rich replied:

chris,
the simple lowdown..3db - hilly, higher waveshape, more likely to traverse slopes and ravines. 9db - long waveshape, more likely to recieve remote area contact in FLAT country.
Personally, I'd throw the 6db section away...

cheers Rich

P.G. (Tas) replied:

Chris, Rich hit the nail on the head. The 6db is a step in between the 3 & 9db gain antenna's. I use a GME AE409L which is 6db/9db. The 6db is fine around town and most rural area's in Tasmania, in fact it is far better a lot of the time than the 9db. When I tour the outback though, there is no comparison, the 9db is the way to go. This is through an old Electrophone TX4000. If I can find a better setup I will buy it, but as yet this is it. Hope this helps. Cheers

rich replied:

Chris,

Of course you need the 6db bit, sorry. Not thinking....

Try this: http://www.roity.com/rc/cbradio/uhfcb.html

It should explain everything.
cheers
rich

Darian replied:

The GME site (www.gme.net.au) has some good info on the antennas page. I have the 6/9 electrophone unit too - my research suggests that the 9 configuration is really good for long distances, but only when the car is stationary - when it flops around while mobile, the signal often goes UP instead of along!. In the (undulating) desert awhile back, the best performance for UHF in our group was a stumpy little 150mm unit. Taught me a lot - have made some of my own quarter/half/5/8 wave UHF antennas now, out of staineless wire - seem to work really well - they are all shorter than the 6db set up. Seems tall antennas have a long skinny pattern (like a pancake) and short antennas have a fat local pattern (like a donut) as explained to me by an expert). I made a page about my project - could be of use (http://homepages.picknowl.com.au/darian/uhf.html).
Cheers /
Darian