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inpedance issues - RF Cafe Forums

RF Cafe Forums closed its virtual doors in 2010 mainly due to other social media platforms dominating public commenting venues. RF Cafe Forums began sometime around August of 2003 and was quite well-attended for many years. By 2010, Facebook and Twitter were overwhelmingly dominating online personal interaction, and RF Cafe Forums activity dropped off precipitously. Regardless, there are still lots of great posts in the archive that ware worth looking at. Below are the old forum threads, including responses to the original posts.

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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

https://www.rfcafe.com/references/electr ... 0-ohms.htm

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