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Homebrew Coil Form Factor
I wonder how much difference it would make if I were to
build a loading coil on a piece of 3''x3" wood? It would be very easy and I could suspend the winding above the wood form with plastic dowel glued on each corner of the wood. I could also make a similar coil using PVC pipe. Even in that case the winding would have a somewhat rectangular form factor. It wouldn't be air core considering that it would be over wood (dry and waterproofed) or PVC pipe. I do require the structure be relatively strong or I would wind the coil, put epoxy glue strips along it to make it like AirDux and the like. Any comments or suggestions?? Irv VE6BP |
Homebrew Coil Form Factor
On Friday, October 4, 2013 10:48:30 PM UTC-5, Irv Finkleman wrote:
Any comments or suggestions?? http://www.g3ynh.info/zdocs/comps/part_6.html |
Homebrew Coil Form Factor
On Fri, 4 Oct 2013 21:48:30 -0600, "Irv Finkleman"
wrote: I wonder how much difference it would make if I were to build a loading coil on a piece of 3''x3" wood? Difference from what? What are you comparing the wood coil with? It would be very easy and I could suspend the winding above the wood form with plastic dowel glued on each corner of the wood. I could also make a similar coil using PVC pipe. Even in that case the winding would have a somewhat rectangular form factor. Yep. Both PCV and wood are lossy. Put a piece in your microwave oven and watch them both get warm. Actually, if the wood has a high moisture content, it will get quite hot. If exposed, both materials also have problems with UV resistance. If you must use plastic tubing, you can possibly find something in polysulfone, polystyrene, polypropylene, or polycarbonate (in order of preference). If you can't find these, white ABS schedule 40 sorta works at low power levels. High power or low power? If low power, you could probably wind the loading coal on kiln dried and sealed wood or PVC and it will work. On the other foot, high power will heat anything that's lossy, including the coil form. High Q or low Q? If you need a really high Q loading coil, the material losses might be a problem. Hints: http://www.w8ji.com/loading_inductors.htm http://www.seed-solutions.com/gregordy/Amateur%20Radio/Experimentation/HiQCoil.htm Notice the preferred loading coil construction. This might give you some ideas (good and bad): https://www.google.com/search?tbm=isch&q=antenna+loading+coil It wouldn't be air core considering that it would be over wood (dry and waterproofed) or PVC pipe. I do require the structure be relatively strong or I would wind the coil, put epoxy glue strips along it to make it like AirDux and the like. Strong, relative to what? Are you supporting a tower on the coil, or a length of wire? Some clues as to the weight load, and other stresses (torque, shear, vibration, etc) would be helpful. Any comments or suggestions?? Nope. You haven't stated what you're trying to accomplish or what you have to work with. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Homebrew Coil Form Factor
Hi Jeff, and thanks for your reply.
To begin with I run QRP (5W on a Yaesu ft-817ND). I have limited workshop space (my desk in a senior's villa), but lots of my old tools. I ran into problems in the last senior's residence I lived in and have just now moved into a new one. All my previous preparations to set up an antenna have been foiled -- one old busybody saw us stringing a line out of my window to a nearby tree. Before anything could be done she had a whole bunch crying to the General Manager that we were (a) killing trees (b) setting up satellite antennas on the roof (c) going to interfere with radios, TVs, heating pads and such. So much attention was drawn to a simple twenty foot piece of small nearly invisible wire that I decided it would be easier to move than fight a battle that I had little chance of winning. The unit I am in now has a balcony, and I have moved in with the understanding that I will not have any wires hanging off the balcony to nearby trees etc., and that anything I do set up will remain within the confines of the small balcony (roughly 6ft x 10ft. They do not mind if I have a collapsible whip or somnething similar which could be taken in (or out ofsight) when I'm not operating -- they don't want it left sticking out. I'm considering a homebrew loaded whip, as it would be quick and simple. Later on I hope to build a magnetic loop. I only run QRP on a Yaesu FT-817ND. I also have at my disposal an artificial ground tuner, an MFJ-949E Antenna Tuner, an MFJ-259B Analyzer, a MFJ-1625 Window/Balcony Mount Antenna system, and a MFJ-931 Artificial Ground. The Windowsill/Balcony tuner also has an Artificial Ground Tuner in it too. The loading coil with the MFJ-1625 is pretty flimsy and I might just consider rewinding the coil with heavier copper (the orginal coil had a broken turn). All of the aforementioned equipment I picked up used or broken and fixed up (a little extra solder in the right places never hurt MFJ stuff), the 931 had a blown meter, the FT-817ND had a burned foil on the board due to faulty hookup or something, and the 949 needed a switch replaced. The 259B I bought new in the box! I was comparing a wood coil with an air wound coil. I should have said ABS rather than PVC, and I am well aware of dielectric losses although I don't worry about them too much as even 5W minus the losses will keep me on the air. I'm not overly concerned about Q as long as I can get a signal out! My main concern was with winding a loading coil on a square form, and I was just wondering how much effect that would have. Coincidentally, today was our local Ham Flea Market, but I am somewhat handicapped and was not up to going -- normally I would crawl across broken glass to attend. I might have found something there. I've undergone three major surgeries since late 2009 and had to sell my house. I gave all my ham stuff to the local radio club thinking then that I'd never be able to ham again -- now I'm starting again! I've had my ticket for 55 years and it's not easy to stop!!! After this discussion I think I'll go ABS, and with the aid of some epoxy may even slip it off the pipe and go air core supporting the coil off to the side of the whip mounting. Remember the old 'Gotham Vertical' antennas (1956 Handbook ads)? All of this is planning ahead -- I'll try the MFJ-1625 setup first, just to get going. In any event, what do you think of the homebrew equivalent of AirDux, but square instead of round? Irv VE6BP "Jeff Liebermann" wrote in message ... On Fri, 4 Oct 2013 21:48:30 -0600, "Irv Finkleman" wrote: I wonder how much difference it would make if I were to build a loading coil on a piece of 3''x3" wood? Difference from what? What are you comparing the wood coil with? It would be very easy and I could suspend the winding above the wood form with plastic dowel