+++++++++++++++++++++ See also G5RV Antenna +++++++++++++++++++++ Date: Mon, 15 Apr 2002 11:23:18 EDT From: K5KW at aol.com To: qrp-l at lehigh.edu Subject: [124792] G5RV Antenna Article Download URL Gang, Several have inquired about the article by the late Louis Varney, G5RV, on his conclusions about his G5RV antenna that I mentioned in a recent response on the reflector. I just looked at the article and it lists the URL of the site from which I downloaded it. It is couresy AA3PX and qsl.net. The complete six page article with 10 diagrams (be sure to download the diagrams, too, 16 pages in all) is available at: www.qsl.net/aa3px/g5rv.htm The article will answer nearly any question that can be posed about the G5RV dipole Don, K5KW Fort Gibson +++++++++++++++++++ Date: Mon, 15 Apr 2002 13:54:27 -0400 From: Bill Coleman To: , "Low Power Amateur Radio Discussion" Subject: [124806] Re: G5RV - balun or not On 4/14/02 10:26 PM, Dave Benham at dodgeboy at mindspring.com wrote: >I know there is an age old controversy about whether the G5RV should have a >balun or not, and whether it should be even called a G5RV when it has a >balun. I don't believe the "original" G5RV used a balun. It is really set up as a 20m extended double zepp with a matching section. It also happens to work OK as an untuned doublet on the other bands. >But I would like some opinions >about what sort of "trouble" I might get into if I pull the balun out. Tha balun's purpose is to keep antenna currents off the outside of the coax. If you remove the balun, then you'll get some common-mode currents on the coax, which may be undesirable, but shouldn't overtly affect the performance of the antenna. (You may have some RFI pickup along the route of the coax, as well as exposing items along the route of the coax to RFI when you transmit) >Also, if I do that, how do I hook the coax to the twinlead (I have the heavy >duty TV twinlead, not wide spaced ladder line)? Do I just solder the coax >directly to the twinlead (that seems so crude)? Yes. > Now I have a coffee can >size loop with about 7 turns of coax just before the balun -- do I keep that >or not? That sounds like an air-wound choke balun to me. Just be sure to keep the turns in one layer -- not bunched. This is an effective balun for 30-10m. If you use the balun, you don't need the turns of coax, and vice versa. Bill Coleman, AA4LR, PP-ASEL Mail: aa4lr at arrl.net Quote: "Not within a thousand years will man ever fly!" -- Wilbur Wright, 1901 ++++++++++++++++++++ Date: Mon, 15 Apr 2002 13:56:03 -0400 From: Bill Coleman To: , "Low Power Amateur Radio Discussion" Subject: [124807] Re: G5RV Balun or Not? On 4/14/02 11:22 PM, K5KW at aol.com at K5KW at aol.com wrote: >I have an article written by Louis Varney, G5RV himself, (now an SK) perhaps >the last one he wrote about his antenna design. In that article he says the >balun is not useful and he recommends against using one. What KIND of balun did he say was not useful? > However, he does >recommend an 8 or 10 turn six inch diameter coil of coax immediately below >the point where the coax connects to the ladder line (or open wire feeders). Gosh, that's a coaxial choke balun.... Isn't it odd that he recommends against baluns, but then recommends a balun? Bill Coleman, AA4LR, PP-ASEL Mail: aa4lr at arrl.net Quote: "Not within a thousand years will man ever fly!" -- Wilbur Wright, 1901 +++++++++++++++++++++ Date: Mon, 15 Apr 2002 20:09:16 -0600 From: "James R. Duffey" To: qrp-l Subject: [124842] G5RV - Use a Balun Dave - Whenever there is an unbalanced to balanced transition, good engineering practice calls for a balun. The G5RV has a balanced to unbalanced transition at the junction of the balanced feeder to the coax. A 1:1 current or choke balun should be used at the transition. There are instructions for air core coax scramble wound baluns in the handbook and antenna book. These will work OK, but the bandwidth is not as wide as one would always like. They are cheap and effective though. It sounds like your coil of coax is adequate for this. Air core baluns can also be wound on form resulting in wider bandwidth. See: http://www.k1ttt.net/technote/airbalun.html for details on building one and performance details. As many turns of RG-58 as you can get on a 1.5 inch OD or greater OD type 43 ferrite core will work fine, and probably be as broad band as your can get. G5RV made his caution against baluns before current baluns were widely recognized and used in the ham community. I believe his caution is against the common 4:1 voltage baluns, which are not designed for this application. A 1:1 current balun (or choke, or sorta balun) should be used. Keep the coil of coax and you will should be happy. Happy birthday to QRP-L. Thanks