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TV 4:1 BALUN
I was considering using a TV type 4:1 balun on 2 meters. Does anyone
know how much power these can handle? I remember a guy doing this when I was a teenager(long ago) but I think the baluns were built a little stouter back then than they are now. Jimmie |
TV 4:1 BALUN
On Sat, 17 Jan 2009 12:44:05 -0800 (PST), JIMMIE
wrote: I was considering using a TV type 4:1 balun on 2 meters. Does anyone know how much power these can handle? I remember a guy doing this when I was a teenager(long ago) but I think the baluns were built a little stouter back then than they are now. Hi Jimmie, Have your tried researching the archives for this topic? Google's search tools can easily provide those answers. What do you have that is 1. a 200 Ohm load, or 2. a 12.5 Ohm load? Is it balanced, or unbalanced? Does this BalUn have a pedigree (like Radio Shack's "Best TV") or could it actually be an FM BalUn? If it is a TV BalUn, which band? How much power are you going to apply to the load? 73's Richard Clark, KB7QHC |
TV 4:1 BALUN
On Jan 17, 2:44*pm, JIMMIE wrote:
I was considering using a TV type 4:1 balun on 2 meters. Does anyone know how much power these can handle? I remember a guy doing this when I was a teenager(long ago) but I think the baluns were built a little stouter back then than they are now. Jimmie I wouldn't bother with those.. Tiny gauge wire.. Might be usable for a receive antenna, but I sure as heck wouldn't use one for transmit. I bet they are fairly lossy. Also.. they may not work too well on the HF frequencies being they are designed for VHF/UHF. |
TV 4:1 BALUN
On Jan 17, 4:59*pm, Richard Clark wrote:
On Sat, 17 Jan 2009 12:44:05 -0800 (PST), JIMMIE wrote: I was considering using a TV type 4:1 balun on 2 meters. Does anyone know how much power these can handle? I remember a guy doing this when I was a teenager(long ago) but I think the baluns were built a little stouter back then than they are now. Hi Jimmie, Have your tried researching the archives for this topic? *Google's search tools can easily provide those answers. What do you have that is 1. a 200 Ohm load, or 2. a 12.5 Ohm load? Is it balanced, or unbalanced? Does this BalUn have a pedigree (like Radio Shack's "Best TV") or could it actually be an FM BalUn? If it is a TV BalUn, which band? How much power are you going to apply to the load? 73's Richard Clark, KB7QHC Googling TV BalUn was useless but searching fot 2M Balun proved more useful. Per an article by K3MT they should be able to handle power in the 5 to 10 watt range. More than enough for my purpose. I cracked open a couple and foundd that tthe type that go frm screw connectors to male F connector have a larger transformer than the barrel type. This was at least true for the couple that I sacrificed to the radio gods. K3MT"s data was on the barrrel or tubular type. Jimmie |
TV 4:1 BALUN
On Sun, 18 Jan 2009 00:52:28 -0800 (PST), JIMMIE
wrote: Googling TV BalUn was useless but searching fot 2M Balun proved more useful. Per an article by K3MT they should be able to handle power in the 5 to 10 watt range. More than enough for my purpose. I cracked open a couple and foundd that tthe type that go frm screw connectors to male F connector have a larger transformer than the barrel type. This was at least true for the couple that I sacrificed to the radio gods. K3MT"s data was on the barrrel or tubular type. Jimmie Hi Jimmie, So, going further with this resource you found, was there any report of how "well" it worked? Merely surviving the application of 5 to 10 Watts isn't exactly proof of suitability for performance. Even a SWR report could mask the fact that a BalUn inappropriately applied is operating as a padding resistor. Going further yet, was it reported what style of BalUn it was? Guanella? Ruthroff? Not all BalUns perform equally, and for reception (the class of BalUn you are mining for transmission application) it is arguable that it matters. Lastly to your first statement Googling TV BalUn was useless but searching fot 2M Balun proved more useful. The distinction was useful, but were you Googling the Web, or this group? 73's Richard Clark, KB7QHC |
TV 4:1 BALUN
On Jan 18, 1:19*pm, Richard Clark wrote:
On Sun, 18 Jan 2009 00:52:28 -0800 (PST), JIMMIE wrote: Googling TV BalUn was useless but searching fot 2M Balun proved more useful. Per an article by K3MT they should be able to handle power in the 5 to 10 watt range. More than enough for my purpose. I cracked open a couple and foundd that tthe type that go *frm screw connectors to male F connector have a larger transformer than the barrel type. This was at least true for the couple that I sacrificed to the radio gods. K3MT"s data was on the barrrel or tubular type. Jimmie Hi Jimmie, So, going further with this resource you found, was there any report of how "well" it worked? *Merely surviving the application of 5 to 10 Watts isn't exactly proof of suitability for performance. *Even a SWR report could mask the fact that a BalUn inappropriately applied is operating as a padding resistor. Going further yet, was it reported what style of BalUn it was? Guanella? *Ruthroff? *Not all BalUns perform equally, and for reception (the class of BalUn you are mining for transmission application) it is arguable that it matters. Lastly to your first statementGoogling TV BalUn was useless but searching fot 2M Balun proved more useful. The distinction was useful, but were you Googling the Web, or this group? 73's Richard Clark, KB7QHC K3MT had used them in 2M project so for the time being I will let it go at that for now. Iam concerned about the cores saturating at that power level but I doubt if there is a lot of info on it. When I get off the road in a couple of weeks I will try hooking a couple of them back to back to a dummy load, putting 10 watts in and seeing what happens. The web. Jimmie |
TV 4:1 BALUN
"Richard Clark" wrote in message ... On Sun, 18 Jan 2009 00:52:28 -0800 (PST), JIMMIE wrote: Googling TV BalUn was useless but searching fot 2M Balun proved more useful. Per an article by K3MT they should be able to handle power in the 5 to 10 watt range. More than enough for my purpose. I cracked open a couple and foundd that tthe type that go frm screw connectors to male F connector have a larger transformer than the barrel type. This was at least true for the couple that I sacrificed to the radio gods. K3MT"s data was on the barrrel or tubular type. Jimmie Hi Jimmie, So, going further with this resource you found, was there any report of how "well" it worked? Merely surviving the application of 5 to 10 Watts isn't exactly proof of suitability for performance. Even a SWR report could mask the fact that a BalUn inappropriately applied is operating as a padding resistor. Going further yet, was it reported what style of BalUn it was? Guanella? Ruthroff? Not all BalUns perform equally, and for reception (the class of BalUn you are mining for transmission application) it is arguable that it matters. Lastly to your first statement Googling TV BalUn was useless but searching fot 2M Balun proved more useful. The distinction was useful, but were you Googling the Web, or this group? 73's Richard Clark, KB7QHC Hi Richard I made some insertion loss measurements on some of the low cost TV (4:1) baluns when I was trying to understand that 137 MHz antenna. I didnt save any data. I did use several types of baluns. They were all typically the Radio Shack quality. At 137 MHz, the insertion loss was about 2.5 dB for two baluns connected in series, back to back. I know that seems high, but the units are really not well built. It seems that the original poster, Jimmie, might consider using RFI ferrites around the coax instead of the TV 4:1 baluns. My measured data indicates the low cost ferrites, intended to be used to minimize RFI conduction on the outside of cables, work quite well at 144 MHz. Jerry |
TV 4:1 BALUN
On Sun, 18 Jan 2009 12:35:01 -0800 (PST), JIMMIE
wrote: K3MT had used them in 2M project so for the time being I will let it go at that for now. Iam concerned about the cores saturating at that power level but I doubt if there is a lot of info on it. When I get off the road in a couple of weeks I will try hooking a couple of them back to back to a dummy load, putting 10 watts in and seeing what happens. The web. Jimmie Hi Jimmie, Last things first, you should Google in "Groups," specifically this group. This isn't a guarantee, but at least you will land in a thread where discussion will reveal flaws where they exist. For a core to saturate reveals a misunderstanding of how the BalUn works (it goes to the same correspondents who speak of "turns ratio"). The most effective BalUn provides a high common mode reactance or resistance to current. Hence current in that mode will be low. With low current into a high resistance you have low power dissipation. Core saturation never becomes a problem, and is a distinctly separate issue - although solved through the same mechanism. The most effective BalUn adds absolutely no differential mode reactance or resistance. Again, where there is high current and no resistance, there is no power dissipation and zero core saturation (for the same reasons, but through different mechanisms). Practical BalUns have some residual reactances and resistances that they add to the transmission circuit. A Ruthroff BalUn design even purposely introduces this to its own limitation (and no advantage over other designs). The Ruthroff design invites core saturation. A Guanella BalUn seeks to be the most effective design to its advantage over the Ruthroff. The Guanella design suppresses core saturation. There are limitations, of course. You can still flame out a Guanella if the core reactance/resistance is under designed, or your load is unbalanced and not suited to the transformation ratio. This can be aided through choking the input to the BalUn (which serves as a choke, too, for controlled loads). The back-to-back test is useful. Take one BalUn between a finger and thumb and count to 10. If you don't raise a welt, then they probably are not too lossy. 73's Richard Clark, KB7QHC |
TV 4:1 BALUN
On Sat, 17 Jan 2009 12:44:05 -0800 (PST), JIMMIE
wrote: I was considering using a TV type 4:1 balun on 2 meters. Does anyone know how much power these can handle? I remember a guy doing this when I was a teenager(long ago) but I think the baluns were built a little stouter back then than they are now. May I suggest using a coaxial cable 4:1 balun instead of ferrite core type. A 1/2 wave electrical length of coax cable, some soldering, and you're done. For just 2 meters, the bandwidth is just fine and the loss is no more than that of the coax cable. For low power, small diameter RG-174 type coax is fine. I use 4:1 coax baluns for matching 300 ohm folded dipole antennas: http://users.belgacom.net/hamradio/schemas/14balun.gif The common TV balun has two xfomers inside, which are sometimes combined on a single core. See schematics at: http://members.tripod.com/rclindia/trans.html http://www.electronics-tutorials.com/basics/baluns.htm However, if size is an issue, I guess the coax balun is a bit large. For just 2 meters, the ferrite core is not necessary. Just find a block of PTFE (Teflon) or plastic, and drill it to resemble the TV balun core, use 2 PTFE toroid cores (if you can find them), or simulate a torroid with a stack of nylon washers. Then wind the 2 pairs of 2 wires through the holes and bring out the connections. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
TV 4:1 BALUN
On Jan 18, 10:32*pm, Jeff Liebermann wrote:
On Sat, 17 Jan 2009 12:44:05 -0800 (PST), JIMMIE wrote: I was considering using a TV type 4:1 balun on 2 meters. Does anyone know how much power these can handle? I remember a guy doing this when I was a teenager(long ago) but I think the baluns were built a little stouter back then than they are now. May I suggest using a coaxial cable 4:1 balun instead of ferrite core type. *A 1/2 wave electrical length of coax cable, some soldering, and you're done. *For just 2 meters, the bandwidth is just fine and the loss is no more than that of the coax cable. *For low power, small diameter RG-174 type coax is fine. *I use 4:1 coax baluns for matching 300 ohm folded dipole antennas: http://users.belgacom.net/hamradio/schemas/14balun.gif The common TV balun has two xfomers inside, which are sometimes combined on a single core. *See schematics at: http://members.tripod.com/rclindia/trans.html http://www.electronics-tutorials.com/basics/baluns.htm However, if size is an issue, I guess the coax balun is a bit large. For just 2 meters, the ferrite core is not necessary. *Just find a block of PTFE (Teflon) or plastic, and drill it to resemble the TV balun core, use 2 PTFE toroid cores (if you can find them), or simulate a torroid with a stack of nylon washers. *Then wind the 2 pairs of 2 wires through the holes and bring out the connections. -- Jeff Liebermann * * 150 Felker St #D * *http://www.LearnByDestroying.com Santa Cruz CA 95060http://802.11junk.com Skype: JeffLiebermann * * AE6KS * *831-336-2558 I was rummaging through my mobil junk er toolbox and came across an old package of air core TV baluns. These date back to the day when TVs were usually fed with twin lead. Tuesday I may be able to get to some test equipment to check out the losses on those. Gee getting to spend a 3day weekend on the road is such fun. Jimmie |
TV 4:1 BALUN
On Mon, 19 Jan 2009 01:33:32 GMT, "Jerry"
wrote: At 137 MHz, the insertion loss was about 2.5 dB for two baluns connected in series, back to back. OUCH! I know that seems high, but the units are really not well built. Hi Jerry, So it would seem. 73's Richard Clark, KB7QHC |
TV 4:1 BALUN
On Jan 18, 10:32*pm, Jeff Liebermann wrote:
On Sat, 17 Jan 2009 12:44:05 -0800 (PST), JIMMIE wrote: I was considering using a TV type 4:1 balun on 2 meters. Does anyone know how much power these can handle? I remember a guy doing this when I was a teenager(long ago) but I think the baluns were built a little stouter back then than they are now. May I suggest using a coaxial cable 4:1 balun instead of ferrite core type. *A 1/2 wave electrical length of coax cable, some soldering, and you're done. *For just 2 meters, the bandwidth is just fine and the loss is no more than that of the coax cable. *For low power, small diameter RG-174 type coax is fine. *I use 4:1 coax baluns for matching 300 ohm folded dipole antennas: http://users.belgacom.net/hamradio/schemas/14balun.gif The common TV balun has two xfomers inside, which are sometimes combined on a single core. *See schematics at: http://members.tripod.com/rclindia/trans.html http://www.electronics-tutorials.com/basics/baluns.htm However, if size is an issue, I guess the coax balun is a bit large. For just 2 meters, the ferrite core is not necessary. *Just find a block of PTFE (Teflon) or plastic, and drill it to resemble the TV balun core, use 2 PTFE toroid cores (if you can find them), or simulate a torroid with a stack of nylon washers. *Then wind the 2 pairs of 2 wires through the holes and bring out the connections. -- Jeff Liebermann * * 150 Felker St #D * *http://www.LearnByDestroying.com Santa Cruz CA 95060http://802.11junk.com Skype: JeffLiebermann * * AE6KS * *831-336-2558 Jeff, Apparently TV matching transformers used to be air core and their use was quite common on 6 and 2 meter antennas.I knew the ones built into the old tuners were but I hadnt thought the old line transformers also being air core.They were per some of the locals on 2m repeater. If they aare the ones I am thinking of(big fat ones) I have a few at home. Jimmie |
TV 4:1 BALUN
On Mon, 19 Jan 2009 08:10:07 -0800 (PST), JIMMIE
wrote: Jeff, Apparently TV matching transformers used to be air core and their use was quite common on 6 and 2 meter antennas. Not on any 2m or 6m antenna I've seen or build. Most of what I've seen used T-match, hair-pin match, gamma match, or something similar. For the vertical collinears, I used a tapped coil. If I wanted lots of bandwidth, perhaps a ferrite core might be useful, but for single VHF band antennas, it's a lossy waste. I knew the ones built into the old tuners were but I hadnt thought the old line transformers also being air core. The over-simplified idea behind the ferrite (or powdered iron for HF) cores is to increase the inductance of the windings so the xformer works at lower frequencies. At VHF and UHF frequencies, the core mostly disappears and you're relying totally on the coupling between the bifilar windings. They were per some of the locals on 2m repeater. If they aare the ones I am thinking of(big fat ones) I have a few at home. Jimmie -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
TV 4:1 BALUN
On Mon, 19 Jan 2009 09:43:27 -0800, Jeff Liebermann
wrote: The over-simplified idea behind the ferrite (or powdered iron for HF) cores is to increase the inductance of the windings so the xformer works at lower frequencies. At VHF and UHF frequencies, the core mostly disappears and you're relying totally on the coupling between the bifilar windings. Actually that is not the mechanism at all, simplified or complexified. Ferrite compounds for BalUn application principally add resistance to the common mode path and have (as a design goal) absolutely no magnetic influence whatever. The increase of inductance is haphazard at best, and some ferrite compounds actually increase the capacitive reactance. As such, ferrites are not principally employed in building inductors. Further, iron cores don't serve much purpose for choking which is the principle requirement for BalUn input to output isolation. If you want to build an iron core, magnetic linkage transformer (AKA audio or power transformer), this is a very different beast from a BalUn, and a miserable replacement. 73's Richard Clark, KB7QHC |
