Re: [Elecraft] BL2 -- Antenna Balun Usage
Even Jasik, ed., "Antenna Engineering Handbook" mentions the balun. My
first ham antenna (1952) was a 40 meter dipole fed with 72-ohm twinlead
and a B 1:1 air-core balun and I once worked on an airborn military
system which used a balun.
The term "unun" has a much more dubious justification, however (my opinion).
73, Bob N7XY
On 5/22/17 10:07 PM, Wes Stewart wrote:
PLEASE ignore all of Jim's pontification.
I find it curious that Terman ("Radio Engineering"), Kraus
("Antennas"), Johnson ("Transmission Lines and Networks") all use the
"meaningless" word "balun" in their books. Clearly, these guys should
have consulted with Jim before doing so, because obviously they didn't
know what they were talking about.
A transmission line transformer can be as simple as a geometric mean
quarter-wave line between two different impedances. No ferrites
required. A balun (pardon me, I'm with Kraus) can be a quarter-wave
open stub at the feedpoint of an antenna. Collins ("Fundamentals of
SSB") calls this a "Bazooka-type balun", but what does Collins Radio
know about anything?) Or, it could be a half-wave line connecting the
two halves of a dipole. A stub balun can be both a balancing device
and an impedance transformer at the same time. And it's nothing but
coax. A two-wire line wound around a core might be a common-mode
choke, but if it's long enough and different in impedance from the
load, then it's an impedance transformer too.
In summary, just removing the term balun from one's lexicon doesn't
simplify anything.
And I almost forgot, that N6BV article Jim mentions is titled, "Don't
blow up your BALUN."
Wes N7WS
On 5/22/2017 2:11 PM, Jim Brown wrote:
On Mon,5/22/2017 12:42 PM, Bill Leonard N0CU wrote:
I am no expert when it comes to baluns
You're not the only one. :)
Some important comments. First, PLEASE strike the word "balun" from
your vocabulary. It is a meaningless word that tells us NOTHING about
the device or circuit element it is used to describe. I can think of
nearly a dozen VERY different devices that are CALLED baluns. Use the
word "balun" conceals what the device actually is and prevents
everyone involved from understanding what it does.
A two-wire line wound around a ferrite core forms a COMMON MODE
CHOKE. It is not a "transmission line transformer," nor is it an
inductor, nor is it a transformer at all! The ferrite core carries
only flux due to common mode current, and loss in the choke is I
squared R, where I is the common mode current and R is the resistive
impedance of the common mode choke.
Arrays of common mode chokes CAN be wired in series/parallel
combinations to match circuits of differing impedance, but that
device is NOT a transformer, it is an array of common mode chokes. If
we want to know how this array of chokes work, we must analyze them
as arrays of common mode chokes, not as a transformer.
A transformer, is, by definition, two windings that are magnetically
coupled, and the impedance transformation ratio is the square of the
turns ratio. If we want to know how a transformer works, we must
analyze it as a transformer. It's as simple as that. The ferrite core
carries ALL of the flux, and thus all of the differential power
carried by the circuit into which it is inserted.
In general, common mode chokes do NOT affect the differential signal,
but there CAN be differential mode loss in the transmission line that
forms the common mode choke due to transmission line effects. For
example, if the common mode choke is inserted in a badly mismatched
transmission line, there can excess loss due to SWR throughout the
line, both in the part of the line that forms the choke and in the
rest of the line. Below UHF, virtually all loss in real transmission
lines is due to I square R; if the combination of the antenna and the
line places a current maxima at the choke, that segment of the line
can burn a high fraction of the transmitter power, greatly reducing
the transmitter power that gets to the antenna and overheating (and
frying) that segment of the line. N6BV wrote an excellent
applications note about this for QST several years ago, to which I
contributed.
It IS practical to model (predict) dissipation in a common mode choke
using NEC. A single wire is added to the model with the geometry and
physical connections of the transmission line, and the known
(measured) impedance of the choke is added as a Load at the point
where it is inserted in the system. NEC is then set to model with a
defined transmitter output power (for example, 1,500W), and currents
are computed. NEC then provides a readout of current at every point
on every conductor, and the current in the choke is used to compute
dissipation in the choke.
Tutorials at k9yc.com/publish.htm show a practical method for
measuring the common mode impedance of ferrite chokes, and for
determining values for a parallel equivalent circuit that can provide
Re: [Elecraft] BL2 -- Antenna Balun Usage
BTW, don't look at the BL2 to help with any CMI, it doesn't do a very good job. Mel, K6KBE From: Clay Autery <caut...@montac.com> To: elecraft@mailman.qth.net Sent: Tuesday, May 23, 2017 6:14 PM Subject: Re: [Elecraft] BL2 -- Antenna Balun Usage You missed my point... I'm gonna let it go, because it's just not that important to argue the point here. 73, __ Clay Autery, KY5G On 5/23/2017 11:45 AM, Lynn W. Taylor, WB6UUT wrote: > Terminology does count, especially in technical areas, like radio. > > If you ask to borrow my truck, and I say "yes" and hand you my > hand-truck (two-wheeled dolly) it's probably not what you were thinking. > > On 5/22/2017 10:19 PM, Clay Autery wrote: >> How about not worrying what to call it, period? __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to farrerfo...@yahoo.com __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] BL2 -- Antenna Balun Usage
You missed my point... I'm gonna let it go, because it's just not that important to argue the point here. 73, __ Clay Autery, KY5G On 5/23/2017 11:45 AM, Lynn W. Taylor, WB6UUT wrote: > Terminology does count, especially in technical areas, like radio. > > If you ask to borrow my truck, and I say "yes" and hand you my > hand-truck (two-wheeled dolly) it's probably not what you were thinking. > > On 5/22/2017 10:19 PM, Clay Autery wrote: >> How about not worrying what to call it, period? __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] BL2 -- Antenna Balun Usage
Since a truck can be defined as a wheeled vehicle for moving (heavy) loads, many variations exist. Likewise, a balun can be defined as a device for converting from a single-ended to a balanced source/load and many variations exist. The fact that both terms are all-inclusive doesn't negate their usefulness or demand their removal from conversation. If people would think of a balun as performing a function rather than a particular device for performing that function they would have less heartburn. In other words, saying, "When feeding a balanced antenna with coax, it is advisable to incorporate a balun at the feed point.", shouldn't start an argument about what constitutes a balun. If we are to follow the commandments of one of our correspondents we should remove "truck" from our vocabulary, since it isn't a precise term. Wes N7WS On 5/23/2017 9:45 AM, Lynn W. Taylor, WB6UUT wrote: Terminology does count, especially in technical areas, like radio. If you ask to borrow my truck, and I say "yes" and hand you my hand-truck (two-wheeled dolly) it's probably not what you were thinking. On 5/22/2017 10:19 PM, Clay Autery wrote: How about not worrying what to call it, period? __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] BL2 -- Antenna Balun Usage
I was going to respond to Jim’s comments about terminology, but Wes presented my thoughts better than I could have. I would like to address two of the comments that were made in the responses. First, EZNEC is powerful tool that can help understand theoretical behavior of ideal antenna systems. It can also, under certain conditions, predict the performance of real world antenna systems with reasonably good accuracy. However, much of the EZNEC Manual is devoted to discussing the model’s limitations. There are at least two (and probably more) that I am aware of that affect how well EZNEC can accurately predict how an antenna “system” will perform with, and without a balun. First is the limitation with respect to ground, and the second is the inability to model unbalanced currents (ie, common mode currents) on a transmission line. Both limitations significantly affect the results for the balun problem. I am aware of two articles that use EZNEC to evaluate how a dipole’s performance is affected by the use of a balun. Both articles address these limitations the same way: -an ideal ground is assumed to be at a known location -the transmission line is eliminated and the source is moved up to the feed point of the dipole. The transmission line is modelled by simply adding a third wire coming off one of the antenna’s feed points. The first assumption is a problem because none of us have an ideal ground, nor do we know how to quantify the location of our ground accurately in the model. The second one removes the component that has the most effect on the results, and tries to simulate it with a piece of wire. Although I have confidence in the behavior the model predicts, I seriously doubt that, for any real world antenna system application, whether EZNEC could be useful in deciding whether adding a balun would be worthwhile, and if so, where to install it and what the margin would be to the balun’s power dissipation limit. I strongly disagree with Clay’s comment that the problem caused by common mode currents is nothing more than an impedance matching problem. If that were true, then all the articles, and EZNEC models that describe how a dipole that is feed directly with coax (also called a “Tripole”) can either have the pattern of a dipole, or the pattern of an inverted L antenna, depending on the common mode currents on the transmission line, are wrong. I agree that the impedance seen at the transmitter changes as the common mode current changes, however, I doubt that many, if any hams know what pattern their antenna actually has because they have no idea what magnitude of the common mode current is that is flowing on their transmission line since the predicted variation in the impedance between the two extremes is well within the 2:1 SWR range that most hams would consider normal. Bill N0CU -- View this message in context: http://elecraft.365791.n2.nabble.com/BL2-Antenna-Balun-Usage-tp7630889p7631044.html Sent from the Elecraft mailing list archive at Nabble.com. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] BL2 -- Antenna Balun Usage
Terminology does count, especially in technical areas, like radio. If you ask to borrow my truck, and I say "yes" and hand you my hand-truck (two-wheeled dolly) it's probably not what you were thinking. On 5/22/2017 10:19 PM, Clay Autery wrote: How about not worrying what to call it, period? __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] BL2 -- Antenna Balun Usage
How about not worrying what to call it, period? Just realize that the entire assembly from the antenna connector on the transceiver to the connector on the driven element is simply an Impedance Matching Network (or Assembly if you prefer or even Impedance Matching Device, because all of those elements act in concert. The method by which you accomplish this task is all but irrelevant really All that REALLY matters is that you develop an IMN that meets your impedance requirements within the required bandwidth and sufficiently robust to bear the brunt of the max power contemplated. 73, __ Clay Autery, KY5G On 5/23/2017 12:07 AM, Wes Stewart wrote: > PLEASE ignore all of Jim's pontification. > __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] BL2 -- Antenna Balun Usage
On Mon,5/22/2017 10:07 PM, Wes Stewart wrote: PLEASE ignore all of Jim's pontification. Then YOU take responsibility for teaching everyone how they work. 73, Jim K9YC __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] BL2 -- Antenna Balun Usage
That is one, but far from the only form of a balun. A single-ended input, differential output amplifier is a balun for example. Wes N7WS On 5/22/2017 2:42 PM, Ron D'Eau Claire wrote: It is useful to remember that a so-called "balun" is nothing more than a length of transmission line - most commonly parallel wires. The line needs to be long enough to have sufficient inductance to produce balanced currents at the terminated end. Greater inductance is achievable by winding the transmission line into a coil, and even more if that coil has a ferrite core. So, as Bill notes, the impedance it presents to the source (your rig) will vary based on the impedance of the load, just like any other transmission line. 73, Ron AC7AC __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] BL2 -- Antenna Balun Usage
PLEASE ignore all of Jim's pontification.
I find it curious that Terman ("Radio Engineering"), Kraus ("Antennas"), Johnson
("Transmission Lines and Networks") all use the "meaningless" word "balun" in
their books. Clearly, these guys should have consulted with Jim before doing so,
because obviously they didn't know what they were talking about.
A transmission line transformer can be as simple as a geometric mean
quarter-wave line between two different impedances. No ferrites required. A
balun (pardon me, I'm with Kraus) can be a quarter-wave open stub at the
feedpoint of an antenna. Collins ("Fundamentals of SSB") calls this a
"Bazooka-type balun", but what does Collins Radio know about anything?) Or, it
could be a half-wave line connecting the two halves of a dipole. A stub balun
can be both a balancing device and an impedance transformer at the same time.
And it's nothing but coax. A two-wire line wound around a core might be a
common-mode choke, but if it's long enough and different in impedance from the
load, then it's an impedance transformer too.
In summary, just removing the term balun from one's lexicon doesn't simplify
anything.
And I almost forgot, that N6BV article Jim mentions is titled, "Don't blow up
your BALUN."
Wes N7WS
On 5/22/2017 2:11 PM, Jim Brown wrote:
On Mon,5/22/2017 12:42 PM, Bill Leonard N0CU wrote:
I am no expert when it comes to baluns
You're not the only one. :)
Some important comments. First, PLEASE strike the word "balun" from your
vocabulary. It is a meaningless word that tells us NOTHING about the device or
circuit element it is used to describe. I can think of nearly a dozen VERY
different devices that are CALLED baluns. Use the word "balun" conceals what
the device actually is and prevents everyone involved from understanding what
it does.
A two-wire line wound around a ferrite core forms a COMMON MODE CHOKE. It is
not a "transmission line transformer," nor is it an inductor, nor is it a
transformer at all! The ferrite core carries only flux due to common mode
current, and loss in the choke is I squared R, where I is the common mode
current and R is the resistive impedance of the common mode choke.
Arrays of common mode chokes CAN be wired in series/parallel combinations to
match circuits of differing impedance, but that device is NOT a transformer,
it is an array of common mode chokes. If we want to know how this array of
chokes work, we must analyze them as arrays of common mode chokes, not as a
transformer.
A transformer, is, by definition, two windings that are magnetically coupled,
and the impedance transformation ratio is the square of the turns ratio. If we
want to know how a transformer works, we must analyze it as a transformer.
It's as simple as that. The ferrite core carries ALL of the flux, and thus all
of the differential power carried by the circuit into which it is inserted.
In general, common mode chokes do NOT affect the differential signal, but
there CAN be differential mode loss in the transmission line that forms the
common mode choke due to transmission line effects. For example, if the common
mode choke is inserted in a badly mismatched transmission line, there can
excess loss due to SWR throughout the line, both in the part of the line that
forms the choke and in the rest of the line. Below UHF, virtually all loss in
real transmission lines is due to I square R; if the combination of the
antenna and the line places a current maxima at the choke, that segment of the
line can burn a high fraction of the transmitter power, greatly reducing the
transmitter power that gets to the antenna and overheating (and frying) that
segment of the line. N6BV wrote an excellent applications note about this for
QST several years ago, to which I contributed.
It IS practical to model (predict) dissipation in a common mode choke using
NEC. A single wire is added to the model with the geometry and physical
connections of the transmission line, and the known (measured) impedance of
the choke is added as a Load at the point where it is inserted in the system.
NEC is then set to model with a defined transmitter output power (for example,
1,500W), and currents are computed. NEC then provides a readout of current at
every point on every conductor, and the current in the choke is used to
compute dissipation in the choke.
Tutorials at k9yc.com/publish.htm show a practical method for measuring the
common mode impedance of ferrite chokes, and for determining values for a
parallel equivalent circuit that can provide a good first approximation of
dissipation.
73, Jim K9YC
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Re: [Elecraft] BL2 -- Antenna Balun Usage
It is useful to remember that a so-called "balun" is nothing more than a length of transmission line - most commonly parallel wires. The line needs to be long enough to have sufficient inductance to produce balanced currents at the terminated end. Greater inductance is achievable by winding the transmission line into a coil, and even more if that coil has a ferrite core. So, as Bill notes, the impedance it presents to the source (your rig) will vary based on the impedance of the load, just like any other transmission line. 73, Ron AC7AC -Original Message- From: Elecraft [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Bill Leonard N0CU Sent: Monday, May 22, 2017 12:42 PM To: elecraft@mailman.qth.net Subject: Re: [Elecraft] BL2 -- Antenna Balun Usage I am no expert when it comes to baluns, but here are several comments that are based upon some research that I have recently done on the subject: 1) Now, unlike in the past, the most commonly used balun is the current balun. Most current baluns use some type of transmission line (if they do, they are called transmission line transformers). If the load on a balun’s output does not represent a 1:1 SWR for the balun, the impedance measured at the input of the balun will be close to the balun load impedance only when the electrical length of the balun’s line is a multiple of an electrical half wavelength. I suggest that you try putting 25 ohm and 100 ohm resistive loads on your baluns and see what you measure at the input. The BL-2 uses a relatively short length of coax (~12 in I believe), however, 12 in of RG58 will show 80+j33 at its input at 30 MHz when terminated with 100 ohms (using TLW). My high power DXE 1:1 current choke (balun) has a much longer length of coax than the BL-2. It reads 43 +j32 ohms at 30MHz with a 25 ohm load (measured with a VNA 2180 network analyzer). If you can determine the length and type of coax in the balun that you are using, you can use ARRL’s TLW software to estimate what the actual balun load impedance is by inputting the line parameters and the impedance you measure at the balun input. 2) What happens to balun performance as the SWR increases is a question that I have yet to find an answer to. I am not aware of any balun manufacturer that attempts to quantify this behavior with any spec. There seems to be general agreement that baluns do not like highly reactive loads. 