Re: [Elecraft] Slightly Unbalanced dipole?
Jim, Your comment about hams not being limited, " Huh? We're hams -- we're not limited to products we can buy! And we can build far better than we can buy.". you may be correct, but from what I see, the majority of hams, at least around here, buy what they need. Even of our more serious hams buy baluns and chokes from sources like DX Engineering and Balun Designs; few are really building these easy to make devices. There are exceptions to what I just said, but in the main, more hams are buying rather than building. Sorry, but that's what it looks like to me. I do like your paper and have it. I also wish that you continue to get more hams to actually build more things. 73, Barry K3NDM -- Original Message -- From: "Jim Brown" To: elecraft@mailman.qth.net Sent: 1/14/2019 2:21:30 PM Subject: Re: [Elecraft] Slightly Unbalanced dipole? On 1/14/2019 9:02 AM, Barry wrote: The simple answer is that the common mode chokes available to hams are of the unbalanced type. Huh? We're hams -- we're not limited to products we can buy! And we can build far better than we can buy. In 2010, I published the design for a common mode choke to cover the HF bands using a pair of #12 THHN wound on a 2.4-in o.d. #31 toroid. k9yc.com/2018Cookbook.pdf has dozens of designs using THHN, teflon pairs, and RG400. These chokes are fairly easy to wind, and all can be built for less than about $35, including connectors. A member of our contest club is building a serious contest station, and asked me to measure a "balun" from a well-known manufacturer. It came in a nice weatherproof non-metallic enclosure, and was nicely made. But it looked NOTHING like the data sheet that WAS on the website at the time (and which has been removed since I showed my data to a few engineering colleagues, one of whom obviously asked the mfr about it.) The problem with choking a two-wire feedline is NOT one of balance -- if it's a good choke, the choke takes "balance" out of the equation. What matters is dissipation in the choke due to excessive voltage or current that is present because the antenna is not matched to the line. 73, Jim K9YC __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to barrylaz...@gmail.com __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Slightly Unbalanced dipole?
I agree. And I maintain that the problem is exactly the same with the common solution of a single-ended tuner feeding a balanced line through a balun. If there is a big mismatch the choke will get hot. 73, Victor, 4X6GP Rehovot, Israel Formerly K2VCO CWops no. 5 http://www.qsl.net/k2vco/ On 14 Jan 2019 21:21, Jim Brown wrote: The problem with choking a two-wire feedline is NOT one of balance -- if it's a good choke, the choke takes "balance" out of the equation. What matters is dissipation in the choke due to excessive voltage or current that is present because the antenna is not matched to the line. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Slightly Unbalanced dipole?
On 1/14/2019 9:02 AM, Barry wrote: The simple answer is that the common mode chokes available to hams are of the unbalanced type. Huh? We're hams -- we're not limited to products we can buy! And we can build far better than we can buy. In 2010, I published the design for a common mode choke to cover the HF bands using a pair of #12 THHN wound on a 2.4-in o.d. #31 toroid. k9yc.com/2018Cookbook.pdf has dozens of designs using THHN, teflon pairs, and RG400. These chokes are fairly easy to wind, and all can be built for less than about $35, including connectors. A member of our contest club is building a serious contest station, and asked me to measure a "balun" from a well-known manufacturer. It came in a nice weatherproof non-metallic enclosure, and was nicely made. But it looked NOTHING like the data sheet that WAS on the website at the time (and which has been removed since I showed my data to a few engineering colleagues, one of whom obviously asked the mfr about it.) The problem with choking a two-wire feedline is NOT one of balance -- if it's a good choke, the choke takes "balance" out of the equation. What matters is dissipation in the choke due to excessive voltage or current that is present because the antenna is not matched to the line. 73, Jim K9YC __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Slightly Unbalanced dipole?
