Fw: Re: Fw: Fw: Re: [Antennas] 450 Ohm Ladder Line

2002年12月15日 18:41:07 -0600

Ran into a few problems using a scope and minimizing the loading
effects of it and matching small changes in transmission line 
impedances (used "average" 420 ohms for all matching), so I'm 
giving relative power loss measurements which should be more 
accurate. I would have liked to have made measurements with a 
Network Analyzer which N7WS used for his article, but I don't 
have one.
Test to be done at 15Mhz, 30Mhz, and 50Mhz on 50ft of Wireman 
type 551 ladder line which consists of 2 #18AWG solid wires 
separated by 0.80". If this was open line, the impedance would be 
very close to 450 ohms. Since this has the polyethylene dielectric, 
the impedance will be less, as pointed out by N7WS.
Original 551 ladder line DRY capacitance 2.96 pf/ft
 WET capacitance 10.32 pf/ft
 DRY/WET 15Mhz -3.0dB/100ft
 DRY/WET 30Mhz -3.8dB/100ft
 DRY/WET 50Mhz -7.6dB/100ft 

551 ladder line modified per #1 below
 DRY capacitance 2.92 pf/ft
 WET capacitance 7.10 pf/ft
 --no power measurements-- 
551 ladder line modified per #2 below
 DRY capacitance 2.86 pf/ft
 WET capacitance 5.20 pf/ft
 DRY/WET 15Mhz -2.4dB/100ft
 DRY/WET 30Mhz -3.4dB/100ft
 DRY/WET 50Mhz -5.0dB/100ft

551 ladder line modified per #3 below
 DRY capacitance 2.82 pf/ft
 WET capacitance 3.66 pf/ft
 DRY/WET 15Mhz -2.3dB/100ft
 DRY/WET 30Mhz -3.0dB/100ft
 DRY/WET 50Mhz -3.6dB/100ft
I thought there was a method to the web sizes which vary in size.
The windows are cut with a 1-1/4" punch so the window size is 
consistent, but apparently wire feed vs punch strokes varies
sometimes.
Modified #1
Add 7/16" holes to the webs. The 7/16" holes were made with 
a gasket punch in the drill press (running) ....real easy and fast. 
Cut the web down to 1/8" between holes. The number of holes 
will vary from 2 to 4 since the webs are different sizes. No 
observable loss of required mechanical rigidity.
Modified #2
Add the 7/16" holes to the webs as per #1 and remove every 
other web, which results in webs at 6.5" (on average) intervals. 
Some problems with twisting tendencies, some trouble to run.
Wire spacing varies more than on #1.
Modified #3
Add two 7/16" holes, spaced 1/8" apart to the center of each web
and remove the rest of the material, tangential to the hole, with 
a cutter. The result is a 1/8" curved web in the center and an 
"oval" type window. Webs are still on 3" centers and mechanical 
rigidity seems fine. Since it's a curve, there is less tendency to
tear. Easier to use than #2 but more work.
The lines, as a result of the above, are also less wind sensitive.
73 Kees K5BCQ