[ARC5] Speaking of 300 Ohm Twin Lead...

[Bruce Long via ARC5]

Impedance matching in my judgement, by changing the characteristic impedance of a section of the twin lead transmission line.

      From: Robert Eleazer <releazer at earthlink.net>
 To: arc5 at mailman.qth.net 
 Sent: Monday, November 10, 2014 9:22 AM
 Subject: [ARC5] Speaking of 300 Ohm Twin Lead...
   
I have wondered for a long time about a practice we employed early in the last century when TV sets were connected to actual antennas externally mounted atop dwellings.  I realize that for some people this news may fall into the category of Bigfoot and UFOs, but it did actually occur.  Some of you may even recall that the Heath Company included instructions for using 300 ohm twin lead and a TV antenna with its HW-30 Twoer transceiver.

Anyway, we used to take aluminum foil and wrap it around the twin lead near the TV set and slide it up and down until the picture was improved.  And it worked, too.  What did this do?  Did it shield the RF input from interference near the set?  Was it some form of impedance matching? Or was it more analogous to the function of an antenna trimmer cap on an HF receiver?

Thanks ... and Happy Veterans Day!  And that means all you surplus radios out there, too.

Wayne
WB5WSV      

  
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