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Folded Dipole Antenna
Hi,
I newbie in antenna area. Currently, I'm trying to design a folded dipole antenna. Thus, I need some ideas on how to design that antenna such the dimensions, length and others. Please help me. Thanks. |
Folded Dipole Antenna
frankieNrosie wrote:
Hi, I newbie in antenna area. Currently, I'm trying to design a folded dipole antenna. Thus, I need some ideas on how to design that antenna such the dimensions, length and others. Please help me. Thanks. http://www.k7mem.150m.com/Electronic...ed_dipole.html -- Jim Pennino Remove .spam.sux to reply. |
Folded Dipole Antenna
On Dec 3, 5:17*am, frankieNrosie frankieNrosie.
wrote: I'm trying to design a folded dipole antenna Please give us some more information. Design frequency? Single-Band? 50-ohm source? Local or DX? -- 73, Cecil, www.w5dxp.com |
Folded Dipole Antenna
On Fri, 03 Dec 2010 11:17:20 +0000, frankieNrosie wrote:
Hi, I newbie in antenna area. Currently, I'm trying to design a folded dipole antenna. Thus, I need some ideas on how to design that antenna such the dimensions, length and others. Please help me. Thanks. http://www.hard-core-dx.com/nordicdx.../t2design.html http://www.hard-core-dx.com/nordicdx...wire/t2fd.html Balan and term resistors can be purchased here http://www.packetradio.com/catalog/i...index&cPath=45 Or you can build the term resistor and balum yourself I used a carbon watercleaner cartridge to build my term resisor :-) |
Folded Dipole Antenna
On Sat, 4 Dec 2010 18:22:21 +0000 (UTC), No Spam
wrote: I used a carbon watercleaner cartridge to build my term resisor :-) ! ! ! ! This demands more discussion. 73's Richard Clark, KB7QHC |
Ho-made non-inductive resitor WAS: Folded Dipole Antenna
On Sat, 04 Dec 2010 11:44:55 -0800, Richard Clark wrote:
On Sat, 4 Dec 2010 18:22:21 +0000 (UTC), No Spam wrote: I used a carbon watercleaner cartridge to build my term resisor :-) ! ! ! ! This demands more discussion. 73's Richard Clark, KB7QHC Sure! I have dremmel-tooled open a used dried-out water filter cartridge from my fridge that contained a hollow carbon shaft about 10" long and 3" in diameter with a 3/4 inch hollow inside diameter. The end to end resistance was about 600ohms. The carbon shaft is a bit soft and crumbles under the pressure of tools. This was how I destroyed the first unit I played with in trying to make it 480ohms by trimming the ends. Using another filter, I encapsulated the carbon shaft inside a sewer tube. (Denser PVC and hopfully more impervious to heat) I attached conductors to the ends using flat washers with springs and left vent holes in the PVC end caps when I attached them to push it all together. I did not attempt to trim the resistance by shaving the length. The modules finished resistance measured ~590ohms. Since this WAS a used water filter, I ran some HV through it to heat it up a bit to see if it would vent gas or smoke. The resistance decreased a bit as it heated but returned to near 600ohms when it cooled. I kept the power to less then 100w using my bench HV power supply. After about 1 minute, the PVC started to feel warm but no smoke was seen though it did stink a bit. The whole PVC module I made sweeps out flat from 1Mhz (bottom of my test gear) to ~40Mhz where I think my wiring started having some effects. I had to use springs on the ends to push the contact washers up against the carbon shaft and suspect I need to come up with something better here. Also, the pressure of the springs and end caps varied the resistance about 20 ohms. I have run about 400w avg for several minutes into the load under voice and so-far the damn thing is still hanging on the T2FD antenna and loads just fine. In usage, the resistance varied about 50ohms upward in the last several months of tracking it. I hope to remove the resistor shortly and inspect if there is any chemical reaction with the steel washers and the carbon rod ends. I need some better way to make this contact and also some way to increase the surface area of the contact to stabilize and perhaps reduce the resistance. I'm thinking copper pipe endcaps heated up and cooled over the ends either on the outer diameter or on the inside hollow part of the carbon shaft. /****/ Another idea I just had is perhaps having someone with a ceramics oven paint on the endcaps with ceramic glaze. It would look like a giant ceramic resistor! But then again, I would guess that as the resistor heated up, it would crack. Never mind... /****/ I now have another filter module to dissect. I hope to come up with a better way to mount contacts to the carbon shaft and some way to assure a nice airflow around and hopefully through it to allow for higher power. In retrospect, with the amount of time and work I've put into this resistor project, I would have been better off purchasing the buxcomm resistors for $25. (I have one) But then again, I had fun playing with this too! If anything, ideally, I hope to come up with something that weighs half the weight of the buxcomm resistor so my T2FD antenna looks more graceful under the burden of the resistor. :-) 73! |