I got this unbalanced common-mode choke from Amateur Radio Supplies. It completely clobbered all of the "bite" I was getting in the shack, and is keeping stray RF out of my bench computer. I got it when I was having trouble with the keyboard I had connected to my PX3 -- when I transmitted CW or PSK31, the RF would cause random characters to get stuffed into the keyboard buffer, and the transmission wouldn't stop until I stopped it manually. It helped, but the way I finally got around it was by using a 2.5ghz non-Bluetooth wireless keyboard for the PX3. Any wired keyboard I used would result in garbage in the transmission as the RF induced current in the keyboard cable. https://www.amateurradiosupplies.com/product-p/iso-max.htm 73, Gwen, NG3P On Mon, Jan 14, 2019 at 12:03 PM Barry wrote: > Vic, > The simple answer is that the common mode chokes available to hams > are of the unbalanced type. That means they are designed to be > unbalanced in to unbalanced out. Some companies make baluns that are > both current baluns that act for choking common mode currents and > transform a balanced load to an unbalanced load. If you place a common > mode choke at the antenna feed point, the system will be unbalanced, > usually. > > Next, most tuners that have built in baluns use voltage type baluns > and can be less than good in a high SWR situation. However, using a good > current balun at or neat the tuner usually prevents common mode issues. > However nothing is 100% when dealing with RF. > > Putting reactance in the line to counter what is already there is > good when dealing with the impedance, but you are correct about > complexity. The very simplest configuration that I know in a multiband > situation is to erect a dipole for the lowest frequency to be used and > feeding it with ladder line, or equal. Where you enter the house mount a > 4:1 current balun and connect coax from there to the tuner. As long as > your tuner can handle the SWR and the coax run is short, you need not > worry about losses due to SWR; I am speaking to the 1 or so db losses > over just the transmission line loss. If you use the tuner in your > Elecraft gear, I just wouldn't worry, period. Elecraft tuners appear to > be able to handle anything I've put in my backyard so far. > > The Johnson matchbox line of tuners were excellent. I no longer have > mine; selling mine was a less than brilliant move on my part, in > retrospect. However, I don't usually recommend this approach. Getting > through some of the walls/windows in the houses around here with > balanced line can be problematic. So, I usually recommend the approach > above for overall simplicity and assurance of maintaining feed balance. > > 73, > Barry > K3NDM > > -- Original Message ------ > From: "Vic Rosenthal" > To: "Al Lorona" > Cc: elecraft@mailman.qth.net > Sent: 1/14/2019 1:12:37 AM > Subject: Re: [Elecraft] Slightly Unbalanced dipole? > > >Why would a common mode choke at the antenna feedpoint present more > problems than the common practice of feeding a balanced line through a > single-ended tuner and balun? > >I’ve done a lot of experimenting with the latter and have learned that a) > the best configuration is with a 1:1 balun, and b) the balun will become > lossy and heat up if the impedance it sees is highly reactive. The solution > to b) is to cancel the reactance by putting the appropriate opposite > reactance in both sides of the line between the balun and the antenna. Of > course this means added complexity. > >I would love to figure out how to make a choke that would work with > balanced line at the antenna feedpoint, on multiple bands without any > additional components. > >FWIW I’ve switched to a real balanced tuner (Johnson Matchbox). > > > >Victor 4X6GP > > > >> On 14 Jan 2019, at 1:42, Al Lorona wrote: > >> > >> By the way, whenever Jim says, "...a very good common mode choke at > the feedpoint of an antenna...," he means an antenna fed with coax. For the > rest of us, of course, that choke would (should) go at the output of the > antenna tuner, whether in the shack or close by. > >> > >> Al W6LX > >> > >> > >> __ > >> Elecraft mailing list > >> Home: http://mailman.qth.net/mailman/listinfo/elecraft > >> Help: http://mailman.qth.net/mmfaq.htm > >> Post: mailto:Elecraft@mailman.qth.net > >> > >> This list hosted by: http://www.qsl.net > >> Please help support this email list: http://www.qsl.net/donate.html > >> Message delivered to k2vco@gmail.com &
Re: [Elecraft] Slightly Unbalanced dipole?
