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#31
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Using speaker wire for a dipole
On 8/3/2011 4:48 PM, Irv Finkleman wrote:
Hear! Hear! I would have been off the air forever if this newsgroup had been my only source of knowledge. I would have been afraid! What I didn't know about Jx and SWR didn't make any difference -- I was on the air and really enjoying the hobby! I didn't even know how to solder then! Right. But I would like to say that it isn't at all that the information is wrong. In fact, the experts are generally 100 percent right. And that is where some of the problems are. A noob comes in, and gets 3 different answers, and becomes hopelessly confused because they would seem to contradict each other. They don't really know how to figure it out. It isn't confined to this group. Another group I'm in where I am a bit of an expert, Amateur telescope making, some times suffers from the same thing. My point is that I'm not trying to chide the experts. After all, it's not very graceful to bust peoples chops when they take the time to answer a question. I's more begging them to realize that I'm a bit of an idiot, and easily confused! - 73 de Mike N3LI - |
#32
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Using speaker wire for a dipole
"Irv Finkleman" wrote in message ... snip After 50 plus years of hamming fun, I have come to the conclusion that anything with a little metal in it will serve as an antenna if you hook it up in the right manner. Yes. I have properly-built 6m jpole which terminates in my shack. If I disconnect the coax from the 6m rig, the connector center pin fits nicely into the LONG WIRE terminal on my HF tuner. Electrically, the antenna is merely a 13' hunk of metal, untuned as far as HF is concerned, except after a little tuner knobulation. It's not the equal of a 'proper" antenna, but it works. |
#34
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Using speaker wire for a dipole
On 8/2/2011 8:24 AM, John S wrote:
On 8/1/2011 7:52 PM, Jim Lux wrote: On 7/31/2011 3:26 PM, Owen Duffy wrote: John wrote in : Maybe because NFPA 70 costs $150 US? Yes, standards are expensive things and it is a frustration when researching. Anyway, NFPA makes recommendation on the wires for ham antennas specifically, and it may be binding in some places. I suspect the reason for ignoring it is that the advice is unaccepable to most hams. That said, it does seem over the top in some areas, and is hardly comprehensive in its thinking. For example, the prescription for feedlines seems to not be aware of the existence and use of coax. You refer to the "continuously enclosed metallic shield", I suspect. I guess it is these gaps that give critics the basis for arguing against the whole thing. Anyway, in respect of antenna wires, it does not 'permit' annealled copper or other low strength materials, and it 'requires' a minimum conductor diameter of #14 for up to 150' span. They may have had in mind the risk to persons and property where low strength conductor are broken in high wind and make contact with power lines. That is precisely why. (ice loads, too) NFPA (according to what you posted) requires heavier gauge wire for transmitting than for receiving. Transmitting makes the wire weigh more? An interesting observation. You'd have to go look at the history of that article in the code to find out why. It's not impossible that they were following standard commercial installation practice/recommendations back in the day, and it was "acceptable power loss" related. (the wire sizing for AC branch circuits is based on tolerating a 2% voltage drop, not overheating of the conductor) |
#35
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Using speaker wire for a dipole
On 8/2/2011 12:24 PM, Sal wrote:
wrote in message ... On 1 Aug, This replaces one which failed a couple of years ago constructed with thin insulated 5A lighting flex not much more than bell wire that had been up nearly 30 years. This got me thinking. (Dangerous, yes, but I occasionally risk it.) Since a normal dipole has current max near the center, is there more localized heating (I-squared-R) nearer the feed point? Seems like it ought to be. Can you overheat a small wire and make it fail there by melting????? No, I don't want to try it. I'm hoping somebody knows. Exciting story even better. "Sal" Fusing current is remarkably high for small conductors in free air, even for 100% duty cycle. AWG30 (0.01" diameter) = about 10 Amps (Preece equation) Scales as 1.5 power.. so, going to AWG 20 (.0316") - about 50 amps.. Considering an inverted V dipole with feedpoint Z of 50 ohms, at 1kW, the current is about 5 amps... So running that legal limit amp with a brick on the key to your AWG30 stealth antenna won't melt it. (it probably will get pretty warm.. and corona at the ends might be spectacular) |