TV 4:1 BALUN
Richard Clark wrote:
On Mon, 19 Jan 2009 09:43:27 -0800, Jeff Liebermann wrote: The over-simplified idea behind the ferrite (or powdered iron for HF) cores is to increase the inductance of the windings so the xformer works at lower frequencies. At VHF and UHF frequencies, the core mostly disappears and you're relying totally on the coupling between the bifilar windings. Actually that is not the mechanism at all, simplified or complexified. Ferrite compounds for BalUn application principally add resistance to the common mode path and have (as a design goal) absolutely no magnetic influence whatever. The increase of inductance is haphazard at best, and some ferrite compounds actually increase the capacitive reactance. As such, ferrites are not principally employed in building inductors. Further, iron cores don't serve much purpose for choking which is the principle requirement for BalUn input to output isolation. If you want to build an iron core, magnetic linkage transformer (AKA audio or power transformer), this is a very different beast from a BalUn, and a miserable replacement. 73's Richard Clark, KB7QHC When designing any transformer, be it audio, power, or RF, you usually want to accomplish three things: 1. Maximize the winding impedance. 2. Minimize the leakage impedance. This is another way of saying you want to maximize the coupling between the windings. 3. Realize an acceptably low loss. At low frequencies, most cores primarily provide inductance, so most literature dealing with transformers speaks of "inductance" rather than "impedance" when discussing the basic goals. But low frequency transformers could be made and would function just fine using resistive core materials if they were available. The third goal can be achieved with resistive materials as long as the first and second goals are accomplished well enough. That is, if the winding impedance is high enough, the magnetizing current will be low, so I^2*R loss will be low. And if coupling is good, increasing the current in one winding won't appreciably increase the core flux and incur extra loss. But at RF, as Richard says, many ferrite cores are more resistive than inductive. Not all are -- there are high frequency ferrites that remain inductive at very high frequencies. However, for the HF range and above, the best choice is usually "low frequency" ferrites which are primarily resistive in that frequency range. They're best for two reasons -- first, they provide much more impedance per turn squared than high frequency ferrites, making the first two goals much easier to achieve; and second, there are no resonance effects. An inductive winding will resonate with stray capacitance at some frequency. The impedance drops above that frequency, limiting the upper range of the transformer. The winding and leakage inductances can also resonate with external capacitance and cause ringing in some applications. A properly designed transformer using an essentially resistive core can operate very well over several decades of frequency. For most RF applications, it's not hard to design a transformer or balun that will have well under 1 dB of loss, which is negligible again in most applications. But if high power is involved, even a fraction of a dB might represent several or may watts of power, resulting in intolerable core heating. In those applications, lower loss, i.e., more inductive and less resistive, cores have to be used, often resulting in more difficult design and/or reduced performance in other respects. Resistive ferrites are also often good choices for RF chokes for the same reasons that they make good transformers. High-Q inductors and tuned transformers are a different critter, though. For those applications you want to use very low loss, that is, inductive and not resistive, core materials. This often leads to confusion, since ferrite manufacturers have traditionally specified a "recommended" frequency range for various materials which refers to the best range for these applications. The best material for an RF transformer is usually one with a "recommended" (for high-Q inductor applications) frequency range well below the transformer operating frequency. Roy Lewallen, W7EL |
TV 4:1 BALUN
Roy Lewallen wrote in
