On 10/28/2014 8:05 PM, Jim Brown wrote:
On 10/28/2014 2:39 PM, Jim Lux wrote:
For TDR (or looking for integer half wavelengths as you sweep the
frequency on an analyzer) you have to assume a particular propagation
factor,
Not only that, there are often small variations in a single length.
There are likely small variations in 4 lengths that long cut from a
single spool. So they may be different electrical lengths.
With a good TDR you can measure the characteristics and find the
electrical lengths at a given frequency.
73
Roger (K8RI)
Mike,
Measuring the length of a long piece of transmission line is tricky
for several reasons, most important because Vf (the velocity factor)
varies a bit with frequency. Study k9yc.com/Coax-Stubs.pdf
An easy way to get close to the actual length is to put a connector on
one end, leave the other end open, and measure the impedance with an
antenna analyzer. At every frequency where it's some odd multiple of
quarter waves long, it will look like a short. So sweep it with
whatever analyzer you own, write down those frequencies, and do the
arithmetic.
73, Jim K9YC
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73
Roger (K8RI)
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