Vic, The simple answer is that the common mode chokes available to hams are of the unbalanced type. That means they are designed to be unbalanced in to unbalanced out. Some companies make baluns that are both current baluns that act for choking common mode currents and transform a balanced load to an unbalanced load. If you place a common mode choke at the antenna feed point, the system will be unbalanced, usually. Next, most tuners that have built in baluns use voltage type baluns and can be less than good in a high SWR situation. However, using a good current balun at or neat the tuner usually prevents common mode issues. However nothing is 100% when dealing with RF. Putting reactance in the line to counter what is already there is good when dealing with the impedance, but you are correct about complexity. The very simplest configuration that I know in a multiband situation is to erect a dipole for the lowest frequency to be used and feeding it with ladder line, or equal. Where you enter the house mount a 4:1 current balun and connect coax from there to the tuner. As long as your tuner can handle the SWR and the coax run is short, you need not worry about losses due to SWR; I am speaking to the 1 or so db losses over just the transmission line loss. If you use the tuner in your Elecraft gear, I just wouldn't worry, period. Elecraft tuners appear to be able to handle anything I've put in my backyard so far. The Johnson matchbox line of tuners were excellent. I no longer have mine; selling mine was a less than brilliant move on my part, in retrospect. However, I don't usually recommend this approach. Getting through some of the walls/windows in the houses around here with balanced line can be problematic. So, I usually recommend the approach above for overall simplicity and assurance of maintaining feed balance. 73, Barry K3NDM -- Original Message -- From: "Vic Rosenthal" To: "Al Lorona" Cc: elecraft@mailman.qth.net Sent: 1/14/2019 1:12:37 AM Subject: Re: [Elecraft] Slightly Unbalanced dipole? Why would a common mode choke at the antenna feedpoint present more problems than the common practice of feeding a balanced line through a single-ended tuner and balun? I’ve done a lot of experimenting with the latter and have learned that a) the best configuration is with a 1:1 balun, and b) the balun will become lossy and heat up if the impedance it sees is highly reactive. The solution to b) is to cancel the reactance by putting the appropriate opposite reactance in both sides of the line between the balun and the antenna. Of course this means added complexity. I would love to figure out how to make a choke that would work with balanced line at the antenna feedpoint, on multiple bands without any additional components. FWIW I’ve switched to a real balanced tuner (Johnson Matchbox). Victor 4X6GP On 14 Jan 2019, at 1:42, Al Lorona wrote: By the way, whenever Jim says, "...a very good common mode choke at the feedpoint of an antenna...," he means an antenna fed with coax. For the rest of us, of course, that choke would (should) go at the output of the antenna tuner, whether in the shack or close by. Al W6LX __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to k2vco@gmail.com __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to barrylaz...@gmail.com __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Slightly Unbalanced dipole?
I’ve measured common mode current when feeding a balanced line with a good DX
Engineering 1:1 balun and an unbalanced tuner, versus a real balanced
link-coupled tuner (Johnson Matchbox). To my surprise, the currents are closer
to equal with the unbalanced tuner and the balun! But the Matchbox seems
quieter.
More investigation needed...
Victor 4X6GP
> On 14 Jan 2019, at 2:44, Al Lorona wrote:
>
> You guys keep talking about coax-fed antennas. Yes, although it may be easy
> to wind coax around a toroid and put it up at the antenna midpoint, that's
> not so easy with open-wire line. This discussion was very coax-centric and I
> wanted to open your minds that not everybody feeds their antenna with coax.
>
> Balanced feedlines ("window line" or "open-wire" line) can have significant
> common-mode current. They're not immune to the effect. (I know you know this;
> I'm saying it for the benefit of all.) A device with high common-mode
> impedance, located right at the output of the tuner, suppresses common-mode
> current on a (balanced) feedline. That's it's purpose.
>
> I'm in agreement with you about the 1/ cause of common-mode current and the
> 2/ cure for it. I'm simply saying that for convenience's sake, consider
> putting the choke at the tuner output.
>
> A choke with high Z to common-mode current, external to the tuner, in a
> non-conductive box, with as short a connection to the tuner as possible, does
> quite well at suppressing common-mode current. I'll be happy to share my
> measurements with you.
>
> There is no coax anywhere in my antenna system. So my solution was to put a
> choke with high impedance to common-mode current right at the output of my
> antenna tuner. I encourage users of open-wire line to do that.
>
> Al W6LX
>
In all cases of a radiator fed with coax,
> __
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Re: [Elecraft] Slightly Unbalanced dipole?