Ho-made non-inductive resitor WAS: Folded Dipole Antenna
On Dec 5, 4:28*pm, No Spam wrote:
On Sat, 04 Dec 2010 11:44:55 -0800, Richard Clark wrote: On Sat, 4 Dec 2010 18:22:21 +0000 (UTC), No Spam wrote: I used a carbon watercleaner cartridge to build my term resisor :-) ! ! ! ! This demands more discussion. 73's Richard Clark, KB7QHC Sure! I have dremmel-tooled open a used dried-out water filter cartridge from my fridge that contained a hollow carbon shaft about 10" long and 3" in diameter with a 3/4 inch hollow inside diameter. The end to end resistance was about 600ohms. The carbon shaft is a bit soft and crumbles under the pressure of tools. This was how I destroyed the first unit I played with in trying to make it 480ohms by trimming the ends. Using another filter, I encapsulated the carbon shaft inside a sewer tube. (Denser PVC and hopfully more impervious to heat) I attached conductors to the ends using flat washers with springs and left vent holes in the PVC end caps when I attached them to push it all together. I did not attempt to trim the resistance by shaving the length. The modules finished resistance measured ~590ohms. Since this WAS a used water filter, I ran some HV through it to heat it up a bit to see if it would vent gas or smoke. The resistance decreased a bit as it heated but returned to near 600ohms when it cooled. I kept the power to less then 100w using my bench HV power supply. After about 1 minute, the PVC started to feel warm but no smoke was seen though it did stink a bit. The whole PVC module I made sweeps out flat from 1Mhz (bottom of my test gear) to ~40Mhz where I think my wiring started having some effects. I had to use springs on the ends to push the contact washers up against the carbon shaft and suspect I need to come up with something better here. Also, the pressure of the springs and end caps varied the resistance about 20 ohms. I have run about 400w avg for several minutes into the load under voice and so-far the damn thing is still hanging on the T2FD antenna and loads just fine. In usage, the resistance varied about 50ohms upward in the last several months of tracking it. I hope to remove the resistor shortly and inspect if there is any chemical reaction with the steel washers and the carbon rod ends. I need some better way to make this contact and also some way to increase the surface area of the contact to stabilize and perhaps reduce the resistance. I'm thinking copper pipe endcaps heated up and cooled over the ends either on the outer diameter or on the inside hollow part of the carbon shaft. /****/ Another idea I just had is perhaps having someone with a ceramics oven paint on the endcaps with ceramic glaze. It would look like a giant ceramic resistor! *But then again, I would guess that as the resistor heated up, it would crack. * Never mind... /****/ I now have another filter module to dissect. I hope to come up with a better way to mount contacts to the carbon shaft and some way to assure a nice airflow around and hopefully through it to allow for higher power. In retrospect, with the amount of time and work I've put into this resistor project, I would have been better off purchasing the buxcomm resistors for $25. (I have one) * But then again, I had fun playing with this too! If anything, ideally, I hope to come up with something that weighs half the weight of the buxcomm resistor so my T2FD antenna looks more graceful under the burden of the resistor. :-) 73! A better way to attach it may be to electroplate Cu on the ends of it. Did this with some battery cores one time. Think I used CuSO4 solution as the electrolyte. Jimmie |
Ho-made non-inductive resitor WAS: Folded Dipole Antenna
"No Spam" wrote in message
... I have dremmel-tooled open a used dried-out water filter cartridge from my fridge that contained a hollow carbon shaft about 10" long and 3" in diameter with a 3/4 inch hollow inside diameter. The end to end resistance was about 600ohms. The carbon shaft is a bit soft and crumbles under the pressure of tools. This was how I destroyed the first unit I played with in trying to make it 480ohms by trimming the ends. Using another filter, I encapsulated the carbon shaft inside a sewer tube. (Denser PVC and hopfully more impervious to heat) I attached conductors to the ends using flat washers with springs and left vent holes in the PVC end caps when I attached them to push it all together. I did not attempt to trim the resistance by shaving the length. The modules finished resistance measured ~590ohms. Since this WAS a used water filter, I ran some HV through it to heat it up a bit to see if it would vent gas or smoke. The resistance decreased a bit as it heated but returned to near 600ohms when it cooled. I kept the power to less then 100w using my bench HV power supply. After about 1 minute, the PVC started to feel warm but no smoke was seen though it did stink a bit. The whole PVC module I made sweeps out flat from 1Mhz (bottom of my test gear) to ~40Mhz where I think my wiring started having some effects. I had to use springs on the ends to push the contact washers up against the carbon shaft and suspect I need to come up with something better here. Also, the pressure of the springs and end caps varied the resistance about 20 ohms. I have run about 400w avg for several minutes into the load under voice and so-far the damn thing is still hanging on the T2FD antenna and loads just fine. In usage, the resistance varied about 50ohms upward in the last several months of tracking it. I hope to remove the resistor shortly and inspect if there is any chemical reaction with the steel washers and the carbon rod ends. I need some better way to make this contact and also some way to increase the surface area of the contact to stabilize and perhaps reduce the resistance. I'm thinking copper pipe endcaps heated up and cooled over the ends either on the outer diameter or on the inside hollow part of the carbon shaft. /****/ Another idea I just had is perhaps having someone with a ceramics oven paint on the endcaps with ceramic glaze. It would look like a giant ceramic resistor! But then again, I would guess that as the resistor heated up, it would crack. Never mind... /****/ I now have another filter module to dissect. I hope to come up with a better way to mount contacts to the carbon shaft and some way to assure a nice airflow around and hopefully through it to allow for higher power. In retrospect, with the amount of time and work I've put into this resistor project, I would have been better off purchasing the buxcomm resistors for $25. (I have one) But then again, I had fun playing with this too! If anything, ideally, I hope to come up with something that weighs half the weight of the buxcomm resistor so my T2FD antenna looks more graceful under the burden of the resistor. :-) The water cleaner cartridge is activated charcoal with a small amount of organic binder. It is not graphite as graphite will not function to clean the water. Activated charcoal has an extremely large surface area which adsorbs contaminants. Depending on how it is produced, a gram of activated charcoal can have from 100 to 1000 square meters of surface area. Your idea of a metallic ceramic glaze will not work as the glaze is a low temperature melting glass (usually a lead glass) with fine metallic particles in it. Once fired, the glass melts, but the metallic particles are still insulated from each other. You can buy conductive copper, nickel, and silver based paints for repairing printed circuit boards. GC Electronics sells small bottles of silver print paint (Part No. 22-024 1 troy oz. Bottle) which has a surface resistivity of 0.1 ohms per square, and nickel print paint (Part No. 22-207 2 fl. oz. Bottle) which has a surface resistivity of 5 to 6 ohms per square. Be extremely careful when diluting these paints. Use only chemically pure solvents as any oil or other such material in the solvent will serve to insulate the particles from each other. GC Part No. 10-4102 Polystyrene Q-dope thinner (toluene) might be suitable. I would suggest the nickel print paint as the silver print is quite expensive. Heed the warnings in the respective MSDS's for these products. Another alternative is to have the ends of the activated charcoal rod electroplated. A thin copper flash film applied to each end, followed by a thicker conventional electroplate would give you contacts that could be soldered to. If there is someone in your area that does electroless nickel plating, this would also be suitable. An entirely different approach would be to use a conductive liquid for the resistance. An old QST article in June, 1965, entitled "Aqueous Dummy Loads" by Alexander Marion, W2CUE (now a silent key, I believe), should give you some ideas. 73, Dr. Barry L. Ornitz WA4VZQ |
Ho-made non-inductive resitor WAS: Folded Dipole Antenna
On Sun, 5 Dec 2010 21:28:56 +0000 (UTC), No Spam
wrote: In retrospect, with the amount of time and work I've put into this resistor project, I would have been better off purchasing the buxcomm resistors for $25. (I have one) But then again, I had fun playing with this too! If anything, ideally, I hope to come up with something that weighs half the weight of the buxcomm resistor so my T2FD antenna looks more graceful under the burden of the resistor. :-) Thanx for the follow-up, it was indeed of interest. 73's Richard Clark, KB7QHC |
Ho-made non-inductive resitor WAS: Folded Dipole Antenna
No Spam wrote:
On Sat, 04 Dec 2010 11:44:55 -0800, Richard Clark wrote: On Sat, 4 Dec 2010 18:22:21 +0000 (UTC), No Spam wrote: I used a carbon watercleaner cartridge to build my term resisor :-) ! ! ! ! This demands more discussion. 73's Richard Clark, KB7QHC Sure! I have dremmel-tooled open a used dried-out water filter cartridge from my fridge that contained a hollow carbon shaft about 10" long and 3" in diameter with a 3/4 inch hollow inside diameter. The end to end resistance was about 600ohms. The carbon shaft is a bit soft and crumbles under the pressure of tools. This was how I destroyed the first unit I played with in trying to make it 480ohms by trimming the ends. /****/ Another idea I just had is perhaps having someone with a ceramics oven paint on the endcaps with ceramic glaze. It would look like a giant ceramic resistor! But then again, I would guess that as the resistor heated up, it would crack. Never mind... /****/ I now have another filter module to dissect. I hope to come up with a better way to mount contacts to the carbon shaft and some way to assure a nice airflow around and hopefully through it to allow for higher power. Electrodes from an carbon arc light or pencil leads can also be used for a non precision resistor. Carbon "suppressor" ignition wire Copper sulfate in water makes a nice resistor, too. It's used a lot for "energy dump" resistors in pulse power applications. The power limiting thing on resistors like this is the packaging. If you put it inside PVC pipe, then the thermal resistance of the PVC limits how fast you can get the heat out (and the maximum temperature, too) |
Ho-made non-inductive resitor WAS: Folded Dipole Antenna
"Jim Lux" wrote in message
... Copper sulfate in water makes a nice resistor, too. It's used a lot for "energy dump" resistors in pulse power applications. From a theoretical standpoint, copper sulfate solutions should increase their resistance with frequency more rapidly than the sodium and ammonium chloride solutions used in the ARRL article. This is mainly due to ion mobiity in solutions. The power limiting thing on resistors like this is the packaging. If you put it inside PVC pipe, then the thermal resistance of the PVC limits how fast you can get the heat out (and the maximum temperature, too) Heat transfer was the primary reason for using transformer oil or mineral oil in the old Heath Cantenna. Without the oil, the Globar carborundum resistor would rapidly overheat. With the oil, the resistor could could dissipate 200 watts continuously. If you started with room temperature mineral oil, it could dissipate a kilowatt for about a minute before the oil got too hot and reached the flash point. Medicinal mineral oils have an open-cup flashpoint between 171 and 221 ºC depending on the specific manufacturer, while that of technical grade oils is somewhat lower. Of course, Heath suggested removing power to the Cantenna when it reached 60 ºC [the temperature at which the can is too hot to touch continuously]. At the time the HN-31 was produced, transformer oils generally contained polychlorinated biphenyl (PCB) additives which reduced their flammability. This is why Heath rated the Cantenna at 1 KW for ten minutes or less when it was filled to the proper level with transformer oil. I have a Bird dummy load rated at 1 kW continuous. It has a larger resistive element, still immersed in oil. However, the case is finned to help dissipate the heat. Jim is quite correct about the PVC pipe limiting the heat transfer. I would suggest using power chip resistors. Digi-Key carries Bournes chip resistors rated at 50 ohms and 100 watts for less than $8 each. 73, Dr. Barry L. Ornitz WA4VZQ |
Ho-made non-inductive resitor WAS: Folded Dipole Antenna
Nordic Breeds WA4VZQ wrote:
"Jim Lux" wrote in message ... Copper sulfate in water makes a nice resistor, too. It's used a lot for "energy dump" resistors in pulse power applications. From a theoretical standpoint, copper sulfate solutions should increase their resistance with frequency more rapidly than the sodium and ammonium chloride solutions used in the ARRL article. This is mainly due to ion mobiity in solutions. Copper sulfate is popular because it is compatible with copper electrodes, too. Sodium chloride tends to corrode the electrodes. There might also be some difference in solubility, which would affect the range of resistances available. http://home.earthlink.net/~jimlux/hv/rwater.htm has a discussion of building water resistors for HV applications. |
Ho-made non-inductive resitor WAS: Folded Dipole Antenna
On Mon, 06 Dec 2010 16:52:21 -0500, Nordic Breeds WA4VZQ rearranged some
electrons to say: Jim is quite correct about the PVC pipe limiting the heat transfer. I would suggest using power chip resistors. Digi-Key carries Bournes chip resistors rated at 50 ohms and 100 watts for less than $8 each. 73, Dr. Barry L. Ornitz WA4VZQ Amen on the thick-film chip resistors. I built a 200W dummy load using two 100 ohm 100W devices in parallel. |
Ho-made non-inductive resitor WAS: Folded Dipole Antenna
On Dec 5, 8:13*pm, "Nordic Breeds WA4VZQ"
