I found the following blurb on the Times Microwave
.......Attenuation is determined by the conductive
and dielectric losses of the cable. Larger cables have
lower conductor losses, reducing attenuation. Dielectric
loss is independent of size. Dielectric losses increase
linearly with frequency, while conductor losses increase
with the square root of frequency. Therefore, dielectric
losses become a larger proportion of the total cable loss
as frequency increases.
BTW, if you don't believe me, here is the website, you
can look for yourself:
Thanks to Tom and Yuri for another spirited debate.
As usual, it forced me to think a little more deeply
about how things work.
73 de Mike, W4EF....................................
----- Original Message -----
Sent: Thursday, January 31, 2002 12:21 PM
Subject: Re: [TowerTalk] Dielectric losses
> One more try to educate the "guru":
> > > The ARRL Antenna Book 17th edition, page 24-16 says:
> > >
> > > "The power handling capability and loss characteristics of coaxial
> > > cable depend largely on the dielectric material between the
> > > conductors...."
> > Of course it does. No one said it doesn't.
> W8JI is "no one" who said:
> ""The vast majority of loss is conductor
> resistance related, and has nothing to do with what dielectric is
> used in a coaxial cable except as that dielectric affects the size of
> conductor you can use for a given outside diameter to have a given
> So "it does" or has "nothing to do" ????
> Problem with logic? You esteemed reflectees be the judge.
> And he contradicts himself (again) and trying to "explain" what "is" is:
> > The reason the power rating changes is some dielectrics have
> > lower voltage ratings, and some allow the use of a larger center
> > conductor for a given power.
> > HF and VHF loss in good quality cable is mostly caused by
> > conductor resistance, not dielectrics. At HF and lower VHF virtually
> > all loss is due to conductor resistance.
> Here we go, from "gospel" statement to what "is" is.
> More quote from ON4UN book (page 6-3 3rd edition) about increasing loses
> higher SWR due to DIELECTRIC losses:
> "The voltages associated with the voltage antinodes will be responsible
> increased dielectric losses. This is the mechanism that makes a line with
> high SWR have more losses than the same line when matched."
> So "has nothing to do with dielectric"?
> > > Fig 22 on the same page shows attenuation vs. frequency. If one looks
> > > at coax like RG8 "regular" dielectric and RG8 foam dielectric curves,
> > > one can see that slope of the curves for both coaxes is different,
> > > indicating that while they have similar or close physical dimensions,
> > > at higher frequencies "regular" dielectric coax has steeper slope,
> > > therefore loses increase with frequency. Curves (lines) for most foam
> > > coaxes closely follow slopes of air dielectric coaxes or lines.
> > > Polyethylene "regular" dielectric has a steeper slope indicating
> > > increasing loses with frequency.
> > RG-8 style cable with foam dielectric uses a #13 conductor.
> > RG-8 style cable with a foam dielectric uses a #10 center
> > conductor.
> > Both have the same outer diameter and impedance.
> That accounts for the offset at the vertical axis of the diagram, then the
> steeper slope of the curves is caused by higher losses in the dielectric.
> you comprehend that, or are you going to dance out of that one? ITS THE
> THAT INDICATES INCREASING LOSES WITH FREQUENCY in lower grade dielectric.
> > > Most of us know that when coax gets contaminated, insulation between
> > > the conductors deteriorates and this shows as sometimes significantly
> > > increased loses. This is clearly caused by change in the quality of
> > > dielectric and not by thinning of the wires or increased resistance
> > Most cables are closed cell, and water does not ingress into the
> > foam any more than it leaks through a foam coffee cup.
> > While water inside the cable will certainly increase loss, even if you
> > dry the cable out loss remains high at higher frequencies. The
> > reason for the loss is the oxidized shield becomes a series of high
> > resistance connections every place it weaves in and out.
> > Remember skin effect causes the current to flow on the inner
> > surface of the shield.
> > The resistance-per-foot of oxidized braid is many times that of a
> > similar sized solid smooth conductor, even though the dc
> > resistance remains virtually unchanged.
> Ignoring mechanics of "propagating" RF in a coax.
> So the wave in the center conductor runs happily to the end of coax, while
> wave traveling through the inner surface of the shield gets "resisted"
> What happens at the end when they meet? :-)
> Ever heard of dielectric causing losses in the capacitor? Inferior
> would heat up, indicating consumption of energy and therefore LOSSES. Same
> goes for coax, it is a wire, it is a waveguide, it is a capacitor, it is
> > > them. Velocity factor in the cable (due to dielectric properties) has
> > > effect also, more "slowing" of the wave in the cable, more
> > > needed to pass through the lengths, more loss. Goes higher with
> > > frequency, more "waves" present.
> > I'm not aware of any physical or electrical property where the
> > number of "waves" in a cable has something to do with loss. The
> > velocity factor does not relate directly to cable loss.
> > It is true that a higher velocity factor cable, for a given outside
> > diameter, can use a larger center conductor and have less loss.
> > But that effect has nothing to do with the "number of electrical
> > waves", whatever that might mean.