to Chuck for pointing this out. We all owe a debt of gratitude to Jim Eshleman for doing yeoman's duty in hosting us all. Thanks Jim. During Jim's time of hosting this list others heavily involved in QRP -L on this list have come and gone and come again -and gone again. And again and again.Others have tried to start competing lists. They have not been as successsful, largely because the operators of those lists lacked Jim's tolerance for free speech. But Jim has put up with all of our antics and maintained the list and not shut us down when he probably had good justification for it. Thanks Jim. Buy you a Beer? I joined in 1994 about a year after it started. It has meant the world to me. It rekindled my interest in Ham radio and has made me many friends in far flung areas of the country. As to Chuck's admonitions about list etiquette. Several years ago I decided that I would only post on technical or QRP operating issues. I would only post about QRP-L issues if attached to a technical post. Like t his one. If everybody did this the list would be much better. Only post things that you yourself would like to see on QRP-L - Dr, Megacycle KK6MC/5 -- James R. Duffey KK6MC/5 Cedar Crest, NM DM65 ++++++++++++++++++++ Date: Mon, 15 Apr 2002 21:50:51 -0500 From: "Tim, N9PUZ" To: , "Low Power Amateur Radio Discussion" Subject: [124844] Re: G5RV - Use a Balun From: "James R. Duffey" > G5RV made his caution against baluns before current baluns were widely > recognized and used in the ham community. I believe his caution is against > the common 4:1 voltage baluns, which are not designed for this application. > A 1:1 current balun (or choke, or sorta balun) should be used. How do the baluns perform that are made by slipping the ferrite beads over the outside of the coax? Are they better or worse than a coil of coax or is this a different application entirely? Tim N9PUZ +++++++++++++++++++ Date: Mon, 15 Apr 2002 20:59:01 -0600 From: "James R. Duffey" To: "Tim, N9PUZ" , Low Power Amateur Radio Discussion Subject: [124845] Re: G5RV - Use a Balun Tim - The bead baluns work OK. Since they only have one turn, they must be made with a high permeability ferrite, which in turn has slightly higher losses than a ferrite that can be used with toroids, but for QRP that is not an issue. - Dr. Megacycle KK6MC/5 James R. Duffey KK6MC/5 Cedar Crest, NM DM65 +++++++++++++++++++++++ Date: Tue, 16 Apr 2002 07:09:50 -0400 From: "Pastor-KC1DI" To: , "Low Power Amateur Radio Discussion" Subject: [124851] Re: G5RV - Use a Balun SNIP > As many turns of RG-58 as you can get on a 1.5 inch OD or greater OD type > 43 ferrite core will work fine, and probably be as broad band as your can > get. Snip What James has to say is good stuff.. but I would warn of one thing make sure the RG58 is not of the foam insulation type. I had problems with a G5RV here that was finally traced back to center conductor migration due to sun's heat softening the foam insulation of the coax. This is more important the tighter you make the coil turns the more likely the foam coax will break down Under load. Look of coax with teflon, or P.E. insulation for this application. Oh by the way Air wond coax chokes worked fine here with G5RV antennas. 73 Dave Kc1di/// qrp +++++++++++++++++++ Date: Tue, 16 Apr 2002 10:35:08 -0400 From: Bill Coleman To: , "Low Power Amateur Radio Discussion" Subject: [124861] Re: G5RV - Use a Balun On 4/15/02 10:09 PM, James R. Duffey at jamesd1 at flash.net wrote: >Dave - Whenever there is an unbalanced to balanced transition, good >engineering practice calls for a balun. Indeed. >A 1:1 current or choke balun should be used at the transition. There are >instructions for air core coax scramble wound baluns in the handbook and >antenna book. Don't scramble wind them. The capacitive coupling between turns reduces the effectiveness of the balun, especially at higher frequencies. Wind them in a single layer, closely spaced, and use a form. 4" PVC works good, although is kinda tight for some of the 1/2" coax in terms of bending radius. >These will work OK, but the bandwidth is not as wide as one >would always like. You can't really get 80-10m coverage with this type of balun. Once you have enough turns for 80m, you have too much capacitive coupling for 10m. For wide-band coverage, use a balun with ferrite beads (W2DU, W0IYH) or toroidial ferrite core (W1JR, Guanella). >Air core baluns can also be wound on form resulting in wider bandwidth. See: > >http://www.k1ttt.net/technote/airbalun.html > >for details on building one and performance details. This is Ed Gilbert's seminal posting on air-wound baluns. They work very well for single-band or several-band coverage. W8JI uses them all over his antenna farm. They are cheap, easy to construct, handle lots of power, and virtually indestructable. >As many turns of RG-58 as you can get on a 1.5 inch OD or greater OD type >43 ferrite core will work fine, and probably be as broad band as your can >get. This is the W1JR balun. RG-58 may have trouble negotiating the tight turning radius required. RG-174 can be used only for QRP (especially if there are reactive impendances involved), due to potential voltage breakdown in the coax. If you want higher power, use teflon-insulated coax. RG-142, RG-303 and RG-316 are good choices. 