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What's this SWR-meter thing?

 
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What's this SWR-meter thing?
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Tobbstar
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Joined: 24 Jun 2006
Posts: 12

Post What's this SWR-meter thing? Reply with quote
Hallo everybody
I want to start a little radio station in my town in Germany. I thought about a range of 5 km and want therefore buy the CYBER MAX 15W transmitter and the Comet antenna. But now I wonder if there's also needed such a SWR- Meter. Can you help me for what use this thing is and if I need it for normal operation? I hope. Thanks for attention!
Tobi
Fri Jul 07, 2006 10:46 am View user's profile Send private message
pcs
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Joined: 18 Jan 2002
Posts: 3063
Location: Radio Land

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http://www.pcs-electronics.com/test/guide_coax.php


SO WHAT IS THIS SWR (VSWR) EVERYONE TALKS ABOUT?
VSWR is a measure of how well two devices are impedance matched to each other. Typical radio equipment is designed for 50 ohm load impedance, so we usually use 50 ohm cables and build or buy antennas that are specified for 50 ohm. While most cables have a flat impedance over frequency (they measure 50 ohm at all frequencies you are likely to use), the same is not true of the antennas. A 1.0:1 VSWR is a perfect match. That means the load impedance is exactly 50 ohms. A 2.0:1 VSWR is obtained when the load impedance is either 25 ohms or 100 ohms. Because most transmitters will deliver full power with a load VSWR of up to 2.0:1, this value is usually considered the limit for acceptable operation. Many prefer to keep their VSWR below that however, but for all practical purposes, it is unnecessary to spend time or money trying to get much below a VSWR of 1.5:1. The benefits will be hard to measure and even harder to notice. On the other hand, coaxial cable losses increase rapidly, for a given frequency of operation, when the antenna VSWR exceeds 2.0:1. This can even, in some extreme cases, result in the coaxial cable burning, even when running 100 W. Using a higher grade of cable will definitely improve things, but even high quality coaxial cable becomes very lossy when VSWR exceeds 3.0:1 at higher HF frequencies (or VHF and higher).

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