> Why does loss in a cable increase with frequency? Take "perfect" open wire
> line, with almost perfect dielectric - air, no green stuff on braid, why
> does the attenuation go up with frequency? (besides skin effect)
> > > So W8JI "gospel" that there is "virtually no difference" is dumbest
> > > statement of the year #2. ("Explanation" by W8JI to follow, dancing
> > > around the what "is" is. :-)
> > I'm not so sure I hold the record for dumb statements.
> > > I was glad to see Tom (sorry, it is Nathan :-) W6XR "correcting" W8JI
> statement about
> > > "inferiority" of Force 12. Contesters and DXers I know, have nothing
> > There was nothing to "correct". I never said Force-12 antennas
> > were "inferior". I simply stated one should NEVER depend on
> > anything written that trys to sell or promote a product for technical
> > accuracy.
> > That is true, and "the article" published in QST was full of technical
> > inaccuracies. Most of the inaccurate statements centered around
> > hyperbole that was designed to sell antennas.
> > It is the quality of the technical information I question.
> Maybe time to question your own?
> > To set the record straight, I never said anything about the quality of
> > the product. That was someone else, not me.
> > > about things I am not sure about. Some might remember Tom's attacks
> > > some of my postings about my findings about 160m propagation, etc.
> > But Yuri, you didn't "find" anything. You claimed a low dipole (1/8th
> > wl high) beats a four-square because of ducting, and I said it was
> > bad science to form a theory based on the results you saw
> > VE1ZZ's QTH for one weekend, which:
> Worng, wrong, wrong!
> I didn't form "my theory" on one weekend at VE1ZZ. I wrote my refractive
> propagation article way before I met VE1ZZ, this was one of the arguments
> think supports my theory.
> I said that at the times low inverted Vee would hear what beverages or 4
> square could not, interpreting that there are times when incoming signals
> coming at higher angles. You are twisting it into that " low dipole (1/8th
> high) beats a four-square (not)"
> The other subject was sqewed path whitch you denied, now you are expert
> That wasn't based on one weekend operation from VE1ZZ, but on numerous
> and others (W4ZV, etc.) observations also.
> > 1.) Is about half the distance to Europe from people in my area
> What's that got to do with it? It can be observed at any place on earth
> conditions allow that.
> > 2.) Was only one weekend
> How you figuered that? Big BS, I have been hamming around for 44 years and
> seen it happen many times.
> > 3.) Never included blind A-B tests
> That's for you to scientifically investigate, write a paper and get the
> glory. I simply reported what I experienced, made note of it, used it to
> corner bunch of records and slept happy. Where are the blind tests
> your claims?
> > 4.) Is on a rock ledge a few hundred feet above the ocean
> You never been to his place, yet claim that you know how it looks. That is
> really pushing it. I have been there about 10 times, it didn't ever change
> and is nothing like you describe. Another wrong "gospel"?
> > I pointed out I have dipoles at low and high heights, and have
> > NEVER in hundreds and hundreds of blind tests seen a low dipole
> > "win" for DX. As a matter of fact, the low dipole only wins within a
> > few hundred miles.
> > Virtually all of the time the verticals win over any horizontal antenna
> > at any distance beyond a few hundred miles on 160 meters.
> Sure, when signals are coming at low angles, verticals win. When
> is at higher angles, the antenna that exhibits higher gain at that angle
> Another wrong "gospel", have you checked KC1XX 80m quad array?
> Verticals produce stronger low angle radiation, allow to build
> arrays (esp. at low bands) easier than horizontal (size).
> Turning it into a debate verticals vs. horizontals?
> > Most other people in the world using good verticals with real ground
> > systems share my experience, although people with small ground
> > systems sometimes find dipoles to be more competitive than their
> > poorly-grounded verticals.
> > That's why the vast majority of successful DX'ers on 160 use
> > verticals.
> > I'm sorry you take any critical comment personally, but there is no
> > reason to carry a grudge over a simple questioning of the science
> > used in forming your theory to the point that you feel compelled to
> > insult me on a personal level at every chance.
> I am taking your critical comments (personal attacks) personally but
> insulting you (by making critical comments)? OK turn it around. You forgot
> what you called me?
> I am not arguing that verticals are not better than horizontal antennas
> some situations). I reported that I found that I had situations when low
> inverted Vee was hearing stuff that 4 sq or beverages could not. Happens
> the time? Not. Happens sometimes? Yes. As a contester, I love to have
> antenna that can hear stuff that others can't. Period. I share it with
> so if they like it, they can use it. If you need scientific study - go for
> > > If you care to read comments on the coax subject by one of my mentors
> > > who was removed from the reflector, here it is:
> > >
> > > He claimed "the lower loss of polyfoam is more due to the larger
> > > center
> > > conductor than the polyfoam dielectric without any qualifications
> > > as the frequency--the major factor." A blanket statement without the
> > > necessary qualifiers is "technically irresponsible."
> > I'm glad your friend agrees with me.
> No, he agrees with me (A blanket statement without the necessary
> is "technically irresponsible.)! He means YOU!
> I guess you don't get it. :-)
> > 73, Tom W8JI
> > W8JI@contesting.com
> This is my last free lesson, next one I will charge consulting fee :-)
> 73 and happy dielectrin'
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