6-8 turns on a type 77 core works great for 80m-10m. Use about 9-12 turns for 160m coverage. For high-power handling, you may have to use multiple cores. Type 43 cores work as well, but you may need a few more turns to get sufficient choking inductance at HF. (Type 43 material reaches peak inductance at 200 MHz!) Bill Coleman, AA4LR, PP-ASEL Mail: aa4lr at arrl.net Quote: "Not within a thousand years will man ever fly!" -- Wilbur Wright, 1901 ++++++++++++++++++ Date: Tue, 16 Apr 2002 10:41:32 -0400 From: Bill Coleman To: , "Low Power Amateur Radio Discussion" Subject: [124863] Re: G5RV - Use a Balun Message-ID: <1020316104045.KAA13794 at gate.iterated.com> Mime-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" On 4/15/02 10:50 PM, Tim, N9PUZ at N9PUZ at arrl.net wrote: >How do the baluns perform that are made by slipping the ferrite beads over >the outside of the coax? Are they better or worse than a coil of coax or is >this a different application entirely? This is the W2DU balun. Any choke made with ferrite material has roughly the same qualities as the coiled-coax choke, here are the key differences: * Ferrite chokes allow wider frequency bandwidth than coiled-coax. Impedance of coil chokes on the low end is limited by the number of turns, and the high end by mutual coupling between turns. Ferrite has roughly the same impedance over a wide frequency range. * Ferrite chokes are subject to core losses and the subsequent detrimental effects of those losses (heating). High-power and high-reactance loads may require substantial amounts of ferrite (in the form of more, larger beads, or more or larger cores). Coil chokes made from coax have extremely high power and reactance handling capability -- essentially unlimited in amatuer use. Bill Coleman, AA4LR, PP-ASEL Mail: aa4lr at arrl.net Quote: "Not within a thousand years will man ever fly!" -- Wilbur Wright, 1901 +++++++++++++++++++ Date: Wed, 17 Apr 2002 17:30:29 -0600 From: "James R. Duffey" To: Cc: , Subject: [124987] Re: G5RV - Use a Balun Message-ID: Mime-version: 1.0 Content-type: text/plain; charset="US-ASCII" Content-transfer-encoding: 7bit Zack - You make some good points. After trying to figure out how to design an effective balun that will present a high enough impedance over a wide enough bandwidth, one quickly jumps to the conclusion that a balanced tuner such as a Z-match is the best solution. Or a 1:1 balun with differing lengths of transmission line to present a low impedance would also work. Bill - Although the scramble wound baluns have less bandwidth than a similar one wound on a form, they are still effective. A look at Gilbert's data is interesting. For example, an 8 turn scramble wound balun will present a peak choking impedance of 8530 Ohms at 6 MHz, while the same 8 turns on a 6 5/8 inch form will yield roughly twice the peak choking impedance, 15840 Ohms at 12 MHz. If you want a scramble wound balun at higher frequencies, use less turns. Again, W7EL's designs in the handbook and antenna book are good guides. For comparison, a good commercial (Aztec) bead balun will have a choking impedance peak of 1400 Ohms at 7 MHz. This lower peak is due to the increased resistive loss in the bead balun due to the high permeability ferrites used. The added stray capacitance of the scramble wound balun does not effect the choking impedance substantially (well x2), or at least as much as the resistive loss introduced by the beads does. The capacitance is added in parallel with the balun's inductance yielding a parallel LC circuit, which raises the choking impedance at the resonance frequency. It does deteriorate the high frequency response, as I stated. Of course, the bandwidth is effected by the added capacitance at the high end. The scramble wound balun is useful from about 3.5 MHz to 14 MHz but marginal at the high end. The coil wound on the form is useful from 3.5 MHz (marginal here) to about 29 MHz, marginal here as well. Now the interesting thing is that the form wound balun is superior because there is an impedance peak of 1123 Ohms at the second harmonic of original peak, about 20 MHz. This suggests to me that the superior wide band usefulness of the form wound balun is due