wrote: "No Spam" wrote in message ... I have dremmel-tooled open a used dried-out water filter cartridge from my fridge that contained a hollow carbon shaft about 10" long and 3" in diameter with a 3/4 inch hollow inside diameter. The end to end resistance was about 600ohms. The carbon shaft is a bit soft and crumbles under the pressure of tools. This was how I destroyed the first unit I played with in trying to make it 480ohms by trimming the ends. Using another filter, I encapsulated the carbon shaft inside a sewer tube. (Denser PVC and hopfully more impervious to heat) I attached conductors to the ends using flat washers with springs and left vent holes in the PVC end caps when I attached them to push it all together. I did not attempt to trim the resistance by shaving the length. The modules finished resistance measured ~590ohms. Since this WAS a used water filter, I ran some HV through it to heat it up a bit to see if it would vent gas or smoke. The resistance decreased a bit as it heated but returned to near 600ohms when it cooled. I kept the power to less then 100w using my bench HV power supply. After about 1 minute, the PVC started to feel warm but no smoke was seen though it did stink a bit. The whole PVC module I made sweeps out flat from 1Mhz (bottom of my test gear) to ~40Mhz where I think my wiring started having some effects. I had to use springs on the ends to push the contact washers up against the carbon shaft and suspect I need to come up with something better here. Also, the pressure of the springs and end caps varied the resistance about 20 ohms. I have run about 400w avg for several minutes into the load under voice and so-far the damn thing is still hanging on the T2FD antenna and loads just fine. In usage, the resistance varied about 50ohms upward in the last several months of tracking it. I hope to remove the resistor shortly and inspect if there is any chemical reaction with the steel washers and the carbon rod ends. I need some better way to make this contact and also some way to increase the surface area of the contact to stabilize and perhaps reduce the resistance. I'm thinking copper pipe endcaps heated up and cooled over the ends either on the outer diameter or on the inside hollow part of the carbon shaft. /****/ Another idea I just had is perhaps having someone with a ceramics oven paint on the endcaps with ceramic glaze. It would look like a giant ceramic resistor! *But then again, I would guess that as the resistor heated up, it would crack. * Never mind... /****/ I now have another filter module to dissect. I hope to come up with a better way to mount contacts to the carbon shaft and some way to assure a nice airflow around and hopefully through it to allow for higher power. In retrospect, with the amount of time and work I've put into this resistor project, I would have been better off purchasing the buxcomm resistors for $25. (I have one) * But then again, I had fun playing with this too! If anything, ideally, I hope to come up with something that weighs half the weight of the buxcomm resistor so my T2FD antenna looks more graceful under the burden of the resistor. :-) The water cleaner cartridge is activated charcoal with a small amount of organic binder. *It is not graphite as graphite will not function to clean the water. *Activated charcoal has an extremely large surface area which adsorbs contaminants. *Depending on how it is produced, a gram of activated charcoal can have from 100 to 1000 square meters of surface area. Your idea of a metallic ceramic glaze will not work as the glaze is a low temperature melting glass (usually a lead glass) with fine metallic particles in it. *Once fired, the glass melts, but the metallic particles are still insulated from each other. You can buy conductive copper, nickel, and silver based paints for repairing printed circuit boards. *GC Electronics sells small bottles of silver print paint (Part No. 22-024 1 troy oz. Bottle) which has a surface resistivity of 0.1 ohms per square, and nickel print paint (Part No. 22-207 2 fl. oz. Bottle) which has a surface resistivity of 5 to 6 ohms per square. *Be extremely careful when diluting these paints. *Use only chemically pure solvents as any oil or other such material in the solvent will serve to insulate the particles from each other. *GC Part No. 10-4102 Polystyrene Q-dope thinner (toluene) might be suitable. *I would suggest the nickel print paint as the silver print is quite expensive. *Heed the warnings in the respective MSDS's for these products. Another alternative is to have the ends of the activated charcoal rod electroplated. *A thin copper flash film applied to each end, followed by a thicker conventional electroplate would give you contacts that could be soldered to. *If there is someone in your area that does electroless nickel plating, this would also be suitable. An entirely different approach would be to use a conductive liquid for the resistance. *An old QST article in June, 1965, entitled "Aqueous Dummy Loads" by Alexander Marion, W2CUE (now a silent key, I believe), should give you some ideas. * * 73, Dr. Barry L. Ornitz * * WA4VZQ Yes, I had a friend who was in the Navy during WWII, he described how they used buckets of salt(sea) water for dummy loads. The further you put the electrode in the bucket the lower the resistance. Jimmie |
Ho-made non-inductive resitor WAS: Folded Dipole Antenna
On Dec 8, 12:25*pm, Jim Higgins wrote:
On Sun, 5 Dec 2010 21:28:56 +0000 (UTC), No Spam wrote: Another idea I just had is perhaps having someone with a ceramics oven paint on the endcaps with ceramic glaze. It would look like a giant ceramic resistor! *But then again, I would guess that as the resistor heated up, it would crack. * Never mind... I'd guess the high heat used to fire ceramics would simply cause the carbon to burn up. In the Navy, the shipyards all have a device called a Load Bank. It's a large metal tank on an insulated vehicle. The tank is filled up with salt water and electrodes lowered into it to test the output of the ship's generators. Any chance that it has ham applications? I intend to try it first with an antenna analyzer and then, if it looks promising, my rig. |
Ho-made non-inductive resitor WAS: Folded Dipole Antenna
On Dec 9, 12:42*am, "Sal M. Onella" wrote:
On Dec 8, 12:25*pm, Jim Higgins wrote: On Sun, 5 Dec 2010 21:28:56 +0000 (UTC), No Spam wrote: Another idea I just had is perhaps having someone with a ceramics oven paint on the endcaps with ceramic glaze. It would look like a giant ceramic resistor! *But then again, I would guess that as the resistor heated up, it would crack. * Never mind... I'd guess the high heat used to fire ceramics would simply cause the carbon to burn up. In the Navy, the shipyards all have a device called a Load Bank. *It's a large metal tank on an insulated vehicle. The tank is filled up with salt water and electrodes lowered into it to test the output of the ship's generators. *Any chance that it has ham applications? *I intend to try it first with an antenna analyzer and then, if it looks promising, my rig. Yes they did the same with transmitters, often all you need was a metal mop bucket and a piece of copper pipe. Jimmie |
Ho-made non-inductive resitor WAS: Folded Dipole Antenna
On 12/9/2010 7:56 AM, JIMMIE wrote:
On Dec 9, 12:42 am, "Sal M. wrote: On Dec 8, 12:25 pm, Jim wrote: On Sun, 5 Dec 2010 21:28:56 +0000 (UTC), No wrote: Another idea I just had is perhaps having someone with a ceramics oven paint on the endcaps with ceramic glaze. It would look like a giant ceramic resistor! But then again, I would guess that as the resistor heated up, it would crack. Never mind... I'd guess the high heat used to fire ceramics would simply cause the carbon to burn up. In the Navy, the shipyards all have a device called a Load Bank. It's a large metal tank on an insulated vehicle. The tank is filled up with salt water and electrodes lowered into it to test the output of the ship's generators. Any chance that it has ham applications? I intend to try it first with an antenna analyzer and then, if it looks promising, my rig. Yes they did the same with transmitters, often all you need was a metal mop bucket and a piece of copper pipe Jimmie A water load bank is good for hundreds of KW at 60hz. For use with a pair of 6146's we used to wire a lamp to a coax connector. We had a load as well as visual indication of the relative power output. |
Ho-made non-inductive resitor WAS: Folded Dipole Antenna
On Dec 9, 1:51*pm, Jim wrote:
On 12/9/2010 7:56 AM, JIMMIE wrote: On Dec 9, 12:42 am, "Sal M. *wrote: On Dec 8, 12:25 pm, Jim *wrote: On Sun, 5 Dec 2010 21:28:56 +0000 (UTC), No wrote: Another idea I just had is perhaps having someone with a ceramics oven paint on the endcaps with ceramic glaze. It would look like a giant ceramic resistor! *But then again, I would guess that as the resistor heated up, it would crack. * Never mind... I'd guess the high heat used to fire ceramics would simply cause the carbon to burn up. In the Navy, the shipyards all have a device called a Load Bank. *It's a large metal tank on an insulated vehicle. The tank is filled up with salt water and electrodes lowered into it to test the output of the ship's generators. *Any chance that it has ham applications? *I intend to try it first with an antenna analyzer and then, if it looks promising, my rig.. Yes they did the same with transmitters, often all you need was a metal mop bucket and a piece of copper pipe Jimmie A water load bank is good for hundreds of KW at 60hz. For use with a pair of 6146's we used to wire a lamp to a coax connector. We had a load as well as visual indication of the relative power output.- Hide quoted text - - Show quoted text - I built a wattmeter of sorts around a circuit like that. After tuning up the transmitter to light bulb dummy load I would measure the resistnace of a photo resistor exposed to the light then see how much 60Hz AC voltage and current took to light the lamps to the same brillance. Jimmie |
Ho-made non-inductive resitor WAS: Folded Dipole Antenna
Yes they did the same with transmitters, often all you need was a metal mop bucket and a piece of copper pipe Jimmie A water load bank is good for hundreds of KW at 60hz. For use with a pair of 6146's we used to wire a lamp to a coax connector. We had a load as well as visual indication of the relative power output.- Hide quoted text - - Show quoted text - I built a wattmeter of sorts around a circuit like that. After tuning up the transmitter to light bulb dummy load I would measure the resistnace of a photo resistor exposed to the light then see how much 60Hz AC voltage and current took to light the lamps to the same brillance. Jimmie if you were really good you could estimate the power from the brightness in real time. it did take a lot of practice. |
