Shorten Radio Antenna - BMW Luxury Touring Community
 
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post #1 of 14 Old Aug 26th, 2006, 2:01 pm Thread Starter
Gene
 
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Shorten Radio Antenna

Just curious if anyone has shortened their radio antenna and if so was there any negative impact (i.e. reception).

Gene
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post #2 of 14 Old Aug 26th, 2006, 2:44 pm
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I'm interested in this too, my antenna catches on the garage cross beams and I've already managed to whip the ceiling light out.

2002 K1200LT SE
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post #3 of 14 Old Aug 26th, 2006, 2:47 pm
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Greg (Griffscoots) has been running with one for several years. I have not heard him complain about reception.

There's a picture of his setup somewhere in archives.



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Last edited by RaffyK; Aug 26th, 2006 at 4:06 pm.
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post #4 of 14 Old Aug 26th, 2006, 3:48 pm
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http://www.crutchfield.com/S-EGpwmXH...50&I=12044UA20

check out this site this is a little different.

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post #5 of 14 Old Aug 26th, 2006, 4:15 pm
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My lady friend caught mine in the garage door and broke off about 1.5 feet. I dont notice any difference on the FM bands but have not tried it on the AM band. I am sure that it is tuned to a specific length and is not working to its max potential in its shortened state.

Fred Rosenbaum
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post #6 of 14 Old Aug 26th, 2006, 4:23 pm
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I simply cut mine in half and put the end cap back on. The antenna length is tuned for a specific frequency, (which is a compromise since the AM and FM bands span multiple frequencies), but you can still get good results with a shorter antenna (which is therefore tuned to a higher frequency). In rural CT, my radio reception with my 1/2 length antenna is no worse then it was with the stock antenna, which means, it still sucks!

A simple FM dipole antenna for an FM transmitter (or receiver) system has it's length determined by:

The wavelength, l, of the frequency you wish to tune to (say the middle of the FM band, (108 - 87.5)/2 + 87.5 = 97.75 Mhz, by dividing the speed of light (11,784,960,000 in/sec) by the frequency (97,750,000 cycles/sec) = 120.5. Thats for a full dipole, most antennas are 1/4 dipole, or in this case about 30 in. I think the stock LT antenna is about 36 in.

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post #7 of 14 Old Aug 26th, 2006, 4:27 pm
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When I remember, I tuck the end of my antenna just under the far side of the chrome luggage rack (I knew it had a use !!) before I ride into my garage and hit the 'close' button. If I forget, there are a lot of graunchy noises, but the antenna has not snapped yet.

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post #8 of 14 Old Aug 28th, 2006, 10:01 am
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Just call him Sir Fred!

Quote:
Originally Posted by FredR
My lady friend caught mine in the garage door and broke off about 1.5 feet.
What else can one say?

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post #9 of 14 Old Aug 28th, 2006, 11:53 am
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Thanks

Fred Rosenbaum
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post #10 of 14 Old Aug 28th, 2006, 12:42 pm
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Go satellite radio and you can cut off however much you want....of the antenna that is!

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post #11 of 14 Old Aug 28th, 2006, 2:00 pm
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Shortened it today

This morning I was standing next to the bike waiting for the wife to come out of the house
and getting ready to roll her (the bike) out of the garage
and have the antenna catch on the garage door like it always does.
When I thought to myself, I wonder how hard it would be to cut this thing of?
30 seconds later I was looking at 4-5 inches of antenna in my hand saying it's fiberglass,
I don't know what had me thinking it was metal?
Sprayed a little WD40 into the rubber cap and wiggled it back on,
went for a ride and didn't notice any difference,
excepting it don't piss me off catching on the overhead door no more.


Hans
St. Petersburg FL

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post #12 of 14 Old Aug 28th, 2006, 2:19 pm
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Does it make any difference on the CB antenna....?
My CB antenna is much longer than the radio antenna.
Is anybody else having problems with the J&M CB unit?
My bike is 2006 and the CB has never transmitted correctly......?
The Dealer has worked on it three times and now I have this very tall CB antenna.
While transmitting it breaks up and nobody can understand what I said.
Someone mentioned to me this weekend there are problems with the Intercom?
My motorcycle has the BMW Comm System V.O.I.C.E. II installed by dealer
Are there problems with this intercom system that I am not aware of ?

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post #13 of 14 Old Aug 28th, 2006, 3:57 pm
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All radio antennas work on the same principle, so size does matter!

'07 - R1200RT Slippery Silver

MOA #107139
RA #28511

Past rides:
'03 R1150RT - MAXed out
'03 K1200LTC - Gone to the Darko side
'00 Kawasaki Concours - Buzz
'71 Honda SL350 - The original dual-sport
'72 Kawasaki 250 triple - The smoking gun
'67 Montgomery Wards 125 - Thrashed to death
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post #14 of 14 Old Aug 28th, 2006, 6:05 pm
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Quote:
Originally Posted by zimbazi
Does it make any difference on the CB antenna....?
My CB antenna is much longer than the radio antenna.
Is anybody else having problems with the J&M CB unit?
My bike is 2006 and the CB has never transmitted correctly......?
?
Not sure about your intercom or your CB unit but your transmitting antenna needs to be a specific length. A standard calcuation for a full wave antenna would be 486/freq in Mhz and divide that by 4 to get to a 1/4 wave size. using 27.2Mhz as a midpoint for the cb band would result in an antenna approx 4.5 feet in length. CB antenna mfgs quite often use a coil or wind the antenna on a fibre core to keep the length down. So dont cut your CB antenna unless you have a reliable SWR meter or ant analyzer and know what your are doing or you could wipe out the final amplifier in your CB radio. Just my .02

Fred Rosenbaum
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