Mobile Antennas, Part 1
by Ramon Gandia, AL7X 2/23/2013
See also Part 2 and
The other day I was sitting at the Polar Cafe, and
Bruce Tungwenuk KL0OT came in and asked me about a
"mag mount" for his pickup.
No problem, I thought.
But then, I got to looking at various mobile antennas, to
see what is out there ... besides Mag Mounted ones.
My search took me to the MARC
and BA-MARC sites. These are
the Motorcycle Amateur Radio Club sites, and they have quite
a bit of information concerning putting antennas on Motorcycles
(and trucks too)!
Magmounts are not very useful in Motorcycles, but many antennas
can be put on a mag mount if you purchase the magnet/mount
separately from the antenna.
MOBILE ANTENNAS 101
There are three types of mountings.
(1) 3/8-24 stud mount. Like used on those 9 ft tall whips
CB'ers use. Amateur HF mobile antennas frequently use this
mount too. Not very common for VHF, or four our purposes here
in Nome. Basically the antenna ends in a threaded stud with
3/8-24 threads, and the mount accepts that. You are on your
own here, I am not an expert on them.
(2) NMO mounts. Pioneered by Motorola, and 99% of all
police cars, etc., you see out there will have this mount. By
the way, MMO stands for New MOtorola mount.
Basically the antenna ends in a one inch female thread. The
Automobile (or the magmount) have the male counterpart. Look at
the picture on the left.
If mounted on the roof of a car, the mount is very low profile,
maybe a quarter inch above the roof. When the antenna is
screwed on, thre is an o-ring type of gasket that seals the
whole shebang from rain, etc.
If you look carefully, you will see that there is a large
nut with outside threads. There are flats to grip a wrench and
to tighten it. The o-ring is beneath this nut. The center piece
is part of the mount, and the two dimples are to put a spanner
wrench to hold it while the big nut is tightened.
The antenna itself fits like a cup over this mount, and
screws on that threaded nut. Often it has a gasket of its own.
Notice the center conductor of the coax ends in a single contact
at the center of the mount, surrounded by white teflon or plastic.
The advantage of this mount is the size. It spreads the load
out on your roof so things dont twist and break. This type
of mount generally runs about $15 - $35 and includes the coax.
It requires you to drill a 3/4" hole in the roof of the car.
The usual mount comes with the coax connector NOT installed,
and the antenna can be wormed into the 3/4 hole from outside the
car, thus you do not need to get to the underside of the roof.
You would have to drill carefully not to go thru your headliner,
but once you do, start pushing in the coax, and fish it up
inside the car. Everthing is tightened up from the outside.
The NMO mount was made to be strong and easy to install from
the outside. Speeds up installation in vehicles.
(3) The UHF mount. This is basically a coax receptacle mouunted
to the roof of the car. There are numerous variants of this
mount. Some are good, and some not so good.
I have one of the good ones in my Jeep; I do not think you can
break it. It comes in a bracket that sandwiches between my
tail lamp and the body. The bracket simply has a hole for the
coax socket. The coax socket itself is very nice assembly with
big shoulders and washers and nuts that spread the load. The
coax came with a two piece coax plug.
This coax plug is nifty. The end on the cable is an SMA male
plug that will go thru a
3/8 hole. Once fished through, the main sma to PL-259 the connector is
screwed on to the end of the coax and you now have a full size
plug to go into your mobile radio. Neat. A bit spendy, but worth
every dime. This particular mount and setup is every bit as
strong as the NMO.
I should also mention that the SMA male (without the adapter) will
plug right into a modern Yaesu HT.
Others I have seen have smaller nuts, no shoulders, and upon
hitting a branch or something will twist your car roof or even
When you decide to mount a mobile antenna on a vehicle,
decide first what type of mount is acceptable to you. The
NMO or a good UHF PL259 type.
My next article will show you the best places to
put an antenna on a vehicle, and discuss available antennas.
Copyright © 2013, Ramon Gandia, all rights reserved.