to the higher Q of the inductance, not the lower distributed capacitance. Interesting. The bead balun, since it is of higher resistive material, has a low Q and the response is broad. It is good from 1.8 MHz to 29 MHz, marginal at the high end. But the peak choking reactance is substantially down from the air core baluns. A good toroid balun can be made from a lower permeability material than a bead balun since the impedance scales as the square of the turns. A bead balun is limited to a single turn. In fact, effective baluns can be made from lower permeability material (say FT61 at 120 ) than the bead baluns, which are of type FT77 and FT73 at 1800 and 2500 respectively. Type FT43 is intermediate at 850. 43 is not recommended too often for the bead baluns as the choking impedance is less and more beads are required. W1JR used type 61, with a permeability of 120, in the construction of his toroid balun. This makes it quite different from the bead baluns in terms of resistive losses Sevick covers all of this in his book. W1JR also used the super toroid configuration with a crossover winding to reduce distributed capacitance, although this doesn't make much difference at HF. Sevick recommends baluns with even lower, say 40, permeabilities. So the cores for bead baluns and toroids are not the same, and a toroid balun can be designed with lower permeability ferrites that have lower resistive losses and higher efficiencies. The differences may not be significant for QRP, but they are real. I question the need for wide band baluns that cover 1.8 MHz to 30 MHz. For some reason we have been indoctrinated with the idea that one antenna that does all is the best. However, most hams would be better served by two or more antennas that covered the bands they work most. Most of us do most of our operating on one or two bands. The bands may vary over the sunspot cycle, but few of us have evenly distributed activity on all of the HF bands. Once one has accepted using several antennas to cover this range, the balun issue become easier. For instance, a 44 ft doublet fed with balanced feeder will do a great job form 10 MHz to 30 MHz and a good job on 7 MHz. The radiation will be in the same direction on all bands. An 88 ft doublet will do from the same from 80M to 20 M providing some overlap with the first antenna. If you have some extra length this could be made 112 ft long with 30 M now being the top end and with some improved efficiency at 80 M. Either antenna can be fed as a vertical on 160 M with the ends of the feeders tied together and fed against the ground. I have rambled, but I hope that this has been useful for somebody. - Dr. Megacycle KK6MC/5 -- James R. Duffey KK6MC/5 Cedar Crest, NM DM65 +++++++++++++++++++ Date: Thu, 18 Apr 2002 14:04:57 -0400 From: Bill Coleman To: "James R. Duffey" , "QRP" Subject: [125031] Re: G5RV - Use a Balun On 4/17/02 7:30 PM, James R. Duffey at jamesd1 at flash.net wrote: >Bill - Although the scramble wound baluns have less bandwidth than a similar >one wound on a form, they are still effective. A look at Gilbert's data is >interesting. For example, an 8 turn scramble wound balun will present a peak >choking impedance of 8530 Ohms at 6 MHz, while the same 8 turns on a 6 5/8 >inch form will yield roughly twice the peak choking impedance, 15840 Ohms at >12 MHz. I always interpreted this as the scramble winding increasing the distribute capacitance and thus lowering the parallel-resonant frequency of the coil (hence the peak at 6 MHz, instead of at 12 MHz). You really don't want to operate much beyond the parallel-resonant frequency, since the impedance drops off quickly, as the coil moves toward series-resonance. Although, for a single frequency balun, a parallel-resonant coil might be the best way to achieve high choking impedances (eg beyond 2 k Ohm) >If you want a scramble wound balun at higher frequencies, use less >turns. Ed Gilbert's own recommendation (from the article): - Don't bunch the turns together. Wind them as a single layer on a form. Bunching the turns kills the choking effect at higher frequencies. See for full details. >Again, W7EL's designs in the handbook and antenna book are good >guides. For comparison, a good commercial (Aztec) bead balun will have a >choking impedance peak of 1400 Ohms at 7 MHz. This lower peak is due to the >increased resistive loss in the bead balun due to the high permeability >ferrites used. The advantage of the ferrites is that the majority of the impedance is resistive in nature. In a choke, this is exactly the behavior we want, especially if we want to choke a range of frequencies. That's what ferrites are a great choice for a wideband device. >The added stray capacitance of the scramble wound balun does not