treetonline: .... But at RF, as Richard says, many ferrite cores are more resistive than inductive. Not all are -- there are high frequency ferrites that remain inductive at very high frequencies. However, for the HF range and above, the best choice is usually "low frequency" ferrites which are primarily resistive in that frequency range. They're best for two reasons -- first, they provide much more impedance per turn squared than high frequency ferrites, making the first two goals much easier to achieve; and second, there are no resonance effects. An inductive winding will resonate with stray capacitance at some frequency. The impedance drops above that frequency, limiting the upper range of the transformer. The winding and leakage inductances can also resonate with external capacitance and cause ringing in some applications. A properly designed transformer using an essentially resistive core can operate very well over several decades of frequency. Hams have a affinity for powdered iron cores in RF applications, mislead by the thought that low loss material naturally produces a better solution. Thing is that it is a huge leap from low loss *material* to a low loss *solution*. Here is a recent design for a Guanella 1:1 balun for 6m and 2m on a #61 ferrite co http://www.vk1od.net/balun/G1-1-FT140-61/index.htm . The article contains a graph of the material characteristics, which shows that at 2m, µ' has fallen to 10% or so of µi, and µ'' has risen, so an inductor will be more resistive than inductive. But, does that make it a poor TLT? Not at all, it has very high common mode or choking impedance (a critical performance parameter that is rarely reported for commercial baluns). Would such a balun wound on a powdered iron core work better? Probably not. I say probably because I have been unable to find manufacturer's loss data for powdered iron materials above about 5MHz. The probability is that a powdered iron core would yeild a balun with a choking impedance that is lower and more inductive than resistive and may likely be *more* lossy. (I have a prospective project to measure a couple of powdered iron cores at 6m to further explore this, but they will not be lab grade measurements.) The key is in thinking about I^2*R. The lossy ferrite balun has very high Z, so very low I, very high R, and the product of I^2*R is relatively low. A powdered iron choke will have lower Z, so higher I, low R, and the product I^2*R may be quite higher than the ferrite. Higher choking impedance can reduce loss, even if the higher choking impedance is by way of a lower Q inductor. The characteristic is a curve, concave down and the trick is to choose a design (whether it is powdered iron, air cored, or ferrite cored) for acceptable loss, and that often means an operating point that is well on the right hand side or the left hand of the curve maximum. Another facet of ferrite TLTs operated in their lossy region, is that they remain useful well above the device self resonance, whereas when choking depends on a high Q impedance, it rapidly falls above resonance. (Self resonance is ignored in most models of balun performance that I have seen.) Owen |
TV 4:1 BALUN
Owen Duffy wrote:
Hams have a affinity for powdered iron cores in RF applications, mislead by the thought that low loss material naturally produces a better solution. Thing is that it is a huge leap from low loss *material* to a low loss *solution*. . . . Would such a balun wound on a powdered iron core work better? Probably not. I say probably because I have been unable to find manufacturer's loss data for powdered iron materials above about 5MHz. The probability is that a powdered iron core would yeild a balun with a choking impedance that is lower and more inductive than resistive and may likely be *more* lossy. (I have a prospective project to measure a couple of powdered iron cores at 6m to further explore this, but they will not be lab grade measurements.) . . . Like ferrites, powdered irons come with a wide range of characteristics. Micrometals (http://micrometals.com) makes the popular -2 (red), -6 (yellow), and other cores which are very suitable for high-Q inductors at HF, as well as lower frequency mixes. I have a book of "Q curves" they published which characterizes a number of inductors to fairly high frequencies. But for most of my work I've simply wound inductors and measured their Qs with a simple home made Q meter. I use -6 and to a lesser extent -2 cores for inductors in nearly all HF filter and matching applications. I've used lower frequency powdered iron cores for RF chokes. They behave a lot like low frequency ferrites, but are characterized by tolerance of very high flux densities. I'm sure that some low frequency powdered iron cores would be fine for baluns and broad band transformers, but they're not nearly as available as ferrites and high frequency powdered iron cores. I highly recommend that anyone anticipating using ferrite or powdered iron cores invest in an "antenna analyzer". It allows a very quick and easy characterization of cores at the frequencies of interest. Roy Lewallen, W7EL |