3) Balun heating is a complex issue that many “experts” don’t agree on. Looking at it simplistically, there are two sources of heating in current baluns (voltage baluns are very different than current baluns when it comes to heating). The first source of heating is the loss in the transmission line used in the balun. If a short length of high quality coax is used, the loss (ie, heating) should be relatively small. However, the confined space and poor heat transfer in the balun housing could mean that even a small amount of loss can be problematic in a poorly designed, high power balun. What many “experts” don’t realize is that the normal (differential mode) signal flowing down the coax does not cause any heating in the ferrite core in a current balun (this is not the case with a voltage balun). This is because this signal is completely contained between the outer surface of the center conductor and inner surface of the shield in the coax. What does cause heating in a current balun is the common mode current flowing on the outer surface of the shield on the coax used in the balun. This is the unwanted current that the balun is intended to reduce. Also, a number of articles claim that ferrite core temperatures can reach critical values (where the core fails) well before the core saturates and thermal runaway occurs. 4) Heating from common mode current is another area where the “experts” don’t agree. Heating due to common mode current is a function of transmitter power, design of the balun (ie, type of core, core size/mix, style of balun, heat transfer of housing, balun load impedance, etc) and the “system” issues that affect the balun’s performance. Depending on the values of the important system parameters, adding a balun can either increase, decrease, or have no effect upon the common mode current flowing on a transmission line. The common mode current and the resistive component of the balun’s common mode impedance are critical factors that determine the amount of heating in the balun’s ferrite core. A surprising number of “experts” make claims for power handling capabilities of various types of baluns without even mentioning the importance of these “system” issues. Tom Rauch (W8JI) and Tom Thompson (W0IVJ) have written articles that use EZNEC to quantitatively show the importance of these “system” issues when it comes to estimating common mode currents on transmission lines. However, as enlightening as these articles are, I am doubtful that EZNEC can be used to accurate
Re: [Elecraft] BL2 -- Antenna Balun Usage
On Mon,5/22/2017 12:42 PM, Bill Leonard N0CU wrote: I am no expert when it comes to baluns You're not the only one. :) Some important comments. First, PLEASE strike the word "balun" from your vocabulary. It is a meaningless word that tells us NOTHING about the device or circuit element it is used to describe. I can think of nearly a dozen VERY different devices that are CALLED baluns. Use the word "balun" conceals what the device actually is and prevents everyone involved from understanding what it does. A two-wire line wound around a ferrite core forms a COMMON MODE CHOKE. It is not a "transmission line transformer," nor is it an inductor, nor is it a transformer at all! The ferrite core carries only flux due to common mode current, and loss in the choke is I squared R, where I is the common mode current and R is the resistive impedance of the common mode choke. Arrays of common mode chokes CAN be wired in series/parallel combinations to match circuits of differing impedance, but that device is NOT a transformer, it is an array of common mode chokes. If we want to know how this array of chokes work, we must analyze them as arrays of common mode chokes, not as a transformer. A transformer, is, by definition, two windings that are magnetically coupled, and the impedance transformation ratio is the square of the turns ratio. If we want to know how a transformer works, we must analyze it as a transformer. It's as simple as that. The ferrite core carries ALL of the flux, and thus all of the differential power carried by the circuit into which it is inserted. In general, common mode chokes do NOT affect the differential signal, but there CAN be differential mode loss in the transmission line that forms the common mode choke due to transmission line effects. For example, if the common mode choke is inserted in a badly mismatched transmission line, there can excess loss due to SWR throughout the line, both in the part of the line that forms the choke and in the rest of the line. Below UHF, virtually all loss in real transmission lines is due to I square R; if the combination of the antenna and the line places a current maxima at the choke, that segment of the line can burn a high fraction of the transmitter power, greatly reducing the transmitter power that gets to the antenna and overheating (and frying) that segment of the line. N6BV wrote an excellent applications note about this for QST several years ago, to which I contributed. It IS practical to model (predict) dissipation in a common mode choke using NEC. A single wire is added to the model with the geometry and physical connections of the transmission line, and the known (measured) impedance of the choke is added as a Load at the point where it is inserted in the system. NEC is then set to model with a defined transmitter output power (for example, 1,500W), and currents are computed. NEC then provides a readout of current at every point on every conductor, and the current in the choke is used to compute dissipation in the choke. Tutorials at k9yc.com/publish.htm show a practical method for measuring the common mode impedance of ferrite chokes, and for determining values for a parallel equivalent circuit that can provide a good first approximation of dissipation. 73, Jim K9YC __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] BL2 -- Antenna Balun Usage
I am no expert when it comes to baluns, but here are several comments that are based upon some research that I have recently done on the subject: 1) Now, unlike in the past, the most commonly used balun is the current balun. Most current baluns use some type of transmission line (if they do, they are called transmission line transformers). If the load on a balun’s output does not represent a 1:1 SWR for the balun, the impedance measured at the input of the balun will be close to the balun load impedance only when the electrical length of the balun’s line is a multiple of an electrical half wavelength. I suggest that you try putting 25 ohm and 100 ohm resistive loads on your baluns and see what you measure at the input. The BL-2 uses a relatively short length of coax (~12 in I believe), however, 12 in of RG58 will show 80+j33 at its input at 30 MHz when terminated with 100 ohms (using TLW). My high power DXE 1:1 current choke (balun) has a much longer length of coax than the BL-2. It reads 43 +j32 ohms at 30MHz with a 25 ohm load (measured with a VNA 2180 network analyzer). If you can determine the length and type of coax in the balun that you are using, you can use ARRL’s TLW software to estimate what the actual balun load impedance is by inputting the line parameters and the impedance you measure at the balun input. 2) What happens to balun performance as the SWR increases is a question that I have yet to find an answer to. I am not aware of any balun manufacturer that attempts to quantify this behavior with any spec. There seems to be general agreement that baluns do not like highly reactive loads. 3) Balun heating is a complex issue that many “experts” don’t agree on. Looking at it simplistically, there are two sources of heating in current baluns (voltage baluns are very different than current baluns when it comes to heating). The first source of heating is the loss in the transmission line used in the balun. If a short length of high quality coax is used, the loss (ie, heating) should be relatively small. However, the confined space and poor heat transfer in the balun housing could mean that even a small amount of loss can be problematic in a poorly designed, high power balun. What many “experts” don’t realize is that the normal (differential mode) signal flowing down the coax does not cause any heating in the ferrite core in a current balun (this is not the case with a voltage balun). This is because this signal is completely contained between the outer surface of the center conductor and inner surface of the shield in the coax. What does cause heating in a current balun is the common mode current flowing on the outer surface of the shield on the coax used in the balun. This is the unwanted current that the balun is intended to reduce. Also, a number of articles claim that ferrite core temperatures can reach critical values (where the core fails) well before the core saturates and thermal runaway occurs. 4) Heating from common mode current is another area where the “experts” don’t agree. Heating due to common mode current is a function of transmitter power, design of the balun (ie, type of core, core size/mix, style of balun, heat transfer of housing, balun load impedance, etc) and the “system” issues that affect the balun’s performance. Depending on the values of the important system parameters, adding a balun can either increase, decrease, or have no effect upon the common mode current flowing on a transmission line. The common mode current and the resistive component of the balun’s common mode impedance are critical factors that determine the amount of heating in the balun’s ferrite core. A surprising number of “experts” make claims for power handling capabilities of various types of baluns without even mentioning the importance of these “system” issues. Tom Rauch (W8JI) and Tom Thompson (W0IVJ) have written articles that use EZNEC to quantitatively show the importance of these “system” issues when it comes to estimating common mode currents on transmission lines. However, as enlightening as these articles are, I am doubtful that EZNEC can be used to accurately predict the common mode current in any given application. At this point, given the difficulty of either measuring, or predicting, what the common mode current will be in a given application, I have concluded that the best way to evaluate core heating in a balun is to install it and test it at the intended power level. Hope this helps, Bill N0CU P.S.: an “expert” is someone who may be wrong, but is never in doubt! -- View this message in context: http://elecraft.365791.n2.nabble.com/BL2-Antenna-Balun-Usage-tp7630889p7631020.html Sent from the Elecraft mailing list archive at Nabble.com. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by:
