From: "Richard Williams" To: Subject: Re: UL: RE: VHF Antenna Co-ax Date: Monday, June 10, 2002 1:13 PM Bob, you asked for flames. I'll try to give facts instead. To maximize the amount of power going into the antenna, the coax needs to be an ODD number of 1/4th wave lengths. (I.E. 1/4, 3/4, 5/4, etc) The reason for the odd number of 1/4 wave lengths is because the voltage and amperage of the signal need to be 'in-step' at the connection to the antenna. Any 'out-of-step' means that power will be reflected back to the transmitter. In a related matter, the SWR (Standing Wave Ratio), unlike your statement, is very important. At SWR=1:1, all the power is being radiated by the antenna. At SWR=2:1, one-half of the power is being reflected back to the transmitter ... etc. Not only does any SWR over 1:1 GREATLY reduce your range, it is also very bad for the transmitter circuits. However, getting a perfect match (SWR=1:1) is very difficult to get and maintain. In any case, a SWR over 1:1.5 is unacceptable. The antenna/coax installation should be redone. A SWR over 1:1.5 will soon burn out most transmitter circuits, The line losses depend on the material of the coax. The line losses are unavoidable and are trivial in the line lengths found in a typical car/truck. R. Williams ----- Original Message ----- From: bob n To: FLY-UL@yahoogroups.com Sent: Monday, June 10, 2002 11:24 AM Subject: Re: UL: RE: VHF Antenna Co-ax There are a whole buncha threads abt coax, length, SWR, ant construction on both lists' archives. The old demon SWR keeps raring it's lossy head. Remember, if you square the xmtr power, you might get twice the range. Most vehicles can keep their radios within about 10', so your line losses will be about 7% at the frequencies we use. And even with a very badly mismatch load (high swr) you may lose only another 20%. Lotsa cutting, measuring, soldering, cussing---and you'll get about the same range. If you need range, go higher. Staying close to the grnd takes megawatts to even attempt to see over the horizon. Flame away, experts, I got 3 hrs of grass cutting, and not with the FireFly! Bob N.