Monday, Feb 10, 2003 at 17:51
James, here my reply to a question that was posed on th 15th of January. I have simply cut and pasted it here for you...sorry if some of it is irrelevant
Most Half decent UHF HANDHELDs have antennas that are detachable. This is achieved(in most cases) by using standard Co-axial connectors. By obtaining the correct connector type, Most common is "BNC" (bayonnet type) or "TNC" - similar size, but Screw on, You can use either a "magnetic base " type arrangement (if you want something quite temporary) or you can mount an antenna on your Bull bar/ Guard etc. Then using 50 ohm co-axial cable ( refered to as RG- 58) type, run this from your antenna to the co-axial connector BNC/TNC type, then plugs into your HANDHELD. As for the connector, to ascertain type,
check the specs. section of the radio. Ther are two common types of termination methods for most RF connectors - One is crimp, and the other is Compression. A crimp type is generally quicker and cheaper, but the necessary crimp tool is required. - provided this is done correctly, and a strain relieving boot is used directly behind the connector (I would strongly recommend this anyway, as you are using a HANDHELD that would be flexing the cable) A crimp connector will be stronger and last longer than a compression type. - A compression type connector is a hell of a lot more fiddly to terminate, but no speacial
tools required, sidecutters,
stanley knife, soldering iron. thats it. - but I wouldnt reccomend you try this one with no previous experience. - damage to your new HANDHELD would be quite possible, heaps of tiny "outer braid " wirestrands go everywhere when stripping co-ax. one of these inside your connector and your portable wont work/last long.
If you have a radio supplies/workshop nearby, they could do a crimp connector on the end of 5 mtrs of co-ax for you for about $ 10 -15.
As for the antenna,
1. Magnetic base - you can screw a couple of different antenna types onto a common 5/16th thread, I would recomend a " 5/8th co-linear" (these are either stainless wire or fibreglass braided) about 500mm long and have a coiled section just short of half way up. The most common type you would probably see on many 4x4's. or you could use a 1/4 wave - just a 11 cm piece of wire that screws onto the antenna base. - The advantages of the longer antenna are that it Has " GAIN" or operates more efficiently than the smaller antenna. It does this by electrically altering the pattern in which your signals are sent/received. - effectivly Squashing them, - why waste power transmitting straight up ??! - disadvantages - they are a bit more expensive, and may be prone to getting knocked / damaged by overhanging trees. ( even more crucial if you use a magnetic base.) Magnetic bases are also prone to leaving stratches in the middle of your roof. However this is the best place to mount one.
2. Bullbar / guard mount. Would recommend ground independant type base, - this uses a metal tube as a "feeder" for the antenna and produces a more even radiation pattern (more circular around your car!) Used on Most emergency sevice vehicles. i.e.
POLICE. ambos. then you could attach either of the above two antennas. Would suggest the co-linear. You could just use a standard antenna base on the bullbar but transmission distances would be severly reduced in one direction. ( blocked by your cars metal roof.)
Get the antenna installation
check out when complete - the VSWR or Voltage Standing Wave Ratio this will tell you how effectively your antenna is working, and the transmitt power of your HANDHELD. - I would recommend a HANDHELD that has the maximum allowable UHF CB transmit power of 5 watts. ( some only Tx 1 watt.) and all 40 channels and repeater access are a must if you want to be able to communcate with everyboiby
as for DC / extenal power, once aGAIN
check the Specs of the radio. You dont want one that can only be charged by ext. 12V not actually Run on 12V - some claim to but in actual fact just float charge the battery. Most HANDHELDs use Nickel Cadmium (Ni -Cads) cells, and float charging them will kill them quite quickly. They need to be cycled ( which you could do from the cabin of if your car but you need to be quite dilligent, ) and the other thing is you need to let the battery go completely flat before recharging. - something you probably want to avoid !! - Two batteries fixes that one though.!!
My personal opinion, is get a mobile (in car radio.) permanantly mounted. easier to use on the run (see channel No., controls easier), direct wired to your battery, easier to hear if mounted correctly, not getting nocked around, Once you add up cost of HANDHELD, extenal antenna (magnetic base) battery lead/extra battery, you'd be close to the cost af a mobile.
Just my 20 cents worth. ( and 15 yrs in the trade !!!)
Jarrod.
AnswerID:
12819