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#1
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Skin effect question
I was palnning on building a 2M Yagi this weekend and was wondering if
my available bill of materials would have a significant effect on normal design parameters. The plan is to use 3/4 inch EMT conduit for the boom and 3/8 inch all-thread for the elements. My concern was that the threads could change the design frequency. JImmie |
#2
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Skin effect question
On 19 mar, 22:25, JIMMIE wrote:
I was palnning on building a 2M Yagi this weekend and was wondering if my available bill of materials would have a significant effect on normal design parameters. The plan is to use 3/4 inch EMT conduit for the boom and 3/8 inch all-thread for the elements. My concern was that the threads could change the design frequency. JImmie Hello Jimmie, I think it will be OK, but if you want to be 100% sure, make a dipole of same thickness tubing and one from the threaded material of choice. If results are same, you can use it without dimension scaling. Are you using galvanized or alu material? If required, apply some corrosion protection. With kind regards, Wim PA3DJS www.tetech.nl .. |
#3
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Skin effect question
On Mar 19, 5:59*pm, Wimpie wrote:
On 19 mar, 22:25, JIMMIE wrote: I was palnning on building a 2M Yagi this weekend and was wondering if my available bill of materials would have a significant effect on normal design parameters. The plan is to use 3/4 inch EMT conduit for the boom and 3/8 inch all-thread for the elements. My concern was that the threads could change the design frequency. JImmie Hello Jimmie, I think it will be OK, but if you want to be 100% sure, make a dipole of same thickness tubing and one from the threaded material of choice. If results are same, you can use it without dimension scaling. *Are you using galvanized or alu material? If required, apply some corrosion protection. With kind regards, Wim PA3DJSwww.tetech.nl . Galvanized, The pupose was to demostrate that materials can often be adlib and still have a useable antenna. Maybe this one will not last 30 years before it corrodes away but probably 5 or 6. Also I want to demonstrate the value of using a jig when building many antennas all made the same. I have tried the test you mention on 10 meters before replacing a vertical mounted on my truck. Changing materials didn't seem to make much difference. WIll try the same for 2M but I dont have an SWR meter for 2M at this time.. Was hopng someone in the group might think this interesing enough to try. Jimmie |
#4
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Skin effect question
On 3/20/2011 3:09 PM, JIMMIE wrote:
On Mar 19, 5:59 pm, wrote: On 19 mar, 22:25, wrote: I was palnning on building a 2M Yagi this weekend and was wondering if my available bill of materials would have a significant effect on normal design parameters. The plan is to use 3/4 inch EMT conduit for the boom and 3/8 inch all-thread for the elements. My concern was that the threads could change the design frequency. JImmie Hello Jimmie, I think it will be OK, but if you want to be 100% sure, make a dipole of same thickness tubing and one from the threaded material of choice. If results are same, you can use it without dimension scaling. Are you using galvanized or alu material? If required, apply some corrosion protection. With kind regards, Wim PA3DJSwww.tetech.nl . Galvanized, The pupose was to demostrate that materials can often be adlib and still have a useable antenna. Maybe this one will not last 30 years before it corrodes away but probably 5 or 6. Also I want to demonstrate the value of using a jig when building many antennas all made the same. I have tried the test you mention on 10 meters before replacing a vertical mounted on my truck. Changing materials didn't seem to make much difference. WIll try the same for 2M but I dont have an SWR meter for 2M at this time.. Was hopng someone in the group might think this interesing enough to try. Jimmie I made a j-pole from galvanized steel. It worked beautifully. When I replaced it with a commercial antenna I notice very little change in performance and signal strength. I had hoped my kluge was deficient in performance compared to the commercial antenna. Didn't seem so. My QTH was way out in the country side about 20 miles from the nearest repeater. Just a story for you, no hard data. Sorry. John |
#5
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Skin effect question
On 20 mar, 21:09, JIMMIE wrote:
On Mar 19, 5:59*pm, Wimpie wrote: On 19 mar, 22:25, JIMMIE wrote: I was palnning on building a 2M Yagi this weekend and was wondering if my available bill of materials would have a significant effect on normal design parameters. The plan is to use 3/4 inch EMT conduit for the boom and 3/8 inch all-thread for the elements. My concern was that the threads could change the design frequency. JImmie Hello Jimmie, I think it will be OK, but if you want to be 100% sure, make a dipole of same thickness tubing and one from the threaded material of choice. If results are same, you can use it without dimension scaling. *Are you using galvanized or alu material? If required, apply some corrosion protection. With kind regards, Wim PA3DJSwww.tetech.nl . Galvanized, The pupose was to demostrate *that materials can often be adlib and still have a useable antenna. Maybe this one