Topband: Stub measurement error

[George Cutsogeorge]

Here are some measured numbers.  The transmission measured frequency of this
RG-213 stub is 28.535 MHz.  The reflection measured frequency is 28.785 MHz.
The reflection measured frequency with the tee is 28.380 MHz.  The stub has
35.8 dB loss at the null frequency.  If the reflection measurement is used
to cut the stub, the attenuation at the desired frequency will be about 3 to
4 dB less.  That is not acceptable in my book.

 

For many years I have been cutting stubs with a spectrum analyzer and
tracking generator.  It was a surprise to me that the reflection measuring
method produces such poor results.  This is not a fault of the instrument.
It's a result of the way that stubs are used in practice as nulling devices.


 

.George, W2VJN