GM Jim,
Now we are getting to the interesting part! (hi)
I would suggest others not interested in this topic simply hit the DELETE
key now.
This is a VERY LONG RESPONSE.
Fundamentally, ALL of the assumptions you made about how I measured are
wrong.
(details below)
Funny, I was going to ask you a similar question:
Under what circumstances does the balun fry? When used on any frequency at
all or when used on any specific frequencies?
Jim, I am very pleased to have you weigh in on this topic. You indeed have
lots of experience.
When I set out to conduct my own research 3 years ago, I sent out an email
invitation to several highly qualified engineers to help me prepare for the
test. You were one of the ones I invited. I never got a reply. I don't
know if you were too busy at the time or perhaps the invitation landed in
your SPAM filter.
The details of how I measured are posted on my web site.
About half of the results of what I measured are posted on my web site.
A few conclusions are posted there.
The test description begins here: http://www.dj0ip.de/cmc-test/
I spent about 6 months preparing to conduct the tests and then 3 weeks, 7
days per week, about 8 hours per day conducting 'FIELD' measurements (not in
the shack!).
During the preparation for my tests, the following engineers supported me in
the planning, choice of equipment, and tips for testing the calibration and
residual CMC being leaked through the transmitter to earth, etc.
> G3TXQ (member of this group, and creator of the Broadband Hex Beam)
> GM3SEK (technical author for RSGB/RadCom)
> G3UNA (retired engineer from RACAL)
> DJ1AT (wrote the antenna chapters in the book used by German colleges to
train engineers)
> DF4SA (creator of the Spiderbeam Yagi antenna)
These guys were the brains behind the test.
I was the executer.
G3UNA and DJ1AT held my virtual hand through the test, answering many of the
questions that popped up in real time.
AND A BIG THANKS to Spiderbeam and DX-Wire (two Germany companies selling
antenna supplies).
Spiderbeam funded the project, bought the test equipment, and supplied wire
and poles.
DX-Wire supplied me with toroids, Teflon-insulated wire, insulators, etc. at
purchase price rather than sales price. Without that financial backing, I
would not have been able to run the tests.
I have formal training in electronics in the army and civilian life, as well
as many years working as a technician, including 3 years working in the
Rhode und Schwarz lab repairing test equipment and giving courses to
customers including engineers on how to use the equipment.
My tasks were simple:
> Build all the baluns, chokes and antennas
> Apply 100w to the test antennas (using a Ten-Tec Eagle)
> Read a watt meter
> Read an RF Ammeter which is simply a current meter
> Measure antenna parameters with a RigExpert AA-54 analyzer
> Vary the parameters of the configuration and do all of that again
(altogether 500 times)
You don't have to be an engineer to do these simple tasks.
You just have to be a fool willing to risk his marriage to learn about the
CMC behavior of these antennas. After concluding the field test, I didn't
dare even say the work "antenna" out loud around my XYL, for fear of getting
my head chopped off! (hi)
More comments below.
73 - Rick, DJ0IP
(Nr. Frankfurt am Main)
-----Original Message-----
From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Jim Brown
Sent: Monday, September 21, 2015 8:42 AM
To: 'Discussion of Ten-Tec Equipment'
Subject: Re: [TenTec] It's getting cold. Perfect antenna weather for a OCF
dipole
On Sun,9/20/2015 1:23 PM, Rick - DJ0IP / NJ0IP wrote:
> I have measured the common mode current on OCFD antennas with an RF
Ammeter. I'm not guessing or modeling, I'm speaking of real life situations.
But Rick, the common mode current varies along the line, just as it does on
any antenna. I suspect that you measured the current at or near the shack.
That is VERY different from what it is up in the air where the choke is (or
at least where it SHOULD be to be effectively kill common mode current)!
>>> The varying of common mode current along the coax line is well
documented by Steve Hunt, G3TXQ on this page:
http://www.karinya.net/g3txq/chokes/ ... beginning in the text below the
color-chart.
I discussed this topic at length with Steve in order to define 4 different
measuring points:
1. typical length of coax by someone operating portable
2. point of minimum CMC (1/4 wl down the coax or 'odd' multiples thereof)
3. point of maximum CMC (1/2 wl down the coax, or even multiples thereof)
4. worst case: 1/2 wl of coax run very close to and at the same height of
one leg of the antenna.
In the #4, after completing the measurements, I rotated the antenna 180
degrees and measured again to determine if running it to one side was any
worse than running it to the other side.
For the OCFD antennas, measurements were only made on the 4 bands that the
antenna was designed to work on. I did not measure on any WARC bands.
Obviously I did not measure current directly at the feedpoint.
