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inpedance issues - RF Cafe Forums
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Matt
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Post subject: inpedance issues
Posted: Wed Nov 30, 2005 10:18 pm
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Hi there, I am building an antenna out of
copper pipe for 137 Mhz, the original design calls
for 1/2 inch pipe and provides a 30 ohm impedance
when complete, however I would like to use 1/4 in
pipe as it is easier to bend, but it will only have
an impedance calue of 21 ohms. What kind of effects
can I expect? Thanks, Matt
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Kirt Blattenberger
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Post subject:
Posted: Fri Dec 23, 2005 10:13 am
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Site Admin |
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Joined: Sun Aug 03, 2003
2:02 pm Posts: 308 Location: Erie, PA
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Greetings Matt: I am not an antenna expert,
but I would guess that so long as you used an appropriate
impedance transformer to get to your system impedance,
then the efficiency should still be pretty good.
The 30 ohm impedance design was probably done to
exploit the maximum power handling characteristic
of such antennas (see History of 50 Ohms). As long
as your system does not really need the 30 ohm impedance,
and you can build or buy a low-loss transformer,
then you should be OK with the 21 ohm antenna.
History of 50 Ohms
https://www.rfcafe.com/references/electr ... 0-ohms.htm
_________________ - Kirt Blattenberger
RF Cafe Progenitor & Webmaster
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Posted 11/12/2012
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