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CB Antenna


Rancity

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I want to add a CB antenna to my R1150RT. I have the top case and side cases. None of the mounts my cruiser friends use will work on an RT.

I have my eye on the firestik firefly side mount NGP kit. Before I go with this I would like to know if any of you have mounted a CB Antenna to an RT?

Which one did you use and where did you mount it?

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I used a mount developed by Toolman. I bought it from Fernando and have been very happy. The mount is attached to the top case luggage rack. One small hole to drill. Works beautifully with the Top Case. thumbsup.gif

 

Search under my name "SAMSAR" and there is a recent post with pictures. There are other posts from others farther back too.

 

I was having an engine whine problem feeding through the coax cable. I solved it last night by running the coax down the middle of some flat braided grounding cable.

 

If anyone is interested, I have an extra 3' foot antenna if you are interested. I haven't decided yet whether I like the Firestik or Wilson so of course I bought both wink.gif but, in the end will only need one.

 

I also have the Midland handheld CB which wouldn't work with my Autocom so I went with the Cobra. It's also available if anyone is interested and doesn't use an Autocom.

 

Good luck!!!

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I use a 4" Firestik antenna. You dont need to go with a NGP antenna. You just need to get a proper ground from the antenna to the frame of the bike. I think the problem with grounding most motorcycle antennas is not the lack of available metal but the inability to get a proper ground through the typical motorcycle antenna mount. I use a length of 12ga copper wire. It runs from the base of the antenna to a suitable spot under the seat where I can connect it to the metal of the frame. My RT is the 3rd bike I have done this with and it has never failed me.

 

I should say that you must set up the antenna properly. Attaching the ground wire to the wrong portion of the antenna can be worse than not grounding it at all. Follow the instructions carefully. Or like I did, get some help from your local CB shop. They can also help you tune your antenna. This will make a big difference as well.

 

I made my own mount out of a single piece of bar stock. I have a Givi rack which greatly simplfied installation. It simples bolts underneath the rack using a couple of slightly longer bolts. I rounded off the end for safety and painted it for looks.

 

Works great.

 

Yankee Dog

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I want to add a CB antenna to my R1150RT. I have the top case and side cases. None of the mounts my cruiser friends use will work on an RT.

I have my eye on the firestik firefly side mount NGP kit. Before I go with this I would like to know if any of you have mounted a CB Antenna to an RT?

Which one did you use and where did you mount it?

 

I went with the FireStik 2' NGP FG2-DD http://www.firestik.com/Catalog/NGP_Roof.htm

and I use a license plate frame mount.

 

Mick

Tucson

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Biggest problem with most CB antennas is that they are foreshortened (loaded) end-fed quarter wave antennas, and as such require a good "ground plane" to operate properly. A car body is large enough to work as a half-decent ground plane, but a bike is not. As a result, antenna gain (therefore range and reception) generally suffers.

 

But I guess if you want a CB on the bike, this is something one needs to live with! Just be aware that it will likely not work as well as a CB on a car.

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There is not much metal exposed on the rear of an RT to mount and ground an antenna to. With typical antennas you need to be sure to have a good ground path from the antenna base (what the outer part of the coax threads onto) to the frame of the bike. This makes the frame act like a counterpoise to the antenna. In laymen terms it gives the antenna the proper resistance to work against. Without it if you were to measure the standing wave it would likely be very high and it would not recieve or transmit like it should. Wilson makes a very good small antenna that has an extra wire hanging from the windings. This wire can be left open, or in cases where the ground or proximity has to be compromised it can be fastened to the same ground as the base and can net some reduction in standing wave. If you find a place you want the antenna it should be able to function OK with a good grounding wire to the frame, even if mounted to a non metallic object.

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There is not much metal exposed on the rear of an RT to mount and ground an antenna to. With typical antennas you need to be sure to have a good ground path from the antenna base (what the outer part of the coax threads onto) to the frame of the bike. This makes the frame act like a counterpoise to the antenna. In laymen terms it gives the antenna the proper resistance to work against.

In slightly less "laymen's terms", a CB antenna is only half of an antenna, so to speak. The ideal ground plane acts as a sort-of electrical mirror that produces a mirror image (electrically) of the antenna to replace its missing half. The real antenna and its mirror image form the complete radiating antenna.

 

If the ground plane is too small, and not coupled directly to the antenna connector's ground, then the "mirror" action is seriously degraded, resulting in a poor VSWR (high standing waves, resulting in poor power transfer to the antenna), and a poor (often very odd) antenna radiation pattern.

 

Clearly, with a bike, the ground plane formed by the bike itself is much too small for proper performance, but there is not much you can do about that. All that remains is to heed Realshelby's advice regarding ground connection, and hope for the best.

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Biggest problem with most CB antennas is that they are foreshortened (loaded) end-fed quarter wave antennas, and as such require a good "ground plane" to operate properly. A car body is large enough to work as a half-decent ground plane, but a bike is not. As a result, antenna gain (therefore range and reception) generally suffers.
All true, but given the noise floor on 11 meters it's not like a little extra antenna performance is going to help much... wink.gif
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Biggest problem with most CB antennas is that they are foreshortened (loaded) end-fed quarter wave antennas, and as such require a good "ground plane" to operate properly. A car body is large enough to work as a half-decent ground plane, but a bike is not. As a result, antenna gain (therefore range and reception) generally suffers.
All true, but given the noise floor on 11 meters it's not like a little extra antenna performance is going to help much... wink.gif

Yes. Good point!

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Biggest problem with most CB antennas is that they .............require a good "ground plane" to operate properly. A car body is large enough to work as a half-decent ground plane, but a bike is not. ........

