CB Radio Antenna

[santacarver]

CB Antenna:

I have a Itasca Horizon 39' DP 2002. I'm trying to get the radio going for my Alaska trip this summer.

Here is my problem; Winnebago factory installed antenna is a stainless steel whip antenna, and the whip is missing so I don't know how tall (long) the antenna should be. I have purchased a new whip but it is 4' long (smallest I could buy) so I need to cut it down to the prober length using a SWR meter.

I'm looking for someone who still has one on their who can tell me how long their antenna is for a starting point.

Thank you

[kaypsmith]

I'm not quite sure where the whip is located on your mh, but a stainless steel whip for 27 mhz, quarter wave is 102". For anything less you will need a coil loaded antenna, to make work with any satisfaction.

It would almost useless to use anything less. There are many brands of good ones, search k40 antenna, it is one of the better ones.

[dickandlois]

One needs to look for a loaded type antenna, the length of the antenna for channel 19 is 11.027 meters.

Just not practical.

Call Winnebago and ask who's antenna they installed or used, then you could get the length of the missing wipe.

A straight wire length.

1/8th. wave=54.28165in.

1/16th. wave=27.1385in.

1/32th. wave=13.5677

That would not be as effective as a (K-40) style antenna with a short wipe.

Rich.

[hermanmullins]

Go to a CB shop, many truck stops have them. Have them set your antenna with an SWR meter. They will be able to set the correct length.

Herman

[Lenpa]

Santacarver,

On my '02 the "stick" protrudes 23 1/4" above the base. One might think Winnebago used the same antenna on all their coaches but who knows. Someplace for you to start. Suggest you try a coat hanger cut to length before cutting the stainless replacement. Make sure you have bare metal where you stick it in the base.

Lenp

[paulcarson]

I mounted my "no ground plane" fiberglass antenna on the ladder and ran the coax underneath along the frame rails. Works good for me. Mine sticks up about 14 inches above the MH roof.

[santacarver]

It is coil loaded and factory installed on top of coach couch is 12 feet high so I know they wouldn't of put 102 inch whip on it. I tried a 24 inch fire stik on coach but that puts the tip 14' 6" high. and many bridges are just over 14 foot.

will try the coat hanger and see where that works out good suggestion thank you

Bruce Dixon USAF Ret.

[Lenpa]

Bruce,

The tip of mine is probably about 14' 4" and, yes, it does contact things like gas station overheads and low overpasses but it recovers. That might be what happened to yours - one too many impacts.

good luck,

lenp

[kaypsmith]

Us old ham's have used so many concoctions over the years, including long wires with 6 inch standoffs right on top of the rubber roof's, and they worked well. Also motorized shafts mounted just outside the driver window, but that is a little extreme for a CB. But if you want to relocate and get rid of the extra height, as indicated in my earlier reply, k40 does make a fiberglass antenna that is top loaded, come in different lengths, and can be side or rear mounted, since it is top loaded, it would only need to be mounted six to eight inches above the roof line to be effective.

ARS N4WQP

And if anyone would like to know the formula for cutting a wire antenna, pm me, will be happy to oblige.

Kay

[N7KGA]

Good morning, Bruce;

It is a funny thing that you are working on your CB (Citizen's Band, or the old ham radio 11 Meter band) antenna right at this time. I am working on mine also, and it is turning out to be a many faceted endeavor.

Kay Smith has already given to you the standard length of a full size naturally resonant CB radio whip or radiating element length, or 102 inches, or 8.5 feet. Kay and I have talked a couple of times.

Rich, the masculine half of "**** and Lois," has also mentioned that in many cases, we will need to use a "loaded" or shortened antenna length or radiating element length in order to meet the nominal height limitations of our vehicles, usually about 14 feet, which is up from the old limit of 13.5 feet. For best radio results, the antenna radiating element should be vertical.

And you also said that your antenna is "coil loaded," so we do know that it is a shortened antenna radiating element. Without actually seeing it, or a photograph of what you have left of the antenna. it is not easy to suggest what length whip to install to restore your antenna to functionality. One other quick point to keep in mind is the diameter of the hole where the replacement whip will go, as that will dictate what diameter the whip will be. And, yes, stainless steel is probably the best compromise and most easily obtained material to use in this application. Stainless steel is not the best material for an antenna radiating element due to its electrical resistance, but it does remain fairly constant over its lifetime, while other materials will oxidize and increase their resistance and deteriorate over time.

Herman also suggested going to a CB radio shop, which may be located at or near a truck stop. That is a good idea. You may be able to purchase from them a replacement stainless steel whip with the anti-static ball or enlarged diameter tip at one end. It will probably be too long, but it can be trimmed in steps going just one-half or one quarter of an inch at a time untile you get very close to being in the CB radio band, and then you might go in just 1/8 inch increments to get its resonance centered in the band. Yes, it probably is easiest to just take the motor home to them and have them install and trim the replacement whip to get it to resonate in the middle of the Citizen's Band. They can also check the coaxial cable for you while you are there.

