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antenna theory made easy
In my last post I referred to a magloop article by Nitin William, VU3GAO. It was the first magloop I encountered which would handle 80M. I should have mentioned another article by Peter Parker VK3YE who has a similar loop but it covers 160 thru 15 meters. I expect it will be very good on the higher bands, and with a 'little' padding should take me down to 80M for some of the local nets. From all the reading I have done, the Magnetic Loop Antenna seems to be a good performer, and ideally suited to locations where large or long antennas are out of the question. Irv VE6BP |
antenna theory made easy
On Thu, 23 Jan 2014 15:52:40 -0700, "Irv Finkleman"
wrote: From all the reading I have done, the Magnetic Loop Antenna seems to be a good performer, and ideally suited to locations where large or long antennas are out of the question. Irv VE6BP I agree. A magnetic loop will both fit and work best at your location. No grounding system or ground radials required. I don't have a magnetic loop of my own but I've helped build 3 of them (all different) with local hams. Some things to think about before blundering forward: 1. Where are you and the loop going to live? The Q of the loop is very high which means you're going to be retuning the loop every time you change frequency more than a few KHz. If the loop is outside on the balcony, and you're inside near the radio, you're going to be running back and forth all day long. The only saving grace is if you're doing PSK31, which lives on a single frequency per band, and therefore doesn't require constant retuning. Think about motor driven capacitor tuning. 2. Magnetic loops generate rather high voltage across the tuning capacitor. You'll probably need either a wide spaced cheese cutter type capacitor, a Jennings vacuum variable capacitor ($150 to $350 on eBay), or a butterfly type variable capacitor. I prefer the butterfly, but they're difficult to find. So, build your own: http://www.alexloop.com/artigo21.html 3. I've seen problems with the loop tuning drifting with temperature. It's not the transmit power but heating from the sun. Even if you're planning on sitting on one frequency all day, you should check for tuning drift. 4. Magnetic loops are somewhat directional. You may need some method of spinning the loop for maximum signal. When mounted vertically, the loop is horizontally polarized. When hung over the balcony rail horizontally, it's vertically polarized. See photos of mounting arrangements: http://www.alexloop.com 5. Magnetic loop calculators: http://www.66pacific.com/calculators/small_tx_loop_calc.aspx http://www.aa5tb.com/aa5tb_loop_v1.22a.xls 6. Losses. If you plug the numbers into an antenna simulator, you'll find that the losses are HUGE. If you go to the bottom of the page at: http://www.aa5tb.com/loop.html there's a graph of losses versus different loop material sizes. Notice the 1" and 1" (0.5 ohms) plots. Only 0.5 ohms of added resistance and the losses increase by about 16dB at 3.5 MHz. That's a nice way of saying you can't just throw it together. Everything has to be soldered carefully and no sliding contacts on the caps. Your MFJ antenna analyzer will be handy for testing the construction. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
antenna theory made easy
"Jeff Liebermann" wrote in message ... On Thu, 23 Jan 2014 15:52:40 -0700, "Irv Finkleman" wrote: From all the reading I have done, the Magnetic Loop Antenna seems to be a good performer, and ideally suited to locations where large or long antennas are out of the question. Irv VE6BP I agree. A magnetic loop will both fit and work best at your location. No grounding system or ground radials required. I don't have a magnetic loop of my own but I've helped build 3 of them (all different) with local hams. Some things to think about before blundering forward: 1. Where are you and the loop going to live? The Q of the loop is very high which means you're going to be retuning the loop every time you change frequency more than a few KHz. If the loop is outside on the balcony, and you're inside near the radio, you're going to be running back and forth all day long. The only saving grace is if you're doing PSK31, which lives on a single frequency per band, and therefore doesn't require constant retuning. Think about motor driven capacitor tuning. I already have a small 12v motor and have tested it with a number of different capacitors. With a simple 10k wirewound pot I can slow it down to almost nothing, or bring it back up to some value, and that beautiful pot just gets lukewarm. Using a DPDT toggle switch I can control the direction as well. Remote tuning on a shoestring! 2. Magnetic loops generate rather high voltage across the tuning capacitor. You'll probably need either a wide spaced cheese cutter type capacitor, a Jennings vacuum variable capacitor ($150 to $350 on eBay), or a butterfly type variable capacitor. I prefer the butterfly, but they're difficult to find. So, build your own: http://www.alexloop.com/artigo21.html arrangements: http://www.alexloop.com I will be operating QRP and have a good selection of all types of capacitors, some fairly high voltage although many of the QRP designs I have seen will allow a simple broadcast radio capacitor (not those new plastic jobbies) to operate -- sometimes as high as 20W1 3. I've seen problems with the loop tuning drifting with temperature. It's not the transmit power but heating from the sun. Even if you're planning on sitting on one frequency all day, you should check for tuning drift. I plan to cut a big cloth circular case to drop over the loop. It will be some nice flowery design, and a plan to put it over the back of a lawnchair so that anyone who walks by and looks up to my 3rd floor balcony will see what appears to be a nice comfortable highback chair! That's mainly for subterfuge! At the same time, having been experimenting with assorted antennas over the years (before I began to deteriorate) I had a big yard full of wire, ground rods, and a tower with all kinds of things hanging off of it. I always kept an eye on the SWR bridge for any variations, so any of that sun heating drift will be watched carefully. Thanks for the tip though! For all my reading that is one thing I hadn't encountered before. 4. Magnetic loops are somewhat directional. You may need some method of spinning the loop for maximum signal. When mounted vertically, the loop is horizontally polarized. When hung over the balcony rail horizontally, it's vertically polarized. See photos of mounting I plan to mount it vertically using a piece of 2X4 sitting in a big pot or tub filled with gravel. Anticipating lots of experimentation once I get on the air, I can drill it, nail it, or whatever for various forms of support, and even clamp a whip on it. I also anticipate that I will eventually turn it into something akin to swiss cheese, and when that comes about, I can replace my 'cheapo balcony tower' with ease. I will also constuct a small platform to hold the tub/pot and by using some of the small plastic swivel casters I'll make the whole works rotatable. 5. Magnetic loop calculators: http://www.66pacific.com/calculators/small_tx_loop_calc.aspx http://www.aa5tb.com/aa5tb_loop_v1.22a.xls 6. Losses. If you plug the numbers into an antenna simulator, you'll find that the losses are HUGE. If you go to the bottom of the page at: http://www.aa5tb.com/loop.html there's a graph of losses versus different loop material sizes. Notice the 1" and 1" (0.5 ohms) plots. Only 0.5 ohms of added resistance and the losses increase by about 16dB at 3.5 MHz. That's a nice way of saying you can't just throw it together. Everything has to be soldered carefully and no sliding contacts on the caps. Your MFJ antenna analyzer will be handy for testing the construction. I'm counting on the MFJ Analyzer for lots of help. I'm very away of the losses, and where they occur and will be careful. As far as losses are concerned, when running QRP why worry? Under good band conditions like we had in the good old days (with propagation ever again improve?) you can work the world with only a few watts. some guys do it with milliwatts! I only want 75M for very local work within about 200Km, but I know I'll be quite efficient on 20 which is where I have always had the most fun. A few of the magloops I've looked at on the net were not all soldered -- many just used nuts, bolts and starwashers. Whenever I ran across them, I'd get back to the builder/operator and ask how they worked, and had they taken the resistance losses into consideration. In all cases they were happy with the way things were and making lots of contacts. One of the Manufactured loops is made of aluminim strips bolted together, and it seems to get good ratings on EHam. On hand, I also have a yoyo antenna, a Miracle Whip antenna, and the MP1 which will be on the air as soon as I can measure the radials and see how it works indoors. Did I mention two Slinky's that I want to try -- first as a short vertical, and then as a helical magnetic loop! I can hardly wait to get going -- and I'm getting closer every day! Thanks for the tips Jeff -- your contributions to the group are always great. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
antenna theory made easy
On Thu, 23 Jan 2014 21:06:12 -0700, "Irv Finkleman"
wrote: I already have a small 12v motor and have tested it with a number of different capacitors. With a simple 10k wirewound pot I can slow it down to almost nothing, or bring it back up to some value, and that beautiful pot just gets lukewarm. Using a DPDT toggle switch I can control the direction as well. Remote tuning on a shoestring! Loose the potentiometer and replace is with a gearbox reducer. You want to retain all the torque and power from the drive motor. Also, don't forget to hi voltage insulate the motor, so that you don't arc over to the motor in transmit. I plan to cut a big cloth circular case to drop over the loop. It will be some nice flowery design, and a plan to put it over the back of a lawnchair so that anyone who walks by and looks up to my 3rd floor balcony will see what appears to be a nice comfortable highback chair! That's mainly for subterfuge! If the lawn chair has an aluminum frame, it will detune the magnetic loop antenna. All plastic lawn chair is required. Also, don't fire up the transmitter when someone is sitting in the lawn chair. At the same time, having been experimenting with assorted antennas over the years (before I began to deteriorate) I had a big yard full of wire, ground rods, and a tower with all kinds of things hanging off of it. I always kept an eye on the SWR bridge for any variations, so any of that sun heating drift will be watched carefully. Thanks for the tip though! For all my reading that is one thing I hadn't encountered before. It's only a problem with high Q antennas. Figure on a Q of 100 to 200 for the lower bands. On 80 meters, that's a 2:1 VSWR bandwidth of about 25 to 35 KHz. It doesn't take much to drift the antenna off frequency. Most magnetic loop users don't notice because they're constantly tweaking the tuning capacitor. I plan to mount it vertically using a piece of 2X4 sitting in a big pot or tub filled with gravel. So much for the disguise antenna. Don't forget to pound a ground rod into the gravel. It won't do anything useful, but will make an interesting conversation starter as to whether a ground is necessary. Anticipating lots of experimentation once I get on the air, I can drill it, nail it, or whatever for various forms of support, and even clamp a whip on it. I also anticipate that I will eventually turn it into something akin to swiss cheese, and when that comes about, I can replace my 'cheapo balcony tower' with ease. Let me know when you're ready to build my inflatable antenna tower. I will also constuct a small platform to hold the tub/pot and by using some of the small plastic swivel casters I'll make the whole works rotatable. Lazy Susan works well. I use that for my direction finder hacks. Use lots of grease if left outside as the bearings tend to rust. I'm counting on the MFJ Analyzer for lots of help. I'm very away of the losses, and where they occur and will be careful. As far as losses are concerned, when running QRP why worry? If you only have a little power to work with, then losses become even more important than if you had hundreds of watts to waste. Under good band conditions like we had in the good old days (with propagation ever again improve?) you can work the world with only a few watts. some guys do it with milliwatts! I only want 75M for very local work within about 200Km, but I know I'll be quite efficient on 20 which is where I have always had the most fun. They still do it with milliwatts. http://hflink.com/jt65/ I'm not sure what's wrong with propagation these days. Probably global warming, or a government conspiracy. A few of the magloops I've looked at on the net were not all soldered -- many just used nuts, bolts and starwashers. They don't work well. One of those I rescued was initially thrown together but not soldered on the assumption that future modifications would be easier without soldering. It didn't work until after it was soldered. Whenever I ran across them, I'd get back to the builder/operator and ask how they worked, and had they taken the resistance losses into consideration. In all cases they were happy with the way things were and making lots of contacts. You can also make a fair number of contacts with a dummy load. I know, I've done it by accident. I also made a fair number of contacts on one Field Day using a coax cable that was not connected to any antenna. In some cases, a dummy load or no antenna would be an improvement over some of the home brew antennas I've seen. One of the Manufactured loops is made of aluminim strips bolted together, and it seems to get good ratings on EHam. You can test that yourself with your MFJ antenna analyzer. Build a loop that way. Measure the VSWR curve and impedance at resonance. Then, rattle the loop a bit to move the bolts a little. Measure again. My guess is you'll see substantial changes every time you bang on the antenna. It might also be interesting to use an ESR (equivalent series resistance) meter to measure the DC resistance. That's also going to vary. On hand, I also have a yoyo antenna, a Miracle Whip antenna, and the MP1 which will be on the air as soon as I can measure the radials and see how it works indoors. Anything with amazing, magic, miracle, ultimate, or other superlatives is usually over-rated. Did I mention two Slinky's that I want to try -- first as a short vertical, and then as a helical magnetic loop! A what? Never mind. I don't have time to model a pretzel made from a Slinky. I can hardly wait to get going -- and I'm getting closer every day! Oh-oh. Slow down. It might be more fun doing cut-n-try, but it's much easier if you plan your antenna carefully, and build it once, not 20 times. Thanks for the tips Jeff -- your contributions to the group are always great. Y'er welcome. Good luck. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
antenna theory made easy
On Fri, 24 Jan 2014 10:10:01 -0800, Jeff Liebermann
wrote: They still do it with milliwatts. http://hflink.com/jt65/ Sorry, wrong link: http://kk4dsd.com/2012/06/07/jt65-power-calculator/ Note that the power levels are tyically well below 5 watts. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
antenna theory made easy
On 1/24/2014 1:10 PM, Jeff Liebermann wrote:
On Thu, 23 Jan 2014 21:06:12 -0700, "Irv Finkleman" wrote: If the lawn chair has an aluminum frame, it will detune the magnetic loop antenna. All plastic lawn chair is required. Also, don't fire up the transmitter when someone is sitting in the lawn chair. [OT] Reminds me of a friend who put up a ground mounted HF vertical in his back yard (back in the 60's). He was sitting in the shack checking it out when his wife let the dog out. The dog saw the new fire hydrant in the back yard, but my friend was ready. Just as the dog lifted his leg, my friend hit the key - with a full KW going to the antenna. From then on, the dog gave the antenna a wide berth, always watching it suspiciously. -- ================== Remove the "x" from my email address Jerry, AI0K ================== |
antenna theory made easy
-- Political correctness is a doctrine, fostered by a delusional, illogical minority, and rapidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a piece of **** by the clean end. "Jeff Liebermann" wrote in message ... On Thu, 23 Jan 2014 21:06:12 -0700, "Irv Finkleman" wrote: I already have a small 12v motor and have tested it with a number of different capacitors. With a simple 10k wirewound pot I can slow it down to almost nothing, or bring it back up to some value, and that beautiful pot just gets lukewarm. Using a DPDT toggle switch I can control the direction as well. Remote tuning on a shoestring! Loose the potentiometer and replace is with a gearbox reducer. You want to retain all the torque and power from the drive motor. Also, don't forget to hi voltage insulate the motor, so that you don't arc over to the motor in transmit. I don't want to get any more complex or expensive than is absolutely required. I am building it myself with limited shop facilities (my operating table) The motor had more than enough torque in all situations. I have an old plastic ball point pen cut to match the motor to the cap which should suffice -- if not, I'll find a better pen! :-) I plan to cut a big cloth circular case to drop over the loop. It will be some nice flowery design, and a plan to put it over the back of a lawnchair so that anyone who walks by and looks up to my 3rd floor balcony will see what appears to be a nice comfortable highback chair! That's mainly for subterfuge! If the lawn chair has an aluminum frame, it will detune the magnetic loop antenna. All plastic lawn chair is required. Also, don't fire up the transmitter when someone is sitting in the lawn chair. The chair is plastic. Hmmmm, wonder if my ex-mother-in-law would like to sit in the sun! At the same time, having been experimenting with assorted antennas over the years (before I began to deteriorate) I had a big yard full of wire, ground rods, and a tower with all kinds of things hanging off of it. I always kept an eye on the SWR bridge for any variations, so any of that sun heating drift will be watched carefully. Thanks for the tip though! For all my reading that is one thing I hadn't encountered before. It's only a problem with high Q antennas. Figure on a Q of 100 to 200 for the lower bands. On 80 meters, that's a 2:1 VSWR bandwidth of about 25 to 35 KHz. It doesn't take much to drift the antenna off frequency. Most magnetic loop users don't notice because they're constantly tweaking the tuning capacitor. I plan to mount it vertically using a piece of 2X4 sitting in a big pot or tub filled with gravel. So much for the disguise antenna. Don't forget to pound a ground rod into the gravel. It won't do anything useful, but will make an interesting conversation starter as to whether a ground is necessary. I will have a drain hole in the bottom of the pot/pan Anticipating lots of experimentation once I get on the air, I can drill it, nail it, or whatever for various forms of support, and even clamp a whip on it. I also anticipate that I will eventually turn it into something akin to swiss cheese, and when that comes about, I can replace my 'cheapo balcony tower' with ease. Let me know when you're ready to build my inflatable antenna tower. Now that sounds interesting. Is it anything like my inflatable dart board? I will also constuct a small platform to hold the tub/pot and by using some of the small plastic swivel casters I'll make the whole works rotatable. Lazy Susan works well. I use that for my direction finder hacks. Use lots of grease if left outside as the bearings tend to rust. Good idea, thanks! I'm counting on the MFJ Analyzer for lots of help. I'm very away of the losses, and where they occur and will be careful. As far as losses are concerned, when running QRP why worry? If you only have a little power to work with, then losses become even more important than if you had hundreds of watts to waste. Under good band conditions like we had in the good old days (with propagation ever again improve?) you can work the world with only a few watts. some guys do it with milliwatts! I only want 75M for very local work within about 200Km, but I know I'll be quite efficient on 20 which is where I have always had the most fun. They still do it with milliwatts. http://hflink.com/jt65/ I'm not sure what's wrong with propagation these days. Probably global warming, or a government conspiracy. It's bad enough that maybe there is a conspiracy! A few of the magloops I've looked at on the net were not all soldered -- many just used nuts, bolts and starwashers. They don't work well. One of those I rescued was initially thrown together but not soldered on the assumption that future modifications would be easier without soldering. It didn't work until after it was soldered. I have a small handheld torch and do intend to solder the critical points, i.e. the capacitor to the loop gap. Whenever I ran across them, I'd get back to the builder/operator and ask how they worked, and had they taken the resistance losses into consideration. In all cases they were happy with the way things were and making lots of contacts. You can also make a fair number of contacts with a dummy load. I know, I've done it by accident. I also made a fair number of contacts on one Field Day using a coax cable that was not connected to any antenna. In some cases, a dummy load or no antenna would be an improvement over some of the home brew antennas I've seen. I've got to agree with you on some of the home brew antennas. I did have a friend who is one of the top of the lists of DXCC and others who, when he got his first rig, didn't know how to tune it properly and was only putting out 15W -- but like the bumblebee who cannot possibly fly due to mechanical principles, he worked WAC and DXCC quite happily unaware of the problem! And don't forget that antenna they used to advertise in QST et al which was no more than a dummy load with some wire attached. At least you could get a great match! One of the Manufactured loops is made of aluminim strips bolted together, and it seems to get good ratings on EHam. You can test that yourself with your MFJ antenna analyzer. Build a loop that way. Measure the VSWR curve and impedance at resonance. Then, rattle the loop a bit to move the bolts a little. Measure again. My guess is you'll see substantial changes every time you bang on the antenna. It might also be interesting to use an ESR (equivalent series resistance) meter to measure the DC resistance. That's also going to vary. I rely on the MFJ Analyzer for a lot of things and don't know how I got along without it. And other than a cheap $20 Canadian Tire Digital Multimeter that is about as far as my test equipment goes. When I sold my house I gave all my 50 years accumulation of test equipment, rigs, and such to the local ham club. Most of all miss my Fluke Multimeter (Model 75 or 77 -- I forget now) which Sony allowed me to keep when I retired. I keep watching for one on E-bay although some of the newer multimeters are reasonably economical and have lots of nice features. On hand, I also have a yoyo antenna, a Miracle Whip antenna, and the MP1 which will be on the air as soon as I can measure the radials and see how it works indoors. Anything with amazing, magic, miracle, ultimate, or other superlatives is usually over-rated. The Miracle Whip was picked up used and repaired (a simple matter of a loose solder connection on the coax male). It was dirt cheap and surprisingly there are quite a few hams using it and having fun. It's no beam, and no Miracle, but on the higher bands it seems to be a not bad performer. I just had to try one out. When the weather warms up I'll see what I can do with it. Did I mention two Slinky's that I want to try -- first as a short vertical, and then as a helical magnetic loop! A what? Never mind. I don't have time to model a pretzel made from a Slinky. The Pretzel Slinky might just be a new twist! I can hardly wait to get going -- and I'm getting closer every day! Oh-oh. Slow down. It might be more fun doing cut-n-try, but it's much easier if you plan your antenna carefully, and build it once, not 20 times. That's exactly my plan Jeff -- and aside from the weather, it keeps me busy checking things out that others have done in pursuit of the 'measure twice cut once' principle. Thanks again Irv VE6BP Thanks for the tips Jeff -- your contributions to the group are always great. Y'er welcome. Good luck. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
antenna theory made easy
On Fri, 24 Jan 2014 15:06:27 -0500, Jerry Stuckle
wrote: Reminds me of a friend who put up a ground mounted HF vertical in his back yard (back in the 60's). He was sitting in the shack checking it out when his wife let the dog out. The dog saw the new fire hydrant in the back yard, but my friend was ready. Just as the dog lifted his leg, my friend hit the key - with a full KW going to the antenna. From then on, the dog gave the antenna a wide berth, always watching it suspiciously. Mythbusters did a test of urinating on an electrified 3rd rail. http://www.youtube.com/watch?v=pDY-0ijiOEQ It didn't work. Surface tension causes the urine stream to break up into non-connected globules, which will not conduct electricity. Later, they managed to get it to work with a 3 inch stream. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
antenna theory made easy
On 1/24/2014 6:16 PM, Jeff Liebermann wrote:
On Fri, 24 Jan 2014 15:06:27 -0500, Jerry Stuckle wrote: Reminds me of a friend who put up a ground mounted HF vertical in his back yard (back in the 60's). He was sitting in the shack checking it out when his wife let the dog out. The dog saw the new fire hydrant in the back yard, but my friend was ready. Just as the dog lifted his leg, my friend hit the key - with a full KW going to the antenna. From then on, the dog gave the antenna a wide berth, always watching it suspiciously. Mythbusters did a test of urinating on an electrified 3rd rail. http://www.youtube.com/watch?v=pDY-0ijiOEQ It didn't work. Surface tension causes the urine stream to break up into non-connected globules, which will not conduct electricity. Later, they managed to get it to work with a 3 inch stream. Who cares about the 3rd rail? That's 60hz, not RF. A HUGE difference. And they probably weren't 3-4" from the third rail like the dog was. Do you understand ANYTHING? -- ================== Remove the "x" from my email address Jerry, AI0K ================== |
antenna theory made easy
On Friday, January 24, 2014 5:16:15 PM UTC-6, Jeff Liebermann wrote:
Mythbusters did a test of urinating on an electrified 3rd rail. It didn't work. I got a severe static electricity shock in Odessa, TX one time while urinating into a hotel john. I saw the arc between my stream and the water in the john. The hotel had wool carpets and the humidity was very low. -- 73, Cecil, w5dxp.com |
antenna theory made easy
On Fri, 24 Jan 2014 20:35:38 -0500, Jerry Stuckle
wrote: On 1/24/2014 6:16 PM, Jeff Liebermann wrote: On Fri, 24 Jan 2014 15:06:27 -0500, Jerry Stuckle wrote: Reminds me of a friend who put up a ground mounted HF vertical in his back yard (back in the 60's). He was sitting in the shack checking it out when his wife let the dog out. The dog saw the new fire hydrant in the back yard, but my friend was ready. Just as the dog lifted his leg, my friend hit the key - with a full KW going to the antenna. From then on, the dog gave the antenna a wide berth, always watching it suspiciously. Mythbusters did a test of urinating on an electrified 3rd rail. http://www.youtube.com/watch?v=pDY-0ijiOEQ It didn't work. Surface tension causes the urine stream to break up into non-connected globules, which will not conduct electricity. Later, they managed to get it to work with a 3 inch stream. Who cares about the 3rd rail? That's 60hz, not RF. A HUGE difference. And they probably weren't 3-4" from the third rail like the dog was. The 3rd rail is usually about 1500 VAC. Last time I checked, there has to be current flowing though the conduction path. The losses involved in jumping the air gap are just too high to electrocute the dog. The RF field from the antenna might cook the dog, but not electrocute. If you hadn't witten "Just as the dog lifted his leg" I wouldn't have said anything. Incidentally, I've gotten some rather nasty RF burns in the past. In all cases, I was in physical contact with the antenna. Unless the transmitter can produce an arc or possibly a corona discharge, there's not going to be much in the way of RF current or electrocution. Do you understand ANYTHING? Are you able to discuss anything technical without resorting to insults? -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
antenna theory made easy
On Fri, 24 Jan 2014 19:44:38 -0800 (PST), W5DXP
wrote: On Friday, January 24, 2014 5:16:15 PM UTC-6, Jeff Liebermann wrote: Mythbusters did a test of urinating on an electrified 3rd rail. It didn't work. I got a severe static electricity shock in Odessa, TX one time while urinating into a hotel john. I saw the arc between my stream and the water in the john. The hotel had wool carpets and the humidity was very low. Ouch. I feel your pain. Wikipedia claims 3 million volts/meter (or about 75,000 volts/inch) which seems a bit high: http://en.wikipedia.org/wiki/Dielectric_strength#Breakdown_field_strength I've always used 10,000 volts/inch but I don't recall the conditions for which that's accurate. In any case, you had quite a (static) high voltage buildup, which could jump the broken parts of the urine flow. 1000 watts into a ground mounted HF vertical? Is that a good idea? It might be too close to the operator to be within accepted RF exposure (MPE) limits. Checking: http://transition.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet65/oet65b.pdf See table 4a on Pg 23. For 1000 watts the minimum distances for a typical 0dBi gain antenna is: Band Controlled Uncontrolled (meters) 160m 0.5 0.7 80m 0.6 1.3 40m 1.1 2.5 20m 2.2 4.8 15m 3.2 7.2 10m 4.5 10. So, if he's operating on 20 meters, a ground mounted antenna with no gain and 1000 watts can't be any closer than about 14 ft from the operator. Maybe with a big yard and if you don't care about cooking the dog or the neighbors. In order to put the voltage node of the vertical near where the dogs urine stream can reach, it would need to be fairly close to the ground. That leaves very little room for the ground radials, any possible control box, or a balun. Seem an odd vertical antenna with the loading coil at ground level. Maybe for 160 meters or a mono band antenna. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
antenna theory made easy
On Fri, 24 Jan 2014 13:38:08 -0700, "Irv Finkleman"
wrote: I don't want to get any more complex or expensive than is absolutely required. Have you ever seen a project that gets simpler and less expensive as it progresses? I haven't. I suggest you resign yourself to the inevitable. It will become more complicated and more expensive. I have an old plastic ball point pen cut to match the motor to the cap which should suffice -- if not, I'll find a better pen! :-) Maybe something slightly flexible might be better. I suggest a length of Sharkbite 1/4" or 3/8" PEX tubing. Home Depot sells it in various lengths and diameters. I've been using it for coil forms at HF frequencies with acceptable results. However, I haven't tested the high voltage characteristics yet. Give me a few days. The chair is plastic. Hmmmm, wonder if my ex-mother-in-law would like to sit in the sun! Please resist the temptation to convert your antenna into a weapon. Let me know when you're ready to build my inflatable antenna tower. Now that sounds interesting. Is it anything like my inflatable dart board? No. I'm serious. I've been playing with the inflatable concept for several years. I have the material to build a small prototype. The plan was to have an all inflatable Field Day. However, every year, I either lack the time, have a crisis pending, have a paying project in progress, or am so fed up with ham radio, that I stall until it's too late to do anything. Maybe next year. And don't forget that antenna they used to advertise in QST et al which was no more than a dummy load with some wire attached. At