I had no means of doing so.
However it is my understanding that this current repeats itself every 1/2 wl
along the coax.
I did measure that, as stated above.
-------
If you haven't done so, I suggest that you add the choke, coax, and any
matching section to the model. Then compute the currents. Also, turn on the
display of currents in the View Antenna window. W7EL's instructions talk
about how to do that.
>>> I did not model anything. Plenty of engineers have already done that.
Instead I built real life antennas and measured them.
In the common mode circuit, coax and window line has a velocity factor
around 0.98, depending on the thickness of the jacket, and much closer to 1
for open wire line.
>>> Absolutely; one of the advisors suggested it might be closer to 0.95.
We discussed this but it was the consensus that the 0.95 number includes
compensation for "end effect" and there was no end effect in this
application. I think we actually used 0.97 as the factor during the tests.
The vf used is stated somewhere in the test description.
-----
> NO, I AM NOT FRYING THE BALUN. HAVE YOU DONE IT?
YES!
>>>I regularly re-measure the antenna's characteristics, band by band and
compare to how it was 4 years ago. If I were frying the balun, it is my
assumption that something would have changed. It hasn't.
----
> I HAVE BEEN DOING THIS FOR 4 YEARS NOW and I am running a balun with
mid-sized cores.
> My balun uses 2x FT-140-43 cores and I run 600w CW/SSB.
You have been lucky. The values of common mode current and voltage at the
choke vary as noted, depending on frequency and line length.
>>> I don't agree the luck part. I'm a member of the Yahoo!Group for Windom
and OCFD antennas. We have just under 1200 members. Most of these members
run this type of antenna and although the majority run no linear at all,
several hundred run linears, including myself. Occasionally someone reports
frying a balun.
Yes, people have fried baluns. But when you look at how they did it, it was
by doing something VERY STUPID. Specifically, when using a commercial
Windom such as Buckmaster, or W8AMZ, which use a 1/3 - 2/3 split for the
feedpoint, AND ignoring the manufacturers' warning NOT to use the antenna on
15m, used it with a matchbox on that band, running high power. They fried
their balun.
When running high power into a Windom with one of its legs running over a
metal building, you are also likely to fry the balun.
When modeling the Windom for a good SWR on the bands you want it to cover,
building it, and then checking it against the model, measuring each band
with a half wl (or multiple) of coax and the measurements conform to the
model, AND running it only on the bands it was designed for, you are not
likely to fry the balun (assuming you used the right balun design and
dimensioned it properly).
-------
> I can show you my scores and country totals for the past 4 years in CQWW
DX contest.
> No fried balun, but lots of countries, like 70 countries/band average.
That means NOTHING. What is meaningful is the transmit duty cycle. How
much do you RUN? For how long? How much do you run with no response to
your CQs? How much time listening between CQs? How much do you S&P?
Agree. Such statements mean nothing without further qualification. On the
high bands I do run S&P. ON the low bands, especially 80 and 40m, I run CQ
for a couple hours at a time, rarely pausing for anything - except for
working the stations constantly answering. I'm generally running my single
3-500z at about 600 to 700w.
And remember, I have only used mid-sized toroids in my balun. I built it
before I had a linear so originally I was only going to run 100w thru it.
One of these years I will replace it with a heftier balun.
-------
> We are reporting measured data, not modeled data.
But no details of HOW you measured, or WHERE you measured.
>>> The details are on my web site.
-------
Are you suggesting that NEC does not accurately predict how antennas work?
MANY
would disagree with you on this issue.
>>> I don't recall stating anything of the kind.
HOWEVER, I QUESTION that NEC is being properly interpreted.
Under what circumstances does it state that the balun will fry?
High SWR in conjunction with CMC will indeed fry any balun.
But when used on the bands designed for, the OCFD does not have high SWR.
I will make an assumption. NEC is showing CMC flow through the balun across
the spectrum and indeed it will have high current on the vast majority of
frequencies, but I do not believe it is high current within the ham bands
that the antenna was designed for.
THEREFORE it is correct to conclude that the OCFD can fry the balun but
wrong to conclude that it does this under all circumstances. As I stated
earlier, as long as the operator does not do anything stupid, he won't fry
it. Running the antenna on frequencies it was not designed for is very
stupid.
-----
> What is your justification for the claim you just made?
Why the word "claim?" I'm not selling anything. The basis of all of my
statements is a combination of what I've learned while getting my BSEE,
60 years in ham radio, the last ten of which have included extensive
studies of how antennas, transmission lines, ferrites, and common mode
chokes work. I taught math and transmission lines at DeVry in the '60s.
