Thread: UHF trans distances and aerial choice

The performance of an antenna is the same in transmit in terms of antenna gain. What will make a difference is how much power you can push out that antenna which for vehicle untis is set. How high you can get the antenna will make a difference as UHF is more or less line of sight. The signal will bend a little around obstacles and make its way through some foliage and at times you can blast enough signal around/through something as a result of having a very strong transmitter but with CBs your are limited by tx power. You can make up a bit for this by using a higher gain antenna and in your situation the more gain you can get the better.

The issue of where on the vehicle to place the antenna is not as important for UHF antennas as they can easily be made in a ground independant configuration. It is just a case of not letting the body of the vehicle get in the way of the signal so once again the higher the better.

Thanks heaps for that. So i think i will just get the highest gain and I think I have seen mounts that can swivel down, so if I gutter mount on drivers side I can get most height and be able to swing it down when trees are about to take it out.

Actually the power output of the radio will make very little difference if you are talking 2w or 5 w.

The type of Antenna and the gain of the antenna WILL make the most difference.
You should try and get a groundplane independent antenna,and if the area that you are in is reasonably flat as you are describing,then a 6db antenna will give better resultsthan a 3db gain antenna,due to its lower angle of radiation,which is what you want ie a long low angle for maximum distance when there are no large hilss or buildings/forests etc to interfere with the signal.
If you had large hills or large forests between yourself and the persons you were wanting to talk to,then you would be better off with a 3db gain antenna with a higher angle of radiation.
And one last thought.Where you mount the antenna does make a difference,even when using a groundplane independent antenna,just not as much as a non groundplane independent antenna.
And the old question about how far can you talk on UHF?The answer is the same as how long is a piece of string?
I have spoken across Australia many times on UHF using a handheld when the conditions have been right(just like HF) using what is called tropospheric ducting.Unfirtunately we can't just dial this up when we need it though

3.9794db difference between 2w and 5w, more difference than 3db to 6db gain antennas.

Originally Posted by slug_burner

3.9794db difference between 2w and 5w, more difference than 3db to 6db gain antennas.

Ahhhh yes,I can read these figures as well from many manufactures web sites.
And it will depend on the manufacturers quoted figures,as to whether the figures are over an isotropic radiator or a 1/4 wave dipole????

Then you need to take into account losses through the transmission line,and if the VSWR is high,you will have more loss ,the higher the power output of the transceiver.

The only way you will notice the difference between a radio with an output of 2w and a radio with an output of 5w is on a test bench,in the real world,the difference will be inconsequential.
Ohh and by the way,if you ever check the output of most so called 5 watt radios,it isn't 5 watts!!!!!