Ho-made non-inductive resitor WAS: Folded Dipole Antenna
On Thu, 9 Dec 2010 19:21:48 -0800 (PST), JIMMIE
wrote: I built a wattmeter of sorts around a circuit like that. After tuning up the transmitter to light bulb dummy load I would measure the resistnace of a photo resistor exposed to the light then see how much 60Hz AC voltage and current took to light the lamps to the same brillance. Hi Jimmie, An excellent example of the concept of a transfer standard. This method is one of the oldest and most robust methods of accurate measurement. It removes a lot of variables (by, ironically, not changing them) that would be exceedingly difficult to determine their impact upon an accurate measurement. 73's Richard Clark, KB7QHC |
Ho-made non-inductive resitor WAS: Folded Dipole Antenna
In message , Richard Clark
writes On Thu, 9 Dec 2010 19:21:48 -0800 (PST), JIMMIE wrote: I built a wattmeter of sorts around a circuit like that. After tuning up the transmitter to light bulb dummy load I would measure the resistnace of a photo resistor exposed to the light then see how much 60Hz AC voltage and current took to light the lamps to the same brillance. Hi Jimmie, An excellent example of the concept of a transfer standard. This method is one of the oldest and most robust methods of accurate measurement. It removes a lot of variables (by, ironically, not changing them) that would be exceedingly difficult to determine their impact upon an accurate measurement. Do a Google on "Grease Spot Photometer" (back to school physics, over 50 years ago!). Very simple to make, and pretty accurate. -- Ian |
Ho-made non-inductive resitor WAS: Folded Dipole Antenna
On Fri, 10 Dec 2010 19:52:55 +0000, Ian Jackson
wrote: Do a Google on "Grease Spot Photometer" (back to school physics, over 50 years ago!). Very simple to make, and pretty accurate. Hi Ian, A very good suggestion which immediately led me to: http://www.phy6.org/outreach/edu/greaspot.htm A variation of this that I calibrated in the lab is an Optical Pyrometer: http://www.pyrometer.com/Pyro_Optical.html Comparison measurements can be very accurate iff what you are comparing to (aka standard) is known to sufficient accuracy. Both references provide more than enough to inform the reader with the essential details. Slightly more elaborate methods of measuring RF power fall into the Calorimetric method (actual heat). Hewlett Packard made the ultimate heat transfer standard - the HP 434A power meter DC to 12GHz! 73's Richard Clark, KB7QHC |
Ho-made non-inductive resitor WAS: Folded Dipole Antenna
Richard Clark wrote:
On Fri, 10 Dec 2010 19:52:55 +0000, Ian Jackson wrote: Do a Google on "Grease Spot Photometer" (back to school physics, over 50 years ago!). Very simple to make, and pretty accurate. Hi Ian, A very good suggestion which immediately led me to: http://www.phy6.org/outreach/edu/greaspot.htm A variation of this that I calibrated in the lab is an Optical Pyrometer: http://www.pyrometer.com/Pyro_Optical.html Comparison measurements can be very accurate iff what you are comparing to (aka standard) is known to sufficient accuracy. Both references provide more than enough to inform the reader with the essential details. Slightly more elaborate methods of measuring RF power fall into the Calorimetric method (actual heat). Hewlett Packard made the ultimate heat transfer standard - the HP 434A power meter DC to 12GHz! I think HP made a number of DC substitution/transfer sorts of power meters The 434 was unique in using flowing oil and it could directly measure watts, without needing attenuators (which have their own calibration issues). Didn't the 432 used the idea of DC power substituting for RF power to bring the sum to a fixed temperature? The difference between the 432 and the 434 is that the thing measuring the temperature is also the RF load in the 432. The 434 just uses the RF as a heater, and relies on the DC powered heater and RF powered heater being matched. A NIST Type IV power meter (like those from Arbiter) definitely does DC power substitution, and uses the HP/Agilent thermistor heads. Once you get away from "replacement heat" sorts of schemes, you'd be into the classic calorimeter.. measure the temperature change over time, and then turn that into energy. You'd calibrate it by putting DC on the same sensor, essentially measuring the thermal capacity. The thermocouple heads (8481A, 8482A for instance) work pretty much the same way as the thermistor mounts.. measuring the heat dissipated by the RF power coming in. They're not a substitution measurement though.. The actual sensor changes voltage in response to temperature (with a clever compensation scheme so that overall temperature doesn't affect it) But these are all basically thermal sensors (as opposed to, say, RF voltmeters, like a diode detector as in a 8481D or 8484A head) and they dissipate the RF power being measured. 73's Richard Clark, KB7QHC |