effect the >choking impedance substantially (well x2), or at least as much as the >resistive loss introduced by the beads does. The added capacitance lowers the parallel-resonant frequency, and greatly reduces the impedances for frequencies above that. >The capacitance is added in >parallel with the balun's inductance yielding a parallel LC circuit, which >raises the choking impedance at the resonance frequency. It does deteriorate >the high frequency response, as I stated. If we want a physical coil to operate like a coil, and not a capacitor, we really want to stay BELOW the parallel-resonant frequency, no? >Of course, the bandwidth is effected by the added capacitance at the high >end. The scramble wound balun is useful from about 3.5 MHz to 14 MHz but >marginal at the high end. >From the Gilbert data, I wouldn't use the scramble-wound balun above 7 MHz. >The coil wound on the form is useful from 3.5 MHz >(marginal here) to about 29 MHz, marginal here as well. Now the interesting >thing is that the form wound balun is superior because there is an impedance >peak of 1123 Ohms at the second harmonic of original peak, about 20 MHz. Curious, yes, but if you note the parallel-resonance about 12 MHz, then you really can't expect much performance from this choke above 14 MHz. This is part of my point. Coiled-coax baluns work great at one frequency, or over a narrow range of frequencies. But Ed Gilbert's data indicates they don't have sufficient choking inductance over the entire HF range. >A good toroid balun can be made from a lower permeability material than a >bead balun since the impedance scales as the square of the turns. A bead >balun is limited to a single turn. In fact, effective baluns can be made >from lower permeability material (say FT61 at 120 ) than the bead baluns, >which are of type FT77 and FT73 at 1800 and 2500 respectively. Type FT43 is >intermediate at 850. 43 is not recommended too often for the bead baluns as >the choking impedance is less and more beads are required. I've seen several balun designs that used type 43 material to avoid loss tangent problems with high power and type 77 material. Indeed, I design a bead balun for my Cushcraft A3S using 12 FB1024-43 beads. My choice of type 43 material came more for the fact I got these beads surplus at a discount price! Type 73 or 77 material would have required fewer beads. The balun works great. >I question the need for wide band baluns that cover 1.8 MHz to 30 MHz. For >some reason we have been indoctrinated with the idea that one antenna that >does all is the best. Indeed. I agree here. They are important for tribanders (perhaps 7-30 MHz), and perhaps for certain multi-band doublets covering several bands (3.5-10 MHz). It's probably best to design devices for each antenna. >However, most hams would be better served by two or >more antennas that covered the bands they work most. Really? >Most of us do most of our operating on one or two bands. I disagree. If you are into contesting, then you've got to present your best antenna choice on 5 or 6 bands. >For instance, a 44 ft doublet fed with balanced >feeder will do a great job form 10 MHz to 30 MHz and a good job on 7 MHz. I don't think there's anything magical about LB Cebik's choice of 44 or 88 feet. The key to making this antenna effective is getting it high enough in the air. Note the height at which Cebik did his modelling of the 88 (/ 44) foot doublet.... But, yeh, this antenna is likely more effective than your typical 40m-10m verticals. I have one of those dummy loads myself.... Bill Coleman, AA4LR, PP-ASEL Mail: aa4lr at arrl.net Quote: "Not within a thousand years will man ever fly!" -- Wilbur Wright, 1901 +++++++++++++++++++ Reply-To: From: "Ron D' Eau Claire" To: Subject: RE: [Elecraft] Balun with a G5RV? Date: Sun, 21 Apr 2002 09:01:25 -0700 As several ops have pointed out, there are many variations of "center fed doublets" called G5RV's out there. When Louis Varney developed his antenna the standard "doublet" was a center fed wire 1/2 wavelength long on the lowest operating frequency. Balanced feedlines were the standard of the day. (One reference I have says that Varney first designed his antenna in 1946, although it was 10 years before the design was published.) What Varney did that was a little different from the common "doublet" was to scale his antenna to be three half waves long on 20 meters, rather than simply 1/2 wavelength long on the lowest band. That offered a somewhat better compromise for a good radiation pattern on 10 meters and a of impedances on the ham bands to make loading the antenna somewhat easier. Since then endless variations have appeared to accommodate the fact that coaxial cable has become the feedline of choice, transmitters