Re: [Elecraft] BL2 -- Antenna Balun Usage
Balun ratings are for a 1:1 SWR. My experience has been that when the impedance gets very reactive, baluns heat up more. I had a 5 kW DXE balun get too hot to touch with around 1 kW in such a situation. Canceling the reactance on the open-wire line side of the balun made it run cool. Measuring the impedance of an open line with an antenna analyzer is tricky. If you use a balun, it will act as an extra piece of transmission line and transform the impedance. I tried to do it without a balun with an Autek VA1 (battery operated) sitting on a plastic stand -- it was difficult to adjust and I didn't feel the results were reliable. What you can do if you know the length of the feedline and the details of the antenna accurately is to use EZNEC to get the impedance at the feedpoint and then TLW or a similar program to compute what it will look like at the shack end of the feedline. This worked for me. 73, Victor, 4X6GP Rehovot, Israel Formerly K2VCO http://www.qsl.net/k2vco/ Vic On 21 May 2017 21:00, Phil Hystad wrote: I am assuming that a question about the Elecraft BL2 is On-Topic (OT) as opposed to Off-Topic (OT)… I am planning to use my BL2 to measure the impedance of my antenna+feedline at the point of entry into my balun (DX Engineering) which then feeds coax to my K-Line. The feedline is 450 ohm ladder (window style). The antenna is an 80-meter, 136 feet, antenna up in the air about 50 to 60 feet. I have two antenna analyzers and I will likely use both of them to see the difference. I will connect the 450-ohm feed line to the balanced side and a BNC to UHF adapter for attaching to my antenna analyzer [ (1) MFJ 259B, (2) Autek Research VA1]. Questions: (1) How much difference would I expect in using the balun verses measuring the balanced line directly with my antenna analyzers (actually, I plan to do both but wondering if anyone else has done this with what results). (2) I bought the BL2 for this particular purpose as it is switchable between 1:1 and 4:1 transformations. I wanted to figure out which would be best to use, a 1:1 or a 4:1 balun (DX Engineering and I have one of each). Due to the location of the balun (DX Engineering that is) it is easier for me to do this measurement first before physically replacing the one balun with the other. Right now, I am using a 4:1 balun. A third un-related (to above) question: The BL2 is rated for maximum of 250 watts. What are the bad effects of pushing more than 250 watts through the device, I mean a lot more like double or triple. My guess is that the ferrite transformer will overheat causing possibly run-away thermal non-linear changes to the transforming. What else will likely happen? 73, phil, K7PEH __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to k2vco@gmail.com __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] BL2 -- Antenna Balun Usage
> Quoted from Fred (“Skip”) K6DGW… > (1) The MFJ-259x series of antenna/feedline analyzers havean N coax > connector. Using the BL2, you can connect it to the balanced ladder line. How > were you planning to connect it without the balun? As you state it, it does > not sound like a reasonable experiment design. Not sure what you are saying above. After the e-mail I sent, since the WX was so nice at 77 degrees, I went out to do the measurements. I attached the 450-ohm ladder line to the balanced terminals on the BL2 and the BL2 was itself attached to the MFJ and also the VA1 via my BNC to UHF (PL-259) adapter. I first did resistor checks at 3.5 MHz to find that all was working as it should in this setup. With 200 ohm resistor on the BL2 terminals using 4:1 I measured 49 ohms with essentially zero X (reactance). In 1:1 mode, I read 203 ohms and 1 or zero on X (it was changing back and forth). Then I measured with the actual antenna by disconnecting the ladder line from my DXEngineering 4:1 balun and connecting it to the balanced terminals on the BL2. I was on a ladder doing this so I decided not to take too many measurements and focused on 80-meter band only. Within a reasonable error factor, the numbers I found for 4:1 switch on BL2 were consistent (close) to the Bypass SWR reported by my KAT500 for the same frequencies: 3.501, 3.6, 3.7, 3.8, 3.9, and 3.99. Most of the 1:1 measures I made were too high SWR (~15:1 and above). > > The MFJ-259x and VA1 are almost guaranteed to give non-identical results. If > they are large differences, youhave some other problem. If they are small, > they are