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inpedance issues - RF Cafe Forums

Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views. It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if you would like to post something on RF Cafe's Facebook page, please do.

Below are all of the forum threads, including all the responses to the original posts.


 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


 
  
 
 Post subject:
Posted: Fri Dec 23, 2005 10:13 am 
 
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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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