glued on each corner of the wood. I could also make a similar coil using PVC pipe. Even in that case the winding would have a somewhat rectangular form factor. Yep. Both PCV and wood are lossy. Put a piece in your microwave oven and watch them both get warm. Actually, if the wood has a high moisture content, it will get quite hot. If exposed, both materials also have problems with UV resistance. If you must use plastic tubing, you can possibly find something in polysulfone, polystyrene, polypropylene, or polycarbonate (in order of preference). If you can't find these, white ABS schedule 40 sorta works at low power levels. High power or low power? If low power, you could probably wind the loading coal on kiln dried and sealed wood or PVC and it will work. On the other foot, high power will heat anything that's lossy, including the coil form. High Q or low Q? If you need a really high Q loading coil, the material losses might be a problem. Hints: http://www.w8ji.com/loading_inductors.htm http://www.seed-solutions.com/gregordy/Amateur%20Radio/Experimentation/HiQCoil.htm Notice the preferred loading coil construction. This might give you some ideas (good and bad): https://www.google.com/search?tbm=isch&q=antenna+loading+coil It wouldn't be air core considering that it would be over wood (dry and waterproofed) or PVC pipe. I do require the structure be relatively strong or I would wind the coil, put epoxy glue strips along it to make it like AirDux and the like. Strong, relative to what? Are you supporting a tower on the coil, or a length of wire? Some clues as to the weight load, and other stresses (torque, shear, vibration, etc) would be helpful. Any comments or suggestions?? Nope. You haven't stated what you're trying to accomplish or what you have to work with. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Homebrew Coil Form Factor
On 10/5/2013 11:11 AM, Jeff Liebermann wrote:
On Fri, 4 Oct 2013 21:48:30 -0600, "Irv Finkleman" wrote: I wonder how much difference it would make if I were to build a loading coil on a piece of 3''x3" wood? Difference from what? What are you comparing the wood coil with? Good question. It would be very easy and I could suspend the winding above the wood form with plastic dowel glued on each corner of the wood. I could also make a similar coil using PVC pipe. Even in that case the winding would have a somewhat rectangular form factor. Yep. Both PCV and wood are lossy. Put a piece in your microwave oven and watch them both get warm. Actually, if the wood has a high moisture content, it will get quite hot. If exposed, both materials also have problems with UV resistance. If you must use plastic tubing, you can possibly find something in polysulfone, polystyrene, polypropylene, or polycarbonate (in order of preference). If you can't find these, white ABS schedule 40 sorta works at low power levels. The microwave oven test is not very useful. The microwave will test whatever at about 2450MHz. I doubt he is trying to make a loading coil for anything near that frequency. There are other resources for that information. Please search. High power or low power? If low power, you could probably wind the loading coal on kiln dried and sealed wood or PVC and it will work. On the other foot, high power will heat anything that's lossy, including the coil form. You are correct. But, the losses (percentage-wise) will be the same barring heating effects. High Q or low Q? If you need a really high Q loading coil, the material losses might be a problem. See above. It wouldn't be air core considering that it would be over wood (dry and waterproofed) or PVC pipe. Try this, Jeff... Wind some turns on an empty plastic soft drink bottle. Measure the L and Q and SRF. Then fill it with water. Measure the L and Q and SRF again. Report back here with the data. I do require the structure be relatively strong or I would wind the coil, put epoxy glue strips along it to make it like AirDux and the like. Irv... You might need a few more turns to get the L you need, but it is hard to read your practical limitations from this. If that is all you have, give it a try. What do you have to lose? Do you have a way of measuring the L? Strong, relative to what? Are you supporting a tower on the coil, or a length of wire? Some clues as to the weight load, and other stresses (torque, shear, vibration, etc) would be helpful. If you have read his previous posts, you would know that he is in an apartment and has a balcony. He wishes to operate from that location. Correct me if I am wrong, Irv. Any comments or suggestions?? Nope. You haven't stated what you're trying to accomplish or what you have to work with. Most posters here do not state all of the facts initially. That's because most of their ideas are still brewing in the brain and some of the details are not formalized. It is the reason we ask for other people's inputs. Cut him some slack and continue to ask how you can help. Wishing you the best, Irv. Cheers and 73, John KD5YI |
Homebrew Coil Form Factor
While it migh be out of your price range, look into the screwdrver
antennas. Usually for mobile,but I don't see why you could not get it to work for you . You do not need a tuner with it as it does its own tuning by a motor. I have worked lots of mobiles that had them and they seem to put out a good signal. "Irv Finkleman" wrote in message ... Hi Jeff, and thanks for your reply. To begin with I run QRP (5W on a Yaesu ft-817ND). I have limited workshop space (my desk in a senior's villa), but lots of my old tools. I ran into problems in the last senior's residence I lived in and have just now moved into a new one. All my previous preparations to set up an antenna have been foiled -- one old busybody saw us stringing a line out of my window to a nearby tree. Before anything could be done she had a whole bunch crying to the General Manager that we were (a) killing trees (b) setting up satellite antennas on the roof (c) going to interfere with radios, TVs, heating pads and such. So much attention was drawn to a simple twenty foot piece of small nearly invisible wire that I decided it would be easier to move than fight a battle that I had little chance of winning. The unit I am in now has a balcony, and I have moved in with the understanding that I will not have any wires hanging off the balcony to nearby trees etc., and that anything I do set up will remain within the confines of the small balcony (roughly 6ft x 10ft. They do not mind if I have a collapsible whip or somnething similar which could be taken in (or out ofsight) when I'm not operating -- they don't want it left sticking out. |
Homebrew Coil Form Factor
Thanks Ealph,
