Bazooka balun measurement

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Ghost Tweaker

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Hi everyone,

i recently designed a dipole antenna and a bazooka balun for it. Does someone know how I can measure my balun, verify that it is working properly?

Thanks in advance

Ghost Tweaker
 

You can consider your balun as a 3-port network having 1 coaxial unbalanced port (feeding of the antenna) and 2 coaxial ports that are balanced with each other.

This means that these two balanced ports must be 180 degrees out-of-phase.

You can measure this 3-port coaxial network/balun in a network analyzer and the equivalent device is a splitter with 180deg out-of-phase outputs.

Hope this helps.
mogwai.
 

Hi all, if it is a three-port network as you described it, you could measure it
with an oscilloscope.
Just feed the unbalanced port with your HF-generator and connect the two balanced to oscilloscope input A and B respectively and measure the phase difference. Correct ?

Speaking of dipole antennas, does anybody know why some people say that the coax radiates if the dipole isn't fed symmetrically ?

regards,
StoppTidigare
 

coax radiation

On the coax radiating. The signal on the coax has a common mode plus a differential mode with respect to the earth. This puts a common mode signal on the dipole which is connected to earth by the coax outer conductor. Current flows on this conductor producing radiation.

There are two ways to stop this. One is to use a genuine transformer where the coax connects to the antenna. The other is to have a common mode choke at the juncture. This choke is in the form of ferrite enclosing the coax.

There is no reason to go through extra expenses in the amateur service to prevent this radiation as such stations communicate with other stations on all azimuths and ranges some of which are improved by this radiation.
 

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