Re: [Elecraft] Bal[un] (was: Buddipole vs. tuner and wire)
Hi Brian I don't recall if you mentioned what power level you would be using with your K2. If it is running barefoot, without the 100w PA, you could use one of the Elecraft switchable baluns. They switch between 1:1 and 4:1 ratios, giving you a good chance to match most balanced feeds. Even though the rig end of the line may be reactive, due to impedance mismatches along the line, the switchable balun can be used to reduce the amount of mismatch the ATU then has to to cope with. This makes a simple dipole with tuned feeders a nice multiband antenna. On a given band, try both switch positions and see which one helps the ATU make the best match. Good luck and 73 Bob N6WG - Original Message - From: Brian Lloyd [EMAIL PROTECTED] To: elecraft Reflector elecraft@mailman.qth.net Sent: Tuesday, May 13, 2008 8:37 AM Subject: [Elecraft] Bal[un] (was: Buddipole vs. tuner and wire) OK, I am convinced - keep the tuner and the wire. So, that brings up a second question: balanced vs. unbalanced. Wire antennas that do not require a counterpoise are usually loops or dipoles, i.e. inherently balanced even if not resonant. Most tuners offer an unbalanced output. SGC says, just connect up the antenna. Seems to me that a balun would improve things and keep RF off the coax and power leads to the tuner. But how well do baluns handle huge mismatch? Just off the top of my head, it seems to me that the tuner at the top of a pole with two legs sloped down, i.e. inverted-V, would make a pretty good omni all-band antenna. More thinking aloud. Brian Lloyd Granite Bay Montessori School 9330 Sierra College Bl brian AT gbmontessori DOT com Roseville, CA 95661 +1.916.367.2131 (voice)+1.791.912.8170 (fax) PGP key ID: 12095C52A32A1B6C PGP key fingerprint: 3B1D BA11 4913 3254 B6E0 CC09 1209 5C52 A32A 1B6C ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Bal[un] (was: Buddipole vs. tuner and wire)
Last year I used an inverted V doublet, supported by a telescopic carbon fibre pole (DK9SQ pole http://www.qsl.net/dk9sq and review at http://www.eham.net/reviews/detail/1094) and fed by a short length of ribbon (300 ohms I think, the clear plastic type) via an SG237. The doublet was not cut for any particular band and I did not use a balun or redials etc. I worked PY from Southern France (~5000 miles) on 20m with 100W SSB from an FT-857. I haven't tried it yet, but I plan on doing the same again with my K3, but via a BL2 this time. 73 de M0XDF, K3 #174 -- The universe is like a safe to which there is a combination. But the combination is locked up in the safe. -Peter De Vries, editor, novelist (1910-1993) On 13 May 2008, at 16:37, Brian Lloyd wrote: OK, I am convinced - keep the tuner and the wire. So, that brings up a second question: balanced vs. unbalanced. Wire antennas that do not require a counterpoise are usually loops or dipoles, i.e. inherently balanced even if not resonant. Most tuners offer an unbalanced output. SGC says, just connect up the antenna. Seems to me that a balun would improve things and keep RF off the coax and power leads to the tuner. But how well do baluns handle huge mismatch? Just off the top of my head, it seems to me that the tuner at the top of a pole with two legs sloped down, i.e. inverted-V, would make a pretty good omni all-band antenna. More thinking aloud. Brian Lloyd Granite Bay Montessori School 9330 Sierra College Bl brian AT gbmontessori DOT com Roseville, CA 95661 +1.916.367.2131 (voice)+1.791.912.8170 (fax) PGP key ID: 12095C52A32A1B6C PGP key fingerprint: 3B1D BA11 4913 3254 B6E0 CC09 1209 5C52 A32A 1B6C ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
RE: [Elecraft] Bal[un] (was: Buddipole vs. tuner and wire)
It would really help if we could drop the incorrect balanced/unbalanced nomenclature, but it's ingrained in Ham lore and it causes misunderstandings. A coaxial RF output to an antenna is *balanced*: the currents flowing out into the coax are as well balanced (perhaps better balanced) than those flowing in any open wire or parallel wire feedline. The real difference is that a so-called balanced output is isolated from the rig ground. It does not mean it's inherently any more balanced than the coaxial connector output. So what's the big deal? When feeding a balanced load such as a loop or center fed wire antenna, it's easier to preserve the balance of currents when using an RF output that is isolated from the rig ground. Of course, preserving that balance does a couple of good things: 1) When using a parallel wire feedline (so-called open wire, ribbon or similar feedline), isolating the RF from the rig ground helps ensure that all the RF is flowing in the two wires to minimize feedline radiation (or pickup). Parallel wire lines with balanced currents do not produce an RF field since the fields produced the wires are opposite in phase and equal in amplitude, so there is no net RF field produced around the feeder. All the RF energy is kept in the feed line to be moved to the load, whether it's energy picked up to be fed to the receiver or energy from a transmitter to be moved to the antenna. 2) A parallel wire feedline maintains the intended RF path at the antenna without complications at the feed point that are found using coax. Consider the center fed wire, fed with a coaxial line. RF flowing along the center conductor of a coaxial line flows out along one wire, while the RF flowing along the inside of the shield flows out along the other wire. But that shield has an inside and an outside. For RF, the inside and outside of the shield are *different* conductors since the RF flows only along the very surface of a conductor, thanks to skin effect. In other words, the inside and outside surface of the shield on a coax looks like two completely different and isolated conductors to the RF. When the RF reaches the edge of the shield where it is connected to one side of a center fed wire, the RF is free to flow along the antenna wire *and* flow back along the outside of the coax shield. That means that you have two conductors connected to one side of your 'center fed wire' - one is the intended antenna wire and the other is the outside of the coax shield. In most cases that current on the outside of the coax shield is not a problem. However, it can be an issue if the electrical length of the feedline produces a voltage loop (high impedance point) at the rig. Properly connected to the rig, a coaxial line shield is unbroken, so the outside of the coax is contiguous with the outside of the metal enclosure on the rig. The currents flowing on the inside surface of the rig flow out only onto the inside surface of the coax. But, if there is RF on the *outside* of the coax it will flow onto the outside of the rig. If the rig is at a voltage loop and if the rig doesn't have a good *RF* ground, the rig can appear hot with RF. Even if you put a balun at the antenna end to stop RF currents from flowing back along the outside of the coax, you can end up with RF on the outside of the shield and so at the rig. That's because the coaxial line is a conductor very close to the radiator. In spite of a choke balun at the feed point, the RF field around antenna easily can induce significant RF currents on the outside of the coax. Those currents can flow down the outside of the coax to the outside of the rig. In that case, a choke balun at the rig can help. So what's the big deal with parallel wire feedlines, if coaxial lines offer balanced currents to the antenna as well? In a word: impedance. Practical coaxial lines have a fairly low impedance, where practical parallel wire lines have a fairly high impedance. A coaxial line with an impedance of, say, 400 ohms, requires a rather large diameter - usually several feet!(The impedance is based on a ratio between the diameter of the shield and the center conductor) Similarly, a parallel wire line with an impedance of, say 50 ohms, requires very close spacing of the wires. Impedance is important to minimize the SWR extremes, hence the resistive losses, in a system that might show a wide range of impedances to the feedline, such as a center fed wire used on several bands. A center fed wire antenna (doublet) might show something from about 50 ohms where it's 1/2 wavelength long, up to maybe 2,000 ohms or so where it's 1 wavelength long. A 400 ohm feed line will show an SWR range of about 5:1 over that entire range. However, a 50 ohm coax line will show an SWR of about 40:1 when feeding an antenna showing a 2000 ohm impedance at the feed point. That 40:1 means very large RF currents at the current loops along the feed line, hence large resistive losses. You are quite right,
Re: [Elecraft] Bal[un] (was: Buddipole vs. tuner and wire)