I'd consider a screwdriver but it's not in my blood to buy something unless (1) I really need it fast, or (2) I can get a used or broken one cheap and fix it up. Most of the gear I have I got under those conditions and they have served me well. I nust admit that I have looked at them and they are getting pretty good reviews. If my lottery comes through I'll reconsider! :-) "Ralph Mowery" wrote in message ... While it migh be out of your price range, look into the screwdrver antennas. Usually for mobile,but I don't see why you could not get it to work for you . You do not need a tuner with it as it does its own tuning by a motor. I have worked lots of mobiles that had them and they seem to put out a good signal. "Irv Finkleman" wrote in message ... Hi Jeff, and thanks for your reply. To begin with I run QRP (5W on a Yaesu ft-817ND). I have limited workshop space (my desk in a senior's villa), but lots of my old tools. I ran into problems in the last senior's residence I lived in and have just now moved into a new one. All my previous preparations to set up an antenna have been foiled -- one old busybody saw us stringing a line out of my window to a nearby tree. Before anything could be done she had a whole bunch crying to the General Manager that we were (a) killing trees (b) setting up satellite antennas on the roof (c) going to interfere with radios, TVs, heating pads and such. So much attention was drawn to a simple twenty foot piece of small nearly invisible wire that I decided it would be easier to move than fight a battle that I had little chance of winning. The unit I am in now has a balcony, and I have moved in with the understanding that I will not have any wires hanging off the balcony to nearby trees etc., and that anything I do set up will remain within the confines of the small balcony (roughly 6ft x 10ft. They do not mind if I have a collapsible whip or somnething similar which could be taken in (or out ofsight) when I'm not operating -- they don't want it left sticking out. |
Homebrew Coil Form Factor
Thanks John,
Taking the cost of copper into account (Unless I can find one of those old power transformers and strip it) I'll just wind 'lots' of turns -- maybe about 50% more than shown in the QST Articles on windowsill antennas. It's easy to short the extra turns if I don't need them. As for Jeff's reply -- he has always been helpful to the max, and some of it is my fault in that I am basically tossing ideas into the air and sparking discussion as part of my preliminary design considerations. The army guys I know (I was diehard Navy) had an expression 'Time spent on recconaissance is seldom wasted" and I tend to work that way which is sort of 'Measure twice, cut once' taking into account Murphy's Laws. It may take me longer to get on the air, but once there, I plan to have a lot of fun! Thanks again all! Irv VE6BP "John S" wrote in message ... On 10/5/2013 11:11 AM, Jeff Liebermann wrote: On Fri, 4 Oct 2013 21:48:30 -0600, "Irv Finkleman" wrote: I wonder how much difference it would make if I were to build a loading coil on a piece of 3''x3" wood? Difference from what? What are you comparing the wood coil with? Good question. It would be very easy and I could suspend the winding above the wood form with plastic dowel glued on each corner of the wood. I could also make a similar coil using PVC pipe. Even in that case the winding would have a somewhat rectangular form factor. Yep. Both PCV and wood are lossy. Put a piece in your microwave oven and watch them both get warm. Actually, if the wood has a high moisture content, it will get quite hot. If exposed, both materials also have problems with UV resistance. If you must use plastic tubing, you can possibly find something in polysulfone, polystyrene, polypropylene, or polycarbonate (in order of preference). If you can't find these, white ABS schedule 40 sorta works at low power levels. The microwave oven test is not very useful. The microwave will test whatever at about 2450MHz. I doubt he is trying to make a loading coil for anything near that frequency. There are other resources for that information. Please search. High power or low power? If low power, you could probably wind the loading coal on kiln dried and sealed wood or PVC and it will work. On the other foot, high power will heat anything that's lossy, including the coil form. You are correct. But, the losses (percentage-wise) will be the same barring heating effects. High Q or low Q? If you need a really high Q loading coil, the material losses might be a problem. See above. It wouldn't be air core considering that it would be over wood (dry and waterproofed) or PVC pipe. Try this, Jeff... Wind some turns on an empty plastic soft drink bottle. Measure the L and Q and SRF. Then fill it with water. Measure the L and Q and SRF again. Report back here with the data. I do require the structure be relatively strong or I would wind the coil, put epoxy glue strips along it to make it like AirDux and the like. Irv... You might need a few more turns to get the L you need, but it is hard to read your practical limitations from this. If that is all you have, give it a try. What do you have to lose? Do you have a way of measuring the L? Strong, relative to what? Are you supporting a tower on the coil, or a length of wire? Some clues as to the weight load, and other stresses (torque, shear, vibration, etc) would be helpful. If you have read his previous posts, you would know that he is in an apartment and has a balcony. He wishes to operate from that location. Correct me if I am wrong, Irv. Any comments or suggestions?? Nope. You haven't stated what you're trying to accomplish or what you have to work with. Most posters here do not state all of the facts initially. That's because most of their ideas are still brewing in the brain and some of the details are not formalized. It is the reason we ask for other people's inputs. Cut him some slack and continue to ask how you can help. Wishing you the best, Irv. Cheers and 73, John KD5YI |
Homebrew Coil Form Factor
"Irv Finkleman" wrote in message ... Hi Jeff, and thanks for your reply. To begin with I run QRP (5W on a Yaesu ft-817ND). I have limited workshop space (my desk in a senior's villa), but lots of my old tools. I was comparing a wood coil with an air wound coil. I should have said ABS rather than PVC, and I am well aware of dielectric losses although I don't worry about them too much as even 5W minus the losses will keep me on the air. I'm not overly concerned about Q as long as I can get a signal out! My main concern was with winding a loading coil on a square form, and I was just wondering how much effect that would have. After this discussion I think I'll go ABS, and with the aid of some epoxy may even slip it off the pipe and go air core supporting the coil off to the side of the whip mounting. Remember the old 'Gotham Vertical' antennas (1956 Handbook ads)? Lots of sutff cut out.. I ran a quick and dirty check for you. I took about 8 turns of about #22 wire and a 100 pf capacitor. Wound the wire around a piece of 1/2 inch PVC pipe that is about 7/8 inch outside diameter. I made a parallel circuit of the two. Put it on a HP 8924c set as a spectrum generator and tracking generator. It resonated about 13.08 mhz and had a relative loss of -46.46 db. Took it off the form and resonated about 13.14 with a loss of -47.0 db back on the pvc and it went back to the first number. I did not have a piece of wood that would exectally fit it,but one that was close. Resonated at 13.05 mhz and loss of -46.94. All in all, I doubt there would be enough loss or change to make any differance. The small loss and frequency change could just be the spreading of the coil slightly and the loss could be how close the leads are to each other. For running the 5 watts like you are, I don't see any problems with changing the forms on the low bands. I doubt that even at 100 watts it would have any noticable effect. |
