[OT] Antenna Question
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In terms of efficiency, is there a substantial difference between having a remote tuner at the feedpoint of a vertical vs having a balun at the feedpoint and the tuner in the rig? Assume a less then 50 ft run of RG58 and at least 4 counterpoise being used in a portable situation with a telescoping vertical of TBD height.
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Hello Rick,
What you consider efficient. What amount of loss are you willing to tolerate? If you give me the particulars on the installation I can run a model and stick it into SimSmith and get an answer for you if you like. Myron WV0H Printed on Recycled Data From: rick jones via Elecraft ______________________________________________________________ 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 Message delivered to [hidden email] |
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In reply to this post by Elecraft mailing list
Rick,
It "all depends" on what you did not communicate. Is the vertical resonant? What frequency? I assume not resonant if a remote tuner might be required. If the SWR is high, then the loss in the RG-58 can be significant if a tuner is not used at that base of the vertical. The loss depends on frequency. TBD height does not add anything to the question regarding efficiency. In other words, there are too many variables to give you an intelligent answer. 73, Don W3FPR On 8/6/2016 9:42 PM, rick jones via Elecraft wrote: > In terms of efficiency, is there a substantial difference between having a remote tuner at the feedpoint of a vertical vs having a balun at the feedpoint and the tuner in the rig? Assume a less then 50 ft run of RG58 and at least 4 counterpoise being used in a portable situation with a telescoping vertical of TBD height. > ______________________________________________________________ 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 Message delivered to [hidden email] |
Re: [OT] Antenna Question
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In reply to this post by Elecraft mailing list
Ok sorry for not providing enough info! Consider this scenario: I have a portable vertical with 4 counterpoise wires that is resonant on 20. Lets say I want to tune the antenna up on 40. I can have a tuner right at the base of the antenna OR I can just use a balun at the base of the antenna and use the built in ATU in the K3. Is there a difference in how much power is getting to the antenna? I assume the tuner at the base is the best option which always makes me doubt the usefulness of having an ATU built in to a rig in terms of getting the most power to the antenna. Am I on the right track? Thanks! Rick
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The SWR on the coax when you are using a 20m vertical on 40 would be
astronomical. I ran a quick EZNEC analysis of a 1/4 wave 20m vertical with its base on the ground and got an impedance of 6.9 - j348. This comes out to an SWR of about 187:1, which you would measure at the rig as only 18:1 due to the massive 13.3 dB loss in the coax. 100 watts in would give you something like 5 watts to the antenna. Short answer: put the tuner at the base. Of course, using a 20m antenna on 40 is about the worst case imaginable! 73, Vic, 4X6GP Rehovot, Israel Formerly K2VCO http://www.qsl.net/k2vco/ On 7 Aug 2016 05:58, rick jones via Elecraft wrote: > Ok sorry for not providing enough info! Consider this scenario: I > have a portable vertical with 4 counterpoise wires that is resonant > on 20. Lets say I want to tune the antenna up on 40. I can have a > tuner right at the base of the antenna OR I can just use a balun at > the base of the antenna and use the built in ATU in the K3. Is there > a difference in how much power is getting to the antenna? I assume > the tuner at the base is the best option which always makes me doubt > the usefulness of having an ATU built in to a rig in terms of getting > the most power to the antenna. Am I on the right track? Thanks! Rick ______________________________________________________________ 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 Message delivered to [hidden email] |
Re: [OT] Antenna Question
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In reply to this post by Elecraft mailing list
OK a very good reality check when you look at the numbers! So I'm still trying to figure out the usefulness of a built in tuner. Two situations come to mind: You have no feedline and are driving a wire right out of your rig with a counterpoise (KX3 portable operations) OR you are using it to just "touch up" the load on the PA from an antenna that is close to resonance. I would hope that a good Elmer would point out that a built in ATU does nothing more then keep your PA happy but does nothing toward getting out a good signal AND that if a tuner is necessary, a remote one is a better choice. Thanks for your patience everyone while I get these concepts "right". Other forums would not have been as accommodating.
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Rick,
The usefulness of an internal tuner is highly dependent on the matched line loss of the feedline. If you have a feedline that has a relatively high matched line loss - and you specified 50 feet of RG-58, then the feedline losses will be high in the case of the antenna you propose. A tuner at the base of the antenna will reduce those feedline losses. For feedlines that have only a moderate loss, the internal tuner is much more useful. 73, Don W3FPR On 8/6/2016 11:57 PM, rick jones via Elecraft wrote: > OK a very good reality check when you look at the numbers! So I'm still trying to figure out the usefulness of a built in tuner. Two situations come to mind: You have no feedline and are driving a wire right out of your rig with a counterpoise (KX3 portable operations) OR you are using it to just "touch up" the load on the PA from an antenna that is close to resonance. I would hope that a good Elmer would point out that a built in ATU does nothing more then keep your PA happy but does nothing toward getting out a good signal AND that if a tuner is necessary, a remote one is a better choice. Thanks for your patience everyone while I get these concepts "right". Other forums would not have been as accommodating. > ______________________________________________________________ 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 Message delivered to [hidden email] |
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In reply to this post by Elecraft mailing list
A lot depends on the band. For example, your 20m vertical would have an
SWR of only 8:1 on 17m. Loss with 50' of RG-58 would be about 2 dB. That's not insignificant, but a lot better than not being able to operate on 17m at all. The built-in K3 tuner would have no trouble matching it. I am actually using a 20m dipole on 40. But my feedline is short (34') and it is 600-ohm open wire line. SWR is something like 85:1, and I am living with a loss of about 3 dB because it is a compromise solution that gets me a 7-band antenna in limited space. 73, Vic, 4X6GP Rehovot, Israel Formerly K2VCO http://www.qsl.net/k2vco/ On 7 Aug 2016 06:57, rick jones via Elecraft wrote: > OK a very good reality check when you look at the numbers! So I'm > still trying to figure out the usefulness of a built in tuner. Two > situations come to mind: You have no feedline and are driving a wire > right out of your rig with a counterpoise (KX3 portable operations) > OR you are using it to just "touch up" the load on the PA from an > antenna that is close to resonance. I would hope that a good Elmer > would point out that a built in ATU does nothing more then keep your > PA happy but does nothing toward getting out a good signal AND that > if a tuner is necessary, a remote one is a better choice. Thanks for > your patience everyone while I get these concepts "right". Other > forums would not have been as accommodating. > ______________________________________________________________ > 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 Message delivered to > [hidden email] > 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 Message delivered to [hidden email] |
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In reply to this post by Elecraft mailing list
On Sat,8/6/2016 7:58 PM, rick jones via Elecraft wrote:
> Ok sorry for not providing enough info! Consider this scenario: I have a portable vertical with 4 counterpoise wires that is resonant on 20. Lets say I want to tune the antenna up on 40. Rick, You're asking the wrong questions. The best solution to your problem involves changing the antenna! When you want to operate on 40 (or 30), improvise a mechanical solution to make the antenna longer. Study the ARRL Antenna Book and the ARRL Handbook so that you better understand how antennas work. Another fundamental principle -- the smaller the coax, the greater the loss. The SHORTER the coax, the less the loss. RG58 is BAD, because it's small. RG8X is better, because it's bigger. RG8 is even better, because it's even bigger. And, as Wayne has observed, we don't need "built" or "purchased" antennas for portable/backpacking use. Throw a wire into a tree, or support it vertically, connect it to the center conductor of the coax connector at the output of the rig. Try to get it close to a quarter wave, but don't lose sleep if it isn't real close. Connect one or more wires to the chassis of the rig to act as a counterpoise. Don't know what that word means? Look in the ARRL Handbook. Try to make those wires close to a quarter wave. Don't lose sleep if they aren't. Fire up the radio, activate the tuner, make it tune, and call CQ. We don't need no stinkin' coax! The great small club of which I was a member in Chicago hosted a QRP night every year. We set up in a "forest preserve" -- local park -- and everyone brought their rig and antennas. I brought a K2, battery, a couple of lengths of #18 wire, and a telescoping fiberglass pole. I taped one wire to the pole, shoved it into space between the parts of a picnic table so that it was somewhere between horizontal and vertical, and connected it to the center of the coax connector on the K2. I connected another length of wire to the chassis, and laid it on some weeds. I fired up on 30M and made a half dozen QSOs, AND broke a pileup from a station in the Caribbean. 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 Message delivered to [hidden email] |
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In reply to this post by Elecraft mailing list
Rick,
You have been getting very good answers. You are right, the internal ATU helps match the rig to the antenna and/or loss is negligible when you feed the antenna directly or with low loss line (open wire). However, I have operated with bad setups and still made contacts. I actually used a low 80m inverted vee (20' at center, 6' at the ends) on 160 and made a few digital contacts. I figure that antenna was 1% efficient and 99% loss! And I used a similar 40m inverted vee on 30m and managed to work a VK station via JT-65. IDK maybe that setup was 25% efficient. A modern rig with an ATU makes the rig more like the boatanchors of the past that were more flexible in what they load. My old Viking II will load just about anything and I tried some pretty terrible pieces of wire for antennas. The only thing it ever failed to load was a 3 ft metal fishing pole....on 160m! 73, Ken WA8JXM On 8/6/16 11:57 PM, rick jones via Elecraft wrote: > OK a very good reality check when you look at the numbers! So I'm still trying to figure out the usefulness of a built in tuner. Two situations come to mind: You have no feedline and are driving a wire right out of your rig with a counterpoise (KX3 portable operations) OR you are using it to just "touch up" the load on the PA from an antenna that is close to resonance. I would hope that a good Elmer would point out that a built in ATU does nothing more then keep your PA happy but does nothing toward getting out a good signal AND that if a tuner is necessary, a remote one is a better choice. Thanks for your patience everyone while I get these concepts "right". Other forums would not have been as accommodating. ______________________________________________________________ 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 Message delivered to [hidden email] |
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