TV 4:1 BALUN
Owen Duffy wrote:
Hams have a affinity for powdered iron cores in RF applications, mislead by the thought that low loss material naturally produces a better solution. All hams? |
TV 4:1 BALUN
Dave wrote in
m: Owen Duffy wrote: Hams have a affinity for powdered iron cores in RF applications, mislead by the thought that low loss material naturally produces a better solution. All hams? Your words, not mine. Owen |
TV 4:1 BALUN
On Tue, 20 Jan 2009 20:15:38 GMT, Owen Duffy wrote:
Hams have a affinity for powdered iron cores in RF applications, mislead by the thought that low loss material naturally produces a better solution. Thing is that it is a huge leap from low loss *material* to a low loss *solution*. Here is a recent design for a Guanella 1:1 balun for 6m and 2m on a #61 ferrite co http://www.vk1od.net/balun/G1-1-FT140-61/index.htm . The article contains a graph of the material characteristics, which shows that at 2m, µ' has fallen to 10% or so of µi, and µ'' has risen, so an inductor will be more resistive than inductive. But, does that make it a poor TLT? Not at all, it has very high common mode or choking impedance (a critical performance parameter that is rarely reported for commercial baluns). Would such a balun wound on a powdered iron core work better? Probably not. I say probably because I have been unable to find manufacturer's loss data for powdered iron materials above about 5MHz. The probability is that a powdered iron core would yeild a balun with a choking impedance that is lower and more inductive than resistive and may likely be *more* lossy. (I have a prospective project to measure a couple of powdered iron cores at 6m to further explore this, but they will not be lab grade measurements.) The key is in thinking about I^2*R. The lossy ferrite balun has very high Z, so very low I, very high R, and the product of I^2*R is relatively low. A powdered iron choke will have lower Z, so higher I, low R, and the product I^2*R may be quite higher than the ferrite. Higher choking impedance can reduce loss, even if the higher choking impedance is by way of a lower Q inductor. The characteristic is a curve, concave down and the trick is to choose a design (whether it is powdered iron, air cored, or ferrite cored) for acceptable loss, and that often means an operating point that is well on the right hand side or the left hand of the curve maximum. Another facet of ferrite TLTs operated in their lossy region, is that they remain useful well above the device self resonance, whereas when choking depends on a high Q impedance, it rapidly falls above resonance. (Self resonance is ignored in most models of balun performance that I have seen.) Owen "A Ham's Guide to RFI, Ferrites, Baluns, and Audio Interfacing" is an very good tutorial written by Jim Brown, K9YC, for understanding and fixing RFI problems. Chapter 6 (page 23) Includes an excellent explanation of balun operation and constrution information. A must read for anyone designing and/or building baluns http://audiosystemsgroup.com/RFI-Ham.pdf Danny, K6MHE |
TV 4:1 BALUN
Jimmie,
I have tried and used these tv baluns so I could run 300-ohm cable to my antenna. BUT I only ran about 5 watts. I used one on both ends of a 100-ft run of 300-ohm cable ( so as to reduce losses) . (And I used it on 10 meters, not 2 meters) I later wound my own impedence-matching 4-to-1 baluns to handle a full 100 watts. You're on the right track of having fun with transmission lines, impedence matching, and antenna building - keep it up. W4PMJ - hal "JIMMIE" wrote in message ... I was considering using a TV type 4:1 balun on 2 meters. Does anyone know how much power these can handle? I remember a guy doing this when I was a teenager(long ago) but I think the baluns were built a little stouter back then than they are now. Jimmie |
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