now offer unbalanced output instead of balanced outputs, and we've added a number of Ham bands to our HF spectrum. With these changes the issue of how to get r-f into a "G5RV" has become more complex and the performance of the antenna is more difficult to predict. Still, like its more common "center fed doublet" cousin, it can be a highly effective radiator. For multiband use, I have always preferred a center fed doublet using high quality open wire line and a BALANCED antenna tuner. Sure, I have to twiddle a few knobs that takes 30 seconds, perhaps, when changing bands, but I gain perhaps 3 dB (doubling my output power) or more by a more efficient antenna system and I can go anywhere in the HF spectrum with equal ease. Also a center fed doublet (and so, too, a G5RV if the feeder losses are not excessive) will work very well down to the frequency at which the doublet is only 1/4 wavelength overall, meaning that a 66 foot radiator will work quite well on 80 meters or a 120 foot radiator will work well on 160 meters if it is high enough off of the ground. But the popularity of coaxial lines and now the proliferation of automatic antenna tuners has kept the "multiband" versions of the G5RV alive. Still, the issue of a good combination of feedline sections to avoid excessive losses is a complicated one. One good resource dealing with G5RV feeder system design issues that I know of on the WEB is at http://www.extremezone.com/~nk7m/ant4.htm. Ron AC7AC K2 # 1289 +++++++++++++++++ Date: Sun, 21 Apr 2002 15:32:31 -0400 (EDT) From: kc4kgu at ENTERZONE.NET To: Tom Crites Cc: elecraft at mailman.qth.net Subject: Re: [Elecraft] Balun with a G5RV? On Sun, 21 Apr 2002, Tom Crites wrote: > I am using a G5RV antenna with my K2 (with KAT2 tuner) fed with 60 feet of 50 > ohm coax. I've been trying to figure out if I need a balun between the 450 > ohm ladder line and the coax. Will a balun improve the antenna performance > or just help keep RF out of the shack? My existing setup with no balun is > marginal on 10 meters. With the G5RV I've seen suggestions just needing just > a tuner, to a 1:1 air-core choke balun, a 4:1 balun, 75 ohm coax,...., etc. > > 73, > Tom, KC8SES > > p.s. I did put a Solarcon A99 this weekend! Your marginal performance on 10m is probably a result of high SWR on the coax. Remember: a tuner provides a 50ohm match to the RADIO. It does NOTHING to improve any mismatch you may be seeing between your antenna and the tuner on the feedline. Last week, I converted the feed to my 80m doublet antenna from 50ohm coax to TWO 50ohm coax (100ohm unbalanced-balanced). Antenna--| v ----------------+ +---------------- | | | |--| | Twin coax -> | | | | with shield | | | | tied together | | | | at antenna end | | | | "floating". | | | | Do NOT connect | |--| |----+ the shield on | | | <- Shields at shack end are tied the antenna | | --- together and grounded. end of the feed | | - to anything! + + = -------- |TUNER | <-- Center wire two coax feeds connects -------- to balanced output of antenna tuner. | | RIG On 75m, signal reports from the guys I ragchew with went from 20-30over to 40-60over and that is with the terrible band conditions we've been having this week. On 10m, I listened to p49mr (Aruba) give 5/7 - 5/9 to folks tons and tons of people. I got 59+30 on 28.445. That was enough validation for me. My feedline is 150ft long from shack to antenna so, I was seeing a LOT of loss using an unbalanced feed. Your milage may vary. Another PLUS of using twin coax vs open-wire or ladderline: You can bury it, run it right against metal objects, moisture on the feedline doesn't effect SWR, no RF in the shack on ANY band, even running 1kw, etc, etc. It's like a dream come true! Next project, remotely switchable N/S/E/W phased arrays. I just have to find (or build) a remote balanced feedline switch. 73 de John - KC4KGU K2 #2490 ++++++++++++++++++ Date: Sun, 21 Apr 2002 22:02:57 -0400 (EDT) From: kc4kgu at ENTERZONE.NET To: "Ron D' Eau Claire" Cc: elecraft at mailman.qth.net Subject: RE: [Elecraft] Balun with a G5RV? On Sun, 21 Apr 2002, Ron D' Eau Claire wrote: > > ...Your marginal performance on 10m is probably a result of high SWR on > the > > coax. Remember: a tuner provides a 50ohm match to the RADIO. It does > > NOTHING to improve any mismatch you may be seeing between your antenna and > > the tuner on the feedline. > > > > Last week, I converted the feed to my 80m doublet antenna from 50ohm coax > > to TWO 50ohm coax (100ohm unbalanced-balanced).... > > 73 de John - KC4KGU > > K2 #2490 > > > High SWR will produce very high losses in coax. These losses increase with > frequency as well. > > Running two coaxial lines in parallel will do nothing to reduce these losses > unless that also produces a lower SWR on the coaxial lines. The two coax lines in parallel are being used as a balanced feed to the antenna. Only the center conductor is being used for the feedline. It acts like any other balanced feedline with the exception that you don't have as many "gotchas" as with the "real" thing. > The losses in the coax are a function of dielectric leakage and breakdown in > the coaxial line at the points where the standing waves produce a high > impedance and high voltage cross the dielectric. There are also additional > losses at the points of high current, although the added losses at the > current "loops" will be small provided the conductors are of adequate size. 73 de John - KC4KGU K2 #2490 +++++++++++++++++ Date: Sun, 21 Apr 2002 23:51:02 -0500 From: "George, W5YR" Organization: AT&T WorldNet Service To: rondec at easystreet.com Cc: kc4kgu at ENTERZONE.NET, elecraft at mailman.qth.net Subject: Re: [Elecraft] Balun with a G5RV? It turns out, Ron, that the coax shields are tied together at each end of the coax/balanced-line run with the coax tied to the tuner ground point at that end and floating at the "other" end. The two coaxes can take any path from the tuner to the "other" end - they do not require any particular attention to spacing, etc. Neither do they need to be kept away from other conductors, any more than a regular coax run. Main requirement is that they be about the same length - to aid in maintaining balance in the system. The coax balanced lines have the same loss as single coax since the same current is flowing on the center conductor where the principal HF loss occurs as I^2R loss. The return current is on the other center conductor instead of the inside of the braid. At HF, dielectric loss is negligible. This technique for bringing balanced lines into the shack is widely used and is very effective. Of course, the coax is subjected to the same peak currents and voltages as the regular open-wire or ladderline since the SWR can be quite high in the coax section. For that reason, it pays to keep the coax run short. The Z mismatch going from 450-ohm ladderline, for example, to 100-ohm coax-pair line (two 50-ohm coaxes) is a non-issue since the entire line operates with standing waves. Interesting stuff . . .this has been written up in QST and the Handbook and Antenna Books for many years. I am installing a new 80-meter full-wave tilted triangular loop that will be fed with ladderline and then transition to parallel coaxes into the shack for about 10-12 feet to a Johnson KW Matchbox tuner. Should handle my 5 watts just fine! <:} 73/72/oo, George W5YR - the Yellow Rose of Texas Fairview, TX 30 mi NE of Dallas in Collin county EM13qe Amateur Radio W5YR, in the 56th year and it just keeps getting better! QRP-L 1373 NETXQRP 6 SOC 262 COG 8 FPQRP 404 TEN-X 11771 I-LINK 11735 Icom IC-756PRO #02121 Kachina 505 DSP #91900556 Icom IC-765 #02437 Ron D' Eau Claire wrote: > > > The two coax lines in parallel are being used as a balanced feed to the > > antenna. Only the center conductor is being used for the feedline. It > > acts like any other balanced feedline with the exception that you don't > > have as many "gotchas" as with the "real" thing. > > 73 de John - KC4KGU > > K2 #2490 > > Hi, John. > > Maybe I misunderstood. I thought that your schematic showed the shields > being grounded. If they are you have losses caused by leakage and dielectric > losses between the center conductor and the shield. These losses increase as > the SWR or the operating frequency increase. > > If the shields are not connected to anything at any point, you are right. > You won't have losses in the dielectric between the center conductor and the > shield. But you will have losses through the dielectric to anything the > cables come in contact with. You need to be sure that each coaxial line is > carefully spaced and well insulated from everything around it including the > other coaxial line. > > In that case I would think that it'd be easier (and cheaper) to use a good > air-insulated open wire line ++++++++++++++++ Reply-To: From: "Ron D' Eau Claire" To: "George, W5YR" Cc: , Subject: RE: [Elecraft] Balun with a G5RV? Date: Mon, 22 Apr 2002 00:41:57 -0700 > It turns out, Ron, that the coax shields are tied together at each end of > the coax/balanced-line run with the coax tied to the tuner ground point at > that end and floating at the "other" end. > ...Of course, the coax is subjected to the same peak > currents and voltages as the regular open-wire or ladderline since the SWR > can be quite high in the coax section. For that reason, it pays > to keep the > coax run short. > George W5YR - the Yellow Rose of Texas True enough George and an old practice to be sure. The key, as you point out