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eHam Forums => Mobile Ham => Topic started by: AB3OL on November 05, 2012, 12:19:22 PM



Title: GE Sentry 3-6702D mobile mount antenna with SS whip - can I use for 2M-440?
Post by: AB3OL on November 05, 2012, 12:19:22 PM
Picked up a GE Sentry (#3-6702D) 3 1/2" mobile mount with coax, PL259 (kinda) plug and stainless steel whip.

Dimensions are: magnetic base = 3 1/2" diameter and 1 1/2" high,
black insulated section = 1" diameter and approx 4 1/4" high including top 3/8" tapered metal to mount antenna,
metal antenna mount to hold ss whip = 1/4" diameter and 1" long with set screw,
stainless steel whip now extends 36" beyond antenna mount

Has about 11 1/2' of RG58U attached to base and a crimped on UHF connector.
Think this was originally a CB antenna.  Can not find any specs on this antenna.

1. Is the mount just that a mount or does the black upright section a loading coil?
2. If I cut the SS whip how long should I make it?  (know a 1/4 wave is about 19 or 19 1/2").
    Should I cut it an inch shorter to allow for the mount which is 1" long?
3. Will I be able to use it dual band (2 M and 440 MHz)?


Title: RE: GE Sentry 3-6702D mobile mount antenna with SS whip - can I use for 2M-440?
Post by: K1CJS on November 06, 2012, 05:08:31 AM
No.  You're right in one thing--this is an old CB radio antenna.  You may be able to use it for ten meter operation, but its power handling capacity may prohibit even that.


Title: RE: GE Sentry 3-6702D mobile mount antenna with SS whip - can I use for 2M-440?
Post by: AB3OL on November 21, 2012, 11:37:25 AM
Removed top metal on black section which screws into the base. Removed a nut holding black plastic section. Underneath there is a loading coil in 2 sections. It is soldered to the shield or grounded section of the base connector. Appears to have a central rod section which goes thru the white plastic insulator on which the coil is wound. Bottom section of the coil is 4 turns loosely wound and about an inch long. Top section is 19 turns of wire closely wound and about 1 1/2 inches long. There is continuity between the shield and the section that is connected to the center conductor of the coax. Appears to be about 2/10 ohm resistance. I was expecting to see a coil not shorted to the center conductor and if so could have removed the coiled wire and simply allowed the center conductor to go to the threaded rod which connects to the stainless steel whip.
Can anyone provide insight as to why the 2 piece loading coil has continuity with the center conductor?


Title: RE: GE Sentry 3-6702D mobile mount antenna with SS whip - can I use for 2M-440?
Post by: K1CJS on November 22, 2012, 08:13:43 AM
It has to do with construction and loading of the antenna.  In other words, the antenna is made that way, it isn't something someone has jerry-rigged.