The BL2 (switchable balun) will handle 250 watts! That should be enough. Dave W7AQK - Original Message - From: Robert Tellefsen [EMAIL PROTECTED] To: Brian Lloyd [EMAIL PROTECTED]; elecraft Reflector elecraft@mailman.qth.net Sent: Tuesday, May 13, 2008 9:54 AM Subject: Re: [Elecraft] Bal[un] (was: Buddipole vs. tuner and wire) Hi Brian I don't recall if you mentioned what power level you would be using with your K2. If it is running barefoot, without the 100w PA, you could use one of the Elecraft switchable baluns. They switch between 1:1 and 4:1 ratios, giving you a good chance to match most balanced feeds. Even though the rig end of the line may be reactive, due to impedance mismatches along the line, the switchable balun can be used to reduce the amount of mismatch the ATU then has to to cope with. This makes a simple dipole with tuned feeders a nice multiband antenna. On a given band, try both switch positions and see which one helps the ATU make the best match. Good luck and 73 Bob N6WG - Original Message - From: Brian Lloyd [EMAIL PROTECTED] To: elecraft Reflector elecraft@mailman.qth.net Sent: Tuesday, May 13, 2008 8:37 AM Subject: [Elecraft] Bal[un] (was: Buddipole vs. tuner and wire) OK, I am convinced - keep the tuner and the wire. So, that brings up a second question: balanced vs. unbalanced. Wire antennas that do not require a counterpoise are usually loops or dipoles, i.e. inherently balanced even if not resonant. Most tuners offer an unbalanced output. SGC says, just connect up the antenna. Seems to me that a balun would improve things and keep RF off the coax and power leads to the tuner. But how well do baluns handle huge mismatch? Just off the top of my head, it seems to me that the tuner at the top of a pole with two legs sloped down, i.e. inverted-V, would make a pretty good omni all-band antenna. More thinking aloud. Brian Lloyd Granite Bay Montessori School 9330 Sierra College Bl brian AT gbmontessori DOT com Roseville, CA 95661 +1.916.367.2131 (voice)+1.791.912.8170 (fax) PGP key ID: 12095C52A32A1B6C PGP key fingerprint: 3B1D BA11 4913 3254 B6E0 CC09 1209 5C52 A32A 1B6C ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Bal[un] (was: Buddipole vs. tuner and wire)
You're right, Dave. I have three of them. Very handy little beasts. 73, Bob N6WG - Original Message - From: David Yarnes [EMAIL PROTECTED] To: Robert Tellefsen [EMAIL PROTECTED]; Brian Lloyd [EMAIL PROTECTED]; elecraft Reflector elecraft@mailman.qth.net Sent: Tuesday, May 13, 2008 2:45 PM Subject: Re: [Elecraft] Bal[un] (was: Buddipole vs. tuner and wire) The BL2 (switchable balun) will handle 250 watts! That should be enough. Dave W7AQK - Original Message - From: Robert Tellefsen [EMAIL PROTECTED] To: Brian Lloyd [EMAIL PROTECTED]; elecraft Reflector elecraft@mailman.qth.net Sent: Tuesday, May 13, 2008 9:54 AM Subject: Re: [Elecraft] Bal[un] (was: Buddipole vs. tuner and wire) Hi Brian I don't recall if you mentioned what power level you would be using with your K2. If it is running barefoot, without the 100w PA, you could use one of the Elecraft switchable baluns. They switch between 1:1 and 4:1 ratios, giving you a good chance to match most balanced feeds. Even though the rig end of the line may be reactive, due to impedance mismatches along the line, the switchable balun can be used to reduce the amount of mismatch the ATU then has to to cope with. This makes a simple dipole with tuned feeders a nice multiband antenna. On a given band, try both switch positions and see which one helps the ATU make the best match. Good luck and 73 Bob N6WG - Original Message - From: Brian Lloyd [EMAIL PROTECTED] To: elecraft Reflector elecraft@mailman.qth.net Sent: Tuesday, May 13, 2008 8:37 AM Subject: [Elecraft] Bal[un] (was: Buddipole vs. tuner and wire) OK, I am convinced - keep the tuner and the wire. So, that brings up a second question: balanced vs. unbalanced. Wire antennas that do not require a counterpoise are usually loops or dipoles, i.e. inherently balanced even if not resonant. Most tuners offer an unbalanced output. SGC says, just connect up the antenna. Seems to me that a balun would improve things and keep RF off the coax and power leads to the tuner. But how well do baluns handle huge mismatch? Just off the top of my head, it seems to me that the tuner at the top of a pole with two legs sloped down, i.e. inverted-V, would make a pretty good omni all-band antenna. More thinking aloud. Brian Lloyd Granite Bay Montessori School 9330 Sierra College Bl brian AT gbmontessori DOT com Roseville, CA 95661 +1.916.367.2131 (voice)+1.791.912.8170 (fax) PGP key ID: 12095C52A32A1B6C PGP key fingerprint: 3B1D BA11 4913 3254 B6E0 CC09 1209 5C52 A32A 1B6C ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