An array of dipoles are common for high power international broadcast stations. They accept a VSWR of about 2:1 from aprox 20 DB gain curtain arrays They almost always use open wire line. It’s mostly about TX output matching. Sent from my iPad > On Jan 13, 2019, at 9:40 PM, Barry wrote: > > Don et al, >I sense this discussion is targeting the use of a dipole on a single band. > What is being missed is that many of us use a dipole cut for for one band and > use it for the bands above. What we see are high SWRs on all of the higher > frequency bands. We use balanced feeds, open wire or ladder line, as far as > we can before we transition to coax. That transition is a good current balun. > What this does is control losses due to high SWR and keeps RF currents off > the outside of the coax shield. What has been said in previous notes might be > true, but they will prevent or make use of balanced feeders quite difficult. > >An 80 meter dipole used on 40 or 20, for example, is a pretty good > antenna. However, it begs to be fed with open wire or equal. That means no > balun can be used at the antenna feed point. The exception is to use very > expensive coax. :-) > > 73, > Barry > K3NDM > > -- Original Message -- > From: "Don Wilhelm" > To: elecraft@mailman.qth.net > Sent: 1/13/2019 6:59:18 PM > Subject: Re: [Elecraft] Slightly Unbalanced dipole? > >> Al, >> >> If not placed at the antenna feedpoint (up at the antenna), then the >> feedline may radiate due to common mode current. >> For feedlines using parallel conductors, the problem is not as bad if the >> feedline exits at right angles from the radiator for at least a half >> wavelength. In that case, the common mode choke can be placed at the >> junction of the parallel line and coax. >> >> In all cases of a radiator fed with coax, a good common mode choke at the >> radiator feedpoint is necessary. Even though the RF on the inside of the >> coax is balanced, when the coax reaches the radiator, the side of the >> antenna connected to the coax shield sees two paths. One is the side of the >> radiator, and the other is the outside of the coax braid - it will dutifully >> split to follow both paths depending on the impedance of each one. A good >> common mode choke will prevent the RF current from seeing the coax shield as >> another conductor. >> >> A similar situation exists at the transition between parallel feedline and >> coax. >> >> 73, >> Don W3FPR >> >> >> On 1/13/2019 6:42 PM, Al Lorona wrote: > __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Slightly Unbalanced dipole?
Why would a common mode choke at the antenna feedpoint present more problems than the common practice of feeding a balanced line through a single-ended tuner and balun? I’ve done a lot of experimenting with the latter and have learned that a) the best configuration is with a 1:1 balun, and b) the balun will become lossy and heat up if the impedance it sees is highly reactive. The solution to b) is to cancel the reactance by putting the appropriate opposite reactance in both sides of the line between the balun and the antenna. Of course this means added complexity. I would love to figure out how to make a choke that would work with balanced line at the antenna feedpoint, on multiple bands without any additional components. FWIW I’ve switched to a real balanced tuner (Johnson Matchbox). Victor 4X6GP > On 14 Jan 2019, at 1:42, Al Lorona wrote: > > By the way, whenever Jim says, "...a very good common mode choke at the > feedpoint of an antenna...," he means an antenna fed with coax. For the rest > of us, of course, that choke would (should) go at the output of the antenna > tuner, whether in the shack or close by. > > Al W6LX > > > __ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to k2vco@gmail.com __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Slightly Unbalanced dipole?
