sorgatz@ttidca.TTI.COM ( Avatar) (08/29/90)
In article <4502@feldspar2.UUCP> svec@motcid.UUCP (Larry Svec) writes: +Another alternative if you don't want to drill a hole is I have seen +in various 'add on junk to cars' catalogs, a duplexer or matching box +that allows you to use your AM/FM Broadcast antenna on CB (27Mhz) +Don't know how it works (or doesn't) but I recall it being about 10 or 15 +bucks... +-- Take some advice from someone that tried all these, THEY'RE JUNK! The thru-glass antennas (Avanti) work marginally at 2m. For 450MHz they will reduce the useful bandwidth to about 1/2 MHz, but don't try to run any power! About 10 watts RMS is maximum...otherwise the coupler-box gets real sick and blows a coil/cap. The AM Broadcast Band/11 meter CB diplexers are even worse! They won't take more than 7 or 8 watts, the radiation pattern sucks and when you try to use them with an in-glass AM/FM radio antenna you run the risk frying your expensive in-the-windshield antenna! The auto manufacturers *never* intended that these be used for transmitting..hence the size of the conductor is quite small and will not withstand the current loading of even a modern 2-4 watt mini-CB unit! These antennas are simply a MONEY_MAKER for the manufacturers! They are terrible performers compared to a real antenna! If you want a good radiation pattern, power handling capability, the best in receive signal strength; buy a ball and spring mount and use it with either a stainless steel 102" whip or a Hustler fold-over, 54" mast and the proper 11 meter resonator coil & tip. Mount it as high and as close to the center of the vehicle as possible. If you are worried about theft, you can add a quick disconnect to make removal and installation easy. I would also recommend that you *AVOID* rg-58u coax! It's lossy, it dies quickly in the UV of sunlight, and it won't handle any real power. - Go with either rg-213, if you've got the space to use it, or the newer mini-8 (which is the same size as rg-58u, but has better specs) if space is a problem. If your scenario dictates concealing the use of a transmitter, my honest recommendation is to use some piano-wire and clear vinyl strapping tape.. ..apply it to either the upper or lower width of the windshield or rear window, having first soldiered a piece of mini-8 (via the center conductor!) to it. Stay clear of the window defroster/defogger heater wires! The braid or outer shield is run to ground via the shortest route possible. Put a PL259 plug on the end of the coax. Then get an antenna tuner box. These can be as costly as you wish or can be made up from the circuits found in any edition of the ARRL handbook, nominally for under $20. <-----------wide as possible!---------------> =========================================== braid ------1/16" piano wire--------------------|-- ............... =========================================== | | |center wire grnd Transceiver <-> Tuner<->SWR meter< --------------- Coax between the units now, no funny stuff! And watch those soldier joints! Tune the tuner for the lowest reflected power, and the highest forward power. We did some of these for our local Police a few years back...worked great but it takes some time and effort to setup and tune, plus it's not exactly an off the shelf item. It will work better than anything you CAN buy in the shops though, and it will handle the power without trouble...too bad you can't run more than 5 watts on CB...(wink!)..if you could, you would put the amp between your radio and the tuner...for instance, if you were a LICENSED AMATEUR, and you wanted to use this setup for 10 meters...be sure to use good quality coax for all the jumpers, at least mini-8. And as a parting shot, why bother with CB?? You can easily get your ham ticket by passing a simple written test of 30 questions, the pool of questions is a published work! There is also a 5 WPM Morse code exam which can be easily learned from tapes whilst driving..there are probably a number of Amateur radio clubs in *your* area that offer classes and help with studying for the exams! Enjoy! -Avatar-> (aka: Erik K. Sorgatz) KB6LUY +-------------------------+ Citicorp(+)TTI *----------> panic trap; type = N+1 * 3100 Ocean Park Blvd. Santa Monica, CA 90405 +-------------------------+ {csun,philabs,psivax,pyramid,quad1,rdlvax,retix}!ttidca!sorgatz ** (OPINIONS EXPRESSED DO NOT REFLECT THE VIEWS OF CITICORP OR ITS MANAGEMENT!)