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1-10 of 10 messages
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Page 1 of 1
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Motorcycle mobile: 1/2 or 5/8 wave antenna??
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by KD7DPU on February 16, 2001
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Greetings all!
I am installing a rig on my motorcycle, which does not have a good ground plane (naturally).
Members of this forum (and elsewhere) have indicated that a 1/2 wave antenna would be better than a 5/8 wave when there is a poor ground plane.
Yet, the counter person at HRO last weekend indicated otherwise (he said 5/8 is better than 1/2).
Can someone definitively tell me which would be better? And more importantly WHY? I am a fairly technical person but new to RF and antennas.
73
Robert
KD7DPU
Anacortes, WA
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RE: Motorcycle mobile: 1/2 or 5/8 wave antenna??
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by WB2WIK on February 22, 2001
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1/2-wave vertical antennas are said to be "ground independent," because if one feeds 1/2-wavelength of wire at one end (in this case, the bottom of a vertical), the feedpoint impedance is extremely high --a reproduction of the tip (end) impedance, which is also extremely high. This is called a "voltage fed," rather than a current-fed antenna. The feedpoint is a voltage maximum, has high impedance, and thus must use a critical matching network to be fed with conventional coaxial cable. Such a network is often no more than an autotransformer with about a 2000 Ohm secondary and a tap at the 50 Ohm point. In any case, since the natural impedance of the end-fed half-wave is so high, it is not influenced by the presence or absence of ground. A 5/8-wave antenna, on the other hand, adds 1/8-wave to the length of the radiator, which shifts the voltage-current relationship by 45 degrees and creates a low-impedance antenna. This is also easier to match to coaxial cable, since the match ratio is much smaller and the network used will be more efficient. Which one will work better on a motorcycle? I really don't know. I think this will largely depend upon where you mount the antenna, and what you mount it to. I'd probably use a fibreglas "marine VHF" antenna, myself. Those are very robust and are mostly ground-independent designs, intended for mounting on fibreglas cowlings and such. And they seem to work very well. Most of the VHF whip manufacturers do have "marine" versions.
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RE: Motorcycle mobile: 1/2 or 5/8 wave antenna??
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by W8BOB on February 28, 2001
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I had a Honda Gold Wing and used a 5/8 wave antenna mounted on a standoff to the rear of the cycle. Opposite the AM/FM antenna. The radio was a Kenwood TH-25 2 meter. I hooked a power adapter to the battery and was heard well, just about everywhere I went. I used this mostly during a bicycle tour that covered 3 counties in central Ohio. The furthest distance was about 20 miles from the repeater.
BOB - W8BOB
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RE: Motorcycle mobile: 1/2 or 5/8 wave antenna??
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by N6SGX on November 5, 2002
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I have a Kawasaki Voyager, What I did was to run 2 lengths at 26 inches of #12 wire in a butterfly fashion inside the trunk lid. With this configuration I have run 5/8 wave, and 1/4 wave antennas with great results. Depending upon your bike, all you will need is at least 19 inch extender on at least 2 sides ( idealy 3 sides) of you antenna base. This will provide an exelent ground reflector.
Good Luck & Happy Rides
Bill - N6SGX
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RE: Motorcycle mobile: 1/2 or 5/8 wave antenna??
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by N3NDW on July 19, 2003
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I think QST did a story on bicycle mobiles a few years ago, and if I remember correctly they used a 1/2 wave antenns. I have a friend who used a 1/2 wave with a radio shack HTX 202 on his Harley, and did very well with his installation.
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RE: Motorcycle mobile: 1/2 or 5/8 wave antenna??
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by K9GRZ on May 24, 2007
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I know this is an old thread, but I'm just now having an issue! Besides, I'm new to ham so I should be granted some leeway, right?
I want to mount an antenna on the back of my ATV so I can go quad mobile. It's the same issues as mounting on a motorcycle, so the solutions should be the same, I should think.
My question: whether using the wire butterfly reflector or the straight rods described in a separate post, what do they connect to?
I'm thinking about mounting a plate on the back rack and using a mag mount antenna so it's easily removeable. Where would I attach the reflector wires (assuming I'm calling them by the right name)?
thanks!
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RE: Motorcycle mobile: 1/2 or 5/8 wave antenna??
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by K6MTT on June 15, 2007
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Think of the butterfly or radials to be the same electrically as a car trunk or roof - it's the ground plane. So, you would wire either the radials or butterfly to the base of the antenna (assuming a standard antenna) or your mounting plate.
I'm about to attempt to do the same thing with an ATV and it seems to me that the rear rack (or front, for that matter) would make a decent plane to work against with most mobile antennas and an adequate mounting arrangement. The thing I'm considering now is the antenna itself - I don't care to be "whipped" by the thing on rough terrain!
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RE: Motorcycle mobile: 1/2 or 5/8 wave antenna??
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by RHETTDUKE on August 26, 2007
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I have run a "ladder line" j pole wire tied to a bicycle flag mast at times on my ATV....it works but is a bit taller than I would like.I am curious just how good a ground could you get with the frame of a larger 4 wheeler....I'm thinking of trying a 1/2 wave mast...it needs to be fairly affordable....I've been known to roll the atv a time or two :)
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RE: Motorcycle mobile: 1/2 or 5/8 wave antenna??
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by KE6SLS on February 14, 2008
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Let's not forget the basic 1/4 wave whip. It's only about 19" and works quite well. Remember, you are not chasing dx here, you are busy riding and need/want to contact a friend or chat. I like keeping it as simple as I can.
I'm going to make my "new to me" 1983 shadow 750 radio active this weekend. haven't decided on mount point yet, but am seriously thinking about a bnc with a good 5 watt whip for my ht. It's all small and robust. Now I need to find a good motorcycle interface for the ht/helmet.
good ride all
73
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RE: Motorcycle mobile: 1/2 or 5/8 wave antenna??
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by KD7TKQ on November 19, 2008
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I was thinking a good option for VHF and/or UHF on a motorcycle (or even a bicycle) might be to find or devise some method of mounting a HT in a position that would be both easy to operate (tho even that isn't critical if you tend to hang out on just one frequency) and a decent antenna location, and then use one of the longer whips that will mount directly on the BNC connector on top of the radio. If the mount is such that the radio can be easily detached, then it can be removed to avoid theft or for off-bike pedestrian use.
I've not looked, but I wouldn't be surprised if there are such mounts commercially available. If not, one of the mounts designed for cellphones or GPS might be adaptable too.
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