Don et al, I sense this discussion is targeting the use of a dipole on a single band. What is being missed is that many of us use a dipole cut for for one band and use it for the bands above. What we see are high SWRs on all of the higher frequency bands. We use balanced feeds, open wire or ladder line, as far as we can before we transition to coax. That transition is a good current balun. What this does is control losses due to high SWR and keeps RF currents off the outside of the coax shield. What has been said in previous notes might be true, but they will prevent or make use of balanced feeders quite difficult. An 80 meter dipole used on 40 or 20, for example, is a pretty good antenna. However, it begs to be fed with open wire or equal. That means no balun can be used at the antenna feed point. The exception is to use very expensive coax. :-) 73, Barry K3NDM -- Original Message -- From: "Don Wilhelm" To: elecraft@mailman.qth.net Sent: 1/13/2019 6:59:18 PM Subject: Re: [Elecraft] Slightly Unbalanced dipole? Al, If not placed at the antenna feedpoint (up at the antenna), then the feedline may radiate due to common mode current. For feedlines using parallel conductors, the problem is not as bad if the feedline exits at right angles from the radiator for at least a half wavelength. In that case, the common mode choke can be placed at the junction of the parallel line and coax. In all cases of a radiator fed with coax, a good common mode choke at the radiator feedpoint is necessary. Even though the RF on the inside of the coax is balanced, when the coax reaches the radiator, the side of the antenna connected to the coax shield sees two paths. One is the side of the radiator, and the other is the outside of the coax braid - it will dutifully split to follow both paths depending on the impedance of each one. A good common mode choke will prevent the RF current from seeing the coax shield as another conductor. A similar situation exists at the transition between parallel feedline and coax. 73, Don W3FPR On 1/13/2019 6:42 PM, Al Lorona wrote: By the way, whenever Jim says, "...a very good common mode choke at the feedpoint of an antenna...," he means an antenna fed with coax. For the rest of us, of course, that choke would (should) go at the output of the antenna tuner, whether in the shack or close by. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to barrylaz...@gmail.com __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Slightly Unbalanced dipole?
Al: Al et al; I do agree. And in fact my 250 ft center fed antenna with 75 ft of window feedline terminates at the operating position into a Balun Designs 1171T. Then a coax jumper of about 2 ft long, which is actually a model 8232 from The Wireman, Common Mode Choke between the balun and the output of the KAT500 tuner. I was asked recently on another discussion group why I used both a balun and a common mode choke. The balun itself does not provide adequate common mode choking ability for all bands 160M - 10M. Since I must use a coax jumper between the balun and tuner, why not just make it a common mode choke. All seems reasonable and simple.. like me. Thus one cable and 2 connectors and a quantity of ferrite beads does double duty. And yes for my coax center fed antennas I use a 1:1 current balun, which is no more than a length of coax with a number of ferrite beads at the feed point in a PVC enclosure that serves as the center insulator. I forget the brands and models. They have been up on the tower for several years. 73 Bob, K4TAX On 1/13/2019 5:42 PM, Al Lorona wrote: By the way, whenever Jim says, "...a very good common mode choke at the feedpoint of an antenna...," he means an antenna fed with coax. For the rest of us, of course, that choke would (should) go at the output of the antenna tuner, whether in the shack or close by. Al W6LX __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Slightly Unbalanced dipole?
For HF, I doubt that many (if any) dipoles are fully balanced. On higher frequencies (VHF), the antenna can be far enough away from other objects and the ground that it could be considered unaffected by the environment. But a 40m dipole at 40 feet is less than a half wave from the ground and other objects so i doubt that it is not influenced by it's unbalanced surroundings. Heck, even the grass is greener on one side than the other (more moisture.) Does it make a difference in operational abilities? Probably not. Sure it might be 3 db better to the north than to the south, but with 6 or 10 db fading, that will never be noticed. Just my opinion. Ken WA8JXM On 1/13/19 3:07 PM, Ron Genovesi wrote: I was asked a question by a newcomer to HF today. After thinking about it, I realized it had never really occurred to me. So I’ll pass it on to the group and see what the antenna gurus think. Is there ever a time where a slight imbalance in a dipole could be beneficial? My first inclination was, No, other than the obvious OCF Dipole. But considering that you could have very different conditions under an antenna, both above the ground and under the ground, not to mention a difference in height above ground. What do you think. Could a couple of inches or so difference in the length of the legs of a dipole ever work in your favor? Ron Genovesi n3...@coastside.net 541-761-1103 __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Slightly Unbalanced dipole?
You guys keep talking about coax-fed antennas. Yes, although it may be easy to
wind coax around a toroid and put it up at the antenna midpoint, that's not so
easy with open-wire line. This discussion was very coax-centric and I wanted to
open your minds that not everybody feeds their antenna with coax.
