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Flex dryer vent hose loop antenna
I've been thinking of building a rather different magnetic loop
antenna. Instead of the usual rigid loop and adjustable tuning capacitor, I want to try a flexible loop and a fixed capacitor. The idea is to eliminate the cost of the tunable vacuum capacitor or cheese grater butterfly capacitor. For a loop, I propose to use a flexible aluminum dryer vent hose: https://www.google.com/search?tbm=isch&q=flexible+dryer+vent+duct http://www.ipagepro.com/dryerventsolutionsllc/logos/BTD48.png http://ace.imageg.net/graphics/product_images/pACE3-17458764enh-z8.jpg I've used similar hoses in my giant inflatable rubber ducky antenna experiments. The major point of failure was that the spiral steel wire antenna inside the hose produced some hot spots, which melted a hole in the vinyl jacket. However, with an aluminum jacket, all the RF will be on the outside, and there's no vinyl to melt. The 8ft dryer hose will (somehow) form a loop when inflated with air from a bicycle or hand pump. Inside the dryer hose is a length of small diameter bungee cord to help collapse the loop. When hose is inflated, the loop expands, which also tunes the loop to the desired frequency. One nice feature is that with the loop deflated and collapsed, it's sufficiently small for portable or stealth use. Fully inflated, an 8ft hose should produce a 31" diameter loop. The rest is fairly conventional. A small wire loop inside the loop to provide impedance matching and coupling for the 50 ohm feed. Maybe some kind of tuning indicator (small fluorescent tube). I'm undecided on whether to mount it vertically, which requires a prop, or horizontally, which can be done on an insulated table surface. Permission to steal and use this idea is hereby granted, as long as you fail to mention my identity in the event that your sanity is questioned by the neighbors or local authorities. No patents are pending. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Flex dryer vent hose loop antenna
On 11/1/2015 2:38 PM, Jeff Liebermann wrote:
I've been thinking of building a rather different magnetic loop antenna. Instead of the usual rigid loop and adjustable tuning capacitor, I want to try a flexible loop and a fixed capacitor. The idea is to eliminate the cost of the tunable vacuum capacitor or cheese grater butterfly capacitor. For a loop, I propose to use a flexible aluminum dryer vent hose: https://www.google.com/search?tbm=isch&q=flexible+dryer+vent+duct http://www.ipagepro.com/dryerventsolutionsllc/logos/BTD48.png http://ace.imageg.net/graphics/product_images/pACE3-17458764enh-z8.jpg I've used similar hoses in my giant inflatable rubber ducky antenna experiments. The major point of failure was that the spiral steel wire antenna inside the hose produced some hot spots, which melted a hole in the vinyl jacket. However, with an aluminum jacket, all the RF will be on the outside, and there's no vinyl to melt. The 8ft dryer hose will (somehow) form a loop when inflated with air from a bicycle or hand pump. Inside the dryer hose is a length of small diameter bungee cord to help collapse the loop. When hose is inflated, the loop expands, which also tunes the loop to the desired frequency. One nice feature is that with the loop deflated and collapsed, it's sufficiently small for portable or stealth use. Fully inflated, an 8ft hose should produce a 31" diameter loop. The rest is fairly conventional. A small wire loop inside the loop to provide impedance matching and coupling for the 50 ohm feed. Maybe some kind of tuning indicator (small fluorescent tube). I'm undecided on whether to mount it vertically, which requires a prop, or horizontally, which can be done on an insulated table surface. Permission to steal and use this idea is hereby granted, as long as you fail to mention my identity in the event that your sanity is questioned by the neighbors or local authorities. No patents are pending. When you say dryer hose, you mean the corrugated aluminum tube that is 3 or 4 inches in diameter. That might work for a loop antenna, but I think the corrugations are hard to collapse once you expand them. So I doubt it will work as the tuning element unless you simply change the shape of the loop rather than keeping it a circle with an adjustable size. I used some of this stuff in a larger diameter to connect a humidifier and it was flexible enough to extend and shape, but didn't go back hardly at all. -- Rick |
Flex dryer vent hose loop antenna
On 11/1/2015 11:38 AM, Jeff Liebermann wrote:
I've been thinking of building a rather different magnetic loop antenna. Instead of the usual rigid loop and adjustable tuning capacitor, I want to try a flexible loop and a fixed capacitor. The idea is to eliminate the cost of the tunable vacuum capacitor or cheese grater butterfly capacitor. For a loop, I propose to use a flexible aluminum dryer vent hose: https://www.google.com/search?tbm=isch&q=flexible+dryer+vent+duct http://www.ipagepro.com/dryerventsolutionsllc/logos/BTD48.png http://ace.imageg.net/graphics/product_images/pACE3-17458764enh-z8.jpg I've used similar hoses in my giant inflatable rubber ducky antenna experiments. The major point of failure was that the spiral steel wire antenna inside the hose produced some hot spots, which melted a hole in the vinyl jacket. However, with an aluminum jacket, all the RF will be on the outside, and there's no vinyl to melt. The 8ft dryer hose will (somehow) form a loop when inflated with air from a bicycle or hand pump. Inside the dryer hose is a length of small diameter bungee cord to help collapse the loop. When hose is inflated, the loop expands, which also tunes the loop to the desired frequency. One nice feature is that with the loop deflated and collapsed, it's sufficiently small for portable or stealth use. Fully inflated, an 8ft hose should produce a 31" diameter loop. The rest is fairly conventional. A small wire loop inside the loop to provide impedance matching and coupling for the 50 ohm feed. Maybe some kind of tuning indicator (small fluorescent tube). I'm undecided on whether to mount it vertically, which requires a prop, or horizontally, which can be done on an insulated table surface. Permission to steal and use this idea is hereby granted, as long as you fail to mention my identity in the event that your sanity is questioned by the neighbors or local authorities. No patents are pending. Probable should clear the lint out first! Paul, KD7HB |
Flex dryer vent hose loop antenna
On Sun, 1 Nov 2015 18:31:55 -0500, rickman wrote:
When you say dryer hose, you mean the corrugated aluminum tube that is 3 or 4 inches in diameter. Yep. Just like the stuff in the links provided. That might work for a loop antenna, but I think the corrugations are hard to collapse once you expand them. So I doubt it will work as the tuning element unless you simply change the shape of the loop rather than keeping it a circle with an adjustable size. The bungee cord down the middle is suppose to help collapse the hose. I must confess that I haven't tried it. If that doesn't work, then some elastic cords. If that fails, a nylon rope and some external springs. I used some of this stuff in a larger diameter to connect a humidifier and it was flexible enough to extend and shape, but didn't go back hardly at all. Yep. It won't go back by itself and needs some additional help. Anyway, if you want to get your picture in QST as the building of the worlds strangest and probably cheapest loop antenna, here's your chance. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Flex dryer vent hose loop antenna
On Sun, 1 Nov 2015 18:10:56 -0800, Paul Drahn
wrote: Probable should clear the lint out first! Paul, KD7HB I know that hams are cheap, but I didn't realize that extended to stealing the neighbors dryer vent hose in order to build an antenna. I highly recommend purchasing a new hose, which comes pre-cleaned: http://www.acehardware.com/family/index.jsp?categoryId=2627981 Incidentally, there's no requirement that the entire loop be made from expandable hose. The loop could be in the form of a square loop, where the flat base and flat top are rigid aluminum structures, and the two vertical sections are flexible dryer vent hose. The weight of the flat top would help collapse the antenna although I suspect that springs or weights would work better. It's not like inflatable antennas and structures are a new thing: http://ltaprojects.com/towers/inflatable-antenna-video-towers/ham -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Flex dryer vent hose loop antenna
On 11/1/2015 9:27 PM, Jeff Liebermann wrote:
On Sun, 1 Nov 2015 18:31:55 -0500, rickman wrote: When you say dryer hose, you mean the corrugated aluminum tube that is 3 or 4 inches in diameter. Yep. Just like the stuff in the links provided. That might work for a loop antenna, but I think the corrugations are hard to collapse once you expand them. So I doubt it will work as the tuning element unless you simply change the shape of the loop rather than keeping it a circle with an adjustable size. The bungee cord down the middle is suppose to help collapse the hose. I must confess that I haven't tried it. If that doesn't work, then some elastic cords. If that fails, a nylon rope and some external springs. I used some of this stuff in a larger diameter to connect a humidifier and it was flexible enough to extend and shape, but didn't go back hardly at all. Yep. It won't go back by itself and needs some additional help. Anyway, if you want to get your picture in QST as the building of the worlds strangest and probably cheapest loop antenna, here's your chance. Ok, so if you can force it to shrink with springs or ropes or whatever, then something will be needed to force it to expand again. I'm having trouble seeing how this will work without the antenna losing all shape. These tubes are just not really easy to manipulate. They are intended to be bent once with more than a little force but more importantly very controlled force. I'm not sure the inductance will change all that much. I have never seen a calculation for the inductance of an accordion. It may have a rather limited tuning range compared to a typical variable cap. At least the frequency will scale the right way with size. Smaller loop, lower inductance, higher frequency which will keep the radiation resistance high. -- Rick |
Flex dryer vent hose loop antenna
On Sun, 1 Nov 2015 21:58:32 -0500, rickman wrote:
Ok, so if you can force it to shrink with springs or ropes or whatever, then something will be needed to force it to expand again. Yep. A bicycle pump, hand pump, crank pump, bellows pump, electric pump, or pressure vessel will all inflate the antenna. I'm having trouble seeing how this will work without the antenna losing all shape. Below some pressure level, it will probably flop over if mounted vertically. That's why I mumbled that I wasn't sure if it should be mounted vertically with a support pole, or horizontally on a flat sheet of plywood. Both will work, but I'm not sure which is better. These tubes are just not really easy to manipulate. They are intended to be bent once with more than a little force but more importantly very controlled force. In other words, after a few inflation deflation cycles, it might fall apart. I have a few that I bought for the inflatable antenna project. It looked quite flexible to me but I'll test it to be sure. I'm not sure the inductance will change all that much. I have never seen a calculation for the inductance of an accordion. It may have a rather limited tuning range compared to a typical variable cap. At least the frequency will scale the right way with size. Smaller loop, lower inductance, higher frequency which will keep the radiation resistance high. Good point. At one time, I was wondering how to increase the bandwidth of a yagi antenna. I knew that rounding the ends of the elements would increase the bandwidth because there was no single length for which to consider the "end" of the antenna rod. Similarly, when calculating the rod length of a yagi antenna, the RF path around the center boom must be added to the rod length. That made me wonder if I could roughen the antenna rod to produce the same effect. I guess corrugation might be considered the ultimate form of antenna "roughness". The question was would the antenna length be the distance from end to end of the accordion, or would it be the distance traveled across the surface along all the ups and downs of the accordion. What I found was that the effect varies with frequency and of course the accordion geometry. At 1MHz, the resonant length was the surface distance traveled. In other words, expanding the accordion had little effect on the antenna resonance. At much higher frequencies (about 150 MHz), there was enough capacitance between the accordion "sides" that the antenna was effectively shortened and the resonant frequency was the end to end distance. However, that's not exactly true because there were multiple path lengths which could be considered resonant, much like the rounded end on the rod. So, at low frequencies, my scheme probably won't work. At higher frequencies, maybe. Your task, should you decide to accept it, is to try it. All it will take is a length of flex aluminum dryer hose and an LRC meter. Please note that my testing was not a proper lab test but more like screwing around with a grid dipper, LRC meter, and network analyzer to help settle a lunch time argument. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Flex dryer vent hose loop antenna
On 11/1/2015 11:32 PM, Jeff Liebermann wrote:
On Sun, 1 Nov 2015 21:58:32 -0500, rickman wrote: Ok, so if you can force it to shrink with springs or ropes or whatever, then something will be needed to force it to expand again. Yep. A bicycle pump, hand pump, crank pump, bellows pump, electric pump, or pressure vessel will all inflate the antenna. Ok, that might be workable. I think the tube will need a liner. I'm not sure this stuff will be easy to seal. I'm having trouble seeing how this will work without the antenna losing all shape. Below some pressure level, it will probably flop over if mounted vertically. That's why I mumbled that I wasn't sure if it should be mounted vertically with a support pole, or horizontally on a flat sheet of plywood. Both will work, but I'm not sure which is better. You are assuming it will maintain something remotely like a circle. I don't see that happening. Have you worked with this stuff? Maybe what you have is more pliable than the stuff I used. These tubes are just not really easy to manipulate. They are intended to be bent once with more than a little force but more importantly very controlled force. In other words, after a few inflation deflation cycles, it might fall apart. I have a few that I bought for the inflatable antenna project. It looked quite flexible to me but I'll test it to be sure. I don't mean fall apart necessarily, but just not be much like a loop antenna. I think the hard part will be shrinking it back down and keeping its shape. Proof of the pudding... I'm not sure the inductance will change all that much. I have never seen a calculation for the inductance of an accordion. It may have a rather limited tuning range compared to a typical variable cap. At least the frequency will scale the right way with size. Smaller loop, lower inductance, higher frequency which will keep the radiation resistance high. Good point. At one time, I was wondering how to increase the bandwidth of a yagi antenna. I knew that rounding the ends of the elements would increase the bandwidth because there was no single length for which to consider the "end" of the antenna rod. Similarly, when calculating the rod length of a yagi antenna, the RF path around the center boom must be added to the rod length. That made me wonder if I could roughen the antenna rod to produce the same effect. I guess corrugation might be considered the ultimate form of antenna "roughness". The question was would the antenna length be the distance from end to end of the accordion, or would it be the distance traveled across the surface along all the ups and downs of the accordion. There are helically wound antennas that have a similar issue. I have yet to see any equations to model them. I wonder if they work or not, in the sense of any better than a simple loop. What I found was that the effect varies with frequency and of course the accordion geometry. At 1MHz, the resonant length was the surface distance traveled. In other words, expanding the accordion had little effect on the antenna resonance. At much higher frequencies (about 150 MHz), there was enough capacitance between the accordion "sides" that the antenna was effectively shortened and the resonant frequency was the end to end distance. However, that's not exactly true because there were multiple path lengths which could be considered resonant, much like the rounded end on the rod. So, at low frequencies, my scheme probably won't work. At higher frequencies, maybe. Your task, should you decide to accept it, is to try it. All it will take is a length of flex aluminum dryer hose and an LRC meter. I don't have any equipment to date. I have a couple of projects ahead of this if I decide to build something. Please note that my testing was not a proper lab test but more like screwing around with a grid dipper, LRC meter, and network analyzer to help settle a lunch time argument. You clearly have much more experience than I do. I wold barely know how to use a SWR meter and don't have an LRC meter... I can't remember what a grid dip meter is. :( -- Rick |
Flex dryer vent hose loop antenna
On 11/1/2015 10:32 PM, Jeff Liebermann wrote:
On Sun, 1 Nov 2015 21:58:32 -0500, rickman wrote: Ok, so if you can force it to shrink with springs or ropes or whatever, then something will be needed to force it to expand again. Yep. A bicycle pump, hand pump, crank pump, bellows pump, electric pump, or pressure vessel will all inflate the antenna. I'm having trouble seeing how this will work without the antenna losing all shape. Below some pressure level, it will probably flop over if mounted vertically. That's why I mumbled that I wasn't sure if it should be mounted vertically with a support pole, or horizontally on a flat sheet of plywood. Both will work, but I'm not sure which is better. Hang it upside down. Mikek |
Flex dryer vent hose loop antenna
On Mon, 2 Nov 2015 00:28:03 -0500, rickman wrote:
You are assuming it will maintain something remotely like a circle. I don't see that happening. Have you worked with this stuff? Maybe what you have is more pliable than the stuff I used. I've worked with the vinyl dryer hose, but not the aluminum foil variety. With the vinyl, I was using the helical "Slinky" part of the hose as an HF antenna. As I mentioned, the steel spring got hot and melted the vinyl. The actual inflatable antenna was a vertical monopole, so I never even tried to make a loop, and am not sure it will work. That's why I'm trying to recruit someone else to do the dirty work. I guess I could go shopping and do it myself, but I'm kinda busy this week (mostly recovering from the last 3 week of overwork). I suspect that there might be problems if I use too much air pressure. With the monopole, the hose would handle about 30 psi before producing a leak. It thinks that's more than enough to inflate the loop, but might not be enough to be self supporting, especially with a capacitor at the top. I don't mean fall apart necessarily, but just not be much like a loop antenna. I think the hard part will be shrinking it back down and keeping its shape. Proof of the pudding... The optimum shape is a circle with square, hexagon and octagon shapes being a tolerable facsimile. I guess the question is whether a random pretzel shape will work. Dunno, difficult to simulate, but easy to try. There are helically wound antennas that have a similar issue. I have yet to see any equations to model them. I wonder if they work or not, in the sense of any better than a simple loop. One of the local club members build a 160 meter vertical rubber ducky (helical antenna) with ground radials and ended up with a usable bandwidth of about 2KHz. Keeping it tuned on frequency was a challenge. I think it was only about 10ft high and reportedly worked fairly well. I tried to model it with 4NEC2 but gave up for some forgotten reason. I think it was my inability to model the ground characteristics. Based on this example, I would say a loop would be better because the grounding isn't part of the puzzle. I don't have any equipment to date. I have a couple of projects ahead of this if I decide to build something. No test equipment? It's difficult to build anything without some basic RF equipment. I can provide a basic shopping list if you would like. My shop, which I've been told should be repurposed a museum. http://802.11junk.com/jeffl/pics/home/slides/lab.html You clearly have much more experience than I do. I wold barely know how to use a SWR meter and don't have an LRC meter... I can't remember what a grid dip meter is. :( Sigh. I have 4 assorted grid dip meters. I can mail you one if you would like to play. It's very handy for measuring the resonant frequencies of any LC circuit or antenna. It's not very accurate but will get you in the ballpark or at least tell you if you're too high or too low in frequency. Like this, but with more paint chipped off and the case missing. At least all the coils are there. http://www.universal-radio.com/used/W483lrg.jpg Note that it won't go down to 60 KHz although I tried making a coil that covered the range. Argh... I'm late (again). -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Flex dryer vent hose loop antenna
On Mon, 2 Nov 2015 09:13:38 -0600, amdx wrote:
