KAT500 update
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We originally had two antenna jacks on the KAT500, with one of them
switchable between balanced and unbalanced. Recently we decided that a third antenna jack would provide greater utility overall. (In my case, I'll be keeping a dummy load on the third jack.) All three jacks will be unbalanced (SO239). We're hoping to add a high-power, high-performance balun to our product line sometime next year that will serve the needs of those using balanced lines. 73, Wayne N6KR ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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Excelent, Wayne and yahoo on the dummy load connection. Thanks. 73, Tom Amateur Radio Operator N5GE ARRL Lifetime Member QCWA Lifetime Member "If somebody has a bad heart, they can plug this jack in at night as they go to bed and it will monitor their heart throughout the night. And the next morning, when they wake up dead, there'll be a record." --Mark S. Fowler, FCC Chairman, 1981 - 1987 On Wed, 7 Dec 2011 17:22:16 -0800, Wayne Burdick <[hidden email]> wrote: >We originally had two antenna jacks on the KAT500, with one of them >switchable between balanced and unbalanced. > >Recently we decided that a third antenna jack would provide greater >utility overall. (In my case, I'll be keeping a dummy load on the >third jack.) All three jacks will be unbalanced (SO239). > >We're hoping to add a high-power, high-performance balun to our >product line sometime next year that will serve the needs of those >using balanced lines. > >73, >Wayne >N6KR >______________________________________________________________ >Elecraft mailing list >Home: http://mailman.qth.net/mailman/listinfo/elecraft >Help: http://mailman.qth.net/mmfaq.htm >Post: mailto:[hidden email] > >This list hosted by: http://www.qsl.net >Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Amateur Radio Operator N5GE
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Excellent, Wayne. You are really listening to the customers - 3 x SO239 sockets.
TNX & 73, Johnny VR2XMC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by wayne burdick
Have you tought about the possibility to combine two of the SO-239 connectors to form a balanced input.
With some relays it is possible to change the configuration in such a way that say selecting Antenna 1 is SO-239 connector 1, selecting Antenna 2 is SO-239 connector 2, selecting Antenna 3 is SO-239 connector 3, selecting Antenna 4 is SO-239 connector 2 senter conductor and SO-239 connector 3 senter conductor with a balun switched in to the circuit by some relais to make the combined inputs of SO-239 connector 2 senter conductor and SO-239 connector 3 senter conductor a balanced input. It is of coarse not possible to use SO-239 connector 2 and SO-239 connector 3 as unbalanced (coaxial) antenna inputs at the same time as the antenna 4 configuration is used, so due to this the control firmware should be set up in such a way that when Antenna 4 is NOT enabled, the following selections are available: Ant 1, Ant 2 and Ant 3, and when Antenna 4 IS enabled, the following selections are available: Ant 1 and Ant 4. I think that something like this would give the users a great flexibility. Martin Storli LA8OKA Oslo, Norway ARCTICPEAK's Radio pages! http://www.arcticpeak.com/radio.htm ________________________________ Fra: Wayne Burdick <[hidden email]> Til: Elecraft Reflector <[hidden email]> Kopi: [hidden email] Sendt: Torsdag, 8. desember 2011 2.22 Emne: [Elecraft] KAT500 update We originally had two antenna jacks on the KAT500, with one of them switchable between balanced and unbalanced. Recently we decided that a third antenna jack would provide greater utility overall. (In my case, I'll be keeping a dummy load on the third jack.) All three jacks will be unbalanced (SO239). We're hoping to add a high-power, high-performance balun to our product line sometime next year that will serve the needs of those using balanced lines. 73, Wayne N6KR ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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Martin,
Actually, for my part the 3 SO-239 connectors offer the greatest flexibility. If a user uses open wire feeders, he likely already has a balun connected to those feeders. To move that balun inside the tuner makes no sense to me. In fact, I have an MFJ 962D tuner that I removed the internal balun just so I could connect a 3rd SO-239 connector. The baluns live at the center of my antennas or at the end of the ladder-line (which is not in the shack). 73, Don W3FPR On 12/8/2011 8:23 AM, Martin Storli - LA8OKA wrote: > Have you tought about the possibility to combine two of the SO-239 connectors to form a balanced input. > With some relays it is possible to change the configuration in such a way that say selecting Antenna 1 is SO-239 connector 1, selecting Antenna 2 is SO-239 connector 2, selecting Antenna 3 is SO-239 connector 3, selecting Antenna 4 is SO-239 connector 2 senter conductor and SO-239 connector 3 senter conductor with a balun switched in to the circuit by some relais to make the combined inputs of SO-239 connector 2 senter conductor and SO-239 connector 3 senter conductor a balanced input. > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by wayne burdick
Wayne,
When I talked to you briefly at the 2010 Pacificon, you seemed to say that the KAT500 would be a "floating-L" design. That is, it would contain an unbalanced L network, but that network and its circuit board would be floating and not connected to the metal enclosure. You said a balun would be put at the 50 ohm end, feeding a SO239 connector for the coax to the rig. The floating-L could then be connected to balanced lines, or to unbalanced ones by tying one side of it to the case at the antenna end. Now it seems that you are talking about a totally unbalanced tuner, with no provision for balanced antenna feeders. Do you mean to add an external balun on the *antenna* side of the tuner? Surely not. That seems an inherently bad idea for many balanced lines. The impedance there will be unpredictable, hence the need for the tuner. Not a good place for a balun IMHO. But if you put the balun on the 50 ohm end where it belongs, then the whole enclosure will be tied to one side of the "balanced" line, which will likely unbalance it. What happened? I had hoped to put the KAT500 in a weatherproof box of my own fabrication and use it between a balanced line to the antenna and a coax feed back to the rig. It could live out near the antenna, where it belongs. 73, Oliver Johns W6ODJ On Dec 7, 2011, at 5:22 PM, Wayne Burdick wrote: > We originally had two antenna jacks on the KAT500, with one of them > switchable between balanced and unbalanced. > > Recently we decided that a third antenna jack would provide greater > utility overall. (In my case, I'll be keeping a dummy load on the > third jack.) All three jacks will be unbalanced (SO239). > > We're hoping to add a high-power, high-performance balun to our > product line sometime next year that will serve the needs of those > using balanced lines. > > 73, > Wayne > N6KR > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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The "balun" needed on the output of an unbalanced tuner to accommodate an
"balanced" feedline is no more than an appropriately designed common mode choke. http://www.audiosystemsgroup.com/RFI-Ham.pdf excellent practical descriptions, tests of real implementations and cookbook recommendations. http://fermi.la.asu.edu/w9cf/articles/balun/ excellent mathematical treatment http://www.w8ji.com/tuner_baluns.htm bottom of page 73 jim ab3cv ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by W6ODJ
I t's been shown conclusively that an unbalanced 'floating' tuner with a balun on the
input does not provide better balance than one with the balun on the output. Yes, I know that there is such a tuner in the ARRL handbook and Alpha is manufacturing one. But the math doesn't lie. So unless Elecraft wanted to use a balanced network -- which would make the tuner MUCH more expensive -- I would prefer one without a balun. Then those who do not use balanced lines would not have to pay for the balun. On 12/8/2011 8:58 AM, Oliver Johns wrote: > Wayne, > > When I talked to you briefly at the 2010 Pacificon, you seemed to say that the KAT500 would be a "floating-L" design. That is, it would contain an unbalanced L network, but that network and its circuit board would be floating and not connected to the metal enclosure. You said a balun would be put at the 50 ohm end, feeding a SO239 connector for the coax to the rig. The floating-L could then be connected to balanced lines, or to unbalanced ones by tying one side of it to the case at the antenna end. > > Now it seems that you are talking about a totally unbalanced tuner, with no provision for balanced antenna feeders. Do you mean to add an external balun on the *antenna* side of the tuner? Surely not. That seems an inherently bad idea for many balanced lines. The impedance there will be unpredictable, hence the need for the tuner. Not a good place for a balun IMHO. But if you put the balun on the 50 ohm end where it belongs, then the whole enclosure will be tied to one side of the "balanced" line, which will likely unbalance it. > > What happened? I had hoped to put the KAT500 in a weatherproof box of my own fabrication and use it between a balanced line to the antenna and a coax feed back to the rig. It could live out near the antenna, where it belongs. > > 73, > > Oliver Johns > W6ODJ > > > On Dec 7, 2011, at 5:22 PM, Wayne Burdick wrote: > >> We originally had two antenna jacks on the KAT500, with one of them >> switchable between balanced and unbalanced. >> >> Recently we decided that a third antenna jack would provide greater >> utility overall. (In my case, I'll be keeping a dummy load on the >> third jack.) All three jacks will be unbalanced (SO239). >> >> We're hoping to add a high-power, high-performance balun to our >> product line sometime next year that will serve the needs of those >> using balanced lines. >> >> 73, >> Wayne >> N6KR >> Vic, K2VCO Fresno CA http://www.qsl.net/k2vco/ ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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You're right, Vic. We'll be posting in greater detail on this topic
shortly. Wayne N6KR On Dec 8, 2011, at 9:22 AM, Vic K2VCO wrote: > I t's been shown conclusively that an unbalanced 'floating' tuner > with a balun on the > input does not provide better balance than one with the balun on the > output. Yes, I know > that there is such a tuner in the ARRL handbook and Alpha is > manufacturing one. But the > math doesn't lie. So unless Elecraft wanted to use a balanced > network -- which would make > the tuner MUCH more expensive -- I would prefer one without a balun. > Then those who do not > use balanced lines would not have to pay for the balun. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by W6ODJ
Hi Oliver,
Sorry to disappoint you. Here's what happened: We originally planned a floating L-network with an input balun, and that's how we wired the prototypes. But recently we studied this configuration in depth, doing both a theoretical analysis and lab measurements. We confirmed the findings of other researchers that the input balun has no advantage over an output balun (more on this below). Taking the balun out in favor of a third antenna jack will reduce the cost of the ATU significantly and enhance utility, and those who need a balanced feed can still use an external balun. Now for the theory: When a balun is located at the output, between the tuner and a balanced line, one side of the balun transformer is connected to ground at the tuner and the other is connected to one side of the balanced line. The full RF voltage is then applied to the the balun transformer. For a given balun design, if that voltage is high enough then the balun transformer will overheat. When the balun is located at the input, between the balanced feedline and an unbalanced network, one side of the balun transformer is still connected to ground, and the other is still connected to one side of the balanced feedline. So the voltage applied to the balun is exactly the same. Therefore there is no advantage to floating the network. Doing so also greatly complicates the tuner and increases cost. If anyone is interested in more detail, we could post a drawing, as well as references. 73, Wayne N6KR On Dec 8, 2011, at 8:58 AM, Oliver Johns wrote: > Wayne, > > When I talked to you briefly at the 2010 Pacificon, you seemed to > say that the KAT500 would be a "floating-L" design. That is, it > would contain an unbalanced L network, but that network and its > circuit board would be floating and not connected to the metal > enclosure. You said a balun would be put at the 50 ohm end, feeding > a SO239 connector for the coax to the rig. The floating-L could > then be connected to balanced lines, or to unbalanced ones by tying > one side of it to the case at the antenna end. > > Now it seems that you are talking about a totally unbalanced tuner, > with no provision for balanced antenna feeders. Do you mean to add > an external balun on the *antenna* side of the tuner? Surely not. > That seems an inherently bad idea for many balanced lines. The > impedance there will be unpredictable, hence the need for the > tuner. Not a good place for a balun IMHO. But if you put the balun > on the 50 ohm end where it belongs, then the whole enclosure will be > tied to one side of the "balanced" line, which will likely unbalance > it. > > What happened? I had hoped to put the KAT500 in a weatherproof box > of my own fabrication and use it between a balanced line to the > antenna and a coax feed back to the rig. It could live out near the > antenna, where it belongs. > > 73, > > Oliver Johns > W6ODJ > > > On Dec 7, 2011, at 5:22 PM, Wayne Burdick wrote: > >> We originally had two antenna jacks on the KAT500, with one of them >> switchable between balanced and unbalanced. >> >> Recently we decided that a third antenna jack would provide greater >> utility overall. (In my case, I'll be keeping a dummy load on the >> third jack.) All three jacks will be unbalanced (SO239). >> >> We're hoping to add a high-power, high-performance balun to our >> product line sometime next year that will serve the needs of those >> using balanced lines. >> >> 73, >> Wayne >> N6KR >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:[hidden email] >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by wayne burdick
Well, I must admit I'm a little bit disappointed... It was said some time in August, the KAT500 would have a built-in balun on the input side. And one of two outputs switchable between balanced and unbalanced. Now we'll had to add a balun at the output, which arguably is suboptimal.
On the other hand, I wonder why Elecraft should go into the trouble and expense of developing a high-power balun. AFIK, there are some good products already available... I second Martin's (LA8OKA) suggestion for a relay-switched configuration. Maybe they'll think it over - or even offer two different versions (just dreaming...) 73 Richard
Richard - HB9ANM
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In reply to this post by Vic Rosenthal
Vic,
Deja vu -- Seems like we had just discussed this on the AMPS list! In this case, I'm with you on keeping the balun external to the tuner. That gives the user an option of installing the balun of their choice immediately after the tuner, or remotely through a short section of high-quality coax to join the balanced line. It's useful in cases where the shack is adjacent to an outside wall and the balun can be hung adjacent to a window or other opening. A symmetrical tuner would still be preferred for balanced lines where the balun *should* be placed at the tuner input. It would be an interesting exercise to compare the production cost and resulting sales price of a switched unbalanced "L" versus a symmetrical tuner with a balun on the input but with switched, fixed components. A few design-related problems: (1) ability to switch between balanced and unbalanced lines with a symmetrical tuner while keeping efficiency high and cost low; and (2) any commercial version would need to be offered so that it could accommodate a line input Z range of not only 50-5K ohm but also Z values less than 50 ohms for folks with short antennas. In the case of a high-pass design, that requires switched reversal of the shunt C so that it can be placed on either side of the balanced inductance. And, that's where it could get messy with cost and component layout to keep efficiency high. After building a motorized AG6K tuner, I realized that the complex vacuum relay arrangement could have been omitted. If reasonably "full-size" antennas are used, it's tough to conceive a condition when using 600-ohm line where the input Z drops below 50-ohms - even with odd quarter-wave multiples. After the tuner was built, I worked out several dipole and loop models using 4Nec2 and TLW software. Change of bands, frequency, and line length all resulted in reasonable input Z. Another factor when operating into low Z line inputs -- the lower the line input Z, the greater the importance of component Q to keep efficiency high, especially on the low bands. So, now there's a bunch of expensive switching components that will never be used since I don't operate with short antennas, at least not at home. Many folks wouldn't have the choice -- and thus the need to offer a "one size fits all" type of tuner. Probably the best approach is an unbalanced tuner for coax and "output balun" feeds, and if there's enough demand, a separate symmetrical tuner just for balanced lines. It sure is nice being able to toss these ideas around and not worry about any financial risk, unlike the manufacturers! Paul, W9AC ----- Original Message ----- From: "Vic K2VCO" <[hidden email]> To: <[hidden email]> Sent: Thursday, December 08, 2011 12:22 PM Subject: Re: [Elecraft] KAT500 update >I t's been shown conclusively that an unbalanced 'floating' tuner with a >balun on the > input does not provide better balance than one with the balun on the > output. Yes, I know > that there is such a tuner in the ARRL handbook and Alpha is manufacturing > one. But the > math doesn't lie. So unless Elecraft wanted to use a balanced network -- > which would make > the tuner MUCH more expensive -- I would prefer one without a balun. Then > those who do not > use balanced lines would not have to pay for the balun. > > On 12/8/2011 8:58 AM, Oliver Johns wrote: >> Wayne, >> >> When I talked to you briefly at the 2010 Pacificon, you seemed to say >> that the KAT500 would be a "floating-L" design. That is, it would >> contain an unbalanced L network, but that network and its circuit board >> would be floating and not connected to the metal enclosure. You said a >> balun would be put at the 50 ohm end, feeding a SO239 connector for the >> coax to the rig. The floating-L could then be connected to balanced >> lines, or to unbalanced ones by tying one side of it to the case at the >> antenna end. >> >> Now it seems that you are talking about a totally unbalanced tuner, with >> no provision for balanced antenna feeders. Do you mean to add an >> external balun on the *antenna* side of the tuner? Surely not. That >> seems an inherently bad idea for many balanced lines. The impedance >> there will be unpredictable, hence the need for the tuner. Not a good >> place for a balun IMHO. But if you put the balun on the 50 ohm end where >> it belongs, then the whole enclosure will be tied to one side of the >> "balanced" line, which will likely unbalance it. >> >> What happened? I had hoped to put the KAT500 in a weatherproof box of my >> own fabrication and use it between a balanced line to the antenna and a >> coax feed back to the rig. It could live out near the antenna, where it >> belongs. >> >> 73, >> >> Oliver Johns >> W6ODJ >> >> >> On Dec 7, 2011, at 5:22 PM, Wayne Burdick wrote: >> >>> We originally had two antenna jacks on the KAT500, with one of them >>> switchable between balanced and unbalanced. >>> >>> Recently we decided that a third antenna jack would provide greater >>> utility overall. (In my case, I'll be keeping a dummy load on the >>> third jack.) All three jacks will be unbalanced (SO239). >>> >>> We're hoping to add a high-power, high-performance balun to our >>> product line sometime next year that will serve the needs of those >>> using balanced lines. >>> >>> 73, >>> Wayne >>> N6KR >>> > -- > Vic, K2VCO > Fresno CA > http://www.qsl.net/k2vco/ > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by Don Wilhelm-4
Hi Don. I think you misunderstood me, because with my suggestion you will have 3 SO-239 conectors, but you have the choise to use two of them for a ballanced feeder. That should give anybody a good flexibility. Martin Storli LA8OKA Oslo, Norway ARCTICPEAK's Radio pages! http://www.arcticpeak.com/radio.htm ________________________________ Fra: Don Wilhelm <[hidden email]> Til: Martin Storli - LA8OKA <[hidden email]> Kopi: Elecraft Reflector <[hidden email]> Sendt: Torsdag, 8. desember 2011 14.46 Emne: Re: [Elecraft] Vedr: KAT500 update Martin, Actually, for my part the 3 SO-239 connectors offer the greatest flexibility. If a user uses open wire feeders, he likely already has a balun connected to those feeders. To move that balun inside the tuner makes no sense to me. In fact, I have an MFJ 962D tuner that I removed the internal balun just so I could connect a 3rd SO-239 connector. The baluns live at the center of my antennas or at the end of the ladder-line (which is not in the shack). 73, Don W3FPR On 12/8/2011 8:23 AM, Martin Storli - LA8OKA wrote: > Have you tought about the possibility to combine two of the SO-239 connectors to form a balanced input. > With some relays it is possible to change the configuration in such a way that say selecting Antenna 1 is SO-239 connector 1, selecting Antenna 2 is SO-239 connector 2, selecting Antenna 3 is SO-239 connector 3, selecting Antenna 4 is SO-239 connector 2 senter conductor and SO-239 connector 3 senter conductor with a balun switched in to the circuit by some relais to make the combined inputs of SO-239 connector 2 senter conductor and SO-239 connector 3 senter conductor a balanced input. > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by wayne burdick
Thanks,
This is exactly what I need! There is only unbalanced coax in my shack. 73 Arie PA3A Op 8-12-2011 2:22, Wayne Burdick : > We originally had two antenna jacks on the KAT500, with one of them > switchable between balanced and unbalanced. > > Recently we decided that a third antenna jack would provide greater > utility overall. (In my case, I'll be keeping a dummy load on the > third jack.) All three jacks will be unbalanced (SO239). > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by wayne burdick
Hear's a link to Roy Lewallen's paper on the ineffective input balun. He mentions Tom Rausch, W8JI who got to this conclusion first.
http://www.eznec.com/misc/ibalbrf.txt Chuck, KE9UW aka Jack, BMW Motorcycles ________________________________________ From: [hidden email] [[hidden email]] on behalf of Wayne Burdick [[hidden email]] Sent: Thursday, December 08, 2011 11:34 AM To: Oliver Johns Cc: Elecraft Reflector; [hidden email] Subject: [Elecraft_K3] Re: [Elecraft] KAT500 update Hi Oliver, Sorry to disappoint you. Here's what happened: We originally planned a floating L-network with an input balun, and that's how we wired the prototypes. But recently we studied this configuration in depth, doing both a theoretical analysis and lab measurements. We confirmed the findings of other researchers that the input balun has no advantage over an output balun (more on this below). Taking the balun out in favor of a third antenna jack will reduce the cost of the ATU significantly and enhance utility, and those who need a balanced feed can still use an external balun. Now for the theory: When a balun is located at the output, between the tuner and a balanced line, one side of the balun transformer is connected to ground at the tuner and the other is connected to one side of the balanced line. The full RF voltage is then applied to the the balun transformer. For a given balun design, if that voltage is high enough then the balun transformer will overheat. When the balun is located at the input, between the balanced feedline and an unbalanced network, one side of the balun transformer is still connected to ground, and the other is still connected to one side of the balanced feedline. So the voltage applied to the balun is exactly the same. Therefore there is no advantage to floating the network. Doing so also greatly complicates the tuner and increases cost. If anyone is interested in more detail, we could post a drawing, as well as references. 73, Wayne N6KR On Dec 8, 2011, at 8:58 AM, Oliver Johns wrote: > Wayne, > > When I talked to you briefly at the 2010 Pacificon, you seemed to > say that the KAT500 would be a "floating-L" design. That is, it > would contain an unbalanced L network, but that network and its > circuit board would be floating and not connected to the metal > enclosure. You said a balun would be put at the 50 ohm end, feeding > a SO239 connector for the coax to the rig. The floating-L could > then be connected to balanced lines, or to unbalanced ones by tying > one side of it to the case at the antenna end. > > Now it seems that you are talking about a totally unbalanced tuner, > with no provision for balanced antenna feeders. Do you mean to add > an external balun on the *antenna* side of the tuner? Surely not. > That seems an inherently bad idea for many balanced lines. The > impedance there will be unpredictable, hence the need for the > tuner. Not a good place for a balun IMHO. But if you put the balun > on the 50 ohm end where it belongs, then the whole enclosure will be > tied to one side of the "balanced" line, which will likely unbalance > it. > > What happened? I had hoped to put the KAT500 in a weatherproof box > of my own fabrication and use it between a balanced line to the > antenna and a coax feed back to the rig. It could live out near the > antenna, where it belongs. > > 73, > > Oliver Johns > W6ODJ > > > On Dec 7, 2011, at 5:22 PM, Wayne Burdick wrote: > >> We originally had two antenna jacks on the KAT500, with one of them >> switchable between balanced and unbalanced. >> >> Recently we decided that a third antenna jack would provide greater >> utility overall. (In my case, I'll be keeping a dummy load on the >> third jack.) All three jacks will be unbalanced (SO239). >> >> We're hoping to add a high-power, high-performance balun to our >> product line sometime next year that will serve the needs of those >> using balanced lines. >> >> 73, >> Wayne >> N6KR >> __________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:[hidden email]<mailto:Elecraft%40mailman.qth.net> >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> __._,_.___ Reply to sender<mailto:[hidden email]?subject=Re%3A%20%5BElecraft%5D%20KAT500%20update> | Reply to group<mailto:[hidden email]?subject=Re%3A%20%5BElecraft%5D%20KAT500%20update> | Reply via web post<http://groups.yahoo.com/group/Elecraft_K3/post;_ylc=X3oDMTJyc21nODU3BF9TAzk3MzU5NzE0BGdycElkAzIwMTQ5NDI4BGdycHNwSWQDMTcwNTA2MzEwOARtc2dJZAMxMjg0MwRzZWMDZnRyBHNsawNycGx5BHN0aW1lAzEzMjMzNjU2NzE-?act=reply&messageNum=12843> | Start a New Topic<http://groups.yahoo.com/group/Elecraft_K3/post;_ylc=X3oDMTJmbDFlMTQ1BF9TAzk3MzU5NzE0BGdycElkAzIwMTQ5NDI4BGdycHNwSWQDMTcwNTA2MzEwOARzZWMDZnRyBHNsawNudHBjBHN0aW1lAzEzMjMzNjU2NzE-> Messages in this topic<http://groups.yahoo.com/group/Elecraft_K3/message/12842;_ylc=X3oDMTM3NTFuMDRsBF9TAzk3MzU5NzE0BGdycElkAzIwMTQ5NDI4BGdycHNwSWQDMTcwNTA2MzEwOARtc2dJZAMxMjg0MwRzZWMDZnRyBHNsawN2dHBjBHN0aW1lAzEzMjMzNjU2NzEEdHBjSWQDMTI4NDI-> (2) Recent Activity: * New Members<http://groups.yahoo.com/group/Elecraft_K3/members;_ylc=X3oDMTJndDVydWk2BF9TAzk3MzU5NzE0BGdycElkAzIwMTQ5NDI4BGdycHNwSWQDMTcwNTA2MzEwOARzZWMDdnRsBHNsawN2bWJycwRzdGltZQMxMzIzMzY1Njcx?o=6> 7 Visit Your Group<http://groups.yahoo.com/group/Elecraft_K3;_ylc=X3oDMTJmdWxpMnAyBF9TAzk3MzU5NzE0BGdycElkAzIwMTQ5NDI4BGdycHNwSWQDMTcwNTA2MzEwOARzZWMDdnRsBHNsawN2Z2hwBHN0aW1lAzEzMjMzNjU2NzE-> MARKETPLACE Stay on top of your group activity without leaving the page you're on - Get the Yahoo! 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In reply to this post by Arie Kleingeld PA3A-2
Actually, it seems to me that an antenna tuner is needed because SWR
is high, and if SWR is high, there are extra losses in the feedline. The lowest cost low loss feeder is open line, and a balanced input to the tuner would be useful. Dick, WO1I At 10:48 PM 12/8/2011, Arie Kleingeld PA3A wrote: >Thanks, > >This is exactly what I need! There is only unbalanced coax in my shack. > >73 > >Arie PA3A > > > >Op 8-12-2011 2:22, Wayne Burdick : > > We originally had two antenna jacks on the KAT500, with one of them > > switchable between balanced and unbalanced. > > > > Recently we decided that a third antenna jack would provide greater > > utility overall. (In my case, I'll be keeping a dummy load on the > > third jack.) All three jacks will be unbalanced (SO239). > > > > >______________________________________________________________ >Elecraft mailing list >Home: http://mailman.qth.net/mailman/listinfo/elecraft >Help: http://mailman.qth.net/mmfaq.htm >Post: mailto:[hidden email] > >This list hosted by: http://www.qsl.net >Please help support this email list: http://www.qsl.net/donate.html =============================== Richard S. Lindzen Alfred P. Sloan Professor of Atmospheric Sciences Office: 54-1720, MIT Cambridge, MA 02139 USA 1 (617) 253-2432 (voice) Home: 301 Lake Avenue Newton, MA 02461-1211 USA 1 (617) 332-4342 (voice) Paris: 103 Avenue de la Republique 75011 Paris FRANCE 33 (0)1 43 14 93 79 Skype: 617-564-1942 =============================== ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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It seems to me that the story is more complex than it sounds.
The input balun always works at low SWR and at 50 Ohm. It is very easy to have such balun. A small balun would easily handle a KW without heating. The output balun can work at high complex impedances. Ferrite baluns are known to absorb nearly all the power at high impedances (including BL200) and be very hot even at low power. Iron baluns work well with true balanced antenna but do not provide enough choking with less balanced antennas. Even if there is balun on input, there are stray capacitances that can disturb the balance. Probably bigger for a bigger tuner and also bigger if a tuner is close to metal boxes. Those who travel and use portable antennas such as random length wires, they find ferrite baluns on output nearly always hot on some bands. Now, I use Z11Pro where both antenna connectors and the control cable are looped through a toroid many times; antenna wires to the tuner are connected directly. No heating whatsoever. No hot touch to the radio. But the tuner is usually on wood 2 ft from the radio. What can be done with portable tuner with single output cannot be done with 500W tuner in a shack with multiple outputs. So Elecraft's decision to not use the input balun is a good one. Balun on input would not be very effective but would increase costs. If an output balun heats up too much or doe not provide enough choking, change the antenna or the balun. Rules of QRO are different than rules of QRP or even 100W. Ignacy, currently VK2/NO9E |
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Hi Ignacy,
This is a common misconception. (One which I held until recently. :-) It turns out there is no advantage to placing the balun at the input of the L-Network tuner. Since one end of the balun is grounded by the input to the tuner, it is still presented with the same stresses under high SWR situations. Baluns at the input and output both drive balanced loads equally well. We've now put together a web page describing the impact of placing the balun at the input or at the output of a L-Network tuner. See: http://www.elecraft.com/KAT500/input_versus_output_balun.htm At the bottom of that page are several links providing detailed technical analysis of these configurations. The first two, by W8JI and W7EL are very clear discussions of this issue. 73, Eric WA6HHQ www.elecraft.com On 12/8/2011 3:17 PM, Ignacy wrote: > It seems to me that the story is more complex than it sounds. > > The input balun always works at low SWR and at 50 Ohm. It is very easy to > have such balun. A small balun would easily handle a KW without heating. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by rlindzen
On 12/8/2011 1:54 PM, Dick Lindzen wrote:
> Actually, it seems to me that an antenna tuner is needed because SWR > is high, and if SWR is high, there are extra losses in the > feedline. The mismatch that affects feedline loss is the match between the antenna and the feedline. Thus, an antenna tuner reduces loss in the feedline ONLY if it is at the antenna end of the feedline. All the tuner in the shack does is make the rig happy, so that it can put full power into the line and not break. > The lowest cost low loss feeder is open line, and a > balanced input to the tuner would be useful. Virtually all the loss in transmission lines at HF (and even VHF) is due to copper (that is, I squared R). Open wire line (and window line) has much lower loss than coax because it has much higher impedance, so the current for the same transmit power is much less than for coax. That is, you're sending power on the line with more voltage and less current. It's still possible to have a lot of loss in window line or open wire line if there is a high SWR. One exception -- window line starts having significant dielectric loss when it is wet. 73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by Eric Swartz - WA6HHQ
This is of interest to me, because in my first experiences with antenna
forums (or was it newsgroups at the time), I recall a lot of exchanges with Tom W8JI on exactly the "balun at the tuner input and isolated unbalanced tuner". I concur with Tom - it does not work -- both from a theoretical basis, and also from Tom's measurements. This was "way back when" - as I recall my situation when all this was going on, I was running Windows 95 and the year was between 1997 and 1998. In the timeframe of this discussion, Zack Lau (ARRL engineer) who had first published the "balun at the tuner input" concept as a QRP tuner, had retracted that design because it did not maintain balance, but Dean Straw (ARRL engineer, editor, etc.) published his design of a high power tuner using the same concepts, and that design can still be seen in the ARRL publications. Apologies for the comments into the politics of the ARRL decisions on what is to be published, but that is both a bit of the history as I know it as well as my view of the technical side of this issue. If anyone can tell me how you can run a signal through a balun - and have equal and opposite currents at its output, and then run it through an unbalanced network with unequal elements in the two series legs and still maintain equal and opposite currents and phase, and I will then concede that an isolated unbalanced tuner with a balun at the input will work, but until that is presented to me along with detailed engineering level test data (not just "it works"), I will continue to believe that using a balun on the input of an isolated unbalanced tuner is a "pipe dream" that does not mesh with reality. 73, Don W3FPR aOn 12/8/2011 6:28 PM, Eric Swartz - WA6HHQ, Elecraft wrote: > Hi Ignacy, > > This is a common misconception. (One which I held until recently. :-) It > turns out there is no advantage to placing the balun at the input of the > L-Network tuner. Since one end of the balun is grounded by the input to > the tuner, it is still presented with the same stresses under high SWR > situations. Baluns at the input and output both drive balanced loads > equally well. > > We've now put together a web page describing the impact of placing the > balun at the input or at the output of a L-Network tuner. See: > > http://www.elecraft.com/KAT500/input_versus_output_balun.htm > > At the bottom of that page are several links providing detailed > technical analysis of these configurations. The first two, by W8JI and > W7EL are very clear discussions of this issue. > > 73, Eric WA6HHQ > > www.elecraft.com > > > On 12/8/2011 3:17 PM, Ignacy wrote: >> It seems to me that the story is more complex than it sounds. >> >> The input balun always works at low SWR and at 50 Ohm. It is very easy to >> have such balun. A small balun would easily handle a KW without heating. > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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