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Bike to bike Antenna alternatives.


CraigT

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Along with Autocom, I use the Kenwood TK250, which comes with a very small antenna probably less than three inches long.

I know that a larger antenna should theoretically give better transmission and reception and thus I'd be keen to try out something that increased both, however the simple application of a half or quarter wave monopole has me having a huge 'whip' style antenna. frown.gif

 

I'm appealing to the tried & tested crew who have fitted a remote antenna to their walkie talkies and also the radio engineers to learn of the true 'gain' attained by such a mod, and for those who did change:- Was there any noticeable difference in either clarity or signal strength/distance achieveable?

I'm an electrical engineer myself, but this is a little out of my field. confused.gif I understand the fundamentals, but just unsure if the bigger factor is the radio transmission wattage, hence amplification (possibly taking me into licence requirements) is what I'm seeking, but not via watts, just antenna efficiency.

 

Sorry for the waffle, but it may get to the answer faster. thanks

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The stub antennae are 'loaded' to make them appear as a 1/4 wave pole to the transmitter, which ensures full power transfer. You are right however, that a longer antenna gives better signal, they are higher gain. A monopole has a gain of 0, the loaded stub a negative gain.

A big whip will give you a greater range but not that much. Terrain masking is a much larger factor. The antenna is low-down and masked by buildings, hills and even cars.

Without moving into licenced PMR or Ham status there is little you can do except for getting a good transceiver. It is the receiver end that will get you the improvements, that is where the ability to pull a signal out of the noise counts.

 

I hope this has not added to the confusion, antenna theory had the lowest pass rate in my technical training ( I got an A-) grin.gif

 

Andy

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I hope this has not added to the confusion, antenna theory had the lowest pass rate in my technical training ( I got an A-) grin.gif Andy

 

A- .........Must try harder!

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Your Kenwood radio has VHF and UHF bands:

 

VHF: 136 ~ 150 MHz/150 ~ 174 MHz

UHF: 406 ~ 430 MHz/450 ~ 470 MHz/470 ~ 490 MHz/490 ~ 512 MHz

 

Compare your VHF band to the band for FM radio frequencies: 87.5 to 108.0 MHz. That's pretty close.

 

Have you tried connecting your radio to the OEM antenna that came with the bike?

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Compare your VHF band to the band for FM radio frequencies: 87.5 to 108.0 MHz. That's pretty close.
But not nearly close enough for a reasonable VSWR, plus the transmission line on that stock antenna is probably pretty poor. I don't know what the radio would see at the operating frequency but it sure wouldn't be 50 ohms. The transmitter would probably reduce power to protect itself from damage negating the gain from the longer wire.

 

A properly tuned external antenna would probably net a significant performance gain (subject to terrain shading), but on a bike you are lacking a decent groundplane so a 1/2-wave antenna would be recommended. These are available commercially for VHF and UHF, take a look at a police bike to get an idea, will probably be about 2-3 feet long. Here's a typical example.

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That police antenna looks great, Seth.

 

OTOH, I would still test the stock antenna at the lowest VHF frequencies first. Okay, it's sure to have an imperfect impedance match as you point out, and for that reason its range will be much more limited than that police antenna, but the stock antenna is already there, it's paid for, and it would be easy to hook up and test before spending money on another solution. Maybe it will work well enough for the distance range the original poster needs.

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A couple of comments.

 

"Close" is not good enough when it comes to antenna transmission. That's why a good antenna has an adjustment (or the ability to cut off part of the radiating element) to provide a perfect match for the desired frequency.

 

The second comment is that most consumer radios do not have the ability to take the existing antenna off. Those that do will have the proper connector to either attach a new antenna directly, or a coax cable to a remote-mount antenna. If you don't want to go with a large, permanent mount 2-3' antenna, you might look at aftermarket 1/2 wave "rubber duckie" antennas. These are usually built for better performance than the stock antenna.

 

While you might get an increase in effective radiated power out of a different antenna, the line-of-sight factor will likely remain as the limiting issue as opposed to the antenna. That being said, I have a dual-band VHF/UHF ham radio antenna on my bike rather than using a rubber duckie so I can hit distant tower-based radio repeaters. For the FRS/GMRS radio, I simply have it in my tank bag with the stock antenna.

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Not sure if you are talking bike-to-bike amateur radio or using the GMRS/FRS frequencies. They are significantly different.

 

For either, try Antenex. They make very high quality commerical and amateur stuff. They have no ground plane required versions and some that are stealth antennae as well.

 

Try their web site... antenex.com and I think you can find what you need.

 

The previous comments on the quality of the antenna (rather dummy load) on your hand held radio are spot on.

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That police antenna looks great, Seth.

 

OTOH, I would still test the stock antenna at the lowest VHF frequencies first. Okay, it's sure to have an imperfect impedance match as you point out, and for that reason its range will be much more limited than that police antenna, but the stock antenna is already there, it's paid for, and it would be easy to hook up and test before spending money on another solution. Maybe it will work well enough for the distance range the original poster needs.

 

If you do this, I hope the radio you are using has a good swr protection circuit. If not, fried finals will soon be another topic of discussion.

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I am not familiar with the radio you are asking about but it sounds like a typical vhf or uhf transceiver. Don't worry about hurting it. These type of transmitters are designed to take a lot of very high SWR conditions. Think about it. How many are held above our heads with no metallic objects near to effect SWR? Thats right-almost never. They are generally held against a handlebar, mirror, tank bag,etc. They can survive indefinately keyed down with a high SWR! Now some input on your question: is your antenna removeable? If so it likely has what is called a BNC connector. I always replace the small rubber antennas that come on HAM band UHF and VHF radios with the "flexible whip" style replacements. These are made by several manufacturers and are about 18" long for the 144-148mhz bands. These could be adjusted for the band you are using. As an example of whether this is worthwhile or not:

I have a hand-held ham radio that can put out 5 watts. On 5 watts of power with the 3 inch rubber antenna I have trouble being heard on the repeaters. Installing the 18" whip antenna will allow me to connect to the repeaters with better sound clarity on 1/2 watt! That lets me use 1/10 of the power and get better results. Antenna effeciency is everything. These "whip" antennas are so flexible you can stuff them into your shirt while attached to the radio in a coil.

rd_98.thumb.jpg

This example is 17" long. Pryme RD-98

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Wow. Impressed I am. Feedback on this thread has been an education. Thanks thumbsup.gif

 

My radio is an Ex-cop version sold off on ebay. The antenna does remove, but it screws off, like a standard cable TV co-ax outlet, not BNC.

I think this whip is exactly what I'm looking for. I've got 8 preset channels and will stick to any particular one if the 'tuning' of the antenna is this tight.

 

I shall now search ofr a UK distributer of this thing, I have tried some other local outlets but I've not been satisfied with the response. This forum has proven it's worth yet again. Back to google for the UK supplier then...

 

Thanks to all who contributed.

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