#36
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Using speaker wire for a dipole
On 8/2/2011 4:42 PM, Tom Horne wrote:
On 8/1/2011 20:42, Jim Lux wrote: On 7/31/2011 2:02 PM, Owen Duffy wrote: PS: hams universally ignore the guidance of NFPA 70 which makes recommendation on conductors for antennas. Are you saying the electrical code is sort of like the pirate code? more guidelines than actual requirements? I think the way that hams can rationalize it is that most wire antennas (particularly those made with fine wire) are, by their nature, "temporary installations". The finer the wire, the more temporary. The National Electric Code limits the use of Temporary installations to power and lighting conductors. "ARTICLE 527 Temporary Installations 527.1 Scope. The provisions of this article apply to temporary electrical power and lighting installations." Copyright 2002 the National Fire Protection Association. -- Tom Horne, W3TDH I was thinking more of local codes or enforcement. After all, the local "Authority Having Jurisdiction" (AHJ in code-speak) can and does override the NEC all the time. There are also a whole lot of other "installations of a temporary nature" in the code: check out the sections about theatrical and motion picture filming. They allow substantially higher currents for a given size wire, on the not unreasonable basis that they're being operated under the (hopefully) continuous supervision of qualified personnel. |
#37
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Using speaker wire for a dipole
"Jim Lux" wrote in message ... Fusing current is remarkably high for small conductors in free air, even for 100% duty cycle. AWG30 (0.01" diameter) = about 10 Amps (Preece equation) Scales as 1.5 power.. so, going to AWG 20 (.0316") - about 50 amps.. Considering an inverted V dipole with feedpoint Z of 50 ohms, at 1kW, the current is about 5 amps... So running that legal limit amp with a brick on the key to your AWG30 stealth antenna won't melt it. (it probably will get pretty warm.. and corona at the ends might be spectacular) Thank you very much. It's exactly what I was wondering about. "Sal" |
#38
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Using speaker wire for a dipole
On Aug 1, 6:32*am, KD2AIP wrote:
Anyone have experience making a dipole from 18 gauge speaker wire? *I have a whole lot of it lying around the house, and was wondering if I could put it to some good use. Well, not sure what gauge wire it is, but I've been using cheap speakerwire for HF dipoles with no problems whatsoever. Not certain, but I think this is the stuff I use he http://www.jaycar.com.au/productView...SUBCATID=992#1 My prime HF antenna started out as a coax-fed 40m half-wave (10m/leg) dipole made of this stuff in an inverted-V configuration. I used a home made 1:1 voltage balun at the feed point. Over time, I moved the feed point to near the back of the tuner with a short 3in length of coax, and ran a random length of 300ohm ribbon to the feed point of the dipole. Later after reading about the G5RV, I extended each leg to 16m long. It is important to note that while similar to a G5RV, my antenna does not feature the same length of ribbon as a G5RV. The antenna is not mounted up high, the apex would be at gutter level (we have a two- storey house here). Legs tie off no higher than 2m in the air. One end ties off to a frangipannie (sp?) tree in our front yard, the other to a piece of rope running to a macadamia tree in our back yard. I have a feeling the frangipannie is helping form part of the antenna. This antenna, while quite deaf I find on the 10m band, has worked into VK5 on 15m, I have had contacts into ZL on 20m, and it works quite well locally on 40m and 80m. I have had successful contacts using QRP power levels on 80m with this antenna, and it is very easy to tune there. It has broken once or twice. It has never taken me any longer than about 15 minutes to repair and get back up in the air. It's also cheap enough to consider being disposable, should disaster truly strike. So I say, go for it … it might as well do something useful. Regards, Stuart VK4MSL |
#39
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Using speaker wire for a dipole
A local job lot store was selling 100' rolls of #18 speaker wire. I bought as many as I could. I use it for not only hf antennas, but am making open wire line with discarded Bic pens as separators (there was an article in QST about this). I have had a lot of success with this.
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#40
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Using speaker wire for a dipole
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