Help with antenna
- Thread starter mr_tunz
- Start date
- Status
jim202
Member
That is what most radio geeks call a ball and spring antenna mount. Normally used for low band
frequencies (30 to 54 Mhz). Takes a good size hole in the sheet metal body of the vehicle you
mount the base on. You need a center hole to allow some space around the center nut so the
transmitter RF will not arc over from the large nut to the metal. You use 1/4 x 20 bolts to hold
the insulator to the sheet metal. The coax ground goes to one of the bolts and the center
conductor of the coax goes under the large nut.
Normally there was a metal back plate used on the inside of the vehicle. This plate provided
support for the bolts so they would not dent the metal body of the vehicle. Without the metal
backing plate, the normal use of the ball and spring will tend to dent or distort the vehicle
body at the mounting point. There was a small set screw on the plate to provide for a good
ground to the body metal. It would pierce the paint and contact the metal.
The antenna is a 1/4 wave length of the transmitter frequency. You tune the antenna by
cutting off the top of the whip. You should be able to find cutting charts here on the
Internet. Just make sure you start longer than what the chart gives for the length. Try
to mount the antenna where there is minimal body metal to interact with the whip.
Cutting the whip is rather a chore as it is made of hard stainless steel. I normally use a
grinder to score the whip a good way through and then try snapping it. Most bolt cutters
will not be able to cut the rod. Hacksaw blades don't do well on the whip.
Jim
frequencies (30 to 54 Mhz). Takes a good size hole in the sheet metal body of the vehicle you
mount the base on. You need a center hole to allow some space around the center nut so the
transmitter RF will not arc over from the large nut to the metal. You use 1/4 x 20 bolts to hold
the insulator to the sheet metal. The coax ground goes to one of the bolts and the center
conductor of the coax goes under the large nut.
Normally there was a metal back plate used on the inside of the vehicle. This plate provided
support for the bolts so they would not dent the metal body of the vehicle. Without the metal
backing plate, the normal use of the ball and spring will tend to dent or distort the vehicle
body at the mounting point. There was a small set screw on the plate to provide for a good
ground to the body metal. It would pierce the paint and contact the metal.
The antenna is a 1/4 wave length of the transmitter frequency. You tune the antenna by
cutting off the top of the whip. You should be able to find cutting charts here on the
Internet. Just make sure you start longer than what the chart gives for the length. Try
to mount the antenna where there is minimal body metal to interact with the whip.
Cutting the whip is rather a chore as it is made of hard stainless steel. I normally use a
grinder to score the whip a good way through and then try snapping it. Most bolt cutters
will not be able to cut the rod. Hacksaw blades don't do well on the whip.
Jim
Last edited:
- Status