essentially meaningless for your application. Hope this all helps. Yes, all of this helps. Later this year I will be doing some experiments with the BL2 — not for ham radio, more for my physics interest. I will be measuring the heating of the ferrite core on the BL2 using my Fluke Infrared Temperature gun. I have already measured the time for the ferrite core to come to thermal equilibrium in two different heat baths. An air conditioned room versus the overheated garage on a hot summer day. That was the very first thing I did with my BL2 after I finished building it. Yes, the MFJ and VA1 always give me different results but they are usually close. The VA1 actually is useful because you can easily determine the sign of the reactance where as with the MFJ you need to change the frequency (like moving it up) to watch which direction the reactance term changes. PEH __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] BL2 -- Antenna Balun Usage
Just to add to one extra reply. Z readings from 259B or VA1 are inaccurate. SWR measurement is pretty good, though. BL2 balun is very good in transforming 200 to 50 or 50 to 50. It is hard to figure out exactly what is does outside the range. When BL2 is not hot, it is good enough. Whether it is hot or not depends not only on power but also on impedances to transform. I used BL1 with too short wires and the balun was hot but I was making contacts. For precision measurements buy VNA that can be calibrated. Ignacy, NO9E -- View this message in context: http://elecraft.365791.n2.nabble.com/BL2-Antenna-Balun-Usage-tp7630889p7630895.html Sent from the Elecraft mailing list archive at Nabble.com. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] BL2 -- Antenna Balun Usage
Hi Phil,
(1) The MFJ-259x series of antenna/feedline analyzers havean N coax
connector. Using the BL2, you can connect it to the balanced ladder
line. How were you planning to connect it without the balun? As you
state it, it does not sound like a reasonable experiment design.
(2) The impedance ratio of both the DXE and BL2 is the square of the
turns ratio. Thus, the 4:1 DXE is a 16:1 ratio in complex ohms.
You can measure the complex impedance at the end of the balanced line
using a very short coax jumper from the BL2 to the analyzerand then
compute the impedance at the balanced terminal using the above. Be
careful of BL2 ratios that give extreme results, they're likely not
really valid.
(3) Transformers are rated for both power and breakdown voltage. My DXE
balun was rated at 11 KV and 10 KW ... although cramming 10 KW into an
SO-239 seems a bit unrealistic. [:-) The transformer will have
lossesmanifested in heat. If it gets too hot, it will do what everything
else does whenit gets too hot.
Depending on the impedance ratio and the complex impedance you're
feeding, the voltagecan exceed the breakdown voltage, creating
well-known effects.
If the applied power saturates the transformer core, power peaks above
saturation will be clipped creating a huge RFI generator. Balun cores
are ferrite of various compositions. Each composition has a specific
Curie temperature, above which the core loses it's ferrimagnetic properties.
The MFJ-259x and VA1 are almost guaranteed to give non-identical
results. If they are large differences, youhave some other problem. If
they are small, they are essentially meaningless for your application.
Hope this all helps.
73,
Fred ("Skip") K6DGW
Sparks NV USA
Washoe County DM09dn
On 5/21/2017 11:00 AM, Phil Hystad wrote:
I am planning to use my BL2 to measure the impedance of my antenna+feedline at
the point of entry into my balun (DX Engineering) which then feeds coax to my
K-Line.
The feedline is 450 ohm ladder (window style). The antenna is an 80-meter, 136
feet, antenna up in the air about 50 to 60 feet.
I have two antenna analyzers and I will likely use both of them to see the
difference. I will connect the 450-ohm feed line to the balanced side and a
BNC to UHF adapter for attaching to my antenna analyzer [ (1) MFJ 259B, (2)
Autek Research VA1].
Questions:
(1) How much difference would I expect in using the balun verses measuring the
balanced line directly with my antenna analyzers (actually, I plan to do both
but wondering if anyone else has done this with what results).
(2) I bought the BL2 for this particular purpose as it is switchable between
1:1 and 4:1 transformations. I wanted to figure out which would be best to
use, a 1:1 or a 4:1 balun (DX Engineering and I have one of each). Due to the
location of the balun (DX Engineering that is) it is easier for me to do this
measurement first before physically replacing the one balun with the other.
Right now, I am using a 4:1 balun.
A third un-related (to above) question: The BL2 is rated for maximum of 250
watts. What are the bad effects of pushing more than 250 watts through the
device, I mean a lot more like double or triple. My guess is that the ferrite
transformer will overheat causing possibly run-away thermal non-linear changes
to the transforming. What else will likely happen?
73, phil, K7PEH
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