[Antennas] TIPS, METHODS AND TECHNIQUES RELATING TO USE OF LADDER LINE

[Jim Shaw]

Thanks to everyone who responded to my request for tips on using ladder
lines.

I have compiled the responses and done some editing.  The result follows my
signature.  I hope others benefit from the many wonderful ideas and pointers
contained in it.  I was particularly amazed at the many different ways for
getting the ladder line into the shack.

73 de Jim WA6PXU
Jim@ShawResources.com


TIPS, METHODS AND TECHNIQUES RELATING TO USE OF LADDER LINE

Refer to any ARRL or E&E Handbook published prior to 1960, the older the
better.  The only  commercially produced true ladder line (dielectric being
95% air) I know of is from www.w7fg.com.

Another helpful resource is the articles by L. B. Cebik, W4RNL on the basic
67 and 44ft doublets:
http://www.cebik.com/aledz.html
http://www.cebik.com/radio.html
http://www.cebik.com/edzfeed.html


STAND OFF DISTANCE FROM EXTERNAL INFLUENCES
Different amounts of separation of the line from external influences (e.g.
metal downspouts,  guttering, metal window screens, etc.) were recommended,
ranging from twice the line spacing to 5  times the line spacing.

I use 450 ohm ladder line to the tower.  The line is fed up the tower
through 4" sections of  radiator hose on 1 ft+ plexi glass standoffs, around
the rotor in a large "U" inside heater hose,  and tied directly to the 3
element beam.  Works great (good tuner at the shack end). I've also  tried a
balun at the antenna and didn't notice any difference.
Another solution (a little easier) might be coax to the antenna, choke balun
at the antenna,  around the rotor with the coax, 4:1 balun (easy to make)
from the coax to the balanced 450 ohm  ladder line. This eliminates the "U".
I run 150W or less with this setup, good signal reports all  over the world.


LADDER LINE LENGTHS TO ACHIEVE LOW SWR
Cecil Moore, W5DXP explains how to use different transmission lines to tune
the antenna system on  his web page http://www.qsl.net/w5dxp/notuner.htm.
In my case, for 30 M, the antenna is a half  wave, so I added enough feed
line to bring the total feed line length to a half wavelength and the  feed
point resistance of the dipole is seen at the feed line feed point. I add
other feed line  lengths on 17 M and 12 M to give a low feed point
resistance.

I find feeding my 44 foot doublet antenna quite manageable. Although there
are no "magic" lengths  for center fed doublets and their feed lines, some
lengths work better than others. The antenna I  use was described in a QST
article from the early 80s and is reprinted in the "Wire Antenna  Classics
Volume 2" from the ARRL.
The author crudely modeled this antenna as a shorted one sixth wave length
transmission line (the  antenna) connected to an open one sixth transmission
line (the antenna). This gives a fairly low  primarily resistive feed point
at the end of the transmission line at unusual multiples of the one  sixth
wave frequency, 1,2,4,5,7,8, ... and so forth.


GETTING LADDER LINE INTO THE SHACK
Some folks run ladder line to the house then use a heavy duty balun (e.g.
MFJ 912) to convert to a  short piece of heavy duty coax (e.g. RG-213) in
order to get the feedline into the building.  Although coax is less than
desirable in a high SWR environment, the loss for a short run (10 feet  or
so) is not that big a deal.  One friend of mine does exactly this for his
loop antenna.  Works  OK but he does get some 'RF in the shack' problems on
some bands (his shack is on 2nd floor of  house). He was able to solve these
by using appropriate counterpoises.

I run ladder line to the outside of the shack and then use about 5 feet of
9913 coax from a high  voltage 4:1 step down balun to the tuner.  Coax is
only to get from the balun through the window  sill to the tuner. The 50 ohm
side of the tuner goes to the station master coax switch.  The key  is a
ROLLER INDUCTOR based 3 KW tuner [a 30 year old Murch UT 2000A]. I have
about 0.2 dB loss in  the tuner, coax and balun. That's about 45 watts loss
at 1KW input. Feedline losses at less than  10 MHz are negligible.

I use banana plugs on the outside for connecting the ladder line to the
coax. This allows me to  easily disconnect the antenna when electrical
storms are near, although high winds will often do  the disconnecting for
me.

I prefer the bead balun for convenience and since I run QRP to 100 watts
max, it is more than  adequate. For QRO, however, I would look at 1:1
current baluns using one or more toroids, with  appropriate windings to
handle the power, since beads can get quite hot when exposed to high  power.
All this is discussed in Walt Maxwell's classic article on baluns in QST
March 1983, page  36.

I use two pieces of coax to create a shielded balanced line. Both shields
get tied together and to  ground, center conductors go to the hot leads from
the ladderline.  Line impedance will be 2x that  of the coax. Although there
will be an impedance bump from this connection, and enhanced loss from  the
coax sections, for a short run this should not be a big problem.
NOTE: Lew McCoy suggests bonding and grounding the shields at both ends. The
Wireman in his  booklet suggests keeping them separate and not bonding nor
grounding them.  I bond them at both  ends but only ground them at the tuner
end.  I did not employ Lew's suggestion as I thought there  might be the
possibility of ground loop problems on some frequencies and I felt that
bonding on  each end provided a better overall shielding for running the
line near conductive surfaces.

Terminate the ladder line into two paralleled coaxes; take two equal lengths
of coax - any Zo will  do - and connect the shields together at each end; at
the line end, don't connect the shields to  anything - let them "float;"
connect the ladderline to the two center conductors of the coax; at  the
tuner end, connect the shields to the tuner chassis and the two center
conductors to the tuner  balanced output. The coaxes do not have to be kept
together so don't waste any time fastening them  together exactly parallel,
etc. except for convenience and appearance.  The coax sections, single  or
paralleled, may have quite high SWR on them, but due to their short lengths
the loss is  negligible. The problem is that if a voltage or current max
occurs within the coax run, it will  stress the dielectric (voltage)and/or
the center conductor (current). So I use RG-213 with solid  dielectric that
can handle very high voltage as compared to the foam dielectric lines such
as  RG-8X. Again, this is a QRO problem.  You may find that with certain
antennas and certain bands  that your tuner may have difficulty handling the
line impedance that it sees. In that event, just  add a few feet to the
coax(es) on those bands.  There is some added loss in the coax but that is
the tradeoff for the advantages of NOT bringing ladderline directly into the
shack.

If u have the ladder in the shack u might have rf problems there.  I moved
mine outside via a  balun so I feed it with coax from the amps and the
ladder is away from the radios.  It should not  be near anything - will
detune the resonance point or cause unbalance.  Ladder is a major pain to
keep straight and not under stress in wind etc.  U need to really think
about how u want to attach  it to your eves so it doesn't pull your eves off
in a hi wind...I use a big drip loop to absorb  the stress created by a
moving ant.  Long runs of ladder are to be discouraged if u can.  Twist
every 10-15 feet to help keep it stable.  Also I make my own ladder so it
can be overkill on  strength.  Having one break at the end (or center) of a
big wire is a pain.  Hope this helps a  bit.

I terminate the ladder line in a 1:1 W2DU bead balun just outside the shack
wall - I hang the  balun from the soffet of the roof - and run RG-213 coax
(RG-213 has solid dielectric that can  handle very high voltage as compared
to the foam dielectric lines such as RG-8X) from the balun to  the tuner
coax output.  You may find that with certain antennas and certain bands that
your tuner  may have difficulty handling the line impedance that it sees. In
that event, just add a few feet  to the coax(es) on those bands.  There is
some added loss in the coax but that is the tradeoff for  the advantages of
NOT bringing ladder line directly into the shack.

I bring my "450 ohm" line through the shack window, by replacing a glass
pane with a plastic one,  then drilled holes and mounted two ceramic
pass-through type insulators to make the connection to  the outside. They
have a long brass screw and nuts for making the connections on each side of
the  pane. Works fine.   Oh yes, the antenna is a FW 160 m loop in the
vertical plane hanging from  redwood tress about 110 ft up and I use an HB
"link coupled" tuner to use the loop on 160/80/40  with pretty decent
results.

For �feed thru' (e.g. into the shack): Bring it thru the wall (if
composition material) to  interior wall, using binding posts or banana jacks
for quick disconnect for lightning isolation.   If squeemish about going
thru wall, replace a windowpane with plexiglas panel fitted with banana
jacks.  Bring open wire feeders direct to balanced tuner output.  Coax from
50-ohm tuner input to  rig. Balun not needed with the proper coupler.  If
not, use a coil choke balun on low Z input  side.

I use a short run (three feet in my case) of a parallel run of coax. On the
outside of the shack I  connect the ladder line to the center conductors of
the coax and the two outer shields are bonded  together but not grounded. On
the inside I connect the two center conductors to a balanced tuner.  The
shields are again bonded together however they are grounded at the tuner.
Although coax has a  higher loss than the ladder line anything less than six
to eight feet in length would not be  noticeable to any receiving station.
The method also provides the additional advantage of being  able to place
the transmission line (the coax portion) in close proximity to conductive
surfaces.

I am putting up a new 80-meter tilted triangular full-wave loop antenna that
I plan to feed with  ladder line transitioning to parallel-coax balanced
lines (coming into the shack along with  several other single coaxes going
to other tuners) and running to a Johnson KW Matchbox balanced  output.

I have three ladder line-fed antennas using the balun transition approach
and they work and tune  very well using an MFJ 989C T-section tuner. I
strongly recommend the use of the 1:1 balun over  the 4:1 design since you
are less likely to encounter extremes of line input Z at the tuner. The
current balun is clearly the one to use since all you are trying to
accomplish is to divert the  current from the side of the ladderline
connected to the coax braid to the inner braid only and to  block it from
the outer braid. In this application, the balun is not intended to promote
current  balance in the feedline, although it may have some influence on
that.

I bring my ladderline into the "shack" via short lengths of 50-ohm coax
(about 12 feet) to the  tuner. I ground the shields of these at the tuner
and leave them free at the outside end, thus  they act as Faraday shields.
In using a tuner, we can ignore any impedance mismatch caused by such  a
change in the line. I use an old Heathkit tuner, rated at one KW. I don't
run an amp.

I have a 44 foot doublet fed at the center with ladder line on 10 M through
40 M here. The length  of the ladder line is about 20 ft long. From there I
use a coil of coax for a balun and a short  length of coax to the auto tuner
of my TS-850. Also, I have some different lengths of coax I can  insert to
help the match on some bands.



LONG RUNS of LADDER LINE
The feed line comes away from the antenna at right angles for about 50 feet.
I have a 50# nylon  fishing line that is used to connect the feedline about
2 feet below and 2 feet away from the eves  and aluminum rain gutters. The
distance to the rain gutters is the same for both sides of the  feedline.
The feedline drops about 6 feet to a couple of tv twin lead insulators that
keep the  feedline about 4 inches off the house. The feed then runs
horizontally, equally spaced from the  house using 6 inch tv twin lead
insulators, to a high power [close to 5KW] balun located just  outside the
window of the shack.

For long runs of ladder line, I would not get the 450 ohm "windowed" ladder
line.  It is more of a  glorified twin lead using copper clad steel for the
conductors.   For lowest loss make your own  from 1/2" polyethylene
irrigation tubing spacers or get commercially from www.w7fg.com.  Use black
polyethylene or plexiglas stand-offs, or nylon weed eater line thru spacers
to tie off or hold  taut.


UNDERGROUND RUNS OF LADDER LINE
Although I have not tried underground ladder line runs, I would not run
anything with the ladder  line.  I would use a separate 4" PVC and do the
best I could to keep water from getting into the  conduit.   Perhaps dry air
under pressure.

Ladder line is definitely not suited for use in conduit, buried or
otherwise. There is an RF field  surrounding such a line that needs
protection from:
1) Metal objects (running parallel to it for any appreciable length),
because such will alter the  impedance and (probably) lower the efficiency
by introducing loss near current loops.
2) Poor dielectrics (running parallel) because they will introduce losses
near voltage loops.