Off Road Race Radio Tips
Radios
Antennas
Flexible base vs.
Non-flexible base
Mag Mount
Ground Plane
Trouble shooting
Noise
No Transmit
No Recieve
Alt Radio Mods
Read First!
Kenwood
TM-261a
TH-235
Yaesu
FT-1500M
Intercoms
FAQS
Ask Scoob!
Need a Patch Cable?
The most important things to making a radio work good in a race car are voltage, ground plane and antenna!
ORC Paul
This page will be updated frequently check back often. Questions are welcome.
Cabling
Cable length should not effect radio operation(within reason, most people don't have over 100' of cable in there auto).
Does anything happen if some of the shielding is exposed on the antenna cable?
Depending on how much shielding is exposed it could be a big problem. RF leaks out before it gets to the antenna. This can damage some of the more poorly designed radios. Replace the cable, or cut out the bad section and replace with coax connectors.
Antennae
The electrical type or design of the mobile antenna is commonly referred to in terms of its dimensions in terms of wavelength: 1/4 wave, 1/2 wave, 5/8 wave, etc. Each electrical type has a specific radiating pattern to be considered when selecting a mobile antenna. For example, the signal radiating from a 1/4 wave antenna is directed more vertically, thus making it ideal in urban environments where buildings might obstruct the signal. The design of a 5/8 mobile antenna is designed to direct the signal more towards the horizon.
5/8 wave antennas for autos has a better propagation pattern than 1/4 wave for talking to other mobiles stations across the desert.
The antenna base will affect length of antenna.
The nifty rubber flexible base for antennas are questionable, the conductor inside breaks after awhile and then ruins the radio. I have found some of these broken when checked on swr meter.
Do I have to cut my antenna to make it work properly?
If you buy the right antenna, NO.
I have had good luck with Larsen brand NMO 150 antennas without cutting.
Last resort follow antenna directions for frequency range.
Does the antenna base mount actually have to be "grounded" to the roof of the truck?
The antenna actually has to be grounded metal to metal. you may be able cheat with ground straps, metal plates, or radials.
Ground plane requirements vary given the type of mobile antenna and the frequency of operation. A typical 5/8 wave antenna at 150 MHz requires a ground plane of at least 42” in diameter.
If you have a fiberglass roof, check this diagram out.How to make a ground plane(click)
Amplifiers
Linears won't help unless your on top of a mountain or in a plane. 10w in a plane gets you 200 miles.... 50w or a 1000w more in a mobile will get you to the next mountain face.
For real extended range you need a HF radio, or satellite phone, or airborne/mountain top relay.
Noise
Are Noise Filters just Resistors?
Filters are generally capacitors. I like the MSD filter and the kmart filter "Xtreme" (comes with ziptie mount). The MSD filter is a big capacitor that can go inline on anything not just a MSD Ignition box.
Where do you place the filters?
Best place for filters are at the source, but that may not be practical. Try the easiest least invasive location first, sometimes a filter at the power source for the radio and intercom might work.
Don't run your radio or intercom wires (any of them) in the same loom/bundle as MSD, Alternator wires, fuel injection, fuel pumps, or cooling fans.
Radios
Are Roadmasters and Neutecs the same?
Yes, Exactly. Just different labels.
Where to get Radios
My favorite places online are Ham Radio Outlet and Texas Towers
Formulas
Free Air radio wavelength
5/8 wave in feet = 615/frequency in Mhz
1/4 wave in feet = 234/frequency in Mhz
This document maintained by
scoob@raceflash.net.
Material
Copyright © 1998 Scott "Scoob" Maloney