will not last 30 years before it corrodes away but probably 5 or 6. Also I want to demonstrate the value of using a jig when building many antennas all made the same. I have tried the test you mention on 10 meters before replacing a vertical mounted on my truck. Changing materials didn't seem to make much difference. WIll *try the same for 2M but I dont have an SWR meter for 2M at this time.. Was hopng someone in the group might think this interesing enough to try. Jimmie Hello Jimmie Zinc has about 60% conductivity of alu alloys that are used for antennas, so the surface resistance will be almost 80% of alu tubing (same diameter). Of course you have thread that increases the path length. Given the thread, your net conductivity will be about 40% (w.r.t. alu). This will be OK for doing your experiments and to demonstrate that you can use many materials for antennas. I would recommend you to find some means to determine VSWR (or refl. coeff.) at 2m (home made slotted coaxial line, or home brew coupler?). With kind regards, Wim PA3DJS www.tetech.nl Without abc, PM will reach me |
#6
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Skin effect question
"John - KD5YI" wrote in message ... I made a j-pole from galvanized steel. It worked beautifully. When I replaced it with a commercial antenna I notice very little change in performance and signal strength. I had hoped my kluge was deficient in performance compared to the commercial antenna. Didn't seem so. My QTH was way out in the country side about 20 miles from the nearest repeater. Just a story for you, no hard data. Sorry. John Unless you can tell the differance in a few tenths of a dB, almost any conductive material will work for simple antennas if the diameter is large in terms of a wavelength. If the antenna is built the same or vary similar to a comercial antenna, you usually don't notice any differance. Lots of money is spent on the comercial stuff for little or no improvement. Problem for many is buying the materials. If you only need a small ammount of material , you often have to buy a lot. Then not everyone has the machinery to do the building. |
#7
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Skin effect question
On 3/20/2011 5:14 PM, Ralph Mowery wrote:
"John - wrote in message ... I made a j-pole from galvanized steel. It worked beautifully. When I replaced it with a commercial antenna I notice very little change in performance and signal strength. I had hoped my kluge was deficient in performance compared to the commercial antenna. Didn't seem so. My QTH was way out in the country side about 20 miles from the nearest repeater. Just a story for you, no hard data. Sorry. John Unless you can tell the differance in a few tenths of a dB, almost any conductive material will work for simple antennas if the diameter is large in terms of a wavelength. If the antenna is built the same or vary similar to a comercial antenna, you usually don't notice any differance. Of course. My response is aimed at the OP's subject line. I'm trying to be encouraging. Lots of money is spent on the comercial stuff for little or no improvement. Problem for many is buying the materials. If you only need a small ammount of material , you often have to buy a lot. Then not everyone has the machinery to do the building. I bought a long piece of chain link fence top rail for the mast and a piece of conduit for the 1/4 wave element. I used a hacksaw and a drill to do the machining. I used automobile hose clamps to connect the transmission line to the kluge. It worked well for about 10 years until high winds bent the mast (chain link fence top rail is not that stiff). |
#8
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Skin effect question
On 3/20/2011 5:11 PM, Wimpie wrote:
On 20 mar, 21:09, wrote: On Mar 19, 5:59 pm, wrote: On 19 mar, 22:25, wrote: I was palnning on building a 2M Yagi this weekend and was wondering if my available bill of materials would have a significant effect on normal design parameters. The plan is to use 3/4 inch EMT conduit for the boom and 3/8 inch all-thread for the elements. My concern was that the threads could change the design frequency. JImmie Hello Jimmie, I think it will be OK, but if you want to be 100% sure, make a dipole of same thickness tubing and one from the threaded material of choice. If results are same, you can use it without dimension scaling. Are you using galvanized or alu material? If required, apply some corrosion protection. With kind regards, Wim PA3DJSwww.tetech.nl . Galvanized, The pupose was to demostrate that materials can often be adlib and still have a useable antenna. Maybe this one will not last 30 years before it corrodes away but probably 5 or 6. Also I want to demonstrate the value of using a jig when building many antennas all made the same. I have tried the test you mention on 10 meters before replacing a vertical mounted on my truck. Changing materials didn't seem to make much difference. WIll try the same for 2M but I dont have an SWR meter for 2M at this time.. Was hopng someone in the group might think this interesing enough to try. Jimmie Hello Jimmie Zinc has about 60% conductivity of alu alloys that are used for antennas, so the surface resistance will be almost 80% of alu tubing (same diameter). Of course you have thread that increases the path length. Given the thread, your net conductivity will be about 40% (w.r.t. alu). This will be OK for doing your experiments and to demonstrate that you can use many materials for antennas. I would recommend you to find some means to determine VSWR (or refl. coeff.) at 2m (home made slotted coaxial line, or home brew coupler?). With kind regards, Wim PA3DJS www.tetech.nl Without abc, PM will reach me Here is one the OP can build: http://www.qsl.net/xq2fod/Electron/swr/swr.html |
