[TowerTalk] 120 Film spools as spreaders

[K7GCO@aol.com]

In a message dated 05.05.00 16:09:36 Pacific Daylight Time, k3hx@juno.com 
writes:<< 
 They survived 7 years without trouble outside.  I was WA8MLV when I wrote 
the article in 1986.   73, Tim  K3HX
  >>
     Sounds like they will last.  Some 120 film spools are metal however.  
Based on 2 3/8" spacing of #12 wire, the Zo is 490 ohms and is a good working 
range.  6" spacing results in a 600 ohm Zo line.  I have a commercial balun 
of 50-600 ohms made for rhombics so I'll be using the 600 ohm line.  

I examined the smooth plastic used in coat hangers someone suggested.  It's 
flexible and strong.  It's a bit small in diameter which limits its ability 
to hold the wire under stress with a hole in the end but I will give it a try 
if I can get a bunch of them.  Small diameter is ideal from the standpont of 
low wind resistance and low surface area for dust and smoke to stick to.  In 
the days of a lot of coal burning, it literally shorted out insulators, 
affected receiving and required cleaning.  Bare copper wire even corroded.

There is some rule of thumb of open wire spacing from metal objects like 
runing up the tower of being equal to its spacing.  There is a simple test 
that will show that's not enough they never did.  I use 1' minimum.  When I 
GD open wire line with both ends shorted, I suspend it over the ground no 
less than 3'.  If you let go lower the resonant frequency starts to change.  
I cut it to my magic multiple legth of 135.4' initially for 6" spacers every 
3'.  Shorting the far end is ideal as it can be attached to a rope without 
affecting the resonant frquency.  If 1/4 wave long, the Z at the open end is 
high and sensitive to what supports it.  It can be supported by a spacing 
insulator if strong enough.  More insulators will requires a few % of 
shortening as will insulated wire.  Enameld is a minimum insulation.  After 
installation and still shorted on both ends I GD it again and have to shorten 
it agaIn.  I run it through wood walls with insulated filber sleeves in some 
cases.   It likes total isolation but it all washes out in the Z at the end 
of the feedline.  If it can be matched by the tuner no matter what it is, 
total transfer of power occurs there and to the antenna minus the losses in 
the feedline.  The spacing can actually vary along the way unlike like 
coax--no big deal other can for looks.  

One little known benefit of 1/2 wave resonant lengths of open wire line is 
this.  Assume the desired resonant length of the antenna is 3.562 MHz also 
for example purposes.  With the feedline shorted, GD dip it there.  If it 
doesn't GD there, trim antenna accordingly.  It just assures the tuner sees a 
purely resistive load at the end off the feddline--for ease of matching.  If 
it GD's at 3.8 MHZ, it doesn't necesary mean the antenna is resonant there.  
The feedline is no longer a 1/2 wave there--it's 8.5' too long and part of 
the resonant length.  No big deal as the Z at the end of the feedline is 
purely resistive which is the major consideration.

A little known trick is this I've used for 60 years that has never been 
written up--I will when I get time.  Feed a 160/80/40 individual or parallel 
dipoles with a 1/2 wave multiple feedline and it repeats the antenna Z in the 
shack which can be close to 50 by height selection and or inverted vee 
bending.  Even though this is a balanced feedline you can stick one lead 
right in the coax switch and the other to ground and it works great.  
Resonant each antenna low in the band, add a series BC variable Xc to ground 
in one wire and tune it right up the band.  I'll resonate at 3.56 aprox and 
cover the whole band with a simple BC variable like no other system there is. 
 If a 1:1 balun is used there, it would be better to have a variable BC Xc in 
each leg ganged together.  Without the Xc, lengths of open wire line have to 
be removed for resonance higher in the band.  I've had switches that do that 
for this and othe reasons.  I've switched out or in  a 1/4 WL of open wire 
line just to obtain the Hi or Lo Z I wanted for ease of matching or some 
other reason like direct feed into a Lo-Z link coupled tank circuit with a 
series Xc of years ago--or even a coax switch.  There are all kinds of simple 
open wire tricks that assure maximum transfer of energy to and from the 
antenna unused today.  

With all due respect to Art Collins and his use of Pie/L networks designed 
for coax, he set ham radio behind and cost hams a lot of money for short 
lived coax for less RF to and from the antenna.  Coax convenience is very 
costly and antennas with balanced feedpoints are still made which are still 
misfed causing feedline radiaton filling up Reflectors with all kinds of 
Mickey Mouse Baluns that don't work, affect the resonant frequency of the 
antenna and cause TVI.  Gimme a break.  Designsers still haven't got it 
right.   

I had 4 6M antennas using different feed systems in SD 2 years ago and each 
had TVI with 100W.  When I used balanced 100 ohm coax or open wire line to 
feed a 2 element Killer Quad at 25' into a 275W MatchBox--NO TVI AND A GREAT 
SIGNAL. I could hold the frequency 50.125 MHz for 3 hour stretches.  It 
worked so well I delayed the building of a linear.  Unbalanced coax without a 
Bazooka (Collins did recommend that), Mickey Mouse Baluns that don't work, 
balanced feedpoint beams and the untuned mixers in so called modern radios 
have set ham radio back further than any other so called development.  We 
need more advanced design and thinking--from the last Century.  Stay tuned.  
I'll try and drag you back there for better ways to transfer RF.  Open wire 
line is going to make a dramatic come back. k7gco  

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