Critical NGP Coax Info

Compliments of Firestik® Antenna Company Technical Support Team

Copyright © 2012 Firestik® Antenna Company

The NGP (no-ground-plane) cable is a calculated circuit and unlike a regular coaxial cable that is used in a ground plane dependent installation continuity between the center pin of the PL-259 and the threaded barrel of the PL-259 IS normal. If there is no continuity from center pin to the barrel then the NGP coaxial cable assembly is defective. Many people get this entirely wrong due to inexperience with NGP systems.

On a production cable using an auto-ranging Fluke 122 multimeter:
PL-259 center pin to PL-259 barrel = 0.2 ohms
PL-259 center pin to center conductor at end of cable = 0.4 ohms
PL-259 barrel to center conductor at end of cable = 0.6 ohms

NGP coaxial cables can only be used with NGP designed antennas. A GP antenna will not work with an NGP coaxial cable nor will an NGP antenna work with a common, non-NGP coaxial cable.

All NGP installations ONLY use the center conductor of the coaxial cable. We did not forget to process the cable with a connector on the cable shield. Using the shield of an NGP coaxial cable assembly, as one would with a ground plane dependent installation, will not work and will destroy the functionality of the NGP coaxial cable assembly.

The NGP coaxial cable must be tuned to the correct frequency. The length of the primary cable controls the frequency and we perform the tuning task at the factory. The cable length should never be altered not even so much as a quarter of an inch (6mm). There are some rare instances where adjusting the length is necessary but that has everything to do with technical know how and factual data obtained via standing wave ratio (SWR) measurements. Cutting the cable should never be a random act. There is an article on this site regarding the conditions under which some trimming may be utilized. Guessing is not an acceptable procedure.

Due to the sensitivity of the NGP coaxial cable, we always recommend that the terminating ring terminal be soldered to the cable end. If something needs to be repaired or the cable removed, it is near impossible to remove a crimped-on ring terminal without losing some center conductor length. Depending on the installation, losing as much as a quarter of an inch (6mm) of the center conductor can make the assembly unusable.

Coaxial, in general, is defined as sharing a common center when you pinch or make sharp bends in any coaxial cable, it isn't so much coaxial any longer. Any time you change the relationship between the center conductor and the shield; you alter the characteristic of the coaxial cable. That may or may not affect the over all performance of the system. What may not be exposed with a basic piece of test equipment will still be exposed with a more sophisticated piece of test equipment. You know what a kink in a water hose does to the flow of water ... you just can't see the flow of electrons.

Due to the design necessities of an NGP coaxial cable, applied RF power is limited to 100 watts, regardless of the antenna capabilites.

Updated Dec. 18, 2012


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

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