Re: [Elecraft] 4:1 balun
At 03:03 PM 12/9/2011 -0800, you wrote: >In the 1960's one very popular and cheap H.F. antenna was the folded dipole. >Often they were made from the ubiquitous 300 ohm "twin lead" used on TV >antennas and fed with the same twin lead since the impedance of a folded >dipole is close to 300 ohms. The first time I saw 4:1 baluns being sold to >Hams was to make it easy to connect the 300 ohm feeder to such a folded >dipole to the output of a rig designed to feed 50 ohms. > >As Hams migrated away from rigs with tunable output networks to rigs with >fixed tuned outputs, MFJ and others produced a line of antenna tuners >specifically designed to correct feed line mismatches since that could no >longer be done at the rig. They included the popular 4:1 balun for those who >were feeding various open wire lines (typically 300 to 600 ohms but which >may have significant SWR - so the impedance might vary much more). > >It seems that many Hams considered the 4:1 ratio some sort of magic number, >when all it was intended to do was provide a good transfer between 300 ohms >and 50 ohms. > > >Ron AC7AC Hi Back in late 50's early 60's I bought my first balun from Heathkit ... made from special Bifiler wound Airdux coils which could be connected in either 1:1 or 4:1 configuration. I still have that balun in its 5"x9"x9" aluminium case. I used it with my first Xmiter which was homebrew, 300 watts, and plate modulated AM. I used a folded dipole made of 300 ohm twinlead fed by the same twinlead and the balun in a 4:1 configuration. The dipole was strung between 70ft towers. It was a wonderful setup at a wonderful time (from a propagation point of view). The ZL's and VK's were like locals! es we used to chat about the best way to grow tomatoes hihi These days I still use a balanced feed system with either 300 or 450 ohm feed line ... but with fixed impedance output xmiters and vy much lower power. I no longer use fixed resonant folded dipoles ... but a nonresonant dipole that is useable on multiple bands with a matching unit at the shack. The matching unit I use is a link coupled L network .. often referred to as a "Z-match". The system seems to be vy efficient as I have no problem working the world with 20 watts. SSB for local contacts and nets and CW/PSK for DX. No problems with RFI !! Back in the day .. my 300 watt AM xmiter was a TV killer but then no one in out neighborhood watched TV during the day (week-ends excluded) and the (1 station) shut down at midnight. I just had to stay up late and/or skip school hi hi. Jim, VE3CI >-Original Message- > >I can attest to what Vic says. I have an 88-foot long doublet, hung about 45 >feet up, fed with 85 feet of 600-ohm ladder line. At the shack end I have a >1:1 balun, and then about six feet of RG/8X running to the K3. The K3's >tuner likes the combination. I tried replacing the 1:1 balun with a 4:1 from >the same manufacturer. The K3 was quite unhappy with the change in >components. The 4:1 went back on the shelf, the 1:1 went back inline. YMMV > >Jim / W6JHB __ 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
Re: [Elecraft] 4:1 balun
> It seems that many Hams considered the 4:1 ratio some sort of magic > number, > when all it was intended to do was provide a good transfer between 300 > ohms > and 50 ohms. I just modeled a typical 20m folded twin-lead dipole using 4Nec2 and TLD software. Had never tried that one before. The antenna feed-point Z at a half-wave height (33 FT) above average ground computes to 291-j7.7. That's surprisingly close to 300 ohms resistive. With TLD software, I then coupled the feed-point with 300-ohm twin-lead line. Finally, I varied line length between 0 and 1/2 electrical wavelength and watched the resulting Z at the line input. Z always stays between 290 and 310 ohms with very little reactance. Total system loss never exceeds 0.25 dB. The 300-ohm VSWR stays near 1.05:1 and not surprisingly, the 50-ohm VSWR stays near 6:1. While a 4:1 balun can probably result in efficient transfer of power into the line from a modern 50-ohm output Z transceiver, I think a 6:1 ratio current balun would be a better choice under these circumstances, assuming one wanted to avoid an ATU at (or within) the rig altogether. No wonder this antenna was so popular. The antenna and line all use the same inexpensive 300-ohm twin lead material. The match at the antenna is so good that line VSWR (300) and loss is negligible. Paul, W9AC __ 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
Re: [Elecraft] 4:1 balun