#9
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Skin effect question
On 21 mar, 00:42, John - KD5YI wrote:
On 3/20/2011 5:11 PM, Wimpie wrote: On 20 mar, 21:09, *wrote: On Mar 19, 5:59 pm, *wrote: On 19 mar, 22:25, *wrote: I was palnning on building a 2M Yagi this weekend and was wondering if my available bill of materials would have a significant effect on normal design parameters. The plan is to use 3/4 inch EMT conduit for the boom and 3/8 inch all-thread for the elements. My concern was that the threads could change the design frequency. JImmie Hello Jimmie, I think it will be OK, but if you want to be 100% sure, make a dipole of same thickness tubing and one from the threaded material of choice.. If results are same, you can use it without dimension scaling. *Are you using galvanized or alu material? If required, apply some corrosion protection. With kind regards, Wim PA3DJSwww.tetech.nl . Galvanized, The pupose was to demostrate *that materials can often be adlib and still have a useable antenna. Maybe this one will not last 30 years before it corrodes away but probably 5 or 6. Also I want to demonstrate the value of using a jig when building many antennas all made the same. I have tried the test you mention on 10 meters before replacing a vertical mounted on my truck. Changing materials didn't seem to make much difference. WIll *try the same for 2M but I dont have an SWR meter for 2M at this time.. Was hopng someone in the group might think this interesing enough to try. Jimmie Hello Jimmie Zinc has about 60% conductivity of alu alloys that are used for antennas, so the surface resistance will be almost 80% of alu tubing (same diameter). *Of course you have thread that increases the path length. Given the thread, your net conductivity will be about 40% (w.r.t. alu). This will be OK for doing your experiments and to demonstrate that you can use many materials for antennas. I would recommend you to find some means to determine VSWR (or refl. coeff.) at 2m (home made slotted coaxial line, or home brew coupler?). With kind regards, Wim PA3DJS www.tetech.nl Without abc, PM will reach me Here is one the OP can build: http://www.qsl.net/xq2fod/Electron/swr/swr.html Hello John, I made (and still use) same type of wheatstone bridge refl. coeff. meter with BAT15 diodes (so only low power) and 0805 SMD. Instead of a moving coil indicator I used a 10 MOhm DVM (to get better linearity at low power input). Such a simple device is very useful. Only limitation is that you can't have it in between during normal operation as you have 6 dB insertion loss. Wim PA3DJS www.tetech.nl |
#10
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Skin effect question
On 3/21/2011 7:06 AM, Wimpie wrote:
On 21 mar, 00:42, John - wrote: On 3/20/2011 5:11 PM, Wimpie wrote: On 20 mar, 21:09, wrote: On Mar 19, 5:59 pm, wrote: On 19 mar, 22:25, wrote: I was palnning on building a 2M Yagi this weekend and was wondering if my available bill of materials would have a significant effect on normal design parameters. The plan is to use 3/4 inch EMT conduit for the boom and 3/8 inch all-thread for the elements. My concern was that the threads could change the design frequency. JImmie Hello Jimmie, I think it will be OK, but if you want to be 100% sure, make a dipole of same thickness tubing and one from the threaded material of choice. If results are same, you can use it without dimension scaling. Are you using galvanized or alu material? If required, apply some corrosion protection. With kind regards, Wim PA3DJSwww.tetech.nl . Galvanized, The pupose was to demostrate that materials can often be adlib and still have a useable antenna. Maybe this one will not last 30 years before it corrodes away but probably 5 or 6. Also I want to demonstrate the value of using a jig when building many antennas all made the same. I have tried the test you mention on 10 meters before replacing a vertical mounted on my truck. Changing materials didn't seem to make much difference. WIll try the same for 2M but I dont have an SWR meter for 2M at this time.. Was hopng someone in the group might think this interesing enough to try. Jimmie Hello Jimmie Zinc has about 60% conductivity of alu alloys that are used for antennas, so the surface resistance will be almost 80% of alu tubing (same diameter). Of course you have thread that increases the path length. Given the thread, your net conductivity will be about 40% (w.r.t. alu). This will be OK for doing your experiments and to demonstrate that you can use many materials for antennas. I would recommend you to find some means to determine VSWR (or refl. coeff.) at 2m (home made slotted coaxial line, or home brew coupler?). With kind regards, Wim PA3DJS www.tetech.nl Without abc, PM will reach me Here is one the OP can build: http://www.qsl.net/xq2fod/Electron/swr/swr.html Hello John, I made (and still use) same type of wheatstone bridge refl. coeff. meter with BAT15 diodes (so only low power) and 0805 SMD. Instead of a moving coil indicator I used a 10 MOhm DVM (to get better linearity at low power input). That's a great idea. I wish I had thought of that. John |
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