Hi Arnie,
I guess there has been a discussion on baluns going on. Let me add a
few comments on the subject.
First off, there are alternatives or choices on transmission line
types used in coax baluns. RG58 is fine for low power (100-200 Watts)
but for higher power, you need larger and higher power coax such as
RG213 or teflon dielectric coax. When I wrote the first current
amateur balun article (Simple and efficient broadband balun by W1JR
in Ham Radio Magazine, September 1978) I used RG141 since it was the
only high power coax available at that time that could be fairly
easily wound on a 2.4" OD toroid. However, for the last 15 or so
years I have been using the newer RG303 coax since it is less costly
(than RG141), smaller in outside diameter, easier to use especially
on toroids and will handle full amateur power levels.
In 1989 I helped develop a low cost PTFE coax for the Cushcraft
Corporation. They needed a cost effective coax for installing mobile
antennas in automobiles that wouldn't melt if placed near catalytic
converters etc. Cushcraft marketed it as "Ultra Link" coax. Ultra
Link, as I recall, is about the diameter of RG58. It uses PTFE
(instead of teflon) dielectric. The dielectric is first covered by a
foil shield which in turn is covered by a regular braided shield but
with a polyethylene outer jacket. It can easily handle amateur high
power levels. Furthermore, Ultra Link coax should be widely available
through distributors of mobile products such as Tessco and the like
and should be very reasonable in price versus RG141 or RG303.
The W1JR current balun was mainly intended for 20-10 Meters and only
had 12 turns of coax but did have sufficient impedance to work from
80 meters through 6 meters. I later tried stacking (placing two
toroid on top of each other) and that balun with 12 turns of RG303
coax has sufficient impedance to go down to 160 meters. I see that
Array Solutions (WX0B) markets both types of the W1JR balun. I am in
no way involved financially with this design although I tested them
for Jay and they worked great. Jay used a neat layout by closely and
tightly wrapping the coax which improves the upper frequency limits.
One of the stacked (2 toroid) baluns using 2.4" OD 61 material is
used on my 160/80 meter G5RV dipole and easily handles 1500 Watts
even with poor VSWR (a characteristic of the G5RV dipole). The beauty
of this type of toroid balun is that it is compact, has a good high
frequency response, has low loss and the cross over winding keeps the
input and output separate simplifying isolation and connection to the
outside world. The W1JR balun is arguably the widest distributed
balun to date having been used in every R5, R6, R7and R8 Cushcraft
antenna with over 100,000 antennas sold! Cushcraft used RG303 coax
for that balun. Cushcraft uses a 4:1 balun with Ultra Link coax in
the 17B2 and 13B2 VHF high power Yagis.
Soon after the W1JR balun article was published, several individuals
published articles on the same balun but adding a tertiary wire. This
in effect made it a voltage balun, a poor choice indeed. Shortly
thereafter, W7EL wrote a paper (see ARRL Antenna Compendium, Volume
1) to correct the errors and pointed out the differences between the
current and voltage type baluns. Thus a great mystery was solved ands
two new terms (current baluns and voltage baluns) became widely used
in amateur radio.
Since then, the W2DU in line coax balun has become popular due to its
ease in construction. It uses 50 to 100 ferrite beads with type 73
material. It turns out that this ferrite material has a high loss and
low resistivity in the HF frequency range. The beads W2DU chose had a
small inside and outside diameter so the outer jacket of RG141 coax
had to be removed to insert the coax into the bead. Due to the losses
and small size of these beads, the W2DU balun can get quite hot with
high power and in one documented case (Common Mode Chokes by W1HIS)
started an attic fire!
More recent W2DU type balun designs have emerged (Exploring the 1:1
Current Choke Balun by W0IYH in June 1997 QEX). Basically W0IYH used
larger diameter and longer length ferrite beads with lower loss type
43 ferrite material. This approach seems to improve the
aforementioned problems and less chance of IMD. It uses a 36" string
of ferrite beads! For some time now, I had also been using 30 of a
similar bead (see below) for my HF line decouplers.
I used similar ferrite beads to W0IYH in my commercial antennas
starting in 1992. The beads are 1.125" long, 0.562" OD with a .250"
ID with Fair-Rite 43 material. Three of these beads in a string
covered with a heat shrink tubing with a flooding agent worked great
for 1:1 baluns from 100 MHz through 1000 MHz. For my commercial
antennas in the 40-100 MHz spectrum, we used 5 of these beads. At 50
MHz 5 beads in a string measured over 1000 Ohms and over 500 Ohms at
28 MHz on a Hewlett Packard 8753C network analyzer. I believe that
Amidon part number FB-43-5621 is a very available equivalent. RG58
was used for 100 Watts and less with RG303 for higher power antennas.
This was obviously an economical choice for ease in manufacturing.
Some amateurs don't want to use the smaller RG303 coax and .562" OD
beads since it requires another set of connectors to be compatible
with RG213. Therefore, I also tested some 1" OD ferrite beads about
1.125" long with 43 material and a 0.500" ID. Five (5) of these beads
in a string measured about 500 Ohms at 28 MHz and 900 Ohms at 50 MHz
and would be OK if threaded on to RG213 coax before connector
installation. These beads should be equivalent to Amidon part number
FB-43-1020.
Recently type 31 material has become available from Fair-Rite. K9YC
has mentioned this in his paper on "Understanding and Solving RF
Interference Problems." This material has a higher permeability (1500
versus 850 for 43 material) and thus probably greater loss but should
be better at the lower frequencies than 43 material. I recently
acquired a batch of 1" OD 31 material beads similar to the ones just
mentioned. Five (5) of them in a string measured about 750 Ohms at 28
MHz and 1,000 Ohms at 50 MHz. I don't know if they are available yet
from the typical amateur suppliers.
Finally, several have mentioned the use of clamp on beads. These are
OK but must be properly chosen for size, material, permeability etc.
I don't have any here to test. I would be worried that they stay
closed and that the outside wrapper keep them tightly bound.
Obviously clamp on beads are great if added to an already installed
antenna etc. Exposure to sunlight may deteriorate the clamping shell
so attention must be paid to installation. Also, they are probably
more expensive and require some special mounting.
So, just as amateurs chose their ideal antenna based on their
individual needs, cost, performance, XYL etc. etc. (and every ones
choice is different!), the same goes for baluns. Hopefully the above
information will be informative and complete enough to assist you in
choosing the perfect fit for your application.
73,
Joe, W1JR
At 06:15 PM 7/26/2007, n7ka@comcast.net wrote:
>WOW.
>
>At the risk of getting flamed to death, here goes. Actually, there
>is NO risk as I know it will happen.
>
>I asked for assistance from those who have gone before and could
>help to inform me if I was headed in the correct direction for a
>commom mode choke for a 6M antenna project. I have read I NEED to have one.
>
>I received 1 straight forward comment that said they were using
>something and was having NO problems. It worked OK. TYhanks.
>
>Another answer was to look at the Jim, K9YC, tutorial for info. I
>plan to do that so see if a little knowledge will sink into my
>retired brain. Also,thanks
>
>I have been wearing out my mouse deleting messages that went into
>another galaxy.
>
>IS IT TIME TO HAVE 2 RELECTORS, 1 FOR THE PRACTICAL HOME BUILDER WHO
>ASKS FOR IDEAS AND 1 FOR THE THEORITICAL ENGINEER TO DISCUSS THE
>MERIT OF 0.01 dBi?
>
>I do not own the $30,000 (more or less) worth of test equipment
>needed, so some say, just to make a working choke that might cost
>all of $15.00 to build. Nor do I want to own it. And if I go back
>a number of years I would not think of having anything except
>TEKTRONIX (I worked for then in the 60/70s) equipment in my
>home.though they did not build every kind of test equipment. HP
>built stuff TEKdid not anad we should have all said thanks to thenm
>and others who made test equipment of various types. (Lets see,
>where is my FLUKE DMM, SIMPSON 260, and my TRIPLETT VOM?)
>
>I am glad progress has been made in equipment and ideas but think
>about those of us who go at this hobby from a practical
>approach. We do not need to understand the intricate details of
>something to use it or build it. Yes, its nice to learn
>"something"as we go but!"
>
>If I had to know the REASON in detail before a situation occurs I
>would have to delve deep into propagation to understand why I worked
>S5 on 6M in June at the bottom of the solar cycle, hey with 5el and
>100W from NM guess thats NOT TO SHABBY. I do not know how it
>happened, but the QSL card I received proved it did happen and thats
>good enough for me. Yes, I did learn a little from it and will be
>applying that knowledge in the future, so all is not lost. I also
>learned I needed an amp to help overcome the noise level at the
>other end; S5 was not the only station I heard, just the only one I worked.
>
>Now back to the practical side of this hobby and my DELETE button on
>the mouse will probably get overtime work for a few days.
>
>I acknowledge those learned folks who can delve into and understand
>all of the theory; more power to you. We so called practical
>dummies can benefit when something practical comes from the theory,
>and we thank you.
>
>Thanks to those who did provide ON SUBJECT comments to my query.
>
>Now to refill my drink container with more NM SUN brewed iced tea
>and grease the mouse keys.
>
>Arne N7KA
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>
>
>
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