inpedance issues - RF Cafe Forums

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Matt
 Post subject: inpedance issues
Posted: Wed Nov 30, 2005 10:18 pm 
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
 
  
 
Kirt Blattenberger
 Post subject:
Posted: Fri Dec 23, 2005 10:13 am 
 
Site Admin
User avatar

Joined: Sun Aug 03, 2003 2:02 pm
Posts: 308
Location: Erie, PA
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
http://www.rfcafe.com/references/electr ... 0-ohms.htm

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Posted  11/12/2012