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[CQ-Contest] Air wound coax balun

Subject: [CQ-Contest] Air wound coax balun
From: mspalluzzi@iol.it (Marco Spalluzzi)
Date: Wed Jan 31 20:10:48 2001

Hi guys, I read an interesting message about measurements on coax
air-wound balun; I also tried to contact the author, WA2SRQ, now K2SQ if
I remember well, but my 2 e-mails gets back an error message both.
The message I'm talking about is available at:


I've got a few questions for him, but since he's unavailable, I post them
to the list.

1) Isn't 4 inch diameter dangerous for rg213 when running full legal US 
power on 28?
     I found on some data sheet that the minimum bending radius is 100mm, so
     minimum diameter should be 200mm, equals to approx 8 inches, which is
     double of the test run by WA2SRQ.

2)  In the message it's wrote that balun have to be inductive, to suppress any
      unwanted current flowing on the outside of the coax shield, then that
      6 turns on a 4 inches pipe are enough from 14 to 35 MHz: on 28 the phase
      is not inductive, but capacitive: is the balun still effective at that
      frequency or do I have to use it only when the magnitude is approx 
500 ohm or
      higher and the phase is approaching +90 degrees?

3) If my antenna have an impedance around 100 Ohm (2 el. quad), do I have
     to try for different diameters/turns numbers to achieve the high enough
     reactance? Or simply compare the reactance to 50 Ohm, the coax

4) Between 23 and 24 MHz phase crosses 0: so on that frequency it's an L-C
     resonant circuit. What happens if I use it exactly on that frequency?
     Is there thesame choking effect? So, why look to the phase of the 

5) Talking about power loss, it's wrote that the test air-wound baluns, at
     their resonant frequency, are all about 15KOhm: at 14, 21 or 28 MHz they
     are much less of course: how can I calculate the loss power?

Any answer will be appreciated, here in the list or private.
My home e-mail is ik2xsl@amsat.org
Many thanks in advance, 73 de Marco - IK2XSL.

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