least you could get a great match! That's what I like about antennas. You can't see the RF, it's difficult to measure antenna characteristics, and the difference between quality and junk is difficult to distinguish. If I were a crook, I would definitely be in the antenna business. I remember the antenna but can't recall or find the name. I do recall that the ARRL got suspicious during a product review and ran an xray on the matching box. Inside was just a resistor. My favorite is the 1950's "Turn your house wiring into a giant 500 ft TV antenna". Inside the box was a "capacitator". That was my introduction to antenna design. I rely on the MFJ Analyzer for a lot of things and don't know how I got along without it. I do. I loaned mine to a friend and he refused to give it back. At least he paid me for it twice. Once to buy it and once to fix it after he blew it up. I still don't have one. What I use is a return loss bridge, sweep generator, detector, and scope. Not exactly portable like the MFJ, but good enough. And other than a cheap $20 Canadian Tire Digital Multimeter that is about as far as my test equipment goes. When I sold my house I gave all my 50 years accumulation of test equipment, rigs, and such to the local ham club. Most of all miss my Fluke Multimeter (Model 75 or 77 -- I forget now) which Sony allowed me to keep when I retired. I keep watching for one on E-bay although some of the newer multimeters are reasonably economical and have lots of nice features. I have several Fluke meters including a Model 75. I stole my Model 12(?) from a previous employer. If you're shopping for a new meter, I think you'll do better with a cheaper brand. I have a bunch of Extec meters. Something like this model (but older): http://www.extech.com/instruments/product.asp?catid=48&prodid=644 I really like the large LCD display. No failures or surprises in about 8 years. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
antenna theory made easy
On 1/25/2014 2:11 AM, Jeff Liebermann wrote:
On Fri, 24 Jan 2014 20:35:38 -0500, Jerry Stuckle wrote: On 1/24/2014 6:16 PM, Jeff Liebermann wrote: On Fri, 24 Jan 2014 15:06:27 -0500, Jerry Stuckle wrote: Reminds me of a friend who put up a ground mounted HF vertical in his back yard (back in the 60's). He was sitting in the shack checking it out when his wife let the dog out. The dog saw the new fire hydrant in the back yard, but my friend was ready. Just as the dog lifted his leg, my friend hit the key - with a full KW going to the antenna. From then on, the dog gave the antenna a wide berth, always watching it suspiciously. Mythbusters did a test of urinating on an electrified 3rd rail. http://www.youtube.com/watch?v=pDY-0ijiOEQ It didn't work. Surface tension causes the urine stream to break up into non-connected globules, which will not conduct electricity. Later, they managed to get it to work with a 3 inch stream. Who cares about the 3rd rail? That's 60hz, not RF. A HUGE difference. And they probably weren't 3-4" from the third rail like the dog was. The 3rd rail is usually about 1500 VAC. Last time I checked, there has to be current flowing though the conduction path. The losses involved in jumping the air gap are just too high to electrocute the dog. The RF field from the antenna might cook the dog, but not electrocute. If you hadn't witten "Just as the dog lifted his leg" I wouldn't have said anything. Try again, troll. Here in Washington, DC, it's 750V. And the rest of your comment is pure BS, also. Incidentally, I've gotten some rather nasty RF burns in the past. In all cases, I was in physical contact with the antenna. Unless the transmitter can produce an arc or possibly a corona discharge, there's not going to be much in the way of RF current or electrocution. So what? Do you understand ANYTHING? Are you able to discuss anything technical without resorting to insults? I get real tired of trolls who continue to show their ignorance while trying to contradict science. -- ================== Remove the "x" from my email address Jerry Stuckle ================== |
antenna theory made easy
On 1/25/2014 2:42 AM, Jeff Liebermann wrote:
On Fri, 24 Jan 2014 19:44:38 -0800 (PST), W5DXP wrote: On Friday, January 24, 2014 5:16:15 PM UTC-6, Jeff Liebermann wrote: Mythbusters did a test of urinating on an electrified 3rd rail. It didn't work. I got a severe static electricity shock in Odessa, TX one time while urinating into a hotel john. I saw the arc between my stream and the water in the john. The hotel had wool carpets and the humidity was very low. Ouch. I feel your pain. Wikipedia claims 3 million volts/meter (or about 75,000 volts/inch) which seems a bit high: http://en.wikipedia.org/wiki/Dielectric_strength#Breakdown_field_strength I've always used 10,000 volts/inch but I don't recall the conditions for which that's accurate. In any case, you had quite a (static) high voltage buildup, which could jump the broken parts of the urine flow. 1000 watts into a ground mounted HF vertical? Is that a good idea? It might be too close to the operator to be within accepted RF exposure (MPE) limits. Checking: http://transition.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet65/oet65b.pdf See table 4a on Pg 23. For 1000 watts the minimum distances for a typical 0dBi gain antenna is: Band Controlled Uncontrolled (meters) 160m 0.5 0.7 80m 0.6 1.3 40m 1.1 2.5 20m 2.2 4.8 15m 3.2 7.2 10m 4.5 10. So, if he's operating on 20 meters, a ground mounted antenna with no gain and 1000 watts can't be any closer than about 14 ft from the operator. Maybe with a big yard and if you don't care about cooking the dog or the neighbors. In order to put the voltage node of the vertical near where the dogs urine stream can reach, it would need to be fairly close to the ground. That leaves very little room for the ground radials, any possible control box, or a balun. Seem an odd vertical antenna with the loading coil at ground level. Maybe for 160 meters or a mono band antenna. Who said how close it was to the operator? And who said there was a control box or balun involved? Neither are required for a properly tuned vertical. And radials on a ground mounted vertical go (preferably) UNDER the ground. When I first started out in ham radio, I used a Hy-Gain 18AVQ vertical - 80-10, with the instructions saying to mount one foot (that's twelve inches for the trolls) above ground with an SO-239 to connect to the coax. Quite within range of a large dog. But once again you show your ignorance of facts. OTOH, your lack of knowledge really is entertaining. More so than most trolls, anyway. -- ================== Remove the "x" from my email address Jerry, AI0K ================== |
Quote:
All it would take is for one neighbor to complain and that would be it! This kind of stuff gives all amateurs a black eye when it comes to proper operating procedures. There is a lot of idiots out there that thinks that if they HAVE a 1000 watt amplifier that they automatically HAVE to turn it on in order for everyone to hear them! Too bad there isn't more O&O's out there that would be willing to get involved. I would like to see a lot of these big time operators cited for their actions.. S T U P I D! |
antenna theory made easy
On Saturday, January 25, 2014 5:08:43 PM UTC-6, Channel Jumper wrote:
This kind of stuff gives all amateurs a black eye when it comes to proper operating procedures. There is a lot of idiots out there that thinks that if they HAVE a 1000 watt amplifier that they automatically HAVE to turn it on in order for everyone to hear them! A KW is chump power in the overall scheme of things. I knew a guy who ran 21.5 KW on 75m several years ago. And the FCC finally got after him. What did they do? Not much. They made him dismantle the amp, and restricted him to a small section of 75m for a while. No real biggie. They were actually kind of impressed with his station. His signal was always very clean. I knew another guy in New Orleans that got caught running about 8 KW. Again, they didn't do too much about it. Both are silent keys now.. |
antenna theory made easy
On Saturday, January 25, 2014 9:43:57 AM UTC-6, Jerry Stuckle wrote:
And radials on a ground mounted vertical go (preferably) UNDER the ground. Actually, for a given number of radials, slightly above ground is better than under ground. But not by too much. Most would probably not notice the difference, but there is a bit.. Elevated radials really need to be a good ways up in wavelength to really live up to their potential. Four radials at 1/4 wave up is equal to about 50-60 in the ground. At 1/8 wave up, you need at least 20 or so to equal 50-60 on the ground. At one foot up, you probably need 50-55 to equal 60 in the ground. So really, the real advantage to burying them in such a case is less to trip over when walking across the yard. :| |
antenna theory made easy
wrote in message ... On Saturday, January 25, 2014 5:08:43 PM UTC-6, Channel Jumper wrote: This kind of stuff gives all amateurs a black eye when it comes to proper operating procedures. There is a lot of idiots out there that thinks that if they HAVE a 1000 watt amplifier that they automatically HAVE to turn it on in order for everyone to hear them! # A KW is chump power in the overall scheme of things. # I knew a guy who ran 21.5 KW on 75m several years ago. # And the FCC finally got after him. What did they do? # Not much. They made him dismantle the amp, and restricted # him to a small section of 75m for a while. No real biggie. # They were actually kind of impressed with his station. # His signal was always very clean. # I knew another guy in New Orleans that got caught running # about 8 KW. Again, they didn't do too much about it. # Both are silent keys now.. Many years ago, I did a few shifts handling emergency traffic from Richardson, TX to Wichita Falls after a tornado. We used the Collins radio station at their facility, and had the blessing of the FCC to go up to 10 KW if needed. We had to do that once or twice on 40 meters. Amazing how well 10 KW and a log periodic antenna at 100 feet can clear out a "hole". |
antenna theory made easy
On Sat, 25 Jan 2014 18:54:24 -0500, Jerry Stuckle
wrote: Not necessarily. Above ground, the radials provide only a (very low) capacitive link to the ground. Below ground, they provide a direct link to the soil. The effect creates a better ground plane for the antenna(s). (...) But an even more important point here is maintenance. It's very hard to cut the grass when radials are above ground. Not everyone agrees. See item #4: http://lists.contesting.com/_topband/2002-04/msg00010.html -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
antenna theory made easy
On 1/25/2014 8:41 PM, Jeff Liebermann wrote:
On Sat, 25 Jan 2014 18:54:24 -0500, Jerry Stuckle wrote: Not necessarily. Above ground, the radials provide only a (very low) capacitive link to the ground. Below ground, they provide a direct link to the soil. The effect creates a better ground plane for the antenna(s). (...) But an even more important point here is maintenance. It's very hard to cut the grass when radials are above ground. Not everyone agrees. See item #4: http://lists.contesting.com/_topband/2002-04/msg00010.html I'll go with the experts, instead of some amateur posting on the web. AM radio stations wouldn't go to all of that expense if it weren't worthwhile. And they have professionals advising them; ones with EE degrees and years of experience. But once again, you show your ignorance. Typical. -- ================== Remove the "x" from my email address Jerry Stuckle ================== |
antenna theory made easy
On Sat, 25 Jan 2014 20:46:48 -0500, Jerry Stuckle
wrote: On 1/25/2014 8:41 PM, Jeff Liebermann wrote: On Sat, 25 Jan 2014 18:54:24 -0500, Jerry Stuckle wrote: Not necessarily. Above ground, the radials provide only a (very low) capacitive link to the ground. Below ground, they provide a direct link to the soil. The effect creates a better ground plane for the antenna(s). (...) But an even more important point here is maintenance. It's very hard to cut the grass when radials are above ground. Not everyone agrees. See item #4: http://lists.contesting.com/_topband/2002-04/msg00010.html I'll go with the experts, instead of some amateur posting on the web. Reminder: This is an amateur radio specific newsgroup. AM radio stations wouldn't go to all of that expense if it weren't worthwhile. And they have professionals advising them; ones with EE degrees and years of experience. Elevated Radial AM Antenna Grounding System by Nott Ltd http://www.nottltd.com/amgroundsystems.html A Closer Look at Vertical Antennas With Elevated Ground Systems http://rudys.typepad.com/files/eleva...al-version.pdf Perhaps there's another reason why AM stations bury their radials? http://www.thebdr.net/articles/ops/xmtr/NewThreat.pdf http://www.thebdr.net/articles/steel/gnd/FLAP1.pdf But once again, you show your ignorance. Typical. Claiming that I'm wrong (or ignorant) does not automatically prove your point. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
antenna theory made easy
On 1/25/2014 10:04 PM, Jeff Liebermann wrote:
On Sat, 25 Jan 2014 20:46:48 -0500, Jerry Stuckle wrote: On 1/25/2014 8:41 PM, Jeff Liebermann wrote: On Sat, 25 Jan 2014 18:54:24 -0500, Jerry Stuckle wrote: Not necessarily. Above ground, the radials provide only a (very low) capacitive link to the ground. Below ground, they provide a direct link to the soil. The effect creates a better ground plane for the antenna(s). (...) But an even more important point here is maintenance. It's very hard to cut the grass when radials are above ground. Not everyone agrees. See item #4: http://lists.contesting.com/_topband/2002-04/msg00010.html I'll go with the experts, instead of some amateur posting on the web. Reminder: This is an amateur radio specific newsgroup. So? Do the physics change for Amateur Radio stations? I don't think so. AM radio stations wouldn't go to all of that expense if it weren't worthwhile. And they have professionals advising them; ones with EE degrees and years of experience. Elevated Radial AM Antenna Grounding System by Nott Ltd http://www.nottltd.com/amgroundsystems.html I see their claims. But anyone can claim anything (you're proof of that). I have yet to see any figures that prove elevated radiator systems are significantly "better" than buried ones. And additionally, there are other factors which you conveniently ignore. Probably because you can't read - or are just choosing to ignore facts which conflict with your ideas. But that's nothing new, either - and just what a troll does. A Closer Look at Vertical Antennas With Elevated Ground Systems http://rudys.typepad.com/files/eleva...al-version.pdf Ah, another non-professional opinion. But at least he admits results of multiple tests conflict. Perhaps there's another reason why AM stations bury their radials? http://www.thebdr.net/articles/ops/xmtr/NewThreat.pdf http://www.thebdr.net/articles/steel/gnd/FLAP1.pdf I doubt that was a concern when most AM radio stations were installed. How many new ones do you know of? Besides that, there isn't that much of a market for #22 wire - all that's really needed when you have lots of radials, even with a 5-10KW station, because there is so little current through any one conductor (although buried radials are typically larger just so they last longer). But once again, you show your ignorance. Typical. Claiming that I'm wrong (or ignorant) does not automatically prove your point. Nope, but it once again calls attention to your ignorance. But I also know trolls hate to be proven wrong. You're a perfect example. -- ================== Remove the "x" from my email address Jerry, AI0K ================== |
antenna theory made easy
Jeff Liebermann wrote:
On Sat, 25 Jan 2014 20:46:48 -0500, Jerry Stuckle wrote: On 1/25/2014 8:41 PM, Jeff Liebermann wrote: On Sat, 25 Jan 2014 18:54:24 -0500, Jerry Stuckle wrote: Not necessarily. Above ground, the radials provide only a (very low) capacitive link to the ground. Below ground, they provide a direct link to the soil. The effect creates a better ground plane for the antenna(s). (...) But an even more important point here is maintenance. It's very hard to cut the grass when radials are above ground. Not everyone agrees. See item #4: http://lists.contesting.com/_topband/2002-04/msg00010.html I'll go with the experts, instead of some amateur posting on the web. Reminder: This is an amateur radio specific newsgroup. AM radio stations wouldn't go to all of that expense if it weren't worthwhile. And they have professionals advising them; ones with EE degrees and years of experience. Elevated Radial AM Antenna Grounding System by Nott Ltd http://www.nottltd.com/amgroundsystems.html A Closer Look at Vertical Antennas With Elevated Ground Systems http://rudys.typepad.com/files/eleva...al-version.pdf Perhaps there's another reason why AM stations bury their radials? http://www.thebdr.net/articles/ops/xmtr/NewThreat.pdf http://www.thebdr.net/articles/steel/gnd/FLAP1.pdf But once again, you show your ignorance. Typical. Claiming that I'm wrong (or ignorant) does not automatically prove your point. Welcome to the club; he does that with anyone on any group on any subject when someone has the audacity to disagree with something he has said. -- Jim Pennino |
antenna theory made easy
On Sun, 26 Jan 2014 04:10:28 -0000, wrote:
Welcome to the club; he does that with anyone on any group on any subject when someone has the audacity to disagree with something he has said. Now you tell me. I don't read any other ham radio newsgroups, so I missed the clue. For me, this has became an exercise in diplomacy and tact, things that I usually do rather badly. While my efforts produced nothing useful, it was a somewhat interesting exercise which forced me to do some reading in areas where I know little. I dunno. There do not seem to be many others jumping in, making corrections, asking questions, or displaying any interest in this discussion. It's mostly me and Mr Stuckle. I was tempted to emulate his methods, but I just don't have the ability. Perhaps it's time that I do something else. Thanks much. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
antenna theory made easy
On Sat, 25 Jan 2014 10:43:57 -0500, Jerry Stuckle
wrote: When I first started out in ham radio, I used a Hy-Gain 18AVQ vertical - 80-10, with the instructions saying to mount one foot (that's twelve inches for the trolls) above ground with an SO-239 to connect to the coax. Are you sure? http://www.mediaglobe.it/shop/images/large/HYGAIN18AVQ11--av-18AVQ71_UcLOU9MUvMti_large.gif I doubt that the dog could come anywhere near that antenna with the radials poking out, even if they were buried. http://www.eham.net/data/classifieds/images/244950.jpg The base of the antenna looks like a 50 ohm point, which would be low voltage. I don't have an NEC2 model of the 18AVQ, but my guess(tm) is that the high voltages would be between the loading coils, not near the base. Quite within range of a large dog. Large dog? I would think it would be easier to electrocute a small dog because of the shorter urine stream. If one increases the height of the dog by one inch, then the approximate width of the dog also increases about one inch, thus bringing the urine source 1/2 further away from the antenna. In addition, large dogs have longer legs. The dog needs space to lift the leg, which again increases the distance between the dog and the antenna. I also asked my neighbor, who has a rather large dog, if the dog empties his bladder when marking his territory. Nope. Just a small squirt sufficient to provide a scent marker. If Mythbusters could only keep a 3" simulated stream together long enough to not break into droplets, I suspect that a large dog, with a much longer stream, would not be able to do as well. Myth Busted. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
antenna theory made easy
Jeff Liebermann wrote:
On Sun, 26 Jan 2014 04:10:28 -0000, wrote: Welcome to the club; he does that with anyone on any group on any subject when someone has the audacity to disagree with something he has said. Now you tell me. I don't read any other ham radio newsgroups, so I missed the clue. For me, this has became an exercise in diplomacy and tact, things that I usually do rather badly. While my efforts produced nothing useful, it was a somewhat interesting exercise which forced me to do some reading in areas where I know little. I dunno. There do not seem to be many others jumping in, making corrections, asking questions, or displaying any interest in this discussion. It's mostly me and Mr Stuckle. I was tempted to emulate his methods, but I just don't have the ability. Perhaps it's time that I do something else. Thanks much. You could continue on and eventually he will killfile you, usually after posting a link that proves him wrong about something. And it is not just ham radio groups, he is also an "expert" in various programming languages and the same goes on in those groups all the time. -- Jim Pennino |
antenna theory made easy
On Saturday, January 25, 2014 7:41:18 PM UTC-6, Jeff Liebermann wrote:
Not everyone agrees. See item #4: http://lists.contesting.com/_topband/2002-04/msg00010.html He's not really giving much of a reason though. I think he's more interested in avoiding digging slots for radials, than he is the difference in ground loss. :/ The BC stations bury a large number for day in, day out stability. They are required to do that by the FCC. But as a general rule, the farther away from the lossy earth, the lower the ground loss for a given number of equal length 1/4 wave radials. And I've read that in more than one book. I didn't just make it up, although I have pretty much verified it in the real world by testing. But if elevated, they should be resonant and tuned, which is not needed with buried radials. They are de-tuned by the ground anyway. But I'm also one that disagrees with people who expect a low number of elevated radials at a low height above ground in wavelength, to have some magical property that allows them to use say 4-8 radials just above the ground and equal a large number on the ground. It just won't pan out very well. :+ There is no free lunch. :( If you want to use four radials with good results, you need to be at at least 1/4 wave up. Which say on 160m would be about 120 ft up. That should equal about 60 radials on the ground, which is not bad at all. Four radials at 1/2 wave is about equal to 120 on the ground. But some people will run four radials at 5-10-20 feet off the ground running on 80 or 160m, and then wonder why they are not browning the food. :( I ran a full size 40m GP at 36 ft, which is about 1/4 wave up. Used four radials. It totally smoked the same 32 ft whip ground mounted with 32 radials. But lower the mast and radials down to 15 ft, and the performance dropped off greatly. |
antenna theory made easy
On 1/25/2014 11:10 PM, wrote:
Jeff Liebermann wrote: On Sat, 25 Jan 2014 20:46:48 -0500, Jerry Stuckle wrote: On 1/25/2014 8:41 PM, Jeff Liebermann wrote: On Sat, 25 Jan 2014 18:54:24 -0500, Jerry Stuckle wrote: Not necessarily. Above ground, the radials provide only a (very low) capacitive link to the ground. Below ground, they provide a direct link to the soil. The effect creates a better ground plane for the antenna(s). (...) But an even more important point here is maintenance. It's very hard to cut the grass when radials are above ground. Not everyone agrees. See item #4: http://lists.contesting.com/_topband/2002-04/msg00010.html I'll go with the experts, instead of some amateur posting on the web. Reminder: This is an amateur radio specific newsgroup. AM radio stations wouldn't go to all of that expense if it weren't worthwhile. And they have professionals advising them; ones with EE degrees and years of experience. Elevated Radial AM Antenna Grounding System by Nott Ltd http://www.nottltd.com/amgroundsystems.html A Closer Look at Vertical Antennas With Elevated Ground Systems http://rudys.typepad.com/files/eleva...al-version.pdf Perhaps there's another reason why AM stations bury their radials? http://www.thebdr.net/articles/ops/xmtr/NewThreat.pdf http://www.thebdr.net/articles/steel/gnd/FLAP1.pdf But once again, you show your ignorance. Typical. Claiming that I'm wrong (or ignorant) does not automatically prove your point. Welcome to the club; he does that with anyone on any group on any subject when someone has the audacity to disagree with something he has said. No, just when someone is ignorant. -- ================== Remove the "x" from my email address Jerry Stuckle ================== |
