[Antennas] Ladder line use with beams

[Don Havlicek]

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