>>>I understand all of that and that's why you are at the top of my list of
authorities on this topic.
(actually you are listed at the bottom because I title that one as
"Advanced". The list starts with some simpler documents, then move up to
more advanced sources, yours being the best.)
HOWEVER, the topic of OCFD antennas has been poorly treated in text books.
There is a German ham who is nearly as old as you and I together: DL1VU
He has written a book on "Windom- und Stromsummenantennen".
I have read his book cover to cover many times.
All of the topics you pointed out are handled in this book, including how to
build instruments for measuring CMC. How to measure it is also included. I
understand this.
You've read more text books that I, probably even written some.
>Where does any of these show real life measurements of CMC, even on a
dipole, taken at various lengths of coax and with the coax running at
various angles away from the antenna?
>Where does any of these compare the amount of CMC on the coax when using
a single-core 4:1 Guanella balun, compared to using a dual-core 4:1 Guanella
balun?
In his excellent 1985 article, "Baluns: What they Do and How they Do IT",
Roy Lewallen (W7EL) explains the difference between voltage and current
baluns (even coined those two names), shares with us his CMC measured
results, then goes on to point out where more research is needed in several
areas.
I took is list of where more research is needed and with the help of the 5
engineers listed above, did my best to measure exactly what Roy said remains
to be done. It was my main preoccupation for an entire year.
In addition to doing that with a dipole, I also did it with several
different OCFD antennas.
There is a wealth of measured data still waiting to be evaluated.
However a few things we did learn is how CMC behaves on a 40m OCFD.
I only measured a 40m OCFD in my 2013 tests; I did not have space for an 80m
OCFD.
We also learned how useless a single core 4:1 Guanella balun is in this type
of antenna.
This is my justification for saying that all commercial OCFD antennas are
using the wrong balun technology.
------
> I have fried several baluns in the past running symmetrical center fed
antennas as you are recommending.
> That's because the impedance in these antennas can be super high on even
harmonic bands.
What fool would run a dipole on its second harmonic?
>>> Every man foolish enough to run an openwire-fed dipole on multiple
bands.
People who have recommended this type of antenna include:
> Lew McCoy, W1ICP (SK)
> L.B. Cebik, W4RNL (SK)
> Several fools here on this ten tec list such as K4TAX, DJ0IP, and others.
And there are thousands of these in use around the world today.
----
That's an un-natural act! I have NEVER recommended this. Further, I do NOT
recommend the practice of loading a non-resonant dipole anywhere other
than its fundamental resonant band and third harmonic, where it is a
reasonable match to coax.
>>> You made a false assumption. I made no reference to coax. I was
referring to openwire fed dipoles, and the balun I fried was in front of a
high-power asymmetrical matchbox.
For coax fed antennas, you are more or less correct. There are exceptions.
The exceptions are explained in the concept of the "Stromsummen Antenna".
I have never seen this mentioned in any English language book or paper.
However it is well known among German speaking hams and is published in the
Rothammel Antenna Book and in detail in DL1VU's book on Windoms and
Stromsummen Antennas.
-------
I do NOT recommend the use of open wire line
as a band-aid for badly matched antennas.
>>> Yes, we know you are not a great fan of openwire antennas. You have
said that many times here.
However I believe this to be a "situational opinion."
What one thinks of the openwire-fed dipole depends on his alternatives.
I have seen pictures of your antenna farm at your old Chicago QTH.
Although most of us here view those antenna through eyes of envy, most of us
would also be hung from our coax by our neighbors if we tried to do
something like that.
In the event you must ever move to a QTH where you may have just one single
wire antenna, I predict you will change your opinion!
-----
Further, badly mis-matched feedlines cannot be choked with any of the
chokes I've designed or recommended because of the DIFFERENTIAL loss in
the coax as it goes through the choke. N6BV (retired editor of ARRL
Antenna Book, ON4UN Book, author of HFTA and TLW) clearly showed this in
a talk at Pacificon a few years ago (which he ran past me for peer
review), and which was subsequently published in QST (within the last
year). In my review of Dean's work, I noted that the differential
dissipation he was describing was IN ADDITION TO the common mode
dissipation.
>>> Once again this is a situational opinion.
And perhaps you can never 100% eliminate the CMC with the choke, it is
possible to impede it enough that it does no damage; albeit the radiated
signal is indeed reduced. But let's not forget that 50% is just 3dB, or half
an S-Unit.
I have never seen anyone claim that the OCFD is the best thing since sliced
bread.
It is basically a "last resort antenna" one chooses to use in the event
(s)he can only have one antenna and wants to run all bands, and does not
wish to use openwire.
