[Antennaware] Grid Dipping coax

Terry Conboy n6ry at arrl.net
Fri Oct 19 20:01:27 EDT 2007

At 09:31 AM 2007-10-15, Paul kg7hf at comcast.net wrote:
>I am wondering if anyone knows how to use a grid dip meter to 
>measure coax electrical length.   Must I use a shorted half wave 
>lenght and trim, or can I use an open quarter wave and trim?  How 
>can I couple it to the grid dip meter?  I obviously set the meter at 
>the desired frequency, but do I use the meters coil assembly or plug 
>the coax directly into the meter?

Either the shorted half-wave or open quarter-wave is OK.  Normal 
practice is to use a small coil connected to the coax between center 
conductor and shield, with one or two turns that is just big enough 
to go over the GDO coil for the frequency of interest.  Keep the lead 
length on the coil to a minimum.  You can then sweep the GDO 
frequency and look for a dip near the desired frequency.  Once you 
find the dip, slightly separate the GDO coil from the coil on the 
coax for best accuracy.  Use your receiver to find out the actual GDO 
frequency, since the GDO calibration is usually fairly coarse.

73, Terry N6RY

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