If you do want to do it yourself, you certainly can, and all you really need for test equipment is the SWR meter in your CB radio. Install the new replacement whip into the antenna, and turn on the CB radio and check the SWR at Channel 1 with a short transmission and write down what it reads. It may be rather high at this time, but that is OK. Just do not transmit too long while checking at this stage. Next go up to either Channel 23 or Channel 40, whichever is the highest you have on your radio, and make another short transmission to see what the SWR is on that channel, and write down that SWR number along side of the Channel 1 SWR number. The same precautionary comments apply here also. Now turn off the radio and look at the numbers. The SWR on Channel 23 or 40 should be a little higher than the first measurement you made at the bottom end of the Citizen's Band on Channel 1. If the readings you have fit the description I gave, keep going. Go back outside the motor home to the antenna and take the whip off and trim off perhaps one-half (1/2) inch. The stainless steel material is very hard and may not cut easily with a pair of diagonal cutting pliers. A Dremel tool with a metal cutting wheel makes short and simple work of this task. But there are other ways to do it, and they do not require electrical power. If you have a small fine metal file, or even better a small triangular shaped fine metal file, use the edge of the file to make a slight or shallow groove around the whip bottom at the point where you want to cut it. Then with a regular pair of pliers, you can hold the whip in one hand and grip the piece you want to break off with the pliers, and then bend the whip back and forth a little at the groove, and it will crack and break off. You can use the fine file to trim any sharp edges now on the bottom end of the whip, and then put the shortened whip back into the hole on the top of the antenna. Go back inside, turn the radio back on, and go to Channel 1 again, measure, write down, then go to Channel 23 or 40, measure and write down there also. Turn off the radio. Again, the measurement for Channel 1 probably will still be lower than the one for Channel 23 or 40, but both of them should be lower than the first set of measurements. Go back outside to the antenna again, and remove the whip again, and cut off another one-half (1/2) inch or so, unless the SWR measurements that you made in the last set are coming down toward about 5 to 1, in which case, you now want to shorten the length you are trimming the whip bottom to perhaps one quarter (1/4) inch, again using the file to make a groove around the whip where you want to break off the next piece. Keep doing this until you get the SWR for Channel 1 down to about 1.5 to 1, or so. It may not go down to less than 1.4 to 1, and that is OK. If the measurement for Channel 23 or 40 is still higher than Channel 1, then go back outside to the antenna, remove the whip again, trim it again but using only a one eighth (1/8) inch cut, reinstall, and test again making both measurements again as you did before. You may find that at this point, both of the measurements will be at around 1.5 to 1, or maybe a little higher, but probably less than 2.0 to 1. If so, you are done. The minimum SWR number of 1.5 to 1 or so should be in the middle of the band. If the Channel 23 or 40 measurement now is lower than the Channel 1 measurement, you can adjust the whip to center the point of resonance in the middle of the band by loosening the set screw and pulling the replacement whip back out one sixteenth (1/16) of an inch or so, and retightening the set screw. Make one final check on Channel 1 and Channel 23 or 40 again to confirm that the SWR is just about the same at both the low and the high end of the band, and you are done. You have adjusted the antenna to the best that it can be with the same number at each end, and that 1.4 to 1 or 1.5 to 1 ratio in the middle of the band really is a very good number. Do not worry about trying to get it down to a 1.0 to 1.

While some may question why I suggest such small increments to use when cutting off the bottom of the whip, there are two (2) reasons: (1.) The general prudential rule that you can cut it shorter, but lengthening it is a real chore not easily accomplished while standing beside the motor home. (2.) Most shortened and coil loaded antennas like this will actually tune very rapidly as you cut off a short piece of the replacement whip, so that small increment really is likely to have a much larger effect than you might first think that it will have. Try it. Go slowly and you will get there. If you go too fast and cut off too much, you might need to go back and get another replacement whip, because you have tuned the antenna up into the ham radio 10 Meter band. Not a good thing. Go slowly.

Speaking of ham radio, if you know an amateur radio or ham radio operator, ask him if he might be able to help you. He may have an "antenna analyzer" that makes this measurement process really simple and fast, and you can quickly bring the antenna point of resonance right to the middle of the Citizen's Band very quickly. That "antenna analyzer" instrument is the one that the guys in the CB radio shop probably will be using also. Yes, you still need to slowly cut the replacement whip in small incremental amounts, but the measurement part is much faster.

The only other thing to think about is the shield side of the coaxial cable going to the antenna. it should be making contact and a connection with the ground or vehicle chassis at the base of the CB radio antenna. If it does not, either make that connection to the vehicle frame or chassis, or you can also put an 8.5 foot long insulated wire attached to the shield side of the coaxial cable where it connects to the base of the antenna, with the far end of the wire well insulated from ground. It can be inside the wall, roof, or frame of the motor home This will act as the required radial and work with the antenna to make it radiate the signal you want to send out, and receive the signals you want to hear, if you do not have a good antenna base ground or chassis connection for the shield side of the coaxial cable at the base or feed point of the antenna. The center conductor of the coaxial cable goes to the insulated bottom connection of the antenna itself.

And, if you get the SWR down to a number less than 2.0 to 1, you are doing fine with that. At a 2.0 to 1 Standing Wave Ratio, it means that you have a ten percent (10%) reflected power that is coming back to the transmitter section output circuit, and it can run all day long at that level with the normal duty cycle for which the radio was designed.

Finally, on the subject of shortened antennas, they really are not as good as a full size naturally resonant antenna. Now is a time to discuss "antenna efficiency," since we have been talking about shortened antennas. With the full size antenna as a reference, an antenna that is only one-half the size, or fifty percent (50%), of the size of the naturally resonant full size antenna, that 50% antenna will also radiate a signal that is 3 dB down, or only one-half or 50% as strong as the full size antenna with the same transmitter power going into each antenna. You can hear a 3 dB difference, but it is still pretty useable. Things begin to decline and drop off very rapidly as we go shorter than 50%. At about 30% or about one-third the naturally resonant length, you will be down about 6 dB, or one full "S Unit," and that really is noticeable. It gets even worse as we continue to go shorter. If we go down another 20% increment in antenna length to one-tenth or 10% of the naturally resonant length, there will be a 20 dB drop in the signal (a little over three [3] S units), and the antenna is radiating only about one percent (1.0%) of the Radio Frequency power that you are putting into it. A 1.0% output is really not very efficient. That is a 99% loss in the 10% antenna. There really is a reason why there are no effective sub-miniature antennas. This is not a problem with any antenna design, but instead is a limit in physics which we cannot get around. Sorry.

Enjoy;

Ralph, N7KGA

Latte Land, Washington

n7kga@arrl.net

[elkhartjim]

What a great write-up, Ralph.

[santacarver]

Ralph Thank you for all the time and effort You put into this. It is greatly appreciated Thank you. I'm still having issues Started with a 36" Stainless steel rod. Here is results. Did these steps with channel 1 and 40. Set "REF" to Set position at top right of the red scale. Switched to "FWD" and needle pegged out to far right on both channels At 36" ended up cutting down to 15" and still getting same results of pegged out needle. don't know if I have a bad radio bad coil bad cable. Motor home is all fiberglass and is using a "NGP" antenna system. Don't know where to go from here. was hoping to getting this working before my trip to Alaska in 20 days.

Thank you Bruce Dixon

[elkhartjim]

Just a thought, Bruce. If all else fails before you leave for Alaska (I'm so jealous), buy a good handheld CB. Its better than no CB...maybe.

[santacarver]

Jim

I have looked into the hand held CB's but everything I look at in the reviews are all bad and they complain about only being able to reach out about 300 yards. Most CB's are line of sight except when getting Skip that I'm aware of. There is no wher to mount a magnet type one to my Fiberglass body and finding a "NGP" Antenna is difficult.

Thanks for the input.

[wayne77590]

Mount the magnetic one under the front cowling on the frame, horizontally. Used to do that in the trunk of a car. The care is all tin but the MH is fiberglass. Signal should be better than that in the trunk of a car.

[N7KGA]

Good morning, Bruce Dixon;

OK. There is not too much time before your departure.

I am not yet a recognized member of the FMCA, but I am working on it. When I bought my motor home, I had no of all the different motor home groups there are out here. It may be that until I am a recognized FMCA member with an "F" number, I will not be able to send a message to you through their system. Until then, please contact me directly by e-mail and let us see if we can work out something with this antenna.

If the e-mail address does not come through as shown down below (some systems have sentries that will truncate the domain name or something equal), you can probably interpret the following to get something that will work to get a message to me. Then we can get down to seriously working on this thing.

Enjoy;

Ralph

Latte Land, Washington

[wayne77590]

Click on Ralph's picture, then click on "Send PM."

It will work.

[santacarver]

I ordered a new NGP Antenna Assembly that includes the cable and Side mount. All the reading I'm getting are saying it's a defective coil/ cable causing the SWR to Peg out, Found a great store on line called the http://www.truckers-store.com/ They are fast reliable and lowest prices around.

I let you all know what I find out.

Thanks for all your help.

[wayne77590]

Interesting, and yes I have found cold solder joints on CB antenna coils that the end of the coil would break away from the solder joint. Found some shorted cables many a time also, and that is easy to fix most of the time. usually it is in the connector where a stray piece of shielding finally started touching the center conductor. Just replace the connector or replace the cable if you don't solder well. Cold solder joints can be re-soldered also.

[santacarver]

Wayne

Thank you for your Service.

Taking the factory roof mounted antenna assy. out is more than I have time to do I will need to remove ceiling panels an cabinets to get at the base of the antenna on the roof. Adding a new side mount antenna assy and mounting it on the side just behind the Windshield only requires 4 screws to remove plastic trim to install, It will also make it easier to make SWR adjustments being as I won't have to climb on top of the coach each time to make an adjustment to length, I'm getting too old to be climbing up and down the useless ladders the mount on these coaches LOL. Soldering is not a problem have soldered at Intel on mother boards.

Thank you for you kind input.

Have a wonderful day, keep the shinny side up

Bruce Dixon

MSgt USAF ret