antenna theory made easy
On 1/26/2014 1:59 AM, wrote:
Jeff Liebermann wrote: On Sun, 26 Jan 2014 04:10:28 -0000, wrote: Welcome to the club; he does that with anyone on any group on any subject when someone has the audacity to disagree with something he has said. Now you tell me. I don't read any other ham radio newsgroups, so I missed the clue. For me, this has became an exercise in diplomacy and tact, things that I usually do rather badly. While my efforts produced nothing useful, it was a somewhat interesting exercise which forced me to do some reading in areas where I know little. I dunno. There do not seem to be many others jumping in, making corrections, asking questions, or displaying any interest in this discussion. It's mostly me and Mr Stuckle. I was tempted to emulate his methods, but I just don't have the ability. Perhaps it's time that I do something else. Thanks much. You could continue on and eventually he will killfile you, usually after posting a link that proves him wrong about something. And it is not just ham radio groups, he is also an "expert" in various programming languages and the same goes on in those groups all the time. Yes, you are a well-known troll in several programming newsgroups. So now your trolling here. -- ================== Remove the "x" from my email address Jerry Stuckle ================== |
antenna theory made easy
On 1/26/2014 1:04 AM, Jeff Liebermann wrote:
On Sat, 25 Jan 2014 10:43:57 -0500, Jerry Stuckle wrote: When I first started out in ham radio, I used a Hy-Gain 18AVQ vertical - 80-10, with the instructions saying to mount one foot (that's twelve inches for the trolls) above ground with an SO-239 to connect to the coax. Are you sure? http://www.mediaglobe.it/shop/images/large/HYGAIN18AVQ11--av-18AVQ71_UcLOU9MUvMti_large.gif I doubt that the dog could come anywhere near that antenna with the radials poking out, even if they were buried. The 18AVQ didn't have radials poking out - although it was recommended you add them. http://www.eham.net/data/classifieds/images/244950.jpg The base of the antenna looks like a 50 ohm point, which would be low voltage. I don't have an NEC2 model of the 18AVQ, but my guess(tm) is that the high voltages would be between the loading coils, not near the base. So? Even at 50 ohms, 1KW is a lot of voltage. Quite within range of a large dog. Large dog? I would think it would be easier to electrocute a small dog because of the shorter urine stream. If one increases the height of the dog by one inch, then the approximate width of the dog also increases about one inch, thus bringing the urine source 1/2 further away from the antenna. In addition, large dogs have longer legs. The dog needs space to lift the leg, which again increases the distance between the dog and the antenna. I also asked my neighbor, who has a rather large dog, if the dog empties his bladder when marking his territory. Nope. Just a small squirt sufficient to provide a scent marker. If Mythbusters could only keep a 3" simulated stream together long enough to not break into droplets, I suspect that a large dog, with a much longer stream, would not be able to do as well. Who said it was a small dog, and who said the dog was electrocuted? Myth Busted. Bull****ter busted. -- ================== Remove the "x" from my email address Jerry Stuckle ================== |
antenna theory made easy
On Sunday, January 26, 2014 9:47:36 AM UTC-6, Jerry Stuckle wrote:
Even at 50 ohms, 1KW is a lot of voltage. Pretty close to the 60 Hz AC voltage that runs my clothes dryer and electric range. -- 73, Cecil, w5dxp.com |
antenna theory made easy
On 1/26/2014 11:32 AM, W5DXP wrote:
On Sunday, January 26, 2014 9:47:36 AM UTC-6, Jerry Stuckle wrote: Even at 50 ohms, 1KW is a lot of voltage. Pretty close to the 60 Hz AC voltage that runs my clothes dryer and electric range. -- 73, Cecil, w5dxp.com A bit more than that. Remember - you've only got 117V to ground from either leg of your clothes dryer. And even that can give you a nasty shock or worse. And RF burns. -- ================== Remove the "x" from my email address Jerry Stuckle ================== |
antenna theory made easy
On Sunday, January 26, 2014 10:45:46 AM UTC-6, Jerry Stuckle wrote:
Remember - you've only got 117V to ground from either leg of your clothes dryer. The same thing can be said about a 1000 watt RF amp driving a balanced load and the voltage delivered by that amp to a 50 ohm load is lower than the voltage going to my clothes dryer which I just measured at 250 volts. -- 73, Cecil, w5dxp.com |
antenna theory made easy
On 1/26/2014 3:45 PM, W5DXP wrote:
On Sunday, January 26, 2014 10:45:46 AM UTC-6, Jerry Stuckle wrote: Remember - you've only got 117V to ground from either leg of your clothes dryer. The same thing can be said about a 1000 watt RF amp driving a balanced load and the voltage delivered by that amp to a 50 ohm load is lower than the voltage going to my clothes dryer which I just measured at 250 volts. -- 73, Cecil, w5dxp.com You have 250 V across the lines (actually should be around 234-240), But only about 117-120V to ground. And what the voltage across a balanced load is is immaterial, since verticals are not balanced. -- ================== Remove the "x" from my email address Jerry Stuckle ================== |
antenna theory made easy
On Sunday, January 26, 2014 2:57:32 PM UTC-6, Jerry Stuckle wrote:
And what the voltage across a balanced load is is immaterial, since verticals are not balanced. In the context of "antenna theory made easy", please prove that the voltage across a balanced antenna is immaterial. -- 73, Cecil, w5dxp.com |
antenna theory made easy
On 1/26/2014 7:53 PM, W5DXP wrote:
On Sunday, January 26, 2014 2:57:32 PM UTC-6, Jerry Stuckle wrote: And what the voltage across a balanced load is is immaterial, since verticals are not balanced. In the context of "antenna theory made easy", please prove that the voltage across a balanced antenna is immaterial. -- 73, Cecil, w5dxp.com I didn't say the voltage across a balanced antenna load is immaterial. I said YOUR TEST is immaterial because a vertical is not a balanced load. Sheesh - you used to have to know how to read and actually understand some electronics to get a ham license. Now all you need to do is memorize the answers. -- ================== Remove the "x" from my email address Jerry Stuckle ================== |
antenna theory made easy
On Sunday, January 26, 2014 6:58:05 PM UTC-6, Jerry Stuckle wrote:
I said YOUR TEST is immaterial because a vertical is not a balanced load. Sheesh - you used to have to know how to read ... Jerry, I was probably reading Ramo and Whinnery while you were still messing your diapers.:) Speaking of someone who doesn't know how to read - the title of this thread is NOT verticals and I did NOT say anything about verticals. Exactly why am I prohibited from discussing balanced antennas in a thread titled, "antenna theory made easy"? -- 73, Cecil, w5dxp.com |
antenna theory made easy
On 1/26/2014 9:11 PM, W5DXP wrote:
On Sunday, January 26, 2014 6:58:05 PM UTC-6, Jerry Stuckle wrote: I said YOUR TEST is immaterial because a vertical is not a balanced load. Sheesh - you used to have to know how to read ... Jerry, I was probably reading Ramo and Whinnery while you were still messing your diapers.:) Speaking of someone who doesn't know how to read - the title of this thread is NOT verticals and I did NOT say anything about verticals. Exactly why am I prohibited from discussing balanced antennas in a thread titled, "antenna theory made easy"? Cecil, unless you're over 90, I very much doubt that. And yes, the title is about antennas. But you're replying to messages about verticals. Measuring voltage across a 60Hz 240V balanced line has nothing to do with measuring voltage at the base of a vertical which is unbalanced and running RF. -- 73, Cecil, w5dxp.com -- ================== Remove the "x" from my email address Jerry, AI0K ================== |
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