Tuesday, Mar 18, 2003 at 17:12
Jaycee, I agree with all of the above except for one small point. Mounting a colinear does require a ground plane or ground independent mount.
I travel in Outback Oz, and
Vic High country, and my set up - An RF industries Ground independent base ( with spring), Bull bar mounted on 100 series std wagon. with interchangeable 4.5 db stainless colinear and 9 db fibreglass colinear. (I carry a spare 4.5 db colinear). My radio - an Phillips Fm900 commercial Tranciever. This has served me very well, Never had probs with the 4.5 in the High country, and th "9er" works well in the desert. I have seen too many bleep tered / costly large fibreglass radome antenna's that do the exact same job as mine but dont stand up to a low slung branch like stainless on a spring.
People often forget about insulating against water in lower antenna connections, then there is heat in engine bays ( run coax opposite side of exhuast manifold) and Good quality power cable run direct (fused of course) from battery. It is amazing how much a small voltage drop over thiner cable will effect Tx power. 0.5 volt may reduce Tx power by nearly half!!! ( if engine off, 12.5 ish volts terminal potential, only 12 volts at the radio, when Txing. - theses things are designed and tuned to run at 13.8 volts.)
Buy a radio with GOOD reciever specification. You want to pay particular attention to"Reciever sensitivity" as expressed in microvolts for 12db SINAD I haven't looked on the box of a radio for years but 0.2 uvolts for 12 db sinad would be typical.(the lower the reading the better, i.e., 0.175 uvolts better than 0.25 uV) Compare brands. If its not on the side of the box, ask Mr salesman the question. " What are the reciever sensitivity specs?" Get him to check the manual if need be.
These are the details that will affect the outcome at the end of a days 4X4 ing. It's the whole system that you need to pay attention to detail to.
At the end of the day when everyone is sitting around the
camp fire comparing notes on who could hear who over the air at which times and locations, who was breaking up etc, It's comforting to hear " we could always hear you, and you always answered when we were calling!"
Routine Maintenence on antenna mounts is also important. Remove corrosion, spiderwebs/dirt from threads and connectors.
In all honesty, the difference between 3db to 4.5 db or 4.5db to 6 db is realistically not going to make the Huge difference that the sales person suggests. Is he a radio technician with 15 + years Governmnet feild experience?? - if bigger better antennas were that good, My organization would spend money on antenna's instead of costly Base station sites and repeaters all over the state. - you dont get something for nothing with antenna gain.!!!
Hope there is something here that may benefit.
Jarrod....
AnswerID:
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