Re: [Elecraft] Toroids frequency range and baluns
On Sat, 27 Sep 2008 09:21:11 -0600, James Duffey wrote: Why are choke baluns wound as a coil vastly superior to choke baluns made with a sting of ferrite beads? With the coil type, you're adding additional coax loss... What am I missing here? I didn't see an explicit reply to this on the list, In the interest of brevity on the list, I referred those interested in this to the tutorial I wrote on RFI and the use of Ferrite Chokes. That material is anything but brief, but I believe that it is quite clear and easy to study IF you understand the fundamentals of electrical circuits that include R, L, C, and Z. but the short answer is that with a coil balun, the inductance increases as the square of the number of turns. With the beads, the inductance just increases as the number of the beads. YES So, ignoring stray capacitance, You CANNOT ignore stray capacitance, it makes a VERY major contribution to the behavior of ANY choke. a toroid with 10 turns will have 10 times the inductance of the same cable passed through 10 toroids (beads). You get more bang for your buck by coiling the cable. The additional losses are not too great for most applications. YES. BUT -- it is NOT about INDUCTANCE, it is about the RESISTIVE component of the impedance. And that RESISTANCE is the loss component of the parallel RLC circuit formed by the inductance of the choke, the capacitance, and the loss coupled from the ferrite core. It is the RESISTANCE that solves our problems, NOT the inductance. We use inductance in TRANSFORMERS and in resonant circuits that are part of radios. We use RESISTANCE in RFI suppression and in common mode chokes. The tutorial is at http://audiosystemsgroup.com/RFI-Ham.pdf 73, Jim Brown K9YC ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
RE: [Elecraft] Toroids frequency range and baluns
Hi Bob, See comments interspersed. On Mon, 29 Sep 2008 09:51:11 -0500, Solosko, Robert B \(Bob\) wrote: Jim, I've been reading through your tutorial, and, if I understand it, the best approach is neither a plain wound coax balun nor a string of ferrite beads strung on the coax but is a balun made with coax wound around a ferrite core in a way the minimizes capacitance - is that correct? It depends mostly on the frequency range and the ferrite material, and to a lesser extent, on the power level. Think of the choke you're winding as any other inductor that has VERY low Q (typically around 0.5), and thus a very broad resonance. Like any inductor, we vary the number of turns, their diameter and spacing, and the core material to hit the desired resonance. A choke of #31 material can provide a strongly resistive impedance over a frequency range of roughly 4:1, so we can wind one to cover 160-40 meters. That choke would use closely spaced turns, because we need the additional capacitance and mutual coupling between windings to move the resonance down to about 80 meters. On the other hand, a choke to cover 20-10 meters needs wide-spaced windings, because we only want to move the resonance to about 21 MHz. Power level enters the equation only to the extent that the choke must provide sufficient common mode impedance that it reduces common mode current to the extent that the P=I*E is small enough that it does not overheat the coax or the core. The tutorial shows that's an easily achievable objective once you realize that it's a key design parameter. But I still have several more questions: - it appears that material 31 is the best material to use for baluns. It's the best material to use for a COAXIAL CHOKE that needs to work below 5 MHz. #43 is equally good on 40M, and slightly better above 40M. If you're only stocking up on one material and buying in quantity for the best price, # 31 is the best choice. In addition to my transmission line balun, I also have some problems with power supply birdies on 160m, and to a lesser degree on 80m. Is material 31 still the optimum material for adding additional RFI filtering to my power supply (along with parallel capacitors)? These chokes kill common mode current on the cable you wind around them, but there can also be differential mode coupling that a capacitor ACROSS the line (that is, plut to minus) can suppress, and there can be direct radiation from insffficiently shielded circuitry. No external filtering will kill (or change) that direct radiation. - My transmission line balun is serving two purposes: as a current balun to reduce the RFI in the shack problem that I have had, and as a 4:1 transformer to better match the ladder line from my antenna to the short length of coax to my rig. (My 4:1 balun is made from 2 separate cores as is the BL2, but they're much larger cores to minimize saturation and heating problems.) It seems to me, if I understand your tutorial, that the characteristics of the cores used for transformers (low resistance) and those used for suppression (high resistance) and mutually exclusive. Thus, does it make sense to have a single balun serving these two purposes, or is it better to optimize the balun for the transformer application (material ??) and have a separate balun optimized for suppression? That's a very perceptive question. For the first part of the answer, study the photo of the high power DXE 4:1 balun in my Power Point presentation -- select it from http://audiosystemsgroup.com/publish That balun is essentially two chokes wound with parallel wire transmission line (that is, bifilar) around what could be #31 or #43 cores. On the 50 ohm side, they're wired in parallel, on the 200 ohm side they're in series. Because the chokes are bifilar, there's a lot of leakage flux in that core if you're running power. The choking impedance isn't very high either. A far better design would use coax, #31, and a lot more turns. That balun would have a much higher choking impedance, and would also be a lot more efficient. The second part of the answer is to study the DXE catalog -- they sell a separate product that they call a common mode choke! When you study my measurements (in the Power Point) for three of their high power baluns, it's obvious why -- they have very poor common mode rejection. So the short answer to your question is, YES! Another point of clarification. Both the DXE two-choke series/parallel combo and the one I described wound with coax are NOT transformers -- they are NOT coupling signal through the core, they are using the core to form a choke. They ARE doing impedance transformation and balancing. So it is correct to call them baluns but incorrect to call them transformers. 73, Jim K9YC ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list.
RE: [Elecraft] Toroids frequency range and baluns
Jim, Why are choke baluns wound as a coil vastly superior to choke baluns made with a sting of ferrite beads? With the coil type, you're adding additional coax loss... What am I missing here? 73, Bob W1SRB -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Jim Brown Sent: Saturday, September 20, 2008 4:17 AM To: elecraft@mailman.qth.net Subject: RE: [Elecraft] Toroids frequency range and baluns On Fri, 19 Sep 2008 20:45:57 -0700, Ron D'Eau Claire wrote: Balun is an unfortunate, all-inclusive and misleading term. One so-called balun may be as different from another balun in its requirements and application as a motorcycle is different from railroad locomotive. Yes, it really is. I stand by my statement when talking about a choke balun consisting of a string of ferrite beads on some coax or a coaxial line on a coil form such as I described. The only losses caused by such a balun will be those of the transmission line itself, which cannot be ignored if the SWR is high. Yes on all counts. BUT -- the chokes wound as a coil are vastly superior. So-called baluns that transform impedances are, typically, transformers -- often transmission-line transformers. They're a whole different animal and can be very unpredictable, especially when they use ferrite or powdered iron cores and are exposed to a wide range of impedances. Yes. Again, poor use of words by the industry. 73, Jim K9YC ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
RE: [Elecraft] Toroids frequency range and baluns
On Mon, 22 Sep 2008 08:28:28 -0500, Solosko, Robert B \(Bob\) wrote: Jim, Why are choke baluns wound as a coil vastly superior to choke baluns made with a sting of ferrite beads? With the coil type, you're adding additional coax loss... What am I missing here? Study my tutorial. http://audiosystemsgroup.com/RFI-Ham.pdf 73, Jim K9YC ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
RE: [Elecraft] Toroids frequency range and baluns
On Fri, 19 Sep 2008 20:45:57 -0700, Ron D'Eau Claire wrote: Balun is an unfortunate, all-inclusive and misleading term. One so-called balun may be as different from another balun in its requirements and application as a motorcycle is different from railroad locomotive. Yes, it really is. I stand by my statement when talking about a choke balun consisting of a string of ferrite beads on some coax or a coaxial line on a coil form such as I described. The only losses caused by such a balun will be those of the transmission line itself, which cannot be ignored if the SWR is high. Yes on all counts. BUT -- the chokes wound as a coil are vastly superior. So-called baluns that transform impedances are, typically, transformers -- often transmission-line transformers. They're a whole different animal and can be very unpredictable, especially when they use ferrite or powdered iron cores and are exposed to a wide range of impedances. Yes. Again, poor use of words by the industry. 73, Jim K9YC ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
RE: [Elecraft] Toroids frequency range and baluns
Ron wrote: So-called baluns that transform impedances are, typically, transformers -- often transmission-line transformers. There is a type of choke balun that is both a balanced-to-unbalanced device and an impedance transformer at once. Connecting two ferrite-loaded transmission line baluns in parallel at one end and series at the other will yield a 4:1 transformation. Higher ratios are possible with more series/parallel combinations. Wes N7WS ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Toroids frequency range and baluns
On Thu, 18 Sep 2008 16:20:56 -0500, Solosko, Robert B (Bob) wrote: toroids all have a specified frequency range but what happens when they're used outside of that range? To gain a better understanding of ferrites study my tutorial. http://audiosystemsgroup.com/RFI-Ham.pdf Look at the measured data in that tutorial. STUDY the Fair-Rite data for their products. 73, Jim Brown K9YC ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
RE: [Elecraft] Toroids frequency range and baluns
Bob W1SRB writes: There have been several e-mail threads recently about ferrite cores and about baluns and transmission line loss with high SWR. Related to this is a question that I haven't seen addressed anywhere - toroids all have a specified frequency range but what happens when they're used outside of that range? To be more specific, I have a multiband fan dipole fed with ladder line into a 4:1 current balun that then connects to my rig through about 5 feet of RG-8. I made the balun using a pair of T200-2 powder iron cores, which have a specified frequency range of 0.25 to 10 MHz. Since I'm using this single antenna from 160m to 10m, I'm way beyond the specified frequency range of the cores - is the balun likely to be very inefficient above it 10MHz? The antenna seems to work very well on 40m and 20m and OK on 15m. Since the band conditions haven't been particularly good in the last few years that I've been using this antenna, I can't tell whether my lack of many QSOs on 15m and above is due to inefficiencies in the balun or to band conditions? What do you think? The balun doesn't have any effect on the efficiency of the antenna unless it involves lots of coax at high SWR such as the big coil of coax some Hams use for a choke balun. (They're FB as long as the SWR is low but, like any coax, the losses go up with the SWR.) The only function of the balun in your setup is to manage the flow of RF current to keep it off of the *outside* of the coax and your rig. That's only a concern if the voltages are sufficient to cause your rig to be hot with RF so that touching the rig changes the antenna tuning or you get RF feedback in to the rig through the mic or you have other operational issues. As long as you don't have those issues, you don't need a balun at all. To more directly answer your question, the balun you have probably works as well at 30 MHz as it does at 1.8 MHz. The T200-2 cores will show a high impedance to the RF currents across the HF range. That's all you need. Ron AC7AC ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Toroids frequency range and baluns
Bob, To further add to the confusion, I will throw in my 2 cents worth too. Let me say that a balun wound on a powdered iron core is highly dependent on the inductance. The inductive reactance should be at least 5 times the feedline impedance at the balun's antenna side for it to be effective, so how well it works depends on the antenna too. Also as the frequency gets higher, the resistive loss through the balun becomes more significant and the interwinding capacitance becomes important. For all those reasons (and a few more too), it is common to use a ferrite core rather than a powdered iron core for a balun. The inductance per turn is much higher, so fewer turns are needed to satisfy the inductance requirement at the low frequency end of the scale and the wire resistance and winding capacitance is less at the high frequency end. The core for a balun can be lossy at the frequency of use. You can think of a current balun as a transmission line inside a choke (the coil-of-coax type baluns are a perfect example). The differential signal travels on the transmission line (inside the coax) while the common mode signal on the outside of the coax (the one you want to suppress) encounters the choke impedance. The advantage of a ferrite core is that the transmission line length is shorter than a balun built with a powdered iron core - fewer turns = lower resistance, lower capacitance. I know that did not answer your question directly, but it all depends on the inductance of your balun, the antenna side actual feed impedance, the wire resistance, and the capacitance across the transmission line inside that balun. I don't have enough data to provide a definite answer. 