Pre tuned UHF antenna!!!! Is coax length important??

Hi Olcoolone

These types of antenna's don't rely on the coax length to tune the antenna so cutting the cable to position the antenna plug makes no significant difference.

Had a friend who's antenna stuffed up on a trip. So he took his UHF radio out of its cradle, sat it on the dash and plugged his stubbie antenna into the PL-259 socket on the back of the set - eliminating the antenna cable completely! It worked very well.

Antennas like the GME AE4005 dipole type are not ment to have there coax cut down, this is according to GME as it forms part of the antenna.

Phil the one you might be thinking of is the 1/4 that has a PL259 plug on it.

The antenna was the same as mine and stocked (and highly recommended) at Electric Bug:
Electric Bug 1/4 Wave Flexible Antenna with S0238 (Mopole) Base.

The base has the same thread as the PL259 plug. A fairly indestructible setup which I've used in my last 4 vehicles. I don't believe there is any problem cutting the cable length with this antenna but happy to be corrected.

Hi Olcoolone

Those antenna's like the GME AE4005 dipole can have there cable length changed , shortened on lengthened within reason without any significant effect.

That type of antenna is a half wavelength long and this means that it is very high impedance at the base near the coil and as such anything near the coil will have at effect on its VSWR.
The idea is that the antenna be mounted up and away from anything metallic and the only reason for concern is if the cable is cut so short that it prevents the antenna from being mounted away from other things like bonnet/roof racks.

As a rule of thumb that antenna needs to be at least its own length and preferrably double away from metal.

Some people have been known to mount them on a bonnet/bullbar and then cut of the excess cable - this is what would be wrong.

Phils 1/4 wavelength one is not affected.










tstill don' type are not ment to have there coax cut down, this is according to GME as it forms part of the antenna.

It's either yes or no with these antennas.

"shortened on lengthened within reason without any significant effect. "

Whats within reason, every ones with in reason is differant.

If I had one of these antennas mounted on a roof rack or gutter mount with the radio mounted in an overhead consol is it OK to cut the coax down to 1m long.

As said in my original post most UHF antennas can have the coax cable cut or made longer, but there are always some that you can't.

Hi Olcoolone

Everyones reason can't be different unless they ignore the rules and install it incorrectly.

It can be logicaly deduced as what is reasonable by applying the rule that the antenna should be a wavelength or more from metal panels.

So the coax can be cut to 1 meter as wavelength is 600mm approx, but if you did you would only have 400mm left in which to take the lead into the car and connect to the radio.
Most cars would need a bit more than a meter to achieve the above, hence these units usually come with some 3m or so which allows for a typical install without neededing to re-terminate the cable.