[TowerTalk] Coax Vs Open Wire Line

K7GCO@aol.com K7GCO@aol.com
Wed, 13 Sep 2000 19:48:48 EDT

 In a message dated 9/11/00 7:14:36 AM Pacific Daylight Time, 
alsopb@gloryroad.net writes:<<     
    K7GCO@aol.com wrote:
    > In a message dated 9/10/00 7:23:36 PM Pacific Daylight Time,
    > alsopb@gloryroad.net writes:<<
    > Finally an admission that coax has at least some uses.  We're slowly
    >  converting you.  Can I bury open wire line?
    > *********No but unless you bury coax with a special jacket the ground
    > gremlins will get it and your investment is wasted.  
    So?  They make this stuff.  I wouldn't leave bare wood outside 
unprotected either.  Common sense
    So this is at least two uses for coax that you agree to.  I think if
    you remove your "open wire line" blinders you will find many more.
    How about rotor loops?  As you know rotary slip ring type of
    connectors are very failure prone and preserving any kind of constant
    impedance is difficult.
    73 de Brian/K3KO
  Brian:  Your posts make progressively less sense.  I gave some applications 
where I use coax in an advanced manner you don't even use.  I have many more 
but I kept it short.  I've purchased several thousand feet (lots of bucks) of 
expensive coax and had to throw a lot of it way due to excessive loss, 
cracking and abuse.  I've spent hours testing it and recording the results 
for further reference and have written articles on it.  When you keep loss 
data you will get your coax weak eyes opened.  Open wire line doesn't change 
in loss with insulated wire if the insulators are kept clean.  Even then you 
would be hard pressed to measure the difference.  I use 6" Teflon and 
porcelain spacers that are over 50 years old.  I've shown close ups of the 
cross sections of the various coaxes on and on in CQ.  I purchased from 
Boeing Surplus 4000' of RG8 size Teflon coated and center dielectric silver 
plated dual shielded 50 ohm coax that cost originally $1.75/ft 35 years 
ago--for 11 cents a foot.  I still have 2000'.  I have given some to friends. 
 It compares to polly foam for loss.  I have 3 different ways to test coax 
and open wire line loss.  It's the most stable coax I've ever used.
  Further you are the one with the "open wire blinders" and I'd bet you have 
never properly used it from the comments you make.  I'm not talking about the 
450 ohm ladder line.  It has much higher loss than #12 or larger wire with 6 
inch spacers.  I even have some with 1/4" copper tubing.  I bent it in a sine 
wave and told everyone that asks "it got formed that way from a high SWR and 
high power" and they believed it.  There was even a Jeeves Cartoon on that in 
QST about 50 years ago.
  In regard to the rotary slip ring loops--you brought them up out of the 
clear blue sky and then pointed out they can fail and the spacing can vary 
causing impedance changes.  Don't blame me or others for your failures to 
construct things properly.  The ones I had never failed for power, balance or 
mechanically.  If you learn to space the rings properly (use a ruler) the Z 
doesn't change either.  I intend to use them again.
  Your on a non productive tangent on open wire line that illustrates limited 
experience (and a limited sense of humor) with feedlines.  Can you tell me 
the Impedance Formula for coax and open wire line?
  In 1960 Columbia made the first Pollyfoam coax.  Unfortunately it ended up 
about 60 ohm coax.  They just changed the dielectric.  The dielectric 
constant changed from 2.3 to 1.6 and when that plugs into the formula, it 
requires one other change to maintain 50 ohms.  Since you are so 
knowledgeable you tell me what that is and how much.  When I talked to 
Columbia they didn't know either.  This turned out to be great coax as it's 
the right Zo (that means impedance in technical lingo) for 1/4 WL stubs 
matching 50 to 72 ohm hardline coax.  I suggested they keep making it but 
label it 60 ohms. I can spot it instantly.
  Pollyfoam has a big variable.  If you grid dip a 100' length and then 
another, it may have to be about 3' longer or shorter due to the variation of 
the velocity factor.  Some brands are more stable and it's measurable from 
length to length.  I've measured over 10,000' of it for many applications.  
Would you believe (that's the cue I'm pulling your leg) they mix the Yeast 
better that bubbles up.  They actually blow nitrogen into it and some control 
it better.  That's around a 40 degree error in electrical length on 10M and 
it screwed up an antenna I had requiring equal length feedlines.  It took me 
5 minutes to find the VF (Velocity Factor) problem.  I reconnected the 2 
equal lengths of solid dielectric feedlines I had with the same electrical 
length.  I happen to also use a certain "Magic Length" of 91' 2" as it's an 
electrical 1/2 wave or multiple on 3.562, 7125, 10.687,14.25, 17.812, 21.375, 
24.937 & 28.5 MHz and will Grid Dip to this almost exactly.  One application 
is as I have described in TT when using a variable Xc (that's a variable 
capacitor) in the shack to tune out inductive reactance, I need certain 
lengths to repeat the antenna inductive reactance at the end of the feedline. 
 If the feedline is not exactly the right in say all band trapped antennas, I 
can compensate at the antenna with a slight change there.  When you work with 
coax for 60 year a lot these tricks come to mind with a little "Coax 
Creativity" of many years used on hundreds of antennas.  These idea also work 
with open wire line and it's "making a comeback" from the amount of "Open 
Minded E-mails" I get from those with limited feedline budgets and who want 
more efficient ways to transfer RF.  My first open wire line didn't cost me a 
cent and I still have it--with the same loss.  How much have you spent on 
coax?  What is each length loss in dB at say 10M?
  Do you have any technical experiences you'd like to share on TT that you 
have done with coax has that solved a RF transfer problem?  I've be happy to 
share some more with you.  Meanwhile I have some more "Open Wire E-mails" to 
read telling of how well it works for them and they want more 
information--not criticisms of it's use.  If I can be of further assistance 
in your coax and in particular open wire line education, let me know.  I 
don't think you should be lecturing me and having "Big Ha Ha Ha's" on what 
feedlines to use or recommend after 60 years of using them all.  I'll try not 
to laugh at your questions.  I have some coax I'd like to sell you.  It's 
well broken in.  K7GCO 

Sample below: 
In a message dated 9/12/00 12:59:52 PM Pacific Daylight Time, K7GCO writes:<< 
In a message dated 9/12/00 10:04:50 AM Pacific Daylight Time, W5HNS writes:  
      Just read your post from yesterday's towertalk.  Did you make your own 
      If so....how did you make the spacers and approx what space?
  Henry W5HNS
  Pasadena, Texas >>

 Either Teflon or delrin and at 6".  I would use RTV rubber to hold the 
spacers is place.  Drill snug holes in the end of the spacer.  Make it 
multiples it 136' long.  Get a Johnson Match Box, take it all apart and check 
each switch contact K7GCO. >>

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