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<blockquote data-quote="JimJ" data-source="post: 1014037" data-attributes="member: 555251">It gets really interesting once you get out of audio frequencies, up to radio frequencies //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gifMost transmitters (and therefore antennas and feedlines) are designed for a 50ohm nominal load - it works the same way as in audio where you try to match the load impedance to the source impedance; the only quirks are that amplifiers aren&#039;t really designed to operate at higher impedances unless you put a feedline transformer in line. You could run an RF amp that&#039;s designed for a 50ohm load at 75ohms...but because there&#039;s a mismatch, power would be reflected back instead of being radiated. Get far enough from the source impedance and you have all of the power coming back. In order to go between impedances, you need stuff like matching networks to raise or drop the impedance by a whole number value (like 2:1, 4:1, 9:1...technically you could do the same for audio, but very few are around; the Zero Autotransformer comes to mind).There are also high impedance feedlines and antennas - 300 and 450 ohms are common values for &quot;ladder line&quot;, which is nothing but parallel conductors seperated a certain distance by a dielectric. The high impedance doesn&#039;t make it a bad or lossy feedline, but you need something that can convert the 450ohm load to the 50ohm impedance the transmitter is looking for. Huge variable capacitors and inductors are used for that.[/offtopic]</blockquote>

[QUOTE="JimJ, post: 1014037, member: 555251"] It gets really interesting once you get out of audio frequencies, up to radio frequencies [IMG]//content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif[/IMG] Most transmitters (and therefore antennas and feedlines) are designed for a 50ohm nominal load - it works the same way as in audio where you try to match the load impedance to the source impedance; the only quirks are that amplifiers aren't really designed to operate at higher impedances unless you put a feedline transformer in line. You could run an RF amp that's designed for a 50ohm load at 75ohms...but because there's a mismatch, power would be reflected back instead of being radiated. Get far enough from the source impedance and you have all of the power coming back. In order to go between impedances, you need stuff like matching networks to raise or drop the impedance by a whole number value (like 2:1, 4:1, 9:1...technically you could do the same for audio, but very few are around; the Zero Autotransformer comes to mind). There are also high impedance feedlines and antennas - 300 and 450 ohms are common values for "ladder line", which is nothing but parallel conductors seperated a certain distance by a dielectric. The high impedance doesn't make it a bad or lossy feedline, but you need something that can convert the 450ohm load to the 50ohm impedance the transmitter is looking for. Huge variable capacitors and inductors are used for that. [/offtopic] [/QUOTE]

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