[TowerTalk] 2 Meter Phasing Lines

Ray, W4BYG w4byg at att.net
Sat Apr 12 16:03:00 EDT 2014

I believe that is right.  

Further clarification: one would use any matched lengths of 50 ohm cables,
when using a 50 ohm in/out power divider.  1/4 wave 75 ohm cables (or odd
multiples thereof), would only be used when you are fabricating a Williams
type divider or at a minimum, using a simple "T" connector for a
non-isolated combiner. 

Ray, W4BYG

"The Republic can survive a fool for a president...  It is less likely to
survive a multitude of fools, such as those who made him their president."

-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of
mikflathead at aol.com
Sent: Saturday, April 12, 2014 3:53 PM
To: bjtatum1 at att.net; TowerTalk at contesting.com
Subject: Re: [TowerTalk] 2 Meter Phasing Lines

 By using the power divider you can use any length of cable as long as the 2
are the same. Not sure what you are asking. Mike



-----Original Message-----
From: Byron Tatum <bjtatum1 at att.net>
To: TowerTalk <TowerTalk at contesting.com>
Sent: Sat, Apr 12, 2014 3:42 pm
Subject: [TowerTalk] 2 Meter Phasing Lines

   I thought I would post this for any comments that may help me to
understand what may be going on. What started it all is that years ago I
stored away some unused Plastoid RG-13A/U 75 ohm coax from a surplus source.
The cable is old, but it appears very nice physically with a clear
dielectric and nice shiny copper. I was thinking this cable would be worth
saving because of the double shield. My intentions are to use it for
Q-sections for HF antennas and possibly phasing lines for VHF antennas. 
   I measured off an exact 25' of the RG-13A/U and installed a PL-259
I used the MFJ-259B in 2 different methods to measure the velocity factor of
the cable. I obtained a 0.67 and a 0.66 figure, instilling a little
re-assurance in me in the analyzer.
  So, I thought I would measure some factory-built M2 phasing equipment for
2 meters to see how the MFJ-259B stacked up, as I am wanting to use the
to measure the Q-sections and phasing lines of future projects.     
    Several years back I had a pair of M2 2M18XXX antennas stacked about 14
feet apart. I bought the power divider and phasing lines from M2. The system
worked fantastic but was up only about 1 year, as a spring storm bent the
booms on both antennas, so I took down the array and stored the phasing
lines and power divider. The power divider is the M2 2M2PTPD and the phasing
lines are Times Microwave LMR-400 with the silver plated crimp-on N-Male
connectors. There was no damage to the phasing lines and they were all
sealed up real good.
  I thought I would check out the phasing lines and power divider with my
MFJ-259B analyzer. Firstly, I connected each phasing line individually, with
a lab-grade 50 ohm load at far end, and measured the SWR, which showed 1.0
for each phasing line, at every freq checked. I removed the terminations and
measured the cable loss, which was an identical 0.3 dB for each phasing
  Next, I connected each phasing line individually, with a short at far end,
and measured the freq of zero reactance ("X" on analyzer) nearest 2 meters,
each one came out to be much higher, at 162.2 Mhz. However, this reading was
very broad.
  I used the MFJ-259B to measure the velocity factor of one phasing line and
it came out to be 0.87 (Times Microwave specs are 0.85). This aroused some
curiosity in me, as I measured each phasing line to be 287-1/4". Using the
published velocity factor of 0.85 for the LMR-400 cable a length of 287-1/4"

would not be a half wave multiple at 144.2 Mhz. However, using the measured
VF of 0.87, the 287-1/4" length is 8.05 half-waves.
  Another thing I did was to connect identical lab-grade 50 ohm terminations
to the far end of each phasing line, and connect each phasing line to the
power divider. Then, I connected the power divider to the MFJ-259B and
measured SWR. 
Again, this reading was very broad, and my best reading was higher, up at
161.2 Mhz. However, the SWR was reading good(1.1-1.2) at 144.2 Mhz.
  The last thing I did was to remove the phasing lines from the power
divider and leave the 2 ports un-terminated, then measure the freq of lowest
reactance ("R"), this was above 2 meters at 158 Mhz.
   So, am I doing something wrong or is the analyzer unreliable? This
analyzer is several years old but has seen very little use. Is there any
"standard" that I can check it against, or a test I can do?
              Thanks, Byron WA5THJ

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