[TowerTalk] Matched "Bury Flex" cables

[Michael Tope]

----- Original Message ----- 
From: "Jim Lux" <jimlux at earthlink.net>

> It's a bit tricky.. If the line matches the source (or the load), so
> there's only a mismatch at one end, then the phase error will be equal to
> the length error, because the matched (at one end) line just moves the
> reference plane.  So, what we're really talking about is a line which is
> mismatched at both ends.

In terms of the phase of the current delivered to the load (what we care
about when driving antennas), the  current phase error won't necessarily
be equal to the length error even if the source is matched. Here are
some simulation numbers that illustrate this point:

For Zload = 50 Ohms and Zo = 50 ohms

Load Current Phase = -40 deg for L = 40 deg
Load Current Phase = -45 deg for L = 45 deg
Load Current Phase = -50 deg for L = 50 deg

Load Current Phase = -85 deg for L = 85 deg
Load Current Phase = -90 deg for L = 90 deg
Load Current Phase = -95 deg for L = 95 deg

For Zload = 50 - j50 Ohms and Zo = 50 ohms

Load Current Phase = +9.133 deg for L = 40 deg
Load Current Phase = -0.01 deg for L = 45 deg
Load Current Phase = -10.86 deg for L = 50 deg

Load Current Phase = -84.52 deg for L = 85 deg
Load Current Phase = -89.99 deg for L = 90 deg
Load Current Phase = -94.59 deg for L = 95 deg

For Zload = 50 + j50 Ohms and Zo = 50 ohms

Load Current Phase = -61.47 deg for L = 40 deg
Load Current Phase = -63.44 deg for L = 45 deg
Load Current Phase = -65.48 deg for L = 50 deg

Load Current Phase = -85.41 deg for L = 85 deg
Load Current Phase = -90.01 deg for L = 90 deg
Load Current Phase = -95.48 deg for L = 95 deg

In all cases L is the electrical length of the phasing
line. You can see that when the phasing line is close
to 90 degrees long, the phase of the load current
tracks the electrical length of the phasing line closely.
At 1/8 lambda (e.g. 45 degrees), the phase of the load
current and the change in phase of the load current for
a given change in phasing line electrical length both
become very dependent on the load impedance.

Note that in all of the above cases, the source impedance
and the delay line impedance were matched (e.g. Zs = Zo
= 50 ohms).

73 de Mike, W4EF......................................................