The down side of the 300 ohm twin lead folded dipole is that 300 ohm twin lead usually is made from small wire and not mechanically very strong, so it is not durable for fixed stations with varying weather conditions and the wire is too small for anything but low power. With either the 300 ohm twin lead or a folded dipole fabricated from #14 or heavier conductors a 4:1 balun is needed to tune well with a 50 ohm output or to transition to coax. Then it is about as good as a well made dipole. Willis 'Cookie' Cooke K5EWJ & Trustee N5BPS, USS Cavalla, USS Stewart From: Paul Christensen To: elecraft@mailman.qth.net Sent: Saturday, December 10, 2011 8:58 AM Subject: Re: [Elecraft] 4:1 balun > It seems that many Hams considered the 4:1 ratio some sort of magic > number, > when all it was intended to do was provide a good transfer between 300 > ohms > and 50 ohms. I just modeled a typical 20m folded twin-lead dipole using 4Nec2 and TLD software. Had never tried that one before. The antenna feed-point Z at a half-wave height (33 FT) above average ground computes to 291-j7.7. That's surprisingly close to 300 ohms resistive. With TLD software, I then coupled the feed-point with 300-ohm twin-lead line. Finally, I varied line length between 0 and 1/2 electrical wavelength and watched the resulting Z at the line input. Z always stays between 290 and 310 ohms with very little reactance. Total system loss never exceeds 0.25 dB. The 300-ohm VSWR stays near 1.05:1 and not surprisingly, the 50-ohm VSWR stays near 6:1. While a 4:1 balun can probably result in efficient transfer of power into the line from a modern 50-ohm output Z transceiver, I think a 6:1 ratio current balun would be a better choice under these circumstances, assuming one wanted to avoid an ATU at (or within) the rig altogether. No wonder this antenna was so popular. The antenna and line all use the same inexpensive 300-ohm twin lead material. The match at the antenna is so good that line VSWR (300) and loss is negligible. Paul, W9AC __ 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 __ 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
Re: [Elecraft] 4:1 balun
> "The down side of the 300 ohm twin lead folded dipole is that 300 ohm twin > lead usually is made from small wire and not mechanically very strong, so it > is not durable for fixed stations with varying weather conditions and the > wire is too small for anything but low power. With either the 300 ohm twin > lead or a folded dipole fabricated from #14 or heavier conductors a 4:1 balun > is needed to tune well with a 50 ohm output or to transition to coax. Then > it is about as good as a well made dipole." I think the mechanical issues can be managed. Generally, there's also less opportunity for water ingress than a coaxial line termination, unless more complex measures are taken for water-proofing. I've got new respect for the folded dipole (FD). The bandwidth of the FD is about 40% better between 2:1 VSWR points than a straight wire dipole. This is due primarily to an effectively larger radiating conductor size (rather than end stub effects), wire size remaining constant. For 80m-75m operating, the FD would be a good choice among the die-hard "I only use resonant antenna" ops. For K2 or K3 owners, any common ratio current balun ratio would work reasonably well if equipped with the internal ATU. If no ATU, then a 6:1 current balun would do the best job of transferring power into the line. The big drawback is that the FD won't work efficiently on even harmonics, even with a tuner at the shack end of the line. But for mono-band performance, cost, ease of construction, it seems tough to beat. Paul, W9AC __ 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
Re: [Elecraft] 4:1 balun
Advice I read years back cautioned to stay away from the foam dielectric 300 Ohm ribbon lead. The solid dielectric handles more power and doesn't get water contamination in the dielectric. How does modeling with 450 Ohm window lead work out? That would suggest a 9:1 balun. The reason I ask is because I built a double Zepp type antenna in the early '90s and fed it with 300 Ohm ribbon lead from the doublet to the shack. There was a noteable performance increase when the wind took it down and I used 450 Ohm window lead instead. Also, the 450 Ohm window lead has proven very rugged for me. The doublet has been up at three different QTHs and is almost 20 years old. 73, de Nate N0NB >> -- "The optimist proclaims that we live in the best of all possible worlds. The pessimist fears this is true." Ham radio, Linux, bikes, and more: http://www.n0nb.us __ 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
Re: [Elecraft] 4:1 balun