However it is unfair to insinuate that this antenna is not a good antenna or
will not work.
My definition of "work" is not the same as the one expressed in the article
"everything works". (hi)
Again, it's a situational decision.
More and more people are turning to portable operations due to HOA
nightmares.
Operations like SOTA, COTA, LHOTH, and IOTA are becoming more and more
popular.
People traveling to these events are finding great appeal in the OCFD
antenna.
To say they are bad ... let's have a look:
Barry, N1EU recently took first place overall in a SOTA contest, using an
ultra lightweight 40m OCFD antenna which I designed and built for him.
Paul, DL5CW recently took first place overall, world-wide, in the IOTA
contest, using an ultra lightweight 80m OCFD antenna that I designed and
built for him. His first place was in the class of "Island Expedition,
100w, 12 hrs participation".
My definition of "work" is, you at least have a shot at turning in a
respectable contest score in big contest.
Simple, lightweight multi-band antennas are very desirable to many hams.
They may not be the antenna of choice for the Big Gun - California
Kilowatts, but a lot of little pistols are having a lot of fun running these
antennas.
----------------
> I contend that the chances of frying a balun are higher with center-bed
antennas than with OCFD antennas.
On what basis do you say that?
>>> EXPERIENCE.
But also ignorance - hi. I was gullible enough to believe the marketing
hype and lies of those commercial manufacturers wanting to sell us stuff. I
was using their poorly designed baluns well within the published specs.
This was over 20 years ago when I had no clue at all about baluns.
Eventually I woke up, studied up, including your material, and began
building my own baluns.
I have never burned up one of my own, but I know what it can and cannot do.
-----------------
Are you talking about a center-fed wire that is mis-matched at the operating
frequency because it is far from resonance? If so, I agree -- see the
paragraph above. But again, this is
an un-natural act. It is stupidity.
>>> I don't think you meant that the way it came across. A full wavelength
dipole is certainly a resonant antenna, yet it has a very high impedance.
It was in this case that I burned up some of the baluns.
But I also burned them up running short, non-resonant openwire fed dipoles.
Again this is situational.
Germany has one of the highest population density countries in the western
world.
People do not have space. Many live with postage stamp sized gardens and
are forced to run a shortened dipole fed with openwire. Nothing else fits.
I have burned up commercial baluns running these too.
Then Bob, K4TAX taught me how to build a balun that would cope with the task
and not burn up.
Using this short antenna (abt 66', fed with openwire) at my QTH and running
in the QRP class, DL6RDR made the second highest score overall in Europe in
1996. Of course he didn't stress the balun with QRP but he did prove that
such a short antenna can still work effectively.
Luckily I was able to move to another QTH 3 years later and the antenna was
extended to full size.
It was a situational solution at the time.
IMO it does not add much value to tell people it is a stupid idea, if that's
the only solution available to them. At the end of the day they will do it
or do nothing at all.
What helps is to suggest the best possible way of using it and highlight the
risks, such as saying "don't run your OCFD on bands it was not designed
for."
--------
My choke designs are specifically limited for use on symmetrical,
resonant antennas that are matched to the feedline at the operating
frequency. In a slide presentation (on my website) on ferrite chokes, I
showed how dissipation in the choke increases as the feedpoint moves off
center.
>>> The ODFD antenna is one of the most popular and probably most widely
used antenna here in Europe. That's because most of us have limited space
and must run something inconspicuous to hide if from the neighbors.
Antennas with traps are much heavier, require thicker wire and more massive
poles.
People are not frying baluns left and right.
Admittedly most of us are not running 1.5 KW. In most EU countries the
power limit is under 1 kW.
I am a HUGE fan and user of antenna modeled data.
We have thousands of modeled data points on the OCFD antenna.
When I designed the two antennas listed above in the contest results (SOTA
and IOTA), I spent many hours studying modeled results, then built and
tested the antennas, pruning the feedpoint one centimeter at a time in order
to optimize them.
The field work was crucial to the success of the antenna, but it never would
have happened at all without the model. IT TAKES BOTH.
IN THEORY I would have a Telrex Christmas Tree (showing my age here - hi).
IN PRACTICE I have one single milti-band antenna; an 80m OCFD, plus a very
simple Inverted-L for 160m, well hidden in the woods about 100 yards from
the house.
AND "THAT" Jim, is the justification for the OCFD antenna.
It solves a specific antenna need.
Until someone can suggest a better multi-band antenna that is affordable,
we'll just have to keep using what we have.
RESPECT to everyone who read all the way to this point! You're a trooper!
Cheers! - Rick, DJ0IP
----------------------------------------
73, Jim K9YC
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