 

Not true. There is plenty of metal in a motorcycle frame. The problem is getting a good connection from your antenna base to the frame. Most motorcycle antenna mounts are attached via plastic body parts or at best powdercoated luggage racks. Not the best material for conducting electricity.

 

I have found that a short section of 12 ga copper wire from the antenna base to the the frame works wonders. I run the wire under the seat and attach it to an availble bolt. I file a bit of paint off the frame to insure a good connection.

 

The local CB shop was able to tune the setup to 1.2 on an SWR meter. Better than some big rigs.

 

Also, remember your antenna has to stick up above your bike to work properly. Those short antennas wont work as well as a longer one. Dont worry about a long antenaa affecting your handling. I have a 4" mounted at the base of my topbox. Sticks way up there but I never even notice it is there.

 

Yankee Dog

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The local CB shop was able to tune the setup to 1.2 on an SWR meter. Better than some big rigs.
I hate to tell you this but a low SWR reading by itself doesn't necessarily mean very much. There are many ways to achieve what appears to be a good impedence match with the transmission line that have little to do with actual antenna radiation efficiency.
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By using an antenna tuner I can "tune" a garbage can lid to radiate with a low SWR! However, if no tuning aids are used and you can get the SWR below 2 stop right there and smile. On these applications nothing is gained by going lower. A low SWR does not mean you have an effecient antenna. Antenna location is important and does effect standing wave. Don't expect a 4' antenna mounted to a footpeg to work well, if the base is seat high that is about all you can do on a MC. I have had much better luck using the top loaded (especially Wilson) antennas when using the 3-4'tall versions.

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Biggest problem with most CB antennas is that they .............require a good "ground plane" to operate properly. A car body is large enough to work as a half-decent ground plane, but a bike is not. ........

 

Not true. There is plenty of metal in a motorcycle frame.

Not "plenty" enough for optimal antenna operation. A "proper" ground plane is not a bunch of metal tubing and and an engine block. In order for optimal operation of a quarterwave monopole (which a CB anrenna is a foreshortened version of), the ground plane ideally needs to be a a flat plate of metal that is close to the antenna's length in radius, or alternatively 4 to 8 stiff wires the approximate length of the antenna, radiating horizontally outward at its base.

 

You can find more technical info about this in the ARRL handbook, which is a sort-of bible of radio amateurs.

 

Obviously even a car body falls short of this, and as a result the radiation pattern and performance of a CB antenna of this type mounted on a car does in fact fall short of ideal performance. But it nonetheless works acceptably enough for most situations.

 

But a motocycle has NOWHERE NEAR enough metal to act as a decent ground plane. Not even close! As a result, a standard quarterwave monopole CB antenna, or one which is foreshortened by the use of inductive loading (so-called integrated "loading coils") will far FAR short of ideal antenna characteristics.

 

Again, this is just basic antenna design theory which can easly be verified buy the above source, or any other book on simple antenna design. Therefore when one installs a CB antenna on a bike, one has no choice but to accept degraded performance as compared to the same antenna even on a car. Unfortunate, but them's the breaks!

 

The only way out of this situation is to choose the type of CB antenna used in marine installations, where a ground plane (on a fiberglass boat) is not possible. These use an end-fed halfwave antenna, which by definition needs no ground plane to operate. Unfortunately, a halfwave antenna is twice as long as a quarterwave type, which gets a bit unwieldy on a bike!

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Top loaded antenna- simply end fed from the "top" instead of the bottom. Most antennas for mobile operation (shorter than about 7') will have an enclosed coil at the base or the wires will be wound around the base of the antenna and can be seen thru the plastic coating. A certain amount of wire has to be used (to meet electrical length for a given wavelength) and since it can't be straight it is wound around the antenna form. A top loaded antenna has the conductor run up the middle of the form and the "coils" are started down from the top. Under the exact same mounting I have seen these antennas to be superior in recieve and transmit. BTW, these are usually a little more expensive.

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Top loaded antenna- simply end fed from the "top" instead of the bottom. Most antennas for mobile operation (shorter than about 7') will have an enclosed coil at the base or the wires will be wound around the base of the antenna and can be seen thru the plastic coating. A certain amount of wire has to be used (to meet electrical length for a given wavelength) and since it can't be straight it is wound around the antenna form. A top loaded antenna has the conductor run up the middle of the form and the "coils" are started down from the top. Under the exact same mounting I have seen these antennas to be superior in recieve and transmit. BTW, these are usually a little more expensive.

Agreed. Top loading is generally superior because the higher current lower section is preserved, and only the lower current upper section is foreshortened. This results in a greater radiated signal strength, but also the antenna pattern is improved as well. Because bottom loaded (or continuous loaded ....wire lazily wound along the entire antenna length) are easier to make than top loaded antennas, are easier to make, they are indeed cheaper.

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I also use a Firestick Firefly and the antenna mount made by Toolman (Mike W.) of this forum. He was very helpful in coaching me on how to set it up to work properly. Ground plane is very important. I used braided flat (1/4" wide) cable from the antenna base to three bolts (in series) into the frame under the rear pillion. I covered the flat cables with shrink wrap to insulate. Works fine. I also had to install a noise filter between bike's 12V power and the radio (Midland 75-822) and "tuned" the antenna with my buddy's Radio Shack SWR meter. It took some fine tuning, but it was all very doable and the CB works pretty good. Recommend you PM Toolman if you're interested in buying one of his custom made antenna mounts. Also, PM me if you want to see photos of my RT's antenna set up. wave.gif

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