Ho-made non-inductive resitor WAS: Folded Dipole Antenna
On Fri, 10 Dec 2010 17:09:25 -0800, Jim Lux
wrote: Didn't the 432 used the idea of DC power substituting for RF power to bring the sum to a fixed temperature? The difference between the 432 and the 434 is that the thing measuring the temperature is also the RF load in the 432. The 434 just uses the RF as a heater, and relies on the DC powered heater and RF powered heater being matched. Hi Jim, I worked with a world of different methods of measuring RF power. Thermistors, Thermocouples (the 8481A, 8482 you identify - refer to HP Application Note 64-1, "Fundamentals of RF and Microwave Power Measurements"), and the older technologies of Thermopile, Wollaston wire, Bolometers (which encompass the same things as those already mentioned), and Barreters (a variation upon, or exactly the same as the Wollaston wire - I've seen 10mA fuses used for the same purpose), diodes certainly (generally for peak power). I have had the occasion to burn out more than a couple of these. Those in a bridge configurations (many in fact as the 434 is an example) are temperature tracking. An excellent description can be found on page 14 of: http://www.hpmemory.org/an/pdf/an_64-1a.pdf for a thermistor bridge that compensates for ambient heat. "The fundamental premise in using a thermistor for power measurements is that the RF power absorbed by the thermistor has the same heating effect on the thermistor as the DC power." This from the HP432A which has a dual thermistor, dual bridge design. Pages 18 through 20 describe how heats are separated in a thermocouple bridge to compensate for ambient. From page 26 is discussion of diodes. As for accuracies: "All thermocouple and diode power sensors require a power reference to absolute power, traceable to the manufacturer or national standards." A good remainder of the application note goes into the issues of accurate determination. Pages 51 and 60 each has a table of all the various sources of error (rarely considered outside of the Metrology Lab, but ever present nonetheless). This was standard consideration and the examples the author offers yields roughly 5% accurate measurements from the best of instrumentation - an accuracy figure that I frequently read here as commonly available from the Bird RF meter (and I have the experience to the matter having calibrated these meters to know that is a fantasy of the first order). 73's Richard Clark, KB7QHC |
Quote:
i'm wanna design multiband antenna, not sure about impedance.. |
Folded Dipole Antenna
On Sat, 11 Dec 2010 16:56:34 +0000, frankieNrosie
wrote: freq=5.8GHz i'm wanna design multiband antenna, not sure about impedance.. If you want one frequency, then it would imply one band. If you want multiband, then you need to give us the other frequencies. 73's Richard Clark, KB7QHC |
Quote:
i use the diode as the switch to reconfigure the freq..later on i will upload the figure of proposed antenna |
Folded Dipole Antenna
On Sun, 12 Dec 2010 12:18:11 +0000, frankieNrosie
wrote: If you want one frequency, then it would imply one band. If you want multiband, then you need to give us the other frequencies. the other freq, not specific yet.. Then how do you know it is multiband? Your most specific request is for a folded dipole at one frequency. From end-to-end it will be slightly less than 1/2 wavelength long at that frequency. Now, if you add another frequency, your folded dipole will need to be 1/2 wavelength long at that frequency. Obviously to be "multiband" your folded dipole cannot be both lengths at the same time. The requirment for the fold of the folded dipole is obscure. A fan dipole would work for multiband. i use the diode as the switch to reconfigure the freq..later on i will upload the figure of proposed antenna I have not the vaguest idea what that is about. "The diode"? 73's Richard Clark, KB7QHC |
Quote:
so, if i got many length of the driven element, thus i'll have many freq.. do u understand me? |
Folded Dipole Antenna
On Tue, 14 Dec 2010 06:19:35 +0000, frankieNrosie
wrote: i use the diode as the switch to reconfigure the freq..later on i will upload the figure of proposed antenna- I have not the vaguest idea what that is about. "The diode"? diode is use as a switch to vary the length of the driven element.. so, if i got many length of the driven element, thus i'll have many freq.. do u understand me? I understand what you write, but not why you choose this arrangement. I can guess many configurations, but your goal is obscure. Inventive to say the least. Conventional antenna design already has passive solutions for your active element requirement and they stand the chance of reducing the risks inherent in putting a diode into an antenna structure for switching its length. 73's Richard Clark, KB7QHC |
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