is to have short runs where the losses were acceptable. The writer of the original post mentioned using two coaxial lines for the ENTIRE RUN of feedline from the antenna to the rig! That was what I was commenting on. In that case, if the shields are used to prevent radiation, one would expect the same sort of losses that any long coaxial cable run at high SWR's would produce. Ron AC7AC ++++++++++++++++ From: "Christian GONDARD" To: "elecraft" Date: Wed, 24 Apr 2002 19:38:22 +0100 Subject: [Elecraft] G5RV saga Another point of view : I am using a 2x20 m doublet and a 300 ohms ladder line for 3 years, and I am very glad with it, especially for its "all bands capability". I am following with interest the discussion about the advantage/disavantage to use a balun with this kind of antenna, which is rolling on the reflector for some days. Generally speaking, I think that they are no general rules on this subject, because the impedance appearing at the end of the feed line near the transmitter can vary in large proportions, and a balun can have very strange behaviour/performances, depending on the bands, the length of the feed line, the length of the doublet, the height over the ground and its quality (resistivity). In most cases, losses in the feed line (parallel line or coax) can be "moderate", i.e some dB and just "noticeable"; it is perheaps not so moderate on the high part of the spectrum (21, 24, 28 MHZ), and here a parallel line can have a strong advantage over the coax. I want to emphasize on another side of the story, which can have, on my point of view, a much stronger effect on the "effeciency" of the antenna : I want to speak of the radiation pattern of such antennas, especially in the vertical plane. It is easy to show (many softwares compute that very easely) that this pattern is characterized by "lobes" which send and receive HF waves in specific directions. This is true in the horizontal plane, and that will give some directivity to select some specific area of interest to establish a radio contact. This is also true on the vertical plane, and that will give the way radio waves will hit and be reflected by the ionosphere.This interaction directly impacts on the capability to reach long distances. Generally speaking, if you are interested in DX ing, you need low or very low angle of radiation, that means radiation lobes in the vertical plane very close to the horizon. The position of the main lobe is depending on 2 main factors : * the length of the doublet : the more the length, the higher the lobe (not good) * the ratio between the wave length and the height of the doublet over the ground : under a ratio of 1/4, the main lobe is vertical (you warm the clouds) : not good for DX, very good for short distance QSO. And here, we are not speaking of "some dB" of losses in transmission lines; the difference between a low lobe and a high lobe can easely reach 10 to 20 dB !!! If you consider the situation of a "very small pistol" (or a "pebble launcher" : french expression : any english equivalent ? !!), the antenna will be less that 10 m (30 feet) high and 2x15 or 2x20 m long. That means that the antenna will have a good behaviour on 40 and 30 m bands; if it is 2x20 m long it will work also well on 80 m (but main lobe will be high, because the antenna is too low); on 20 m main lobe will be near 30 degree; on high bands main lobe can be at 45 degree : really not good for DX ing !!! By the way, this is (was) my situation; I worked many DX (QRP and QRO), but I am very patient by nature, so I spend 99% of my time to listen ; listen and listen ..... : one day or another I am always able to achieve QSO with rare DX stations : I need 10 days to log VP6DI, the last day of the expedition .... I am now using 2 kind of doublets, because I think that a single one can not efficiently cover all the bands between 80 and 10 m. Doublet n°1 is a 2 x 20 m doublet at 10 m high for 80 to 30 m Doublet n°2 is a 2 x 8 m doublet at 10 m high for 20 to 10 m The 2 antennas are spaced by 20 m and are at right angle; the separate transmission lines are 300 ohms parralel lines (without balun) about 20 m long. After some months of use and many A/B comparisons, I found a large difference, especially on high bands (15 to 10 m), at the advantage of doublet n°2 for long distances DX : 1 to 3 S points = 6 to 18 dB ...., with a correlated disadvantage for short skip stations ("you can not have the butter and the money for the butter" : another french expression). Doublet 2 is also efficient on 30 m DX but it is not so clear. I hope that this page can help in the discussion, despite my "rough" english ... Best regards to everybody 73 Chris / F6FTB ex FB8XV / K2 #644 (waiting for the KPA100 ....) +++++++++++++++++