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On Tue, 28 Jun 2005 21:01:52 -0700, "Steveo"
wrote: if you have over a 2:1 standing wave you can do damage to your finals or linear ***** Only if you are exceeding the power dissapation of the devices. Considering the way most CBers use radios and amplifiers, your statement maybe more ture than false. Generaly if the power disapation of the finals is not exceeded and there is sufficient margin to handle the reflected power, it will just dissapate as heat in the output circuits and the fianls. Then this is only true if the reflection coefficient of the radio is zero. If other than zero then there will be some of the antenna power reflected back to the transmitter reflected back to the load. Then the rest is dissapated as heat. Then you get all kinds of funny things happening inside the coax. But that is another subject. james "Frank Gilliland" wrote in message .. . On 28 Jun 2005 17:51:10 -0700, "K7ITM" wrote in . com: snip But there's a real problem in communicating this. If you hook a 50 ohm SWR meter to the input of a 75 ohm, 300 ohm, or line of any impedance other than 50 ohms, the meter reading won't be the SWR on the transmission line. That can mislead people into thinking that the SWR is changing with line length when it actually isn't. In addition, most hams (and other non-professionals -- and even many professionals) don't bother to check that their SWR meter is properly calibrated to the impedance they think it is. Most are nominally 50 ohms, but they can be built for any practical line impedance. Checking calibration is not all that difficult, if you take the time to do it. In addition, your nominally 50 ohm line (or 75 or whatever) can have an actual impedance 10% or more from the nominal value. If you have properly calibrated your meter to 50 ohms, and your line is 60 ohms, you would read 1.2:1 SWR when your line is actually 1:1. And if the SWR on the 60 ohm line is 1.2:1, that 50 ohm SWR meter can read anything between 1:1 and 1.44:1, depending on the line length and its load. Finally, though you may have checked that the meter to reads 1:1 with a 50 ohm load and infinity to 1 with a short or open load, the construction of inexpensive meters may cause them to have significant errors at other load impedances. Impedance matching of an SWR meter is generally unimportant since most SWR meters used for HF have a directional coupler that is much shorter than the operating wavelength. Regardless, I'm not a big fan of SWR meters -- they are good for detecting a major malfunction but that's about it. Antenna tuning/matching is best done with a field strength meter. ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |