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#1
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"Mike Coslo" wrote in message
6 wrote: If the only antennas we have are trapped verticals, tribanders or dipoles/inverted vees cut for the band to be used, we might get away with not having to use a tuner at all. Still there are likely to be frequencies significantly removed from the antenna's resonant frequency where one might need a tuner to enable the transmitter to make full power. We aren't likely to need a wide range tuner for those times. A simple T-match will likely enable us to find a combination of settings which will present a low VSWR to the transmitter. The main alternative is to have a variety of antennas which present a VSWR of under 2:1 to a transmitter. That brings up a related issue. Lots of Hams today are restricted to one antenna, yet they would like all band operation. I think it would be a great idea for a manufacturer to have a transciever that included a tuner right in the rig itself. - 73 de Mike KB3EIA - They do exist, although being primarily interested in VHF/UHF operation (we only recently had the morse requirement for HF dropped over here in the UK, but that's another topic..!!) I've had little experience of them. I do remember vividly using a Drake commercial HF transceiver (I think it came out of a ship's radio room) back in the late 80's at a special event station that had this feature, you could operate on any band without any form of tuning at all, although of course how much power would get out on a really bad antenna is debatable ;-) Of course if you've enough money, there are those antennas that tune themselves. A friend has a 3-element beam that is computer controlled; as you tune across the bands, the elements automatically adjust themselves to the correct length..! I don't recall the make/model, but it is of American origin, does anyone know of it..? 73 Ivor G6URP |
#2
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![]() "Ivor Jones" wrote in message ... "Mike Coslo" wrote in message 6 wrote: [snip] That brings up a related issue. Lots of Hams today are restricted to one antenna, yet they would like all band operation. I think it would be a great idea for a manufacturer to have a transciever that included a tuner right in the rig itself. - 73 de Mike KB3EIA - They do exist, although being primarily interested in VHF/UHF operation (we only recently had the morse requirement for HF dropped over here in the UK, but that's another topic..!!) I've had little experience of them. My main HF rig and my husband's main HF rig both have built in tuners. Both work pretty well. However they do not have the range of outboard tuners. I do remember vividly using a Drake commercial HF transceiver (I think it came out of a ship's radio room) back in the late 80's at a special event station that had this feature, you could operate on any band without any form of tuning at all, although of course how much power would get out on a really bad antenna is debatable ;-) A lot of commericial and military equipment have built in tuners with quite significant tuning ranges. Of course this comes at a price so amateur gear doesn't have as much range in their tuning capacity on the built in tuners. Of course if you've enough money, there are those antennas that tune themselves. A friend has a 3-element beam that is computer controlled; as you tune across the bands, the elements automatically adjust themselves to the correct length..! I don't recall the make/model, but it is of American origin, does anyone know of it..? 73 Ivor G6URP I think it is called the SteppIR. Too rich for my pocket book. Dee, N8UZE |
#3
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"Dee Flint" wrote in
: My main HF rig and my husband's main HF rig both have built in tuners. Both work pretty well. However they do not have the range of outboard tuners. I should have noted large range and balanced/unbalanced output. My IC-761 has an autotuner on it that works pretty well with my vertical antenna. The dipole is run with balanced line, and needs a different tuner. A lot of commericial and military equipment have built in tuners with quite significant tuning ranges. Of course this comes at a price so amateur gear doesn't have as much range in their tuning capacity on the built in tuners. Size can be an issue too. The IC 761's tuner is a pretty tiny thing. I had to take an IC 765's autotuner 9 (very similar) apart once to repair it, and it was around the size of one of the mfj tiny tuners. A little bigger components, plus a 4:1 balun, and they would have it. - 73 de Mike KB3EIA - |
#4
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On Mar 4, 10:23�pm, Mike Coslo wrote:
* * * * I should have noted large range and balanced/unbalanced output. My IC-761 has an autotuner on it that works pretty well with my vertical antenna. The dipole is run with balanced line, and needs a different tuner. --- * * * * A little bigger components, plus a 4:1 balun, and they would have it. Well, sort of. The Ancient Ones used antenna matching devices to feed balanced lines. The Johnson Matchboxes are one example of a commercial version. Most Handbooks have examples of link-coupled balanced wide-range tuners. The problem was that such link-coupled tuners are large and not easy to bandswitch. About 1970, a new idea in tuners appeared: Use an unbalanced matching network such as a T or L network with a roller inductor or tapped inductor, with a balun if balanced output was wanted. 4:1 iron-core toroid baluns were compact and broadband, the T or L tuner could be made wide-range without complex bandswitching, and the whole works seemed an improvement on the old link-coupled balanced tuner. The problem was that baluns aren't magic devices. The system works well if the shack-end of the transmission line is around 200 ohms impedance and not too reactive. But in many cases the shack-end impedance with balanced line is very high or very low, and/or very reactive. Under such conditions the balun may not do a very good job because it is being asked to work far outside its design parameters. Also, if the shack-end impedance is low (say, 12 ohms), the use of a 4:1 balun will make it so low (3 ohms) that it may be outside the efficient matching range of the T or L network. These conditions may be partially remedied by use of a balun that can be switched to either 4:1 or 1:1 ratio, and by choosing antenna and feedline combinations that don't result in extreme values of shack-end impedance/reactance. But that reduces the flexibility of the system. The "unbalanced tuner followed by a balun" idea is clearly one where "newer" wasn't necessarily "better" in all cases. Yet it became very popular because it usually worked. But in many cases the balanced line was actually doing a lot of radiating and there was considerable loss in the system. Back in 1990, AG6K came up with an answer to the shortcomings of that method. He put a 1:1 balun between the rig and a simple balanced tuner, so the balun only has to deal with a pure 50 ohm load once the tuner is adjusted. Although AG6K favors baluns made from coax wound on PVC pipe, other forms of balun such as ferrite-bead and wound-toroid can be used if preferred. You can read AG6K's article he http://www.somis.org/bbat.html and judge for yourself. AG6K's approach used two ganged roller inductors and a single variable capacitor, compared to most commercial manual tuners that use two variable caps and a single variable inductor. Because there are only two controls, remoting the tuner is made easier. 73 de Jim, N2EY |
#6
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On Mar 6, 4:30?pm, Michael Coslo wrote:
wrote: You can read AG6K's article he http://www.somis.org/bbat.html and judge for yourself. I have gathered the parts to make just that!. I'd have it up now, but I switched to a coax fed antenna for a while, and built a more traditional tuner. In the interim I went back to balanced line. The AG6K tuner can be used with balanced or unbalanced line. All you have to do to use it with an unbalanced line is to ground the coax shield at the tuner end of the coax balun, and use the "other side" to feed the ungrounded line. A simple SPST switch of adequate ratings can do the job. The AG6K tuner, as described, has adequate matching range for most dipole-fed-with-balanced-line amateur antennas. A little care in choosing the antenna and feedline length can make the tuner's job a lot easier. Reg Edwards' DIPOLE3 program can be a big help in figuring out the shack-end impedance of various antenna/transmission line combinations. AG6K's approach used two ganged roller inductors and a single variable capacitor, compared to most commercial manual tuners that use two variable caps and a single variable inductor. Because there are only two controls, remoting the tuner is made easier. Some day I'll report on how mine is doing. In the present situation I don't need remote tuning, but will probably motorize the unit anyway. Although not mentioned in the article, the roller inductors could be replaced by a pair of tapped coils and a double-pole switch. The tap positions would have to be found by experiment, but could be made permanent once they were found. Tuner adjustment could then consist of simply selecting the correct tap postion with the switch, and adjusting the variable capacitor for minimum SWR. Automatic tuners are not new to amateur radio, btw. An automatic balanced tuner was described in QST for July, 1952. It would automatically retune itself within an amateur band. Changing bands meant changing coils, but once that was done the tuner would do the rest automatically. 73 de Jim, N2EY |
#7
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#8
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#9
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Mike Coslo wrote:
A little bigger components, plus a 4:1 balun, and they would have it. I wish that the manufacturers would include the provision for balanced feedline. The random-length dipole, fed with balanced line, is an ideal antenna in many cases. It's especially appropriate for disaster situations (and simulated disasters, like Field Day). Find the two highest supports that are available, as far apart as possible, measure the distance, cut the wire and install the middle insulator and feedline, hoist each end, and you're done. Now you've got a reasonably efficient radiator (especially if there's enough distance between those two supports) that you can use on any band, and the length of the feedline isn't particularly critical. But it takes a tuner and balun to make it work, and if this was included in the rig and was automatic, it would be ideal. 73, Steve KB9X |
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