. By that I mean that it's as if somebody had turned down the volume almost all the way and it can't be turned back up. If it's quiet enough in the truck you can still hear both the CB and the weather radio clearly, but not loud enough to be useful. This morning when I'm at the jobsite I'm gonna see if one of the other trucks that has a CB can hear me transmit.

Any ideas? Does it sound like something that'll be worthwhile to fix, or is it just time for a new one? It won't be any great loss or inconvenience. It's been on a shelf in the garage until a week or so ago anyway. Last time it was used before that was in October of 2002, and on that occasion it failed to tell me about the particularly critical location of one Pennsylvania State trooper. :mad:

Thanks in advance for your advice...

[Roger Dodger]

The radio's receiver section could be the culprit but, even a bad antenna can cause that as well. Capacitors in the radio can and have failed from sitting for long periods, exposed to humidity & temp extremes. Difficult to diagnose without having it on a bench infront of me. As for having it serviced at a shop, often the cost of repair can far exceed the radio's value and it's cheaper to buy new. The exceptions may be radios of certain brand & model whereby it's design and performance exceed most of todays tame, whimpy radios.

chtucker - I understand your stance on CB communcations however, it still serves a purpose for many, otherwise the FCC would have eliminated the service all together. There are a vast number of occasional plowers out there that the realm of CB fits just fine, provided they aren't actually running a business through it as per FCC rules & regs. I still hear a good amount of chatter on a certain channel in my locale by a plowing outfit. I rmember another plowing outfit that employed a linear amp on the base dispatch unit to assure being heard. I know so, the moron lived one block behind me at my old residence. What's worse is they splattered on many adjacent channels, and spent 50% of their time chasing people off the channel that they claimed as their stake. They even started to freeband, going on freqs. below ch. 1. As you know, some of those freqs. are Mexican comm. and US Navy!!! Boy the number of times that I wanted to sneak at night and push a straight pin into their coax!

[chtucker]

I did not want to infer that anyone was from the stone age..... just that the technology is.

It does have its place in local communications. I find HAM radio to much more useful in my life, repeaters everywhere, cool conversations with the space shuttle (back 1989 no less) and the technology involved.

Howard

[Roger Dodger]

Operation Moonbounce is a cool event to get involved with. Dunno if hams are still beaming a signal to that dish or not? There's a mirror left behind as well for bouncing laser beams off of (for measurement purposes).

[phoenix827]

Originally posted by chtucker

, talk to MIR,

Howard

IIRC, Thats gotta be one heck of a big radio to talk to Mir!:D Didn't it come down a couple years ago? lol:huh :grinz