Homebrew Coil Form Factor
On Sat, 5 Oct 2013 13:27:43 -0600, "Irv Finkleman"
wrote: To begin with I run QRP (5W on a Yaesu ft-817ND). In that case, almost any coil form will work. There's little danger from losses causing the plastic to melt. However, I'm not so thrilled with the idea of using wood. The wood is not the problem. It's the water in the wood. You can seal it with the traditional bees wax, but that tends to become a sticky mess. I'm considering a homebrew loaded whip, as it would be quick and simple. Nothing is both quick and simple. The simple things take forever to get right and the quick things that are thrown together never seem to work. Later on I hope to build a magnetic loop. That's the best idea yet. They're very narrow band, kinda temperamental, require plenty of expensive copper, good soldering, giant air dielectric or vacuum capacitors, but work better than anything their size. However, if you must waste your time with a base loaded whip, your first problem will be finding a suitable ground. That's a problem you don't have with a dipole or loop. I guess some welded wire mesh on the balcony will barely suffice. Next, you need a base insulator. I recommend an empty thick glass wine bottle. Wrap some stiff insulated wire around the bottle as a loading coil. Use your MFJ259 to tune to the right band. Make an assortment of wine bottle loading coils, one for each band. I only run QRP on a Yaesu FT-817ND. I also have at my disposal an artificial ground tuner, an MFJ-949E Antenna Tuner, an MFJ-259B Analyzer, a MFJ-1625 Window/Balcony Mount Antenna system, and a MFJ-931 Artificial Ground. The Windowsill/Balcony tuner also has an Artificial Ground Tuner in it too. Tuners are fun to play with but are often lossy. If you get the loading coil close to 50 ohms at the operating frequency, you can live without the tuner. At worst, use the tuner for minor VSWR adjustments when you change frequency, and don't want to play with the loading coil. The 259B I bought new in the box! For when you blow it up: http://802.11junk.com/jeffl/MFJ-269-repair/ That's for an MFJ269, which is similar. I'm not overly concerned about Q as long as I can get a signal out! Besides bandwidth, Q is also way to express losses. Basically, it's a measure of either the series resistance or parallel resistance of an ideal inductor. For parallel: Rp = Xl * Q Rp = 2 * Pi * freq * L * Q For Series: Rs = Xc / Q Rs = 1 / (2 * Pi * freq * Q) (Note that Rs is also known as the capacitor ESR). A high Q coil has a large resistor across it with minimal effects, while a low Q coil will have a much smaller resistor across it. Since pure reactances do NOT dissipate any power, all the power loss in the coil is dissipated in this equivalent resistance. There's also the DC resistance of the coil in series but that's not part of the current discussion. My main concern was with winding a loading coil on a square form, and I was just wondering how much effect that would have. Obviously, it produces square waves. The shape of the form will have almost no effect on the inductance, Q, or radiation characteristics of the antenna. If you look carefully at the cross section of a torroid core, you'll find that it's wound in a square pattern. I've undergone three major surgeries since late 2009 and had to sell my house. Ouch. Get better please. I gave all my ham stuff to the local radio club thinking then that I'd never be able to ham again -- now I'm starting again! I've had my ticket for 55 years and it's not easy to stop!!! No sympathy. I've moved about 4 times. Each time, I purged my ham radio, magazine, auto parts, and junk collections in the anticipation of never needing them again. Each time, I quickly rebuilt the mess. I don't plan to move, but the mess has once again reached the safe occupancy level and needs to be purged. Sigh... After this discussion I think I'll go ABS, and with the aid of some epoxy may even slip it off the pipe and go air core supporting the coil off to the side of the whip mounting. Remember the old 'Gotham Vertical' antennas (1956 Handbook ads)? Ok. Just use the white ABS pipe, not the black ABS irrigation pipe. In any event, what do you think of the homebrew equivalent of AirDux, but square instead of round? No problem. It should work the same as the round flavor. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Homebrew Coil Form Factor
On Sat, 05 Oct 2013 15:24:01 -0500, John S
wrote: The microwave oven test is not very useful. The microwave will test whatever at about 2450MHz. I doubt he is trying to make a loading coil for anything near that frequency. Actually, it's very useful. In my admittedly limited experience, anything that survives the microwave oven test, will usually work nicely at HF frequencies. Those that get warm in the oven, might work ok. Those that melt, burn or explode, will probably not work very well at HF. While testing at 1000 times the frequency, and 30 times the power, might be considered overkill, it does yield some useful information. Incidentally, the loss tangent changes over frequency on many materials. See table at: http://www.kayelaby.npl.co.uk/general_physics/2_6/2_6_5.html There are other resources for that information. Please search. Well, there's the loss tangent tables for various materials. http://www.rfcafe.com/references/electrical/dielectric-constants-strengths.htm Is that what you mean? The problem here is that the ABS or PVC coil form is hollow. There's only a little plastic and plenty of air. If the PVC tube were thin enough, it might be considered air core. You are correct. But, the losses (percentage-wise) will be the same barring heating effects. The losses are fairly small, but the effects on the material at different power levels quite different. For example, a 1dB power loss at the 5 watt level will produce about 1 watt of heat. That same 1dB loss at 150 watts will produce 30 watts of heat, which will probably melt the coil form. It wouldn't be air core considering that it would be over wood (dry and waterproofed) or PVC pipe. For a hollow PVC or ABS pipe, it's mostly air core. (For a solid wood coil form, it's all wood with some absorbed water.) I'm not sure how to calculate the effective dielectric constant of a hollow plastic pipe. Probably by measuring the inductance of a surrounding coil with and without the pipe, and calculating what dielectric constant was necessary to produce the change. Unfortunately, that doesn't help calculate the combined losses or loss tangent. Most posters here do not state all of the facts initially. That's because most of their ideas are still brewing in the brain and some of the details are not formalized. It is the reason we ask for other people's inputs. Cut him some slack and continue to ask how you can help. Of course. However, I post far too many "answers" in far too many newsgroups and mailing lists to remember everyones situation. If I'm expected to spend my time answering a question or solving a problem, I expect to be provided with: 1. What problem are you trying to solve? A one line description is sufficient. 