[TowerTalk] Coax Vs Open Wire Line
GALE STEWARD
k3nd@yahoo.com
Thu, 14 Sep 2000 05:04:34 -0700 (PDT)
Anybody actually read this stuff? Much too long, way
to short on substance, IMHO.
Regards,
Stew K3ND
> > 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
>
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