Balanced feedlines ("window line" or "open-wire" line) can have significant
common-mode current. They're not immune to the effect. (I know you know this;
I'm saying it for the benefit of all.) A device with high common-mode
impedance, located right at the output of the tuner, suppresses common-mode
current on a (balanced) feedline. That's it's purpose.
I'm in agreement with you about the 1/ cause of common-mode current and the 2/
cure for it. I'm simply saying that for convenience's sake, consider putting
the choke at the tuner output.
A choke with high Z to common-mode current, external to the tuner, in a
non-conductive box, with as short a connection to the tuner as possible, does
quite well at suppressing common-mode current. I'll be happy to share my
measurements with you.
There is no coax anywhere in my antenna system. So my solution was to put a
choke with high impedance to common-mode current right at the output of my
antenna tuner. I encourage users of open-wire line to do that.
Al W6LX
>>> In all cases of a radiator fed with coax,
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Re: [Elecraft] Slightly Unbalanced dipole?
One of the things that has been hinted at is the OCF dipole. One of the really great attributes is that you can adjust the matching impedance of the antenna by moving the feed point away from center. If you have a SWR of 1.5:1 and the R is 75 and the j is 0, move the feed point away from center and you can find 75 ohms. Of course you will have to address the 75 ohm, but the match will be 1:1. Mel, K6KBE From: Ray Albers To: Elecraft@mailman.qth.net Sent: Sunday, January 13, 2019 1:58 PM Subject: Re: [Elecraft] Slightly Unbalanced dipole? A friend once told me, "Almost none of us has a balanced dipole." What he meant is, few of us are lucky enough to be able to put a dipole high up and completely in the clear - most of us have to put it up where we can, and one side will be closer to houses, trees, gutters, chain link fences. than the other. Probably true! 73 Ray K2HYD __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to farrerfo...@yahoo.com __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Slightly Unbalanced dipole?
Al, If not placed at the antenna feedpoint (up at the antenna), then the feedline may radiate due to common mode current. For feedlines using parallel conductors, the problem is not as bad if the feedline exits at right angles from the radiator for at least a half wavelength. In that case, the common mode choke can be placed at the junction of the parallel line and coax. In all cases of a radiator fed with coax, a good common mode choke at the radiator feedpoint is necessary. Even though the RF on the inside of the coax is balanced, when the coax reaches the radiator, the side of the antenna connected to the coax shield sees two paths. One is the side of the radiator, and the other is the outside of the coax braid - it will dutifully split to follow both paths depending on the impedance of each one. A good common mode choke will prevent the RF current from seeing the coax shield as another conductor. A similar situation exists at the transition between parallel feedline and coax. 73, Don W3FPR On 1/13/2019 6:42 PM, Al Lorona wrote: By the way, whenever Jim says, "...a very good common mode choke at the feedpoint of an antenna...," he means an antenna fed with coax. For the rest of us, of course, that choke would (should) go at the output of the antenna tuner, whether in the shack or close by. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Slightly Unbalanced dipole?
It is reasonable to put a choke at the antenna with open wire line. Open wire isn’t magic, it can carry common mode currents, too. Both wires high, both wires low, and that is common mode. wunder K6WRU Walter Underwood CM87wj http://observer.wunderwood.org/ (my blog) > On Jan 13, 2019, at 3:42 PM, Al Lorona wrote: > > By the way, whenever Jim says, "...a very good common mode choke at the > feedpoint of an antenna...," he means an antenna fed with coax. For the rest > of us, of course, that choke would (should) go at the output of the antenna > tuner, whether in the shack or close by. > > Al W6LX > > > __ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to wun...@wunderwood.org __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Slightly Unbalanced dipole?
By the way, whenever Jim says, "...a very good common mode choke at the feedpoint of an antenna...," he means an antenna fed with coax. For the rest of us, of course, that choke would (should) go at the output of the antenna tuner, whether in the shack or close by. Al W6LX __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Slightly Unbalanced dipole?
On 1/13/2019 12:23 PM, Don Wilhelm wrote: The OCF antennas are infamous for conducting RF into the shack. And for being very noisy on receive. 73, Jim K9YC __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Slightly Unbalanced dipole?
Your friend is a wise man. That is, indeed, reality. There's a discussion about this in one of my tutorials. http://k9yc.com/CoaxChokesPPT.pdf The PRIMARY reason for putting a very good common mode choke at the feedpoint of an antenna is to prevent the feedline from radiating into your neighbor's living room and from picking up noise from his living room on receive. The reason this works is that the feedline probably runs closer to his living room (and yours) than the antenna itself. A choke will not eliminate all noise, because the antenna is picking it up, and it won't eliminate all of your TX RF in his living room, because your antenna radiates it. 73, Jim K9YC On 1/13/2019 1:55 PM, Ray Albers wrote: A friend once told me, "Almost none of us has a balanced dipole." What he meant is, few of us are lucky enough to be able to put a dipole high up and completely in the clear - most of us have to put it up where we can, and one side will be closer to houses, trees, gutters, chain link fences. than the other. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Slightly Unbalanced dipole?
That's why I use the statement "xxx ft center fed wire with balanced feed". I do have the ability to measure the current in each side of the feedline. As long as it is within 5%, about the limits of accuracy of measurements, I'm happy. Bob, K4TAX Sent from my iPhone > On Jan 13, 2019, at 3:55 PM, Ray Albers wrote: > > A friend once told me, "Almost none of us has a balanced dipole." > > What he meant is, few of us are lucky enough to be able to put a dipole > high up and completely in the clear - most of us have to put it up where we > can, and one side will be closer to houses, trees, gutters, chain link > fences. than the other. > > Probably true! > > 73 > Ray K2HYD > __ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to rmcg...@blomand.net > __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Slightly Unbalanced dipole?
A friend once told me, "Almost none of us has a balanced dipole." What he meant is, few of us are lucky enough to be able to put a dipole high up and completely in the clear - most of us have to put it up where we can, and one side will be closer to houses, trees, gutters, chain link fences. than the other. Probably true! 73 Ray K2HYD __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Slightly Unbalanced dipole?
To answer the question "Could a couple of inches or so difference in the length of the legs of a dipole ever work in your favor?"..depends on the frequency. For lower frequencies likely NO, for higher frequencies maybe YES. Thus 2" for a 160M dipole would be 0.066% while 2" for a 10M dipole would be 1.02%. In either case..I doubt that it would make a difference due to local installation conditions. i.e. Different height above ground for the 2 sections, different ground conductivity under the 2 sections, different location / proximity to surrounding objects, different types of end insulators, and etc. As pointed out earlier the current may shift a wee bit and thus distort the "ideal" pattern but in the real world of ham antennasNAH. 73 Bob, K4TAX On 1/13/2019 2:07 PM, Ron Genovesi wrote: I was asked a question by a newcomer to HF today. After thinking about it, I realized it had never really occurred to me. So I’ll pass it on to the group and see what the antenna gurus think. Is there ever a time where a slight imbalance in a dipole could be beneficial? My first inclination was, No, other than the obvious OCF Dipole. But considering that you could have very different conditions under an antenna, both above the ground and under the ground, not to mention a difference in height above ground. What do you think. Could a couple of inches or so difference in the length of the legs of a dipole ever work in your favor? Ron Genovesi n3...@coastside.net 541-761-1103 __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to rmcg...@blomand.net __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Slightly Unbalanced dipole?
Ron, With a slight difference, I cannot see that it would either benefit or degrade. The current distribution on the radiator might be a little off-center, but it will still work. But it is one reason for using a very good current choke on the feedline - to keep RF off the outer braid of the coax. The OCF antennas are infamous for conducting RF into the shack. 73, Don W3FPR On 1/13/2019 3:07 PM, Ron Genovesi wrote: I was asked a question by a newcomer to HF today. After thinking about it, I realized it had never really occurred to me. So I’ll pass it on to the group and see what the antenna gurus think. Is there ever a time where a slight imbalance in a dipole could be beneficial? My first inclination was, No, other than the obvious OCF Dipole. But considering that you could have very different conditions under an antenna, both above the ground and under the ground, not to mention a difference in height above ground. What do you think. Could a couple of inches or so difference in the length of the legs of a dipole ever work in your favor? __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