Below some pressure level, it will probably flop over if mounted vertically. That's why I mumbled that I wasn't sure if it should be mounted vertically with a support pole, or horizontally on a flat sheet of plywood. Both will work, but I'm not sure which is better. Hang it upside down. Mikek But, all the photons will fall out of the loop that way. Actually, there's a problem. It doesn't work as well upside down. The magnetic loop has a rather directional field and takeoff angle and does NOT have a constant current around the loop: http://www.nonstopsystems.com/radio/vids-ant/antenna-Mag-Loop-Demo1.wmv https://www.youtube.com/watch?v=SUYI81dkEMA I suspect that an inverted loop will send most of the RF into the ground. I should probably test this. http://www.nonstopsystems.com/radio/img-ant/antenna-magloop-rad-angle.gif You might find this interesting on designing the 50 ohm matching network to the loop, where the impedance varies by where it's fed: http://www.g0cwt.co.uk/magloops/new_page_6.htm -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Flex dryer vent hose loop antenna
On Mon, 02 Nov 2015 16:39:09 -0800, Jeff Liebermann
wrote: You might find this interesting on designing the 50 ohm matching network to the loop, where the impedance varies by where it's fed: http://www.g0cwt.co.uk/magloops/new_page_6.htm Mo https://www.youtube.com/watch?v=NdofH6R22Dg Skip forward to 12:03 for an interesting comment: "Commercial loops are usually radiating towards the ground and a lot of the signal is warming the snails. I don't know how so many people could have got it so wrong for so long". -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Flex dryer vent hose loop antenna
On 11/1/2015 6:42 PM, Jeff Liebermann wrote:
On Sun, 1 Nov 2015 18:10:56 -0800, Paul Drahn wrote: Probable should clear the lint out first! Paul, KD7HB I know that hams are cheap, but I didn't realize that extended to stealing the neighbors dryer vent hose in order to build an antenna. I highly recommend purchasing a new hose, which comes pre-cleaned: http://www.acehardware.com/family/index.jsp?categoryId=2627981 Incidentally, there's no requirement that the entire loop be made from expandable hose. The loop could be in the form of a square loop, where the flat base and flat top are rigid aluminum structures, and the two vertical sections are flexible dryer vent hose. The weight of the flat top would help collapse the antenna although I suspect that springs or weights would work better. It's not like inflatable antennas and structures are a new thing: http://ltaprojects.com/towers/inflatable-antenna-video-towers/ham I am looking at the vent pipe from our reflow oven. We made it up from 4", 4' long vent pipe pieces, including "T" and "EL" pieces. That should work better than the expandable dryer vent hose. Paul, KD7HB |
Flex dryer vent hose loop antenna
On 11/3/2015 11:59 AM, Paul Drahn wrote:
On 11/1/2015 6:42 PM, Jeff Liebermann wrote: On Sun, 1 Nov 2015 18:10:56 -0800, Paul Drahn wrote: Probable should clear the lint out first! Paul, KD7HB I know that hams are cheap, but I didn't realize that extended to stealing the neighbors dryer vent hose in order to build an antenna. I highly recommend purchasing a new hose, which comes pre-cleaned: http://www.acehardware.com/family/index.jsp?categoryId=2627981 Incidentally, there's no requirement that the entire loop be made from expandable hose. The loop could be in the form of a square loop, where the flat base and flat top are rigid aluminum structures, and the two vertical sections are flexible dryer vent hose. The weight of the flat top would help collapse the antenna although I suspect that springs or weights would work better. It's not like inflatable antennas and structures are a new thing: http://ltaprojects.com/towers/inflatable-antenna-video-towers/ham I am looking at the vent pipe from our reflow oven. We made it up from 4", 4' long vent pipe pieces, including "T" and "EL" pieces. That should work better than the expandable dryer vent hose. I think the point is that the flex tubing antenna can be tuned by adjusting the loop rather than the capacitor. Interesting idea although it may not prove practical in the end. -- Rick |
Flex dryer vent hose loop antenna
On 11/2/2015 2:49 PM, Jeff Liebermann wrote:
On Mon, 2 Nov 2015 00:28:03 -0500, rickman wrote: You are assuming it will maintain something remotely like a circle. I don't see that happening. Have you worked with this stuff? Maybe what you have is more pliable than the stuff I used. I've worked with the vinyl dryer hose, but not the aluminum foil variety. With the vinyl, I was using the helical "Slinky" part of the hose as an HF antenna. As I mentioned, the steel spring got hot and melted the vinyl. Sure, there is nothing good about the slinky dryer tube you mention. Steel has horrible conductivity with its high resistance *and* very shallow skin effect. But even a copper wire of that small gauge would not be effective in a transmitter loop antenna. The actual inflatable antenna was a vertical monopole, so I never even tried to make a loop, and am not sure it will work. That's why I'm trying to recruit someone else to do the dirty work. I guess I could go shopping and do it myself, but I'm kinda busy this week (mostly recovering from the last 3 week of overwork). I suspect that there might be problems if I use too much air pressure. With the monopole, the hose would handle about 30 psi before producing a leak. It thinks that's more than enough to inflate the loop, but might not be enough to be self supporting, especially with a capacitor at the top. I bought a piece of dryer aluminum to use in another experiment (btw, a four foot column does not create much chimney effect over a 100 W light bulb) and they are stiff, too stiff to be worked by a balloon. Also they bend by expanding one side and not the other. Once it is bent it is a bit hard to straighten out. I am not trying to dampen your spirits. I suggest you buy a short piece of this stuff and just bend it by hand. Get a feel for it and see if you think this type of tube can be manipulated by simple machinery. I think it will cost less than $10 to try this. I don't mean fall apart necessarily, but just not be much like a loop antenna. I think the hard part will be shrinking it back down and keeping its shape. Proof of the pudding... The optimum shape is a circle with square, hexagon and octagon shapes being a tolerable facsimile. I guess the question is whether a random pretzel shape will work. Dunno, difficult to simulate, but easy to try. The prevailing wisdom is the area is what matters. Given what I saw in those videos which seem to show directionality in the plane of the loop, I'm not so sure. That and the results people seem to get with helical loop antennas make me think we don't really "get" loop antennas. There are helically wound antennas that have a similar issue. I have yet to see any equations to model them. I wonder if they work or not, in the sense of any better than a simple loop. One of the local club members build a 160 meter vertical rubber ducky (helical antenna) with ground radials and ended up with a usable bandwidth of about 2KHz. Keeping it tuned on frequency was a challenge. I think it was only about 10ft high and reportedly worked fairly well. I tried to model it with 4NEC2 but gave up for some forgotten reason. I think it was my inability to model the ground characteristics. Based on this example, I would say a loop would be better because the grounding isn't part of the puzzle. I don't have any equipment to date. I have a couple of projects ahead of this if I decide to build something. No test equipment? It's difficult to build anything without some basic RF equipment. I can provide a basic shopping list if you would like. My shop, which I've been told should be repurposed a museum. http://802.11junk.com/jeffl/pics/home/slides/lab.html You clearly have much more experience than I do. I wold barely know how to use a SWR meter and don't have an LRC meter... I can't remember what a grid dip meter is. :( Sigh. I have 4 assorted grid dip meters. I can mail you one if you would like to play. It's very handy for measuring the resonant frequencies of any LC circuit or antenna. It's not very accurate but will get you in the ballpark or at least tell you if you're too high or too low in frequency. Like this, but with more paint chipped off and the case missing. At least all the coils are there. http://www.universal-radio.com/used/W483lrg.jpg Note that it won't go down to 60 KHz although I tried making a coil that covered the range. Thanks for the offer. Let me get my other stuff out of the way and maybe I'll take you up on this. -- Rick |
Flex dryer vent hose loop antenna
On 11/2/2015 6:39 PM, Jeff Liebermann wrote:
On Mon, 2 Nov 2015 09:13:38 -0600, amdx wrote: Below some pressure level, it will probably flop over if mounted vertically. That's why I mumbled that I wasn't sure if it should be mounted vertically with a support pole, or horizontally on a flat sheet of plywood. Both will work, but I'm not sure which is better. Hang it upside down. Mikek But, all the photons will fall out of the loop that way. Actually, there's a problem. It doesn't work as well upside down. The magnetic loop has a rather directional field and takeoff angle and does NOT have a constant current around the loop: http://www.nonstopsystems.com/radio/vids-ant/antenna-Mag-Loop-Demo1.wmv https://www.youtube.com/watch?v=SUYI81dkEMA I suspect that an inverted loop will send most of the RF into the ground. I should probably test this. http://www.nonstopsystems.com/radio/img-ant/antenna-magloop-rad-angle.gif You might find this interesting on designing the 50 ohm matching network to the loop, where the impedance varies by where it's fed: http://www.g0cwt.co.uk/magloops/new_page_6.htm Sorry Jeff, When my post didn't show up, I noticed I sent it to you. Here it is for the rest. Just to add to the confusion, Helically Loaded You might glean info from here, or at the least admire all the work put into the projects. http://theradioboard.com/rb/viewtopic.php?f=10&t=4399 Copper doughnut with lots of solder connections http://www.aa5tb.com/jl1boh_03.jpg http://www.hlmagneticloopantennas.com/ Hmm, I read a few comments, maybe not the way to go. Mikek |
Flex dryer vent hose loop antenna
On 11/2/2015 7:39 PM, Jeff Liebermann wrote:
On Mon, 2 Nov 2015 09:13:38 -0600, amdx wrote: Below some pressure level, it will probably flop over if mounted vertically. That's why I mumbled that I wasn't sure if it should be mounted vertically with a support pole, or horizontally on a flat sheet of plywood. Both will work, but I'm not sure which is better. Hang it upside down. Mikek But, all the photons will fall out of the loop that way. Actually, there's a problem. It doesn't work as well upside down. The magnetic loop has a rather directional field and takeoff angle and does NOT have a constant current around the loop: http://www.nonstopsystems.com/radio/vids-ant/antenna-Mag-Loop-Demo1.wmv I don't get this video. I can't really hear what he is saying so when he says at the end, "this is not what you would expect" I don't get it. https://www.youtube.com/watch?v=SUYI81dkEMA This video is about the voltage and current around a loop, but he says it is a 1/10 wave loop, but I can't tell that. He has another video showing the directionality of a 1/4 wave delta antenna. I'm wondering if this is also a 1/4 wave antenna. I suspect that an inverted loop will send most of the RF into the ground. I should probably test this. http://www.nonstopsystems.com/radio/img-ant/antenna-magloop-rad-angle.gif Which type of loop antenna are you talking about, 1/4 wave, or 1/10 wave (small, magnetic)? I can't tell anything about this antenna and it seems to contradict the other video. You might find this interesting on designing the 50 ohm matching network to the loop, where the impedance varies by where it's fed: http://www.g0cwt.co.uk/magloops/new_page_6.htm -- Rick |
Flex dryer vent hose loop antenna
In message , rickman
writes https://www.youtube.com/watch?v=SUYI81dkEMA When he's measuring towards the capacitor, won't the presence of his hand be causing the loop to de-tune - hence less current? -- Ian |
Flex dryer vent hose loop antenna
On 11/4/2015 6:49 AM, Ian Jackson wrote:
In message , rickman writes https://www.youtube.com/watch?v=SUYI81dkEMA When he's measuring towards the capacitor, won't the presence of his hand be causing the loop to de-tune - hence less current? Yes. But, is it measurable? |
Flex dryer vent hose loop antenna
In message , John S
writes On 11/4/2015 6:49 AM, Ian Jackson wrote: In message , rickman writes https://www.youtube.com/watch?v=SUYI81dkEMA When he's measuring towards the capacitor, won't the presence of his hand be causing the loop to de-tune - hence less current? Yes. But, is it measurable? Being a high-Q circuit, I would think that a small amount of additional C would cause considerable de-tuning. -- Ian |
Flex dryer vent hose loop antenna
On 11/4/2015 8:52 AM, Ian Jackson wrote:
In message , John S writes On 11/4/2015 6:49 AM, Ian Jackson wrote: In message , rickman writes https://www.youtube.com/watch?v=SUYI81dkEMA When he's measuring towards the capacitor, won't the presence of his hand be causing the loop to de-tune - hence less current? Yes. But, is it measurable? Being a high-Q circuit, I would think that a small amount of additional C would cause considerable de-tuning. Wouldn't that also give less voltage? That didn't seem to go down any. -- Rick |
Flex dryer vent hose loop antenna
In message , rickman
writes On 11/4/2015 8:52 AM, Ian Jackson wrote: In message , John S writes On 11/4/2015 6:49 AM, Ian Jackson wrote: In message , rickman writes https://www.youtube.com/watch?v=SUYI81dkEMA When he's measuring towards the capacitor, won't the presence of his hand be causing the loop to de-tune - hence less current? Yes. But, is it measurable? Being a high-Q circuit, I would think that a small amount of additional C would cause considerable de-tuning. Wouldn't that also give less voltage? That didn't seem to go down any. While I'm not really looking for flaws in the experiment, I've had another quick look, and I don't see anywhere where the voltage is being measured. I would have expected at least the input drive (voltage, current or power) to be monitored just to check that it didn't fluctuate (too much). I note that the analyser VSWR meter reading increases as the current probe is moved towards the capacitor - but what is it measuring? Is it measuring the SWR where the probe is - and if so, how? Is there any reference ground connection (which I'm pretty sure an SWR meter needs)? -- Ian |
Flex dryer vent hose loop antenna
On Wed, 4 Nov 2015 00:17:11 -0500, rickman wrote:
On 11/2/2015 7:39 PM, Jeff Liebermann wrote: On Mon, 2 Nov 2015 09:13:38 -0600, amdx wrote: Below some pressure level, it will probably flop over if mounted vertically. That's why I mumbled that I wasn't sure if it should be mounted vertically with a support pole, or horizontally on a flat sheet of plywood. Both will work, but I'm not sure which is better. Hang it upside down. Mikek But, all the photons will fall out of the loop that way. Actually, there's a problem. It doesn't work as well upside down. The magnetic loop has a rather directional field and takeoff angle and does NOT have a constant current around the loop: http://www.nonstopsystems.com/radio/vids-ant/antenna-Mag-Loop-Demo1.wmv I don't get this video. I can't really hear what he is saying so when he says at the end, "this is not what you would expect" I don't get it. I had the same problem. I would guess(tm) that what he's mumbling is that one would expect the current to be constant around all parts of the loop, yet it displays obvious maxima and minima. https://www.youtube.com/watch?v=SUYI81dkEMA This video is about the voltage and current around a loop, but he says it is a 1/10 wave loop, but I can't tell that. He has another video showing the directionality of a 1/4 wave delta antenna. I'm wondering if this is also a 1/4 wave antenna. At 6:30 in the above video, he proclaims that it's a 1/4 wave loop. At 6:42, the MFJ-259B shows 29.555 MHz on the display. I couldn't find where he said it was a 1/10 wave loop. 1/10 wave is the defacto definition of a "small" loop. I suspect that an inverted loop will send most of the RF into the ground. I should probably test this. http://www.nonstopsystems.com/radio/img-ant/antenna-magloop-rad-angle.gif Which type of loop antenna are you talking about, 1/4 wave, or 1/10 wave (small, magnetic)? I can't tell anything about this antenna and it seems to contradict the other video. I'm not saying anything about the drawing except that it shows that the loop might be somewhat directional, which might be a problem. Where's the contradiction? http://www.nonstopsystems.com/radio/frank_radio_antenna_magloop.htm Gone...(again). -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Flex dryer vent hose loop antenna
On 11/5/2015 8:40 PM, Jeff Liebermann wrote:
On Wed, 4 Nov 2015 00:17:11 -0500, rickman wrote: On 11/2/2015 7:39 PM, Jeff Liebermann wrote: On Mon, 2 Nov 2015 09:13:38 -0600, amdx wrote: Below some pressure level, it will probably flop over if mounted vertically. That's why I mumbled that I wasn't sure if it should be mounted vertically with a support pole, or horizontally on a flat sheet of plywood. Both will work, but I'm not sure which is better. Hang it upside down. Mikek But, all the photons will fall out of the loop that way. Actually, there's a problem. It doesn't work as well upside down. The magnetic loop has a rather directional field and takeoff angle and does NOT have a constant current around the loop: http://www.nonstopsystems.com/radio/vids-ant/antenna-Mag-Loop-Demo1.wmv I don't get this video. I can't really hear what he is saying so when he says at the end, "this is not what you would expect" I don't get it. I had the same problem. I would guess(tm) that what he's mumbling is that one would expect the current to be constant around all parts of the loop, yet it displays obvious maxima and minima. He isn't saying anything about the current since he isn't measuring current. I think the "isn't what you would expect" maybe be about polarization. https://www.youtube.com/watch?v=SUYI81dkEMA This video is about the voltage and current around a loop, but he says it is a 1/10 wave loop, but I can't tell that. He has another video showing the directionality of a 1/4 wave delta antenna. I'm wondering if this is also a 1/4 wave antenna. At 6:30 in the above video, he proclaims that it's a 1/4 wave loop. At 6:42, the MFJ-259B shows 29.555 MHz on the display. I couldn't find where he said it was a 1/10 wave loop. 1/10 wave is the defacto definition of a "small" loop. The start says the purpose is to settle the dispute about current distribution in a 1/10 wave loop. Doesn't make sense he would be doing that with 1/4 wave antenna. At 2:45 it says this loop is 1/10 wave on 10.5 meters 28.26 MHz. The comment at 6:30 is about the impedance in a 1/4 wave loop, but he isn't saying this *is* a 1/4 wave loop. I believe the 1/4 wave loop is the one he uses in the next clip, but this is a bit confusing. I suspect that an inverted loop will send most of the RF into the ground. I should probably test this. http://www.nonstopsystems.com/radio/img-ant/antenna-magloop-rad-angle.gif Which type of loop antenna are you talking about, 1/4 wave, or 1/10 wave (small, magnetic)? I can't tell anything about this antenna and it seems to contradict the other video. I'm not saying anything about the drawing except that it shows that the loop might be somewhat directional, which might be a problem. Where's the contradiction? http://www.nonstopsystems.com/radio/frank_radio_antenna_magloop.htm If you take this drawing literally it shows a maximum at 30-45 degrees from horizontal while all the others show a max at the capacitor. I don't know that this diagram is intended to show field strength, rather just that it may vary and the angle is what you should measure. There will be interaction with the ground unless the antenna is spaced well above it. Once that is done the remaining radiation pattern will be far field which is very different from near field. So I think the "radiating into the ground" thing may be overstated. Place the loop horizontal and it will radiate 360° with a null at the ground. No rotator needed. -- Rick |
Flex dryer vent hose loop antenna
You might want to grab and read this:
"The Underestimated Magnetic Loop HF Antenna V1.2" by Leigh Turner VK5KLT http://802.11junk.com/jeffl/antennas/magnetic-loop/_The%20Underestimated%20Magnetic%20Loop%20HF%20Ant enna_V1.%202.pdf You may have read a previous version. The author updated it recently and posted it to the Yahoo Magloop forum in the files section: https://groups.yahoo.com/neo/groups/MagLoop/info I couldn't find it posted anywhere else on the interknot, so I took the liberty of posting it to my web pile without permission. I just skimmed it quickly but offhand, it looks like a very good explanation of how a magnetic loop antenna works, without going excessively into technobabble and equations. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Flex dryer vent hose loop antenna
You were asking about using a better dielectric than air. I found
this article: http://www.qrpbuilder.com/downloads/loop%20antenna%20110310.pdf which includes construction details for a piston capacitor arrangement using various dielectrics. On Pg 8 is a chart of various plastics, with dielectric constant, dielectric strength, and dissipation factor. For cheap, the author recommends UHMW (polypropylene), which is one tenth the cost of PTFE (Teflon). -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Flex dryer vent hose loop antenna
On 11/8/2015 3:44 PM, Jeff Liebermann wrote:
You might want to grab and read this: "The Underestimated Magnetic Loop HF Antenna V1.2" by Leigh Turner VK5KLT http://802.11junk.com/jeffl/antennas/magnetic-loop/_The%20Underestimated%20Magnetic%20Loop%20HF%20Ant enna_V1.%202.pdf You may have read a previous version. The author updated it recently and posted it to the Yahoo Magloop forum in the files section: https://groups.yahoo.com/neo/groups/MagLoop/info I couldn't find it posted anywhere else on the interknot, so I took the liberty of posting it to my web pile without permission. I just skimmed it quickly but offhand, it looks like a very good explanation of how a magnetic loop antenna works, without going excessively into technobabble and equations. Thanks. I signed up for that group, but only by email. To join Yahoo these days you have to give a mobile number and I'm not willing to do that. I've been getting the emails talking about this file (mostly people saying they can't download it) but no one has made it available outside of that group... until now. -- Rick |
Flex dryer vent hose loop antenna
On 11/8/2015 5:14 PM, Jeff Liebermann wrote:
You were asking about using a better dielectric than air. I found this article: http://www.qrpbuilder.com/downloads/loop%20antenna%20110310.pdf which includes construction details for a piston capacitor arrangement using various dielectrics. On Pg 8 is a chart of various plastics, with dielectric constant, dielectric strength, and dissipation factor. For cheap, the author recommends UHMW (polypropylene), which is one tenth the cost of PTFE (Teflon). Yeah, but he doesn't address the issue of temperature dependance of Er. I don't even see it in his table. The text says he used PEX (cross linked polyethylene) for the capacitor, but I can't find much info on the electrical characteristics. The one that is hardest to find is the temperature dependence of Er. I don't see PEX in his table at all. Very odd. The info on PEX that I can find on the web indicates it may have problems with use outdoors, but maybe this antenna isn't intended to be used outdoors. -- Rick |
Flex dryer vent hose loop antenna
On Sun, 8 Nov 2015 18:02:19 -0500, rickman wrote:
On 11/8/2015 3:44 PM, Jeff Liebermann wrote: You might want to grab and read this: "The Underestimated Magnetic Loop HF Antenna V1.2" by Leigh Turner VK5KLT http://802.11junk.com/jeffl/antennas/magnetic-loop/_The%20Underestimated%20Magnetic%20Loop%20HF%20Ant enna_V1.%202.pdf You may have read a previous version. The author updated it recently and posted it to the Yahoo Magloop forum in the files section: https://groups.yahoo.com/neo/groups/MagLoop/info I couldn't find it posted anywhere else on the interknot, so I took the liberty of posting it to my web pile without permission. I just skimmed it quickly but offhand, it looks like a very good explanation of how a magnetic loop antenna works, without going excessively into technobabble and equations. Thanks. I signed up for that group, but only by email. To join Yahoo these days you have to give a mobile number and I'm not willing to do that. I signed up long ago and have been able to bypass that requirement. Eventually, I'm sure Yahoo, Google, Microsoft, and others will make it mandatory. What ****es me off is that the various vendors involved claim that it's a security feature, when it's really a bad excuse for cell phone calling and SMS spamming. Here's a possible solution: http://www.burnerapp.com Essentially, it's a throw away phone number service. I just found the URL, so I haven't had time to try it or decode the cryptic description on the web page. I've been getting the emails talking about this file (mostly people saying they can't download it) but no one has made it available outside of that group... until now. I'm not sure of the legality or if it's ethically correct. I would get a bit irritated if someone posted a copy of my work, instead of a link to the original. However, as soon as I find it publicly posted elsewhere by the author, I'll take mine down. Some interesting comments on the magloop article: http://www.brisdance.com/vk4amz/VK5KLT.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 |
Flex dryer vent hose loop antenna
On Sun, 8 Nov 2015 19:12:38 -0500, rickman wrote:
On 11/8/2015 5:14 PM, Jeff Liebermann wrote: You were asking about using a better dielectric than air. I found this article: http://www.qrpbuilder.com/downloads/loop%20antenna%20110310.pdf which includes construction details for a piston capacitor arrangement using various dielectrics. On Pg 8 is a chart of various plastics, with dielectric constant, dielectric strength, and dissipation factor. For cheap, the author recommends UHMW (polypropylene), which is one tenth the cost of PTFE (Teflon). Yeah, but he doesn't address the issue of temperature dependance of Er. I don't even see it in his table. True, but I don't think tempco is critical or required. A practical loop antenna, with sufficiently high Q and narrow bandwidth, will require an automatic tuning arrangement. I managed to built one where the operating bandwidth on 80 meters was less than the occupied bandwidth of a SSB signal. With that critical a frequency tuning, manual or fixed tuning isn't going to work. Once you have an automatic tuner, compensating for thermal drift is easy. Incidentally, one of the problems I'm fighting is that the loop tuning is different between TX and RX because the impedance of the receiver and transmitter are slightly different and enought to detune the loop. That's another problem that an automagic tuner should fix. The text says he used PEX (cross linked polyethylene) for the capacitor, but I can't find much info on the electrical characteristics. The one that is hardest to find is the temperature dependence of Er. I don't see PEX in his table at all. Very odd. I use PEX plumbing pipe for coil forms, spacers, standoffs, and spreaders. Works well, but seems a bit expensive. This might help: http://www.smeter.net/daily-facts/11/fact21.php Er = 2.3 and 60-90 kV/mm Here's something on building a trombone capacitor: http://www.eham.net/ehamforum/smf/index.php?topic=70784.0;wap2 Er = 2.25 This looks a bit more authoritative: http://www.comfortprosystems.com/sites/comfortprosystems.com/files/cps_aquaheat_pex_pressdrop_tec-04.pdf Er = 2.3 The info on PEX that I can find on the web indicates it may have problems with use outdoors, but maybe this antenna isn't intended to be used outdoors. Just about everything plastic has problems with UV embrittlement. The best fix I've found is Krylon clear acrylic spray. http://yarchive.net/electr/plastic_uv_resistances.html Hint: Search Yarchive and Google for posting by Dr Barry L. Ornitz WA4VZQ. Lots of really good info on materials, chemicals, processes, and antennas. Incidentally, if you dive into the Yahoo magloop files sections, there are some photos of the insides of the MFJ-1786 mag loop. http://www.mfjenterprises.com/Product.php?productid=MFJ-1786 https://groups.yahoo.com/neo/groups/MagLoop/files/MFJ-1786/MFJ-1786%20coupling%20loop/ Two things worthy of notice. All the aluminum parts are brazed or welded together and the matching(?) coil inside the box appears to be silver plated. If MFJ's reputation for cheap construction is to be believed, they would not silver plate anything if a cheaper alternative would work. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Flex dryer vent hose loop antenna
On 11/8/2015 10:23 PM, Jeff Liebermann wrote:
On Sun, 8 Nov 2015 18:02:19 -0500, rickman wrote: On 11/8/2015 3:44 PM, Jeff Liebermann wrote: You might want to grab and read this: "The Underestimated Magnetic Loop HF Antenna V1.2" by Leigh Turner VK5KLT http://802.11junk.com/jeffl/antennas/magnetic-loop/_The%20Underestimated%20Magnetic%20Loop%20HF%20Ant enna_V1.%202.pdf You may have read a previous version. The author updated it recently and posted it to the Yahoo Magloop forum in the files section: https://groups.yahoo.com/neo/groups/MagLoop/info I couldn't find it posted anywhere else on the interknot, so I took the liberty of posting it to my web pile without permission. I just skimmed it quickly but offhand, it looks like a very good explanation of how a magnetic loop antenna works, without going excessively into technobabble and equations. Thanks. I signed up for that group, but only by email. To join Yahoo these days you have to give a mobile number and I'm not willing to do that. I signed up long ago and have been able to bypass that requirement. Eventually, I'm sure Yahoo, Google, Microsoft, and others will make it mandatory. What ****es me off is that the various vendors involved claim that it's a security feature, when it's really a bad excuse for cell phone calling and SMS spamming. Here's a possible solution: http://www.burnerapp.com Essentially, it's a throw away phone number service. I just found the URL, so I haven't had time to try it or decode the cryptic description on the web page. I found a discussion of this problem which listed a website for getting phone numbers, but it seems Yahoo won't work with this. I'm not sure what Burner app is about, but it looks like they give you a burner phone number which will relay texts and calls. But that just means you have to share your phone number with *them*. I've been getting the emails talking about this file (mostly people saying they can't download it) but no one has made it available outside of that group... until now. I'm not sure of the legality or if it's ethically correct. I would get a bit irritated if someone posted a copy of my work, instead of a link to the original. However, as soon as I find it publicly posted elsewhere by the author, I'll take mine down. Technically it is copyrighted. I'm not sure if that restricts the sharing of the file or not, I think so if he hadn't shared it openly elsewhere. Since it is there for anyone to download, I'm not sure there can be a problem unless he says you need to take it down. Some interesting comments on the magloop article: http://www.brisdance.com/vk4amz/VK5KLT.html -- Rick |
Flex dryer vent hose loop antenna
On 11/8/2015 10:46 PM, Jeff Liebermann wrote:
On Sun, 8 Nov 2015 19:12:38 -0500, rickman wrote: On 11/8/2015 5:14 PM, Jeff Liebermann wrote: You were asking about using a better dielectric than air. I found this article: http://www.qrpbuilder.com/downloads/loop%20antenna%20110310.pdf which includes construction details for a piston capacitor arrangement using various dielectrics. On Pg 8 is a chart of various plastics, with dielectric constant, dielectric strength, and dissipation factor. For cheap, the author recommends UHMW (polypropylene), which is one tenth the cost of PTFE (Teflon). Yeah, but he doesn't address the issue of temperature dependance of Er. I don't even see it in his table. True, but I don't think tempco is critical or required. A practical loop antenna, with sufficiently high Q and narrow bandwidth, will require an automatic tuning arrangement. I managed to built one where the operating bandwidth on 80 meters was less than the occupied bandwidth of a SSB signal. With that critical a frequency tuning, manual or fixed tuning isn't going to work. Once you have an automatic tuner, compensating for thermal drift is easy. I'm not familiar with automatic tuners that can tune the antenna while in use. One of the issues someone pointed out was that the dielectric can heat up from the energy absorbed during transmission. Is an antenna tuner real time in this case? I crunched some numbers and found 100's of PPM change in tuned frequency due to ambient temperature change over the course of a year for an antenna with an air or vacuum tuning capacitor. I can find ceramic dielectrics that would be lower than this and even in the opposite direction to offset the natural drift. But I can't find this info for PEX. Incidentally, one of the problems I'm fighting is that the loop tuning is different between TX and RX because the impedance of the receiver and transmitter are slightly different and enought to detune the loop. That's another problem that an automagic tuner should fix. The text says he used PEX (cross linked polyethylene) for the capacitor, but I can't find much info on the electrical characteristics. The one that is hardest to find is the temperature dependence of Er. I don't see PEX in his table at all. Very odd. I use PEX plumbing pipe for coil forms, spacers, standoffs, and spreaders. Works well, but seems a bit expensive. This might help: http://www.smeter.net/daily-facts/11/fact21.php Er = 2.3 and 60-90 kV/mm I'm not terribly concerned with the actual value of Er and even the dielectric strength. What is important to me is the temperature coefficient of Er. Here's something on building a trombone capacitor: http://www.eham.net/ehamforum/smf/index.php?topic=70784.0;wap2 Er = 2.25 Interesting, but nearly every discussion I find on loop antennas has a lot of fluff content. Here is some from this discussion, "By the way PEX is cross linked polyethylene and is superior to using sheet Teflon in this instance." Unless the reason is stated for considering PEX superior to Teflon, I haven't learned anything. I'm certainly not going to take an anonymous person's word for it. This looks a bit more authoritative: http://www.comfortprosystems.com/sites/comfortprosystems.com/files/cps_aquaheat_pex_pressdrop_tec-04.pdf Er = 2.3 The info on PEX that I can find on the web indicates it may have problems with use outdoors, but maybe this antenna isn't intended to be used outdoors. Just about everything plastic has problems with UV embrittlement. The best fix I've found is Krylon clear acrylic spray. http://yarchive.net/electr/plastic_uv_resistances.html Hint: Search Yarchive and Google for posting by Dr Barry L. Ornitz WA4VZQ. Lots of really good info on materials, chemicals, processes, and antennas. I'm talking about water impacts. Humidity and rain soak into materials. Some by absorption, others by infiltration into micro-cracks. I saw some materials that talked about water trees in PEX. This is not a universal problem in all plastics. Incidentally, if you dive into the Yahoo magloop files sections, there are some photos of the insides of the MFJ-1786 mag loop. http://www.mfjenterprises.com/Product.php?productid=MFJ-1786 https://groups.yahoo.com/neo/groups/MagLoop/files/MFJ-1786/MFJ-1786%20coupling%20loop/ Two things worthy of notice. All the aluminum parts are brazed or welded together and the matching(?) coil inside the box appears to be silver plated. If MFJ's reputation for cheap construction is to be believed, they would not silver plate anything if a cheaper alternative would work. I can't get to the MagLoop files. I don't know anything about MFJ's reputation. There are simple facts about silver that make it only very slightly better than copper for RF circuits. I know that you can increase the size of the conductor by less than 5% as an alternative to using silver plating if the electrical characteristics are the goal. Can you explain why silver is required? The numbers don't show it. -- Rick |
Flex dryer vent hose loop antenna
On 11/9/2015 12:59 AM, rickman wrote:
On 11/8/2015 10:46 PM, Jeff Liebermann wrote: On Sun, 8 Nov 2015 19:12:38 -0500, rickman wrote: On 11/8/2015 5:14 PM, Jeff Liebermann wrote: You were asking about using a better dielectric than air. I found this article: http://www.qrpbuilder.com/downloads/loop%20antenna%20110310.pdf which includes construction details for a piston capacitor arrangement using various dielectrics. On Pg 8 is a chart of various plastics, with dielectric constant, dielectric strength, and dissipation factor. For cheap, the author recommends UHMW (polypropylene), which is one tenth the cost of PTFE (Teflon). Yeah, but he doesn't address the issue of temperature dependance of Er. I don't even see it in his table. True, but I don't think tempco is critical or required. A practical loop antenna, with sufficiently high Q and narrow bandwidth, will require an automatic tuning arrangement. I managed to built one where the operating bandwidth on 80 meters was less than the occupied bandwidth of a SSB signal. With that critical a frequency tuning, manual or fixed tuning isn't going to work. Once you have an automatic tuner, compensating for thermal drift is easy. I'm not familiar with automatic tuners that can tune the antenna while in use. One of the issues someone pointed out was that the dielectric can heat up from the energy absorbed during transmission. Is an antenna tuner real time in this case? I crunched some numbers and found 100's of PPM change in tuned frequency due to ambient temperature change over the course of a year for an antenna with an air or vacuum tuning capacitor. I can find ceramic dielectrics that would be lower than this and even in the opposite direction to offset the natural drift. But I can't find this info for PEX. Incidentally, one of the problems I'm fighting is that the loop tuning is different between TX and RX because the impedance of the receiver and transmitter are slightly different and enought to detune the loop. That's another problem that an automagic tuner should fix. The text says he used PEX (cross linked polyethylene) for the capacitor, but I can't find much info on the electrical characteristics. The one that is hardest to find is the temperature dependence of Er. I don't see PEX in his table at all. Very odd. I use PEX plumbing pipe for coil forms, spacers, standoffs, and spreaders. Works well, but seems a bit expensive. This might help: http://www.smeter.net/daily-facts/11/fact21.php Er = 2.3 and 60-90 kV/mm I'm not terribly concerned with the actual value of Er and even the dielectric strength. What is important to me is the temperature coefficient of Er. Here's something on building a trombone capacitor: http://www.eham.net/ehamforum/smf/index.php?topic=70784.0;wap2 Er = 2.25 Interesting, but nearly every discussion I find on loop antennas has a lot of fluff content. Here is some from this discussion, "By the way PEX is cross linked polyethylene and is superior to using sheet Teflon in this instance." Unless the reason is stated for considering PEX superior to Teflon, I haven't learned anything. I'm certainly not going to take an anonymous person's word for it. This looks a bit more authoritative: http://www.comfortprosystems.com/sites/comfortprosystems.com/files/cps_aquaheat_pex_pressdrop_tec-04.pdf Er = 2.3 The info on PEX that I can find on the web indicates it may have problems with use outdoors, but maybe this antenna isn't intended to be used outdoors. Just about everything plastic has problems with UV embrittlement. The best fix I've found is Krylon clear acrylic spray. http://yarchive.net/electr/plastic_uv_resistances.html Hint: Search Yarchive and Google for posting by Dr Barry L. Ornitz WA4VZQ. Lots of really good info on materials, chemicals, processes, and antennas. I'm talking about water impacts. Humidity and rain soak into materials. Some by absorption, others by infiltration into micro-cracks. I saw some materials that talked about water trees in PEX. This is not a universal problem in all plastics. Incidentally, if you dive into the Yahoo magloop files sections, there are some photos of the insides of the MFJ-1786 mag loop. http://www.mfjenterprises.com/Product.php?productid=MFJ-1786 https://groups.yahoo.com/neo/groups/MagLoop/files/MFJ-1786/MFJ-1786%20coupling%20loop/ Two things worthy of notice. All the aluminum parts are brazed or welded together and the matching(?) coil inside the box appears to be silver plated. If MFJ's reputation for cheap construction is to be believed, they would not silver plate anything if a cheaper alternative would work. I can't get to the MagLoop files. I don't know anything about MFJ's reputation. There are simple facts about silver that make it only very slightly better than copper for RF circuits. I know that you can increase the size of the conductor by less than 5% as an alternative to using silver plating if the electrical characteristics are the goal. Can you explain why silver is required? The numbers don't show it. The silver is simply optimization. If you can make your coil wire 5% bigger, you should have already done that. Then if you want to optimized 1 + 0.05, silver plate it. Mikek |
Flex dryer vent hose loop antenna
On Mon, 9 Nov 2015 01:59:06 -0500, rickman wrote:
I'm not familiar with automatic tuners that can tune the antenna while in use. The basic benefits of having a remote controller a 1. RF safety and you're not part of the antenna system. 2. A controller is easier to umm.... control. 3. Automatic remote tuning reacts to changes when you're not looking at the VSWR meter. 4. White knuckle tuning is difficult. Let the servos do the work. 5. It's the only effective way to tune a loop mounted on a tall pole, tower, or roof. One of the issues someone pointed out was that the dielectric can heat up from the energy absorbed during transmission. Is an antenna tuner real time in this case? Yes in receive. Probably not in transmit. In receive, you can tune all you want and nothing will explode or catch fire. In transmit, you can easily tune through full power and arc over the tuning capacitor. Auto tuning also goes through the optimum VSWR point several times during the tuning cycle. You transmitter may not like operating into a high VSWR load during tuning. The solution is to tune at low tranmit power levels. Once the lowest VSWR point is found, you can increase your power. However, that usually prevents you from "tweaking" the tuning at full power, which is what you need to compensate for thermal drift. It's also difficult to tune with any modulation other than CW. I think (not sure) that some controllers have this ability, probably with warnings and disclaimers. I wouldn't trust it. Basically, to make it work requires a VWSR sensor and calculator that works when there's modulation, and a tuning capacitor that can tolerate moving while passing high currents. Arcing and welding the bearing and bushings might be a problem. I crunched some numbers and found 100's of PPM change in tuned frequency due to ambient temperature change over the course of a year for an antenna with an air or vacuum tuning capacitor. I can find ceramic dielectrics that would be lower than this and even in the opposite direction to offset the natural drift. But I can't find this info for PEX. I looked and also didn't find anything. The problem is that you don't find tempco data for plumbing parts that were not intended to be used for RF components. I'm not terribly concerned with the actual value of Er and even the dielectric strength. What is important to me is the temperature coefficient of Er. Again, I think you might be trying to solve a problem that has already been solved by automatic tuning (which you need anyway). Unless you plan to transmit endlessly, you can simply press the tune button on the controller a few times per hour, and be done with trying to temperature stabilize the loop. Interesting, but nearly every discussion I find on loop antennas has a lot of fluff content. RF is magic. It's difficult to explain some things. Here is some from this discussion, "By the way PEX is cross linked polyethylene and is superior to using sheet Teflon in this instance." Unless the reason is stated for considering PEX superior to Teflon, I haven't learned anything. I'm certainly not going to take an anonymous person's word for it. The world is divided between practitioners of theory and of practice. Those who favor can explain anything, but can't build anything that actually works. Those that favor practice tend to build strange contraptions that they can't explain. That's also probably the main source of what you call "fluff". Sometimes, I run into a theoretician that knows which end of the soldering iron to grab, but they are rare. For the record, I'm a practitioner of practice, trial-n-error, and magic. I have difficulty explaining some things, and I think you've seen my horrid math. I'm talking about water impacts. Humidity and rain soak into materials. Some by absorption, others by infiltration into micro-cracks. I saw some materials that talked about water trees in PEX. This is not a universal problem in all plastics. I come from the marine radio part of the business. Water and corrosion are key parts of the marine radio problem. Many materials are hygroscopic and will absorb moisture. Apply some RF and the water boils out, as in a microwave oven. Do it too fast, and the material can crack. Of course, the tuning will change. Lots of info on plastics selection for minimal water absorption found online. For example: http://www.curbellplastics.com/technical-resources/pdf/water-absorption-plastics.pdf Polypropylene would be my first choice for minimal water absorption. However, it requires UV protection, which for RF applications means some kind of conformal coating. (Adding carbon black is a bad idea as it causes heating problems). There are simple facts about silver that make it only very slightly better than copper for RF circuits. I know that you can increase the size of the conductor by less than 5% as an alternative to using silver plating if the electrical characteristics are the goal. Can you explain why silver is required? The numbers don't show it. Antennas are mounted outdoors where exposed copper is an invitation to corrosion. If one must protect the copper with something, why not use silver, which also improves its RF characteristics? My magloop nightmare come true: http://www.mixw.co.uk/MagLoop/magloopF.htm -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Flex dryer vent hose loop antenna
On 11/9/2015 12:08 PM, amdx wrote:
On 11/9/2015 12:59 AM, rickman wrote: On 11/8/2015 10:46 PM, Jeff Liebermann wrote: On Sun, 8 Nov 2015 19:12:38 -0500, rickman wrote: On 11/8/2015 5:14 PM, Jeff Liebermann wrote: You were asking about using a better dielectric than air. I found this article: http://www.qrpbuilder.com/downloads/loop%20antenna%20110310.pdf which includes construction details for a piston capacitor arrangement using various dielectrics. On Pg 8 is a chart of various plastics, with dielectric constant, dielectric strength, and dissipation factor. For cheap, the author recommends UHMW (polypropylene), which is one tenth the cost of PTFE (Teflon). Yeah, but he doesn't address the issue of temperature dependance of Er. I don't even see it in his table. True, but I don't think tempco is critical or required. A practical loop antenna, with sufficiently high Q and narrow bandwidth, will require an automatic tuning arrangement. I managed to built one where the operating bandwidth on 80 meters was less than the occupied bandwidth of a SSB signal. With that critical a frequency tuning, manual or fixed tuning isn't going to work. Once you have an automatic tuner, compensating for thermal drift is easy. I'm not familiar with automatic tuners that can tune the antenna while in use. One of the issues someone pointed out was that the dielectric can heat up from the energy absorbed during transmission. Is an antenna tuner real time in this case? I crunched some numbers and found 100's of PPM change in tuned frequency due to ambient temperature change over the course of a year for an antenna with an air or vacuum tuning capacitor. I can find ceramic dielectrics that would be lower than this and even in the opposite direction to offset the natural drift. But I can't find this info for PEX. Incidentally, one of the problems I'm fighting is that the loop tuning is different between TX and RX because the impedance of the receiver and transmitter are slightly different and enought to detune the loop. That's another problem that an automagic tuner should fix. The text says he used PEX (cross linked polyethylene) for the capacitor, but I can't find much info on the electrical characteristics. The one that is hardest to find is the temperature dependence of Er. I don't see PEX in his table at all. Very odd. I use PEX plumbing pipe for coil forms, spacers, standoffs, and spreaders. Works well, but seems a bit expensive. This might help: http://www.smeter.net/daily-facts/11/fact21.php Er = 2.3 and 60-90 kV/mm I'm not terribly concerned with the actual value of Er and even the dielectric strength. What is important to me is the temperature coefficient of Er. Here's something on building a trombone capacitor: http://www.eham.net/ehamforum/smf/index.php?topic=70784.0;wap2 Er = 2.25 Interesting, but nearly every discussion I find on loop antennas has a lot of fluff content. Here is some from this discussion, "By the way PEX is cross linked polyethylene and is superior to using sheet Teflon in this instance." Unless the reason is stated for considering PEX superior to Teflon, I haven't learned anything. I'm certainly not going to take an anonymous person's word for it. This looks a bit more authoritative: http://www.comfortprosystems.com/sites/comfortprosystems.com/files/cps_aquaheat_pex_pressdrop_tec-04.pdf Er = 2.3 The info on PEX that I can find on the web indicates it may have problems with use outdoors, but maybe this antenna isn't intended to be used outdoors. Just about everything plastic has problems with UV embrittlement. The best fix I've found is Krylon clear acrylic spray. http://yarchive.net/electr/plastic_uv_resistances.html Hint: Search Yarchive and Google for posting by Dr Barry L. Ornitz WA4VZQ. Lots of really good info on materials, chemicals, processes, and antennas. I'm talking about water impacts. Humidity and rain soak into materials. Some by absorption, others by infiltration into micro-cracks. I saw some materials that talked about water trees in PEX. This is not a universal problem in all plastics. Incidentally, if you dive into the Yahoo magloop files sections, there are some photos of the insides of the MFJ-1786 mag loop. http://www.mfjenterprises.com/Product.php?productid=MFJ-1786 https://groups.yahoo.com/neo/groups/MagLoop/files/MFJ-1786/MFJ-1786%20coupling%20loop/ Two things worthy of notice. All the aluminum parts are brazed or welded together and the matching(?) coil inside the box appears to be silver plated. If MFJ's reputation for cheap construction is to be believed, they would not silver plate anything if a cheaper alternative would work. I can't get to the MagLoop files. I don't know anything about MFJ's reputation. There are simple facts about silver that make it only very slightly better than copper for RF circuits. I know that you can increase the size of the conductor by less than 5% as an alternative to using silver plating if the electrical characteristics are the goal. Can you explain why silver is required? The numbers don't show it. The silver is simply optimization. If you can make your coil wire 5% bigger, you should have already done that. Then if you want to optimized 1 + 0.05, silver plate it. Why can't you make the wire 5% bigger again? Where exactly is the cost? -- Rick |
Flex dryer vent hose loop antenna
On 11/9/2015 7:52 PM, Jeff Liebermann wrote:
On Mon, 9 Nov 2015 01:59:06 -0500, rickman wrote: I'm not familiar with automatic tuners that can tune the antenna while in use. The basic benefits of having a remote controller a 1. RF safety and you're not part of the antenna system. 2. A controller is easier to umm.... control. 3. Automatic remote tuning reacts to changes when you're not looking at the VSWR meter. 4. White knuckle tuning is difficult. Let the servos do the work. 5. It's the only effective way to tune a loop mounted on a tall pole, tower, or roof. A remote controller is not an automatic tuner. Automatic implies the controller tunes the resonance while a remote controller is just that, a control to adjust the tuning remotely. I don't see how this could work while transmitting. The tuning needs to be done separately. One of the issues someone pointed out was that the dielectric can heat up from the energy absorbed during transmission. Is an antenna tuner real time in this case? Yes in receive. Probably not in transmit. In receive, you can tune all you want and nothing will explode or catch fire. In transmit, you can easily tune through full power and arc over the tuning capacitor. Auto tuning also goes through the optimum VSWR point several times during the tuning cycle. You transmitter may not like operating into a high VSWR load during tuning. How does an automatic tuner operate? When you mention VSWR, how is that affected by tuning? The solution is to tune at low tranmit power levels. Once the lowest VSWR point is found, you can increase your power. However, that usually prevents you from "tweaking" the tuning at full power, which is what you need to compensate for thermal drift. It's also difficult to tune with any modulation other than CW. I think (not sure) that some controllers have this ability, probably with warnings and disclaimers. I wouldn't trust it. Basically, to make it work requires a VWSR sensor and calculator that works when there's modulation, and a tuning capacitor that can tolerate moving while passing