2. What do you have to work with? (Equipment, site limitations, available test equipment, numbers, numbers, numbers). 3. What have you done so far and what happened? -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Homebrew Coil Form Factor
On 10/5/2013 3:52 PM, Irv Finkleman wrote:
Thanks John, I do require the structure be relatively strong or I would wind the coil, put epoxy glue strips along it to make it like AirDux and the like. Cheers and 73, John KD5YI Here's a picture of a coil I built years ago using 40 ft Radio Shack Aluminum Ground wire. It comes coiled at about 8". My coil is about 8" x 8". I'm making an educated guess that it's about 150uh. http://s395.photobucket.com/user/Qma...c1dd8.jpg.html I drilled spaced holes in 1/2" pvc pipe and then split it on a band saw and clamped the wire between the pieces. Need more strength add more pvc clamps. There are other ways. I just went to the radio shack website looking for the ground wire, I have one and it's catalog number 15-035, BUT, I can't find it on their site. Hmm, I see one on Ebay, $14.99 including shipping http://www.ebay.com/itm/NEW-Radio-Sh...-/281117465242 Mikek |
Homebrew Coil Form Factor
On 10/4/2013 8:48 PM, Irv Finkleman wrote:
I wonder how much difference it would make if I were to build a loading coil on a piece of 3''x3" wood? It would be very easy and I could suspend the winding above the wood form with plastic dowel glued on each corner of the wood. I could also make a similar coil using PVC pipe. Even in that case the winding would have a somewhat rectangular form factor. It wouldn't be air core considering that it would be over wood (dry and waterproofed) or PVC pipe. I do require the structure be relatively strong or I would wind the coil, put epoxy glue strips along it to make it like AirDux and the like. Any comments or suggestions?? Irv VE6BP Interesting postings. An old friend of mine, Don, K7hsj, and his wife recently moved to an assisted living center in Bend, Oregon. He was very concerned about still being able to get on the air. He approached the management about a wire from their third floor apartment to a pine tree several hundred feet away. They were very enthusiastic about his continuing ham operation and agreed to help if they could. Several of Don't friends from Bend helped get the wire up. I suggested that since the building was fairly new, they probably used steel studs to partition the rooms and they all had to be connected to the electrical ground wire of the building wiring. So he used the screw in the center plate of an outlet cover as ground. His 75 meter signal is MUCH louder than when he was at home with a dipole antenna. He got an auto tuner and works most HF bands, now. So, to make a long story short, try the electrical outlet ground for your rig. It may work fine for you, also. 73 and good luck Paul, KD7HB |
Homebrew Coil Form Factor
On Saturday, October 5, 2013 7:44:30 PM UTC-5, Jeff Liebermann wrote:
On Sat, 05 Oct 2013 15:24:01 -0500, John S wrote: The microwave oven test is not very useful. The microwave will test whatever at about 2450MHz. I doubt he is trying to make a loading coil for anything near that frequency. Actually, it's very useful. In my admittedly limited experience, anything that survives the microwave oven test, will usually work nicely at HF frequencies. Those that get warm in the oven, might work ok. Those that melt, burn or explode, will probably not work very well at HF. While testing at 1000 times the frequency, and 30 times the power, might be considered overkill, it does yield some useful information. I had always heard that if one were to use PVC, the gray type was the best vs the white. I've used gray PVC for mobile whip loading coils for years and never really noticed any real problems. But, I do not run high power, and 100w is the max I run. I've always had good results with the antennas, and noticed no noticeable performance loss vs say an open type bug catcher coil. There may be some, but it's small enough not to be a problem. When I first started using the gray PVC, I stuck it in the microwave with a glass of water, and it did not get warm at all. I have heard the white PVC can be more of a problem. |
Homebrew Coil Form Factor
On 10/5/2013 4:14 PM, Ralph Mowery wrote:
"Irv Finkleman" wrote in message ... Hi Jeff, and thanks for your reply. To begin with I run QRP (5W on a Yaesu ft-817ND). I have limited workshop space (my desk in a senior's villa), but lots of my old tools. I was comparing a wood coil with an air wound coil. I should have said ABS rather than PVC, and I am well aware of dielectric losses although I don't worry about them too much as even 5W minus the losses will keep me on the air. I'm not overly concerned about Q as long as I can get a signal out! My main concern was with winding a loading coil on a square form, and I was just wondering how much effect that would have. After this discussion I think I'll go ABS, and with the aid of some epoxy may even slip it off the pipe and go air core supporting the coil off to the side of the whip mounting. Remember the old 'Gotham Vertical' antennas (1956 Handbook ads)? Lots of sutff cut out.. I ran a quick and dirty check for you. I took about 8 turns of about #22 wire and a 100 pf capacitor. Wound the wire around a piece of 1/2 inch PVC pipe that is about 7/8 inch outside diameter. I made a parallel circuit of the two. Put it on a HP 8924c set as a spectrum generator and tracking generator. It resonated about 13.08 mhz and had a relative loss of -46.46 db. Took it off the form and resonated about 13.14 with a loss of -47.0 db back on the pvc and it went back to the first number. I did not have a piece of wood that would exectally fit it,but one that was close. Resonated at 13.05 mhz and loss of -46.94. All in all, I doubt there would be enough loss or change to make any differance. The small loss and frequency change could just be the spreading of the coil slightly and the loss could be how close the leads are to each other. For running the 5 watts like you are, I don't see any problems with changing the forms on the low bands. I doubt that even at 100 watts it would have any noticable effect. Excellent work, Ralph. This is very useful information. Many thanks! 73, John |
Homebrew Coil Form Factor
Lovely work Mike -- a bit more than I require but I'll keep it
in mind. Thanks! Irv VE6BP "amdx" wrote in message ... On 10/5/2013 3:52 PM, Irv Finkleman wrote: Thanks John, I do require the structure be relatively strong or I would wind the coil, put epoxy glue strips along it to make it like AirDux and the like. Cheers and 73, John KD5YI Here's a picture of a coil I built years ago using 40 ft Radio Shack Aluminum Ground wire. It comes coiled at about 8". My coil is about 8" x 8". I'm making an educated guess that it's about 150uh. http://s395.photobucket.com/user/Qma...c1dd8.jpg.html I drilled spaced holes in 1/2" pvc pipe and then split it on a band saw and clamped the wire between the pieces. Need more strength add more pvc clamps. There are other ways. I just went to the radio shack website looking for the ground wire, I have one and it's catalog number 15-035, BUT, I can't find it on their site. Hmm, I see one on Ebay, $14.99 including shipping http://www.ebay.com/itm/NEW-Radio-Sh...-/281117465242 Mikek |
Homebrew Coil Form Factor
On Sun, 6 Oct 2013 00:32:22 -0700 (PDT), wrote:
I had always heard that if one were to use PVC, the gray type was the best vs the white. I've used gray PVC for mobile whip loading coils for years and never really noticed any real problems. But, I do not run high power, and 100w is the max I run. I've always had good results with the antennas, and noticed no noticeable performance loss vs say an open type bug catcher coil. There may be some, but it's small enough not to be a problem. When I first started using the gray PVC, I stuck it in the microwave with a glass of water, and it did not get warm at all. I have heard the white PVC can be more of a problem. http://lists.contesting.com/_towertalk/2006-12/msg00091.html I ran tests at 2.4GHz about 15 years ago. The plan was to use PVC pipe as a 2.4GHz antenna radome. While heating is obviously not an issue at 1 watt, even small losses and detuning were deemed intolerable. I couldn't measure any difference between grey or white as long as the pipe was the same thickness. However, things went awry when I tried to build prototypes out of a mix of different brands of white PVC pipe. The dielectric constant was all over the map causing the resonance point to move around. After determining that even a single supplier can't keep their electrical characteristics consistent, we switched to the more expensive fiberglass tubing and lived happily thereafter. Another potential problem with a base loaded vertical is not power, but voltage. At 5 watts, there's not going to be much voltage across the coil. At 150 watts, it might arc. No calcs today. Gotta run and watch the solar satellite outage today. http://en.wikipedia.org/wiki/Sun_outage -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Homebrew Coil Form Factor
That's all good info Paul, but with the aid of some ferrite cores and
the like I plan to steer clear of any possible signal entering the local wiring. After I've been on the air for a bit, if I find that I'm not causing any problems, I may run another rig I have (Yaesu ft-857D) and use a bit more power. In the meantime, I just want to get a signal out and see what I can do with 5 watts and assorted attempts at balcony verticals and later magnetic loops. Another interesting thing is how I can feed the antenna through the door to the balcony. I can't drill holes, but I currently have a piece of RG-58 squeezed through the closeddoor. Every day I check to see if anything has happened to it such as migration of the center conductor to the point where it shorts to the sheild. I've only been here for a week, but so far so good. I am aware that there may be an impedance bump, but I'm not at all concerned -- if I can get one or two watts ERP I'll be more than happy. My earliest Elmer/Mentor, VE7YY, used to run a half watt homebrew rig and got all over the place with it although I think that his tower and beam helped a wee bit! I'm not desperate, but nearly so, and anxious to get on the air again. It might take a bit of time, but I hope all the ideas I have put into setting up the system will work right the first time. We had a touch of snow last week, and I'm getting a little beyond the point of enjoying antenna work outdoors in the winter. Irv VE6BP "Paul Drahn" wrote in message ... On 10/4/2013 8:48 PM, Irv Finkleman wrote: I wonder how much difference it would make if I were to build a loading coil on a piece of 3''x3" wood? It would be very easy and I could suspend the winding above the wood form with plastic dowel glued on each corner of the wood. I could also make a similar coil using PVC pipe. Even in that case the winding would have a somewhat rectangular form factor. It wouldn't be air core considering that it would be over wood (dry and waterproofed) or PVC pipe. I do require the structure be relatively strong or I would wind the coil, put epoxy glue strips along it to make it like AirDux and the like. Any comments or suggestions?? Irv VE6BP Interesting postings. An old friend of mine, Don, K7hsj, and his wife recently moved to an assisted living center in Bend, Oregon. He was very concerned about still being able to get on the air. He approached the management about a wire from their third floor apartment to a pine tree several hundred feet away. They were very enthusiastic about his continuing ham operation and agreed to help if they could. Several of Don't friends from Bend helped get the wire up. I suggested that since the building was fairly new, they probably used steel studs to partition the rooms and they all had to be connected to the electrical ground wire of the building wiring. So he used the screw in the center plate of an outlet cover as ground. His 75 meter signal is MUCH louder than when he was at home with a dipole antenna. He got an auto tuner and works most HF bands, now. So, to make a long story short, try the electrical outlet ground for your rig. It may work fine for you, also. 73 and good luck Paul, KD7HB |
Homebrew Coil Form Factor
"Irv Finkleman" wrote in message ... That's all good info Paul, but with the aid of some ferrite cores and the like I plan to steer clear of any possible signal entering the local wiring. After I've been on the air for a bit, if I find that I'm not causing any problems, I may run another rig I have (Yaesu ft-857D) and use a bit more power. In the meantime, I just want to get a signal out and see what I can do with 5 watts and assorted attempts at balcony verticals and later magnetic loops. Another interesting thing is how I can feed the antenna through the door to the balcony. I can't drill holes, but I currently have a piece of RG-58 squeezed through the closeddoor. Every day I check to see if anything has happened to it such as migration of the center conductor to the point where it shorts to the sheild. I've only been here for a week, but so far so good. I am aware that there may be an impedance bump, but I'm not at all concerned -- if I can get one or two watts ERP I'll be more than happy. My earliest Elmer/Mentor, VE7YY, used to run a half watt homebrew rig and got all over the place with it although I think that his tower and beam helped a wee bit! I'm not desperate, but nearly so, and anxious to get on the air again. It might take a bit of time, but I hope all the ideas I have put into setting up the system will work right the first time. We had a touch of snow last week, and I'm getting a little beyond the point of enjoying antenna work outdoors in the winter. Irv you may just be over thinking things. One thought that comes to mind is to make something similar to the ham stick dipole. You take two mobile whips and mount them on a plate so you have a horizontal dipole made of them. http://www.k7su.com/hsdipole.html An easy way to home brew something may be to get a few pieces of PVC pipe. Get a T and don't glue it, but just stick a piece out of each end and make a loaded dipole out of each side for the band you want to work. Then use the long side of the T to come down as a support. All this can be broken down and assembled as needed in a minuit or so. You may be able to get a big flower pot and fill it with cement with a hole in it so you can place the vertical pipe. Too bad that you can not drill about a 3/4 inch hole in the wall and use a long bulkhead coax connector. |
Homebrew Coil Form Factor
On 10/6/2013 10:24 AM, Jeff Liebermann wrote:
Gotta run and watch the solar satellite outage today. http://en.wikipedia.org/wiki/Sun_outage Sorta like watching paint dry. |
Homebrew Coil Form Factor
On 10/6/2013 10:24 AM, Jeff Liebermann wrote: Gotta run and
watch the solar satellite outage today. http://en.wikipedia.org/wiki/Sun_outage I lost several minutes of the nascar race on ESPN and then a while later on radio, a syndicated program (Bob Brinker) was out for 3 to 6 minutes. It all happened (approximately) between 3:45 and 4:20. Was that the sun outage? Mikek |
Homebrew Coil Form Factor
On Sun, 06 Oct 2013 16:37:56 -0500, amdx wrote:
On 10/6/2013 10:24 AM, Jeff Liebermann wrote: Gotta run and watch the solar satellite outage today. http://en.wikipedia.org/wiki/Sun_outage I lost several minutes of the nascar race on ESPN and then a while later on radio, a syndicated program (Bob Brinker) was out for 3 to 6 minutes. It all happened (approximately) between 3:45 and 4:20. Was that the sun outage? Mikek Unless the downlink was in Hawaii, it's unlikely that it was directly caused by the sun outage. It happend on Viasat-1 (Wild Blue or Exede) today at about 12:25PM. The earth rotates at: 24hrs * 60min/hr / 360deg = 4 min/deg With a difference of about 3.5 hrs (210 minutes), the earth will have rotated: 210min / 4 min/deg = 52 degree longitude or about: 122w + 52 = 174w which is almost at the International Date Line. A more sane guess would be that what you were watching was recorded between 12PM and 2PM for delayed broadcast somewhere in the continental USA, during which time there was a solar outage. A 3 to 6 minute outage implies 1 or 2 meter receive dish. Most stations know about the problem and usually have something pre-recorded available to fill in the outage. I'm rather surprised that ESPN wasn't paying attention. Grind your own numbers: http://www.satellite-calculations.com/Satellite/suninterference.php -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Homebrew Coil Form Factor
On Sun, 06 Oct 2013 14:42:31 -0500, John S
wrote: On 10/6/2013 10:24 AM, Jeff Liebermann wrote: Gotta run and watch the solar satellite outage today. http://en.wikipedia.org/wiki/Sun_outage Sorta like watching paint dry. Ummm... no, it's not like watching paint dry. I live in a forest of 50 meter redwood and fir trees. If you want to receive TV or digital audio from a satellite, you need to find or make a hole in the trees. During the solar satellite outage is the perfect time to do this. Any place where the sun is shining during the approximately 4 minutes of the outage is a good dish location. This is my house in 2008: http://802.11junk.com/jeffl/pics/DBS/ It's also a good time to check if any tree branches are blocking reception as they cast a shadow on the dish. Note the branch shadows: http://802.11junk.com/jeffl/pics/DBS/slides/101d.html At 13 and 30GHz, the Fresnel Zone is about the same diameter as the dish, so any hole in the trees bigger than the dish will work (until the wind blows). This year, I was at a customer with a similar problem. During the 4 minutes, we both ran around the property, taking photos of prospective dish locations. We also discovered that his existing Exede dish had a few branch shadows, which explains why it needs to be moved. We found what I think will be a good location, as soon as the concrete sets. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Homebrew Coil Form Factor
On Sunday, October 6, 2013 10:24:55 AM UTC-5, Jeff Liebermann wrote:
Another potential problem with a base loaded vertical is not power, but voltage. At 5 watts, there's not going to be much voltage across the coil. At 150 watts, it might arc. No calcs today. Gotta run and watch the solar satellite outage today. http://en.wikipedia.org/wiki/Sun_outage I haven't had any problems with 100w. Mine are center to above center loading though. Usually not base loaded. In the normal driving mode, it's almost exactly center loaded. But I have a solid mast I add below the glass whip when parked, and then it's probably 2/3 up from the base or so. These antennas are basically plastic bugcatchers. And you could use two back to back as a dipole that could fit in a fairly tight area. |
Homebrew Coil Form Factor
On Sat, 5 Oct 2013 13:27:43 -0600, "Irv Finkleman" wrote:
... and a MFJ-931 Artificial Ground. The Windowsill/Balcony tuner also has an Artificial Ground Tuner in it too. The loading coil with the MFJ-1625 is pretty flimsy and I might just consider rewinding the coil with heavier copper (the orginal coil had a broken turn). All of the aforementioned equipment I picked up used or broken and fixed up (a little extra solder in the right places never hurt MFJ stuff), the 931 had a blown meter, ... Know what you mean. I bought an MFJ 931 a couple of months ago, and only recently hooked it up to find it does nothing at all. No changes in noise level, not a dickey birds worth of movement from the meter with the power cranked up to 100 watts - nothing. So, it looks like I am about to do what you commented on that a little extra solder in the right places never hurt MFJ stuff! Couldn't resist commenting after seeing your post. 73, Bob KB2ZGN |
