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Super-whippy whip antennas
Hi chaps, Can anyone suggest a suitable material from which to make an ultra-flexible mobile whip antenna say about 3 to 4 feet long. I need something that can be bent to 90 degrees at a very small radius and still return to reasonable straightness. Thanks, p. -- "I believe history will be kind to me, since I intend to write it." - Winston Churchill |
Can anyone suggest a suitable material from which to make an
ultra-flexible mobile whip antenna say about 3 to 4 feet long. I need something that can be bent to 90 degrees at a very small radius and still return to reasonable straightness. Sure, get some 1/4 inch fiberglass rod, loosely helix some #22 wire up the length, and secure with some heat-shrink tubing. You can bend this into a near circle. 73 Gary N4AST |
Can anyone suggest a suitable material from which to make an
ultra-flexible mobile whip antenna say about 3 to 4 feet long. I need something that can be bent to 90 degrees at a very small radius and still return to reasonable straightness. Sure, get some 1/4 inch fiberglass rod, loosely helix some #22 wire up the length, and secure with some heat-shrink tubing. You can bend this into a near circle. 73 Gary N4AST |
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On Sat, 02 Aug 2003 03:25:47 GMT, Active8
wrote: In article vKBWa.20717$KF1.308575@amstwist00, lid says... Paul Burridge wrote: Hi chaps, Can anyone suggest a suitable material from which to make an ultra-flexible mