antenna rapair and a ??

ok so I had an atnenna brake on my 91 vr. So I went to the local radio shack and bought a twist on pl 259 coax connector. then a trip to the local truck stop where I purchased a 3 ftK40 antena,stud mount , and 90 degree pl-259 adaptor. This project took more timedeciding what antenna to buy than it did to do. First I cut the coax as close to the original antenna as possible and then screwd on the conector. Then installed the stud mount and 90 degree adaptor and screwed the coax back on. Already had the radio tuned to a channel that Ive never been able to pick up and waalaaa it picked up.

Now for the ?? Will the stock cb handle 2 antennas? I am debating adding a splitter inline and getting 2 new coax cables to hook up 2 antenna instead of one. I just dont want to burn up the unit. And of course either way Ill be getting the swr set as soon as possible.

David

I think it depends on the type of antennas you are using. Being as it is a bike you are unlikely to be using a long whip so the shorter ones should be ok to use a splitter and run two. Shaun

That is called Co-Phasing. To co-phase antennas on the 11 Mtr Band CB ( any band actually ) a minimum of 1/4 wave length ( about 9 feet ) of separation is needed to prevent interaction of the host AKA The Radio. Having them that close could possibly burn something out in the radio.

going to be using the 3ft k 40 antennas like what is used in this repair. But I can drop down to the 2 ft k 40's. Thanks and any advice is appreciated.

David

Likely won't burn up the CB but will probably give you a goofy SWR and poor performance. It's been a long time since I've been into the CB stuff but I seem to recall that they need to be at least 1/4 wave length apart (about 8 feet) to work properly.

If you want the twin antenna look either run the radio to the extra or leave it unattached.

Of course you could fab up some really long mounting brackets......

The CB should handle two with no risk however.............

The problem is with the ground plane. That plays a part in the shape of the signal.

One antenna on the rear will work the best. A single antenna on the rear will throw a signal more towards the direction you are traveling and to the rear in an elongated oval pattern.

Two antenna require some distance between then. About 8ft. to give an almost circular pattern.

Two antenna on the rear within only a 2 1/2 to 3 ft of each other would throw an extremely elongated oval off the the sides with very little reaching to the front and rear.

Take look at an over the road semi that you can talk to for the longest time. They have a huge ground plane from the tractor and trailer and more than likely a single anteena on the passenger side mirror mount. That combination would throw a signal forward and and slightly to their left. Towards oncoming traffic.

Most OTR's run two. That gives a good circular pattern if they are 8 ft or more apart and have been dialed with an adjustable splitter and the SWRs set properly.

Just my from 35 years of using CBs.

By the way....The K40 is an excellent choice. My preference.

Mike

thanks guys . These are the answers I was wanting. Mostly wanted it for the looks of the dual antennas. maybey Ill just add another on the other side and run a seperate coax just for the radio. Or maybey just mount it there for the looks. I didnt use the cb yet as I dont have a swr meter and i am presently looking to find a cb shop or buy on myself. But I did turn it on and was picking up truckers on the highway from my driveway. Never been able to do that even before the antenna broke.

David

Hey David,

Just another thought here.

Talk to your local CB shop about this. The coaxial cable that comes with an antenna is cut to the proper size to create the best wave length. You mentioned you cut the new cable down to the original size of the OEM bike coax. You might want to check that length and ask the shop about about any issues with getting a good wave out of that.

I'm sure YamaMama had a game plan when they set this all up but was it the right one?

I used to use the full length coax on my GWs and wound it in a figure 8 patten and tucked it under the seat. Got good results with that.

Believe it or not....there is a huge differnce in performance on winding the coax in a circular loop and a figure 8.

10-7.......Down and out.

Defiantly make sure you have good VSWR or you will not be talking for long.

Hey David,

 

Just another thought here.

 

Talk to your local CB shop about this. The coaxial cable that comes with an antenna is cut to the proper size to create the best wave length. You mentioned you cut the new cable down to the original size of the OEM bike coax. You might want to check that length and ask the shop about about any issues with getting a good wave out of that.

 

I'm sure YamaMama had a game plan when they set this all up but was it the right one?

 

I used to use the full length coax on my GWs and wound it in a figure 8 patten and tucked it under the seat. Got good results with that.

 

Believe it or not....there is a huge differnce in performance on winding the coax in a circular loop and a figure 8.

 

10-7.......Down and out.

went back and reread my first post. I see what your talking about. but what I did was cut the original cable 1/8 th oof an inch or so from the original antenna base and installed the screw on coaxal conector. So only lost a 1/4 inch of cable at max. Now I just need to find a local cb shop or a member close enough for a ride . Seems cb shops in oue area are no longer in style and my local yamaha dealor doesnt want to touch anything wiht the antenna or coaxal cable. There only sugestion was to buy a new antenna,

David

Well then you are pretty close to the original game plan. SWR meters are pretty cheap so picking one up is a good idea. I used to check on the highest and lowest channels and then dial it in on the channel I used the most.

But your are hearing stuff now that you didn't hear before so you're good to go. But get that SWR dialed in and you will have it made.

Mike

Having a bad SWR will not harm anything as long as you only listen. It is transmitting with a bad SWR that will do damage.

Unless you are co-phasing antennas the length of the coax does not matter, and then they must simply be equal.

Come on down and we can set it.

As has been said, for optimized setup,co-phasing an antenna setup must be a minimum of ¼ wave length apart, which is actually 108¼" for 11meters. Do the math.

Another point missed on the coax is when co-phasing you do not use 50ohm cable for the leads, a 75 ohm is used or the impedance is off balance. Making sure the twin leads are equal length is paramount as was said.

It has been common practice to use a multiple of 3 foot for a CB antenna coax(presuming single ant setup) since the first golden screwdriver award was issued. Not entirely true. If the length of coax affect your swr then your antenna is not resonant to begin with and it is feeding an AC signal back down the coax. Changing the length only changes resonance point for the entire package, not antenna. Use as short of coax as needed to go from point A to point B. If your antenna is resonant on the frequency you want to use it will make no difference if it is 2 foot and 11 inches or 5 foot and 3 inches.

While your choice for a whip is good, cheap setup a center loaded coil could be better. They are touted as being a "no ground plane" antenna, and will normally perform on a boat or bike better than a whip. That being said there are whips with about 90% of the winding near the top, such as the firestick. They were specifically designed many years ago for trucks with little to no ground plane, and that's why they work so well. Avoid a Francis whip, while being superior to most anything on market for power handling they have no wire wrap at the top, they have 10 or more(depending on lenght of whip) fine wires running vertically around the radius of the antenna, from the base to the tip. These type must be above anything(like your head) that could reflect the rf propagation.