Homebrew Coil Form Factor
"Irv Finkleman" wrote in message ... Another interesting thing is how I can feed the antenna through the door to the balcony. I can't drill holes, but I currently have a piece of RG-58 squeezed through the closeddoor. Every day I check to see if anything has happened to it such as migration of the center conductor to the point where it shorts to the sheild. You might benefit from something like this: http://www.cometantenna.com/pdfs/CTC..._and_instr.pdf Alternatively, leave the door open a crack while passing coax through the opening but seal the opening with a full-height strip of masking tape to keep out the wintery winds. I'm not desperate, but nearly so, and anxious to get on the air again. Have you considered single band whips? The names "Hustler" and "Hamstick" come to mind but there are others. They need a counterpoise to work but the following anecdotes will provide some insight, I hope: I assembled and successfully demonstrated (for Field Day this year) a quick-and-dirty portable HF rig. I used the following crap: a pair of steel chassis slides bolted together at the ends and laid on the ground at a right angle. Their weight and orientation will keep them where they are placed. They are magnetic; a very thin single-use aluminum pan with two 20m radials (about 15 feet) bolted firmly to opposite sides of the baking dish; It laid on a flat part of the chassis slides; an MFJ magmount base (from a 1724B I think, whatever one has the 3/8 threaded socket), with the whip removed. It was placed onto the pan in such a location as to stay magnetically "stuck." the magmount base is capacitively coupled to the pan with the radials; (Would direct wiring from the shield to the radials be better? Dunno.) A Hustler 20m element screwed into the above magmount base. This foregoing electrified junkpile worked multiple stations in the Midwest from San Diego on 20m for Field Day. I used it on 20 and 40 (different whips and different baking pan radials, of course) while on a trip earlier this month with considerable success. The radials might prefer to be stretched out but this, too, can be worked-around. I've used them with the ends drooping off the corners of a balcony and had no trouble getting a match with a $5 swap meet manual tuner. More radials would likely be better but unwinding and re-winding radials around the baking pan is already a pain with just two. Irv, does any of this resonate with you and your balcony? Aside: Maybe I can improve the described radial scheme, like something that involves retractable metal tape rules. Then I'd just need one pan and I can set my radial lengths at will. New thought: If I bolted the free ends of some retractable metal tape rules directly to the steel chassis slides i would eliminate the baking pan, altogether. It offers a certain bizarre appeal. "Sal" |
Homebrew Coil Form Factor
Hey Sal -- thanks! I didn't know they made anything like
that. I had considered using a piece of 300 ohm TV Twinlead in a similar manner. For the short distance, and not worrying about the impedance bump and any losses, I think I'll make one up and give it a shot. The CTC-50M is not far different, and for what it does I consider it a little pricey. It will be a quick and easy project -- two UHF females and RTV compound to seal up the ends. What's a guy got to lose? If it works to any degree, then great! If it doesn't, then back to the drawing board. So far, the test piece of RG-58 that has been placed in the closed door has not deformed too badly, nor has it shorted. The temperatures here lately range from just below freezing at night to about 20 degrees on the balcony in direct sunlight (the balcony faces South). Your other suggestions have already been discounted. What I really want is something cheap and simple where I don't have to do too much moving about to change bands, Thanks again, de VE6BP, Irv "Sal" salmonella@food poisoning.org wrote in message ... "Irv Finkleman" wrote in message ... Another interesting thing is how I can feed the antenna through the door to the balcony. I can't drill holes, but I currently have a piece of RG-58 squeezed through the closeddoor. Every day I check to see if anything has happened to it such as migration of the center conductor to the point where it shorts to the sheild. You might benefit from something like this: http://www.cometantenna.com/pdfs/CTC..._and_instr.pdf Alternatively, leave the door open a crack while passing coax through the opening but seal the opening with a full-height strip of masking tape to keep out the wintery winds. I'm not desperate, but nearly so, and anxious to get on the air again. Have you considered single band whips? The names "Hustler" and "Hamstick" come to mind but there are others. They need a counterpoise to work but the following anecdotes will provide some insight, I hope: I assembled and successfully demonstrated (for Field Day this year) a quick-and-dirty portable HF rig. I used the following crap: a pair of steel chassis slides bolted together at the ends and laid on the ground at a right angle. Their weight and orientation will keep them where they are placed. They are magnetic; a very thin single-use aluminum pan with two 20m radials (about 15 feet) bolted firmly to opposite sides of the baking dish; It laid on a flat part of the chassis slides; an MFJ magmount base (from a 1724B I think, whatever one has the 3/8 threaded socket), with the whip removed. It was placed onto the pan in such a location as to stay magnetically "stuck." the magmount base is capacitively coupled to the pan with the radials; (Would direct wiring from the shield to the radials be better? Dunno.) A Hustler 20m element screwed into the above magmount base. This foregoing electrified junkpile worked multiple stations in the Midwest from San Diego on 20m for Field Day. I used it on 20 and 40 (different whips and different baking pan radials, of course) while on a trip earlier this month with considerable success. The radials might prefer to be stretched out but this, too, can be worked-around. I've used them with the ends drooping off the corners of a balcony and had no trouble getting a match with a $5 swap meet manual tuner. More radials would likely be better but unwinding and re-winding radials around the baking pan is already a pain with just two. Irv, does any of this resonate with you and your balcony? Aside: Maybe I can improve the described radial scheme, like something that involves retractable metal tape rules. Then I'd just need one pan and I can set my radial lengths at will. New thought: If I bolted the free ends of some retractable metal tape rules directly to the steel chassis slides i would eliminate the baking pan, altogether. It offers a certain bizarre appeal. "Sal" |
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