[TowerTalk] Force 12 C31XR Modeling

[Leeson]

On 2/22/23 11:46 AM, Jim Lux wrote:

 > I'd try an epsilon of 2.  Most plastics are around 3 (depending on
 > water content), but there's some air space too.
 >
 > Twisted pair with PVC or PTFE insulation has a Z0 of about 100-120
 > ohms -
 > You could measure it if you were ambitious.  It's a short piece, isn't
 > it? Way less than a wavelength? it might not make much difference.

If you're really curious about the Zo of a transmission line, you can 
measure it with almost any antenna impedance instrument: At one end, put 
a resistive load you expect will be a mismatch, say ZL = 50 ohms. 
Connect the other end to the SWR instrument, and measure the highest 
impedance you see over a range of frequencies high enough to include at 
least one quarter wavelength. There will be a peak impedance, which is 
Zo^2/ZL. The rest is up to your calculator.

Of course there will be potential inaccuracies from frequency variation 
of Zo, and from the parasitic reactance of, for example, any lead length 
at load or instrument. But you'll be plenty close enough. If the 
impedance at 1/4 wave is too high for your instrument, try a higher ZL.

"Experiment trumps theory"

Dave, W6NL/HC8L