> How does modeling with 450 Ohm window lead work out? That would suggest > a 9:1 balun. Someone earlier (K2VCO, I believe) cautioned against falling into the trap of believing that the characteristic Z of the line is always the impedance actually present at the end of the line. The Z seen at the line end is determined by several factors, including the magnitude of the line-to-load (mis)match, type of feedline, and feedline length. For multi-band wire antennas, the line input Z can range from less than 10 ohms with some short antennas to over 5K ohm. These numbers appear at the line input. Just because it may be "450-ohm line" does not mean that's the target Z to tune and match. The only time 450-ohm line presents a 450-ohm impedance at the line input regardless of distance, is when the characteristic Z of the line equals the load Z and line loss is small. In the case of the folded dipole for mono-band operation, the antenna feed-point Z can easily be made 300 ohms with little or no reactance with a bit of antenna length pruning and perhaps slight height change. Feeding it only with a 300-ohm characteristic Z line makes best sense, since the Z at the line input, regardless of line length is going to be near 300-ohms at the cut operating frequency, with little reactance. Paul, W9AC __ 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
Re: [Elecraft] 4:1 balun
On Dec 10, 2011, at 12:38 PM, Paul Christensen wrote: > I've got new respect for the folded dipole (FD). The bandwidth of the FD is > about 40% better between 2:1 VSWR points than a straight wire dipole. Yes, and a 3-wire dipole nearly doubles the SWR bandwidth relative to a regular dipole. As you say, the antenna is not useable on even harmonics but for some, having to put up a separate 40-meter dipole is a small price to pay for being able to cover a large chunk of 80/75 meters without having to retune an antenna coupler. Bud, W2RU __ 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
Re: [Elecraft] 4:1 balun
At 09:12 AM 12/10/2011 -0800, you wrote: >The down side of the 300 ohm twin lead folded dipole is that 300 ohm twin >lead usually is made from small wire and not mechanically very strong, so >it is not durable for fixed stations with varying weather conditions and >the wire is too small for anything but low power. With either the 300 ohm >twin lead or a folded dipole fabricated from #14 or heavier conductors a >4:1 balun is needed to tune well with a 50 ohm output or to transition to >coax. Then it is about as good as a well made dipole. > > >Willis 'Cookie' Cooke >K5EWJ & Trustee N5BPS, USS Cavalla, USS Stewart Hi, No problem using good quality 300 TV twinlead with high power. Remember current is much reduced when feeding into a 300 ohm load vs a 75 ohm load. As I mentioned, I consistently used such an arrangement with a 4:1 balun feeding the folded dipole at 70 ft running with 300watts and fully plate modulated AM. In addition since the twinlead is operating with no standing waves there is no chance of magnified voltages and currents as a result of phase shifting. Never had a problem with RF power. Now to be fair TV twinlead was commonly available in at least 3 grades ... heavy, medium, or light. I am not sure what is available today in what is called TV twinlead. I understand it is possible to buy 300 ohm twinlead that is manufactured for power handling I don't know if anyone uses it for making folded dipoles (I suspect not). If one were to construct such a folded dipole for any HF band I can guarantee they will not have any power handling problems to today's legal power limit. I have also used TV twinlead to feed non-resonant doublets (100 inverted vee is a favourite) and used a 100watt AM transmitter (DX-100) with a balanced transmatch again, never had a power problem with the feed line. This arrangement is a bit tricky. Choosing a useable feed line length solves any power problems. However, you are correct about mechanical reliability. I did have to fix the antenna several times a year. At one time the cable manufacturers also made 75 ohm twinlead in both a lightweight and heavy duty version. The 75 ohm versions were more susceptible to current/heat damage due to the much greater current feeding an antenna with with a 75 ohm resonant impedance. The light weight version was only good for 25 to 50 watts but great for portable work as it was very light. It used to be the standard configuration for commercial portable radio service used by northern trappers es miners. Their radios only ran 3 to 5 watts. I used the heavy duty 75 ohm twinlead to feed a cubical quad for years ... again 100watts AM. Jim, VE3CI __ 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
Re: [Elecraft] 4:1 balun
On 12/10/2011 2:35 PM, Jim Dunstan wrote: > ... I don't know if anyone uses it for making folded dipoles (I > suspect not). If one were to construct such a folded dipole for > any HF band I can guarantee they will not have any power handling > problems to today's legal power limit. In this weekend's ARRL 10m contest, one of the antennas I'm using is a vertical folded dipole fashioned from transmitting quality 300 Ohm window line and matched at the TX end via a 4:1 balun. I'm running only 100 watts for this contest, but it can handle full legal limit with ease. This antenna system provides a minimum VSWR of about 1.4:1 at resonance (28.5 MHz) due to the slight mismatch (75 vs 50 Ohms) and less than 1.7:1 at the 10 meter band band edges. 73, Gus Hansen KB0YH __ 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
