To cut your 72 degree line using an analyzer, convert it to a freq
where it's a 1/4 wave. For 7 mhz, a 72 deg line would be a 1/4 wave
or 90 degree line at 8.75 mhz. easier to measure this way. Frank
raises some good points, sounds like you are going to try the
Christman method. I'm in the middle of a similar project, but like
you, am kinda stuck here. While it sounds simple, it obviously
isn't.....keep me posted how you make out....
73, Jamie WW3S
On Sun 06/ 1/08 7:32 PM , sent:
Hi Tom,
Your question has been discussed many times on TowerTalk.
Coaxial lines can NOT simply cut coaxial lines to produce 72 and 80
degree phase delays in an array of phased verticals, because the
phased array places significant VSWR on the phasing lines. The phase
shift in any coaxial line is a factor of T W O properties:
- physical length, and
- VSWR
If you have an dual trace oscilloscope, its very easy to observe
this property of a mispmatched transmission line, by varying the
termination impedance of the line and observing the change in phase
shift.
A coaxial line will produce a delay equal to its electrical length
only if its VSWR is 1:1, except for the special case where its
electrical line length is 90 degrees (1/4 wavelength) or any
multiple.
73
Frank
W3LPL
---- Original message ----
>Date: Sun, 01 Jun 2008 16:04:44 -0700
>From: "Tom Osborne"
>Subject: [TowerTalk] Phasing lines
>To: "Towertalk"
>
>Hi All
>
>If 90 degrees is 360/4 (1/4 wave) then is 72 degrees 360/5 (1/5
wave)?
>
>Would that make a 72 degree phasing line 23.4 feet (133/5 * .88)?
>
>Then an 80 degree phasing line would be 26.1 feet (133/4.5 * .88)?
>
>I am actually trying to figure 80 and 71 degrees lines for 40
meters using
>RG8X.
>
>My high school math is buried somewhere in the back of my brain.
>
>If this is true, how can I find which frequencies these would be a
1/4 wave
>at so I could use the analyzer to cut them to length?
>
>I want to make phased verticals with an 80 degree feedlines with a
71 degree
>phasing line. 73
>Tom W7WHY
>
>
>
>
>
>
>
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