high currents. Arcing and welding the bearing and bushings might be a problem. I crunched some numbers and found 100's of PPM change in tuned frequency due to ambient temperature change over the course of a year for an antenna with an air or vacuum tuning capacitor. I can find ceramic dielectrics that would be lower than this and even in the opposite direction to offset the natural drift. But I can't find this info for PEX. I looked and also didn't find anything. The problem is that you don't find tempco data for plumbing parts that were not intended to be used for RF components. Substances have properties regardless of usage. PEX is not just used for plumbing. It is also used in electrical cables where the dielectric properties are very important. I'm not terribly concerned with the actual value of Er and even the dielectric strength. What is important to me is the temperature coefficient of Er. Again, I think you might be trying to solve a problem that has already been solved by automatic tuning (which you need anyway). Unless you plan to transmit endlessly, you can simply press the tune button on the controller a few times per hour, and be done with trying to temperature stabilize the loop. That's not how it was presented to me. The suggestion was that tuning will change during transmission due to heating from the power being transmitted. Of course that depends on not just the Er dependance with temperature, but also the dissipation factor. So perhaps with material of a sufficiently low DF the Er dependence on temperature is not so important. Interesting, but nearly every discussion I find on loop antennas has a lot of fluff content. RF is magic. It's difficult to explain some things. You mean people don't understand it. Anything that is understood can be explained. If you don't understand it, you can't explain it. Even so, that's not fluff. Fluff is when things are described in non-rigorous ways like, "solder joints result in sub-optimum performance". Hard to prove or disprove. Clearly they will have some effect even if that effect too small to be measurable. "Sub-optimal" is pretty meaningless in general until you define the details of "optimal". Here is some from this discussion, "By the way PEX is cross linked polyethylene and is superior to using sheet Teflon in this instance." Unless the reason is stated for considering PEX superior to Teflon, I haven't learned anything. I'm certainly not going to take an anonymous person's word for it. The world is divided between practitioners of theory and of practice. Those who favor can explain anything, but can't build anything that actually works. Those that favor practice tend to build strange contraptions that they can't explain. That's also probably the main source of what you call "fluff". Sometimes, I run into a theoretician that knows which end of the soldering iron to grab, but they are rare. For the record, I'm a practitioner of practice, trial-n-error, and magic. I have difficulty explaining some things, and I think you've seen my horrid math. I think the world is *not* divided at all, rather there is a range of abilities on both theory and practice scales with independent values. Fluff is fluff no mater what you are good at. If someone can't recognize fluff, then they are missing a lot of understanding. I'm used to seeing this sort of lack of rigor in many pursuits, cars, sports, etc. I've also seen it in safety. Lots of people use seat of the pants concepts in analyzing safety. It shows up very easily when you simply ask questions about the source of the info. Same with the amateur design of antennas. Lots of talk, but very little data in most cases, like with solder joints. I'm talking about water impacts. Humidity and rain soak into materials. Some by absorption, others by infiltration into micro-cracks. I saw some materials that talked about water trees in PEX. This is not a universal problem in all plastics. I come from the marine radio part of the business. Water and corrosion are key parts of the marine radio problem. Many materials are hygroscopic and will absorb moisture. Apply some RF and the water boils out, as in a microwave oven. Do it too fast, and the material can crack. Of course, the tuning will change. Lots of info on plastics selection for minimal water absorption found online. For example: http://www.curbellplastics.com/technical-resources/pdf/water-absorption-plastics.pdf Polypropylene would be my first choice for minimal water absorption. However, it requires UV protection, which for RF applications means some kind of conformal coating. (Adding carbon black is a bad idea as it causes heating problems). Plastic in a tuning capacitor should be protected from the elements in other ways. Conformal coating is not really needed if the entire capacitor is in a box, even a transparent plastic box as long as it blocks the UV. Most plastics do. There are simple facts about silver that make it only very slightly better than copper for RF circuits. I know that you can increase the size of the conductor by less than 5% as an alternative to using silver plating if the electrical characteristics are the goal. Can you explain why silver is required? The numbers don't show it. Antennas are mounted outdoors where exposed copper is an invitation to corrosion. If one must protect the copper with something, why not use silver, which also improves its RF characteristics? My solution would be to use aluminum instead. Copper is not really superior in a meaningful way and costs a lot more. My magloop nightmare come true: http://www.mixw.co.uk/MagLoop/magloopF.htm I don't get your point here. -- Rick |
Flex dryer vent hose loop antenna
On 11/10/2015 1:41 AM, rickman wrote:
On 11/9/2015 12:08 PM, amdx wrote: The silver is simply optimization. If you can make your coil wire 5% bigger, you should have already done that. Then if you want to optimized 1 + 0.05, silver plate it. Why can't you make the wire 5% bigger again? Where exactly is the cost? You can. I don't think ultimate optimizing is for you. Just make your coil with as much surface area as room will allow. Then know it could have just a tiny bit less loss if you had the silver. That tiny bit of loss will not be noticed in use, except for that little nagging thought... I once had a 6 or 7 turn loop made with 1/4" copper tubing*, Q was about 800 at 1MHz. I could have made it with 1/2" tubing, probably would have had higher Q. I guess the limits are money and how you want to limit physical size and maximum inductance you can use. Did I miss any? Mikek *It had a vacuum variable mounted on it, I had it in the garage and my young son moved it and broke the glass on the vacuum variable, it was a sad day for me. |
Flex dryer vent hose loop antenna
On 11/10/2015 2:02 AM, rickman wrote:
On 11/9/2015 7:52 PM, Jeff Liebermann wrote: My solution would be to use aluminum instead. Copper is not really superior in a meaningful way and costs a lot more. Money rears it's head as an issue, aluminum is cheaper. +1 for aluminum. Resistivity is 65% higher for aluminum. I'd give that a -1, however, if maximizing Q is not important in your design then still at +1. Oxidation: Copper oxide vs Aluminum oxide. Aluminum oxide is an insulator. How does that affect skin resistance? I don't know, does it just shrink your tubing by the thickness of the oxide? Copper oxide is said to be a semiconductor, has much, much lower resistance than aluminum oxide. Page 5, http://www.ets-lindgren.com/pdf/emctd_1293_weibler.pdf Or just varnish it. Bottom of page, http://hamwaves.com/coils/en/ Aluminum is a great material to work with. My magloop nightmare come true: http://www.mixw.co.uk/MagLoop/magloopF.htm I don't get your point here. Build one, monitor your dreams. Jeff, I don't like the parallel sections, seems like it could be made more complicated using x, y, and z right angles. Nap on that! :-) Mikek |
Flex dryer vent hose loop antenna
On 11/10/2015 9:12 AM, amdx wrote:
On 11/10/2015 1:41 AM, rickman wrote: On 11/9/2015 12:08 PM, amdx wrote: The silver is simply optimization. If you can make your coil wire 5% bigger, you should have already done that. Then if you want to optimized 1 + 0.05, silver plate it. Why can't you make the wire 5% bigger again? Where exactly is the cost? You can. I don't think ultimate optimizing is for you. Just make your coil with as much surface area as room will allow. Then know it could have just a tiny bit less loss if you had the silver. That tiny bit of loss will not be noticed in use, except for that little nagging thought... I once had a 6 or 7 turn loop made with 1/4" copper tubing*, Q was about 800 at 1MHz. I could have made it with 1/2" tubing, probably would have had higher Q. I guess the limits are money and how you want to limit physical size and maximum inductance you can use. Did I miss any? People seem to go nuts with ideas that you need to optimize every little thing without any evidence to show the significance of the impact on performance. Your example is perfect. Increasing the copper tube from 1/4 inch to even just 3/8 inch would more than make up for silver plating and not really cost that much more. There are guys who talk about using single piece, 3 inch copper tube bent into a loop to avoid having solder joints when using straight pieces even though those solder joints will be about the same resistance as a quarter inch of the tube or a microscopic increase in the resistance. Then they conveniently forget about the resistance of the clamp connection to the vacuum variable capacitor swamping out the solder joint resistance even more. It makes me want to scream, "Enough of the maddness"! -- Rick |
Flex dryer vent hose loop antenna
On 11/10/2015 10:10 AM, amdx wrote:
On 11/10/2015 2:02 AM, rickman wrote: On 11/9/2015 7:52 PM, Jeff Liebermann wrote: My solution would be to use aluminum instead. Copper is not really superior in a meaningful way and costs a lot more. Money rears it's head as an issue, aluminum is cheaper. +1 for aluminum. Resistivity is 65% higher for aluminum. I'd give that a -1, however, if maximizing Q is not important in your design then still at +1. I can overcompensate for the increased resistivity by using larger tubing and still save $$$, +1 for aluminum. Resistivity is not resistance. Oxidation: Copper oxide vs Aluminum oxide. Aluminum oxide is an insulator. How does that affect skin resistance? I don't know, does it just shrink your tubing by the thickness of the oxide? How many atoms is that in aluminum? So we are talking nanometers? I started with a tube that is 100% larger, so still lower conductivity. Copper oxide is said to be a semiconductor, has much, much lower resistance than aluminum oxide. Page 5, http://www.ets-lindgren.com/pdf/emctd_1293_weibler.pdf Or just varnish it. Bottom of page, http://hamwaves.com/coils/en/ Aluminum is a great material to work with. The oxides are irrelevant. -- Rick |
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