73, Don W3FPR Solosko, Robert B (Bob) wrote: Hello All, There have been several e-mail threads recently about ferrite cores and about baluns and transmission line loss with high SWR. Related to this is a question that I haven't seen addressed anywhere - toroids all have a specified frequency range but what happens when they're used outside of that range? To be more specific, I have a multiband fan dipole fed with ladder line into a 4:1 current balun that then connects to my rig through about 5 feet of RG-8. I made the balun using a pair of T200-2 powder iron cores, which have a specified frequency range of 0.25 to 10 MHz. Since I'm using this single antenna from 160m to 10m, I'm way beyond the specified frequency range of the cores - is the balun likely to be very inefficient above it 10MHz? The antenna seems to work very well on 40m and 20m and OK on 15m. Since the band conditions haven't been particularly good in the last few years that I've been using this antenna, I can't tell whether my lack of many QSOs on 15m and above is due to inefficiencies in the balun or to band conditions? What do you think? Bob W1SRB ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
RE: [Elecraft] Toroids frequency range and baluns
On Fri, 19 Sep 2008 10:21:44 -0700, Ron D'Eau Claire wrote: The balun doesn't have any effect on the efficiency of the antenna unless it involves lots of coax at high SWR such as the big coil of coax some Hams use for a choke balun. (They're FB as long as the SWR is low but, like any coax, the losses go up with the SWR.) WRONG! There are three fundamental cases of ferrite baluns or chokes. 1) A choke wound with coax 2) a choke wound with parallel wires (bifilar) 3) a transformer (voltage balun). Case #1: Coax contains 100% of the differential power (transmitter feeding antenna) within the dielectric. The ferrite core of a COAX CHOKE sees ONLY the common mode voltage and current. If the impedance of the choke is high enough, the current is very small, so the dissipation in the choke is very small. Case #2: A choke with a bifilar winding (that is, two parallel wires, NOT coax) puts a significant fraction of the transmitted power in the core. This is leakage flux from the bifilar winding (really a short length of parallel wire transmission line). This leakage flux is typically 30% of the transmitted power, and is NOT related to common mode current. Case #3: A VOLTAGE balun is VERY different -- it puts 100% of the transmitted power in the ferrite. All of this is discussed in the tutorials, previously referenced. BTW -- earlier work and publications by W7EL, W2DU, and W1JR are all very good, but they were done 30 years ago. My work builds on theirs, and is considerably more advanced. Also, the #31 material that is so useful for HF chokes was developed only a few years ago. 73, Jim K9YC ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
RE: [Elecraft] Toroids frequency range and baluns
Jim wrote: WRONG! There are three fundamental cases of ferrite baluns or chokes. 1) A choke wound with coax 2) a choke wound with parallel wires (bifilar) 3) a transformer (voltage balun). - You are absolutely right Jim. I read current balun and thought choke balun. I missed the 4:1 comment. Balun is an unfortunate, all-inclusive and misleading term. One so-called balun may be as different from another balun in its requirements and application as a motorcycle is different from railroad locomotive. I stand by my statement when talking about a choke balun consisting of a string of ferrite beads on some coax or a coaxial line on a coil form such as I described. The only losses caused by such a balun will be those of the transmission line itself, which cannot be ignored if the SWR is high. So-called baluns that transform impedances are, typically, transformers -- often transmission-line transformers. They're a whole different animal and can be very unpredictable, especially when they use ferrite or powdered iron cores and are exposed to a wide range of impedances. Ron AC7AC ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
