VHF Transmit coax, RG/8 or RG/6 ?

[jcmios]

I have a new radio install, VHF 136 MHz to 174 MHz @ 45 watts (Motorola CM300) that will be using a simple 1/4th wave mobile antenna. Can or should I use RG/6 or is it better to use RG/8 coax? The length would be between 40 to 60 feet.

Thank you
Jim

 

[ReceiverBeaver]

Hi guy,

Signal losses through coax start going up markedly once you hit VHF and steadily increase as you go higher. With that length of run you definately want not only RG8, but the best, lowest loss you can obtain. 13 gauge center conductor and 100% shielded. An example of good coax like this that is commonly used by hams and is readily available is Belden 9913F.

Get the antenna as high as you can and that 1/4 wave can be greatly approved upon. The typical ham or business or repeater is a co-linear 5/8 or a 4 element dipole array.

The point is you want to talk and hear and have range. Your radio is good but don't hitch your bass boat to a lawn tractor to get down the road.

Even a $10,000 radio will not yield satisfying performance if connected to an inadequate antenna system.

good luck Let us know what you decide on

 

[tspainiv]

Plus, RG/6 is 75 ohm, and with a tx rig, you'll need 50 ohm cable so stick with RG/8 or RG/8x.

 

[jcmios]

Thank you for the information, RG8 it will be. I know to buy the best, the reason for the use of a mobile antenna is that I live about 3/4th of a mile from our repeater and thus I will not need to go to the expense of mounting a base antenna on my house. Currently I have the radio hooked up in my basement office with a homemade coax antenna plugged into the radio and I get great reception and have great transmition. The antenna is just a 4 inch piece if RG58 with 3 inches of the center wire exposed, crud but it work for the time being.