[Antennas] Ladder line use with beams

[Joe Giacobello, K2XX]

I had thought of feeding a multi-band quad with ladder line, but have never
actually done it.  My objective was to design the quad for maximum forward
gain on each band irrespective of feed impedance (i.e., resistance, assuming
it's at resonance) and then use low loss open wire line and a tuner in the
shack to feed it.  If the ladder line does not radiate, I don't see why
there should be any loss of gain or F/B.  If the ladder line sees a balanced
load and it's properly positioned so as not to pick up any radiation from
the antenna (That's the hard part.), then it should not radiate to disrupt
the pattern.

BTW, Kees:  We worked on CW many years ago and you sent me a hand-sketched
diagram of your set-up.  I have it somewhere in the shack to this day.

73, Joe


Don Havlicek wrote:

> Comments inserted below:  [I'm sure I won't be the only one to reply!]
>
> Sandy and Kees Talen wrote:
> >
> > I'd like to ask some opinions on this.....
> >
> > I have a 250ft run to the HF beam and typically drive at
> > 150W or less. Since low loss (and low cost) is desired,
> > I settled on a long run of 450 ohm ladder line through the
> > trees, smooth long radius bends (most through radiator
> > hose where it touches something, etc. An antenna tuner
> > is used at the Tx/Rx end.
>
> Using open-wire line to feed a remote antenna is a good idea IF you use
> the open-wire for the long, LOW stretch to the tower, then, using a
> matching network [balun?], running coax to the yagi.
>
> > At the tower, it runs through pieces of PVC spaced 12" out
> > from the tower with plastic stock and  20 ft apart (55ft tower).
> > At the top it runs through a "loop" of smaller heater hose to
> > get around the rotor and is tied directly to the beam. Seems
> > to work fine. I was going to use a 9:1 or at least a 4:1 balun
> > at the beam end (or at least so I could get around the rotor
> > with coax) but figured that the mismatch wouldn't affect
> > anything because of the low IR loss in the ladder line and
> > I could always match to the Tx with the tuner.....so I tied it
> > directly to the beam. There may be some substantial
> > voltages developed at the beam end (and ?) because of the
> > mismatch.  What else do I need to look for ?
>
> There are usually TWO major reason for using a rotary beam antenna:
> 1.  Gain
> 2.  Rejection of signals in directions other than the desired one.
> With your arrangement, the open-wire feedline is PART OF THE ANTENNA,
> and :
> 1.  MAY Reduce GAIN
> 2.  WILL allow undesired signal to reach the shack.
>
> > Any ladder line is affected by moisture, I've heard that open
> > (4"+ spacing) is not. Any verification of this ? What is
> > a good cheap spacer ? ...light, cheap, easy to rework, stable,
> > easy to attach, strong, low wind resistance. 250 old BIC pens ?
> > ...just kidding. I'm not boiling wood sticks in hot parafin with
> > PVC available.
>
> Putting the open-wire feedline inside PVC will INCREASE losses, due to
> the nature of the PVC changing the impedance [and PVC is terrible lossy
> anyway!].  Your best bet is to simply run the open-wire to the base of
> the antenna above 'head-level', and connect it to a run of coax going up
> to the antenna.
> As for 'low-loss', homemade open-wire  .. the worst spacers are probably
> those wooden sticks, boiled in parafin .. the best are probably ceramic
> [terribly fragile and costly], but you can manufacture some excellent
> spacers from small diameter teflon or delrin tubing.  Another choice is
> those 'clear-plastic' tubes that are used to ship/store high-quality
> bits for boring machines.  They are about 5" long and .5" in diameter.
> If there is a machine shop near you, it can't hurt to find out if they
> throw those plastic tubes away or save them in a 'barrel' .. [that's
> where I found mine!].  BTW, those tubes  also have end-caps that work
> super on .5" element tips!
>
> Good luck!
> Don
> N8DE
>
> >
> > Comments ?
> >
> > 73s  Kees K5BCQ
> - - -
>
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