NGP Cable Length & Motorcycles

Compliments of Firestik® Antenna Company Technical Support Team

Copyright © 2006 Firestik® Antenna Company

If there is one request that we get over and over again with regards to NGP (no-ground-plane) antennas and motorcycles, it is, "Can I get that with a shorter cable?" The answer to that question is, NO! There is a reason for this.

Two-way radio systems, be it the antenna or any related element or circuit, must be resonant within the frequency band of the transmitter. You cannot use [effectively or without the potential of damaging the radio] an antenna system that is not specifically designed to match the radios transmit frequency. Unlike receive only equipment that can be connected to anything from a coat hanger to a garbage can, if you are casual about what you connect to a transmitter you will fry the transmitter circuits. That is the way it was when 2-way radio was first invented and that is the way it is today. Radio propagation deals with the natural laws of physics and to expect otherwise is similar to expecting gravity to work or not work based upon your desires.

The NGP system has two key elements the antenna and the coax. Both MUST be resonant within the frequency band being used. In developing the NGP system for CB we found three cable lengths to be resonant. The first is in the mid-80 inch area. While that length would be more desirable for a motorcycle, the sub 2.0:1 SWR bandwidth is only 320KHz ... or enough to safely work with no more than about 25-30 of the 40 CB channels (the CB band is 440KHz wide) in an actual real-world application.

At the other end of the resonant world is a cable that is over 40-feet long certainly nothing any motorcycle owner would ever want ... even if it could work efficiently, which it doesn't. From a frequency perspective, the coax has a bandwidth a little over 800KHz plenty enough for the CB band. But, due to the long length the loss of power is totally unacceptable. Over 50% of the radios power is consumed within the cable assembly.

Then there is the middle of the road the 17-foot cable that we use in all of our NGP antenna kits. The frequency is correct and the bandwidth is approximately 725KHz.

If you cut the NGP cable it will no longer be at the right frequency and it will no longer work for your radio PERIOD! The process goes like this

  • I want a CB on my motorcycle.
  • My motorcycle does not provide sufficient ground plane for a GP antenna.
  • I will either use an NGP antenna system or not have a CB radio.
  • I want a CB on my motorcycle.
  • I will need to deal with 17-feet of cable or not have a CB radio on my motorcycle.

If you have a month or so to spare, have an understanding of 2-way radio antennas and their requirements, have the support and/or willingness of an antenna manufacture to work with you and the financial resources to endure the cost of designing a custom antenna for your motorcycle, there is a "possibility" that a custom GP antenna could be designed for your cruiser. But then again maybe not! We did it once successfully for a 2002 Goldwing owner.

The smartest and most cost efficient thing to do is to use an NGP system and spend your "battle time" on the issue of stowing the excess coax. Some people run it up the frame, around the tank or seat as many times as it takes to use up the excess. Some people just stow it in a saddlebag or trunk (if you chose to do this ... do not coil the excess up. It is better to just let it lay loose or loop it into a bowtie type configuration with a single wire-tie in the center).

If we could make a short coax that would work for the motorcyclist we would. But since we choose to supply antenna systems that offer the most efficiency within the design limitations we come face to face with a two-part thought process

Offer an NGP system that is as efficient as possible, or
Do not offer an NGP system at all.

The market needs NGP antenna systems and we need to give that market something that works. Firestik NGP systems represent the best we can do today and for now, that is the least you deserve.

Firestik Antenna Company - 2614 E Adams St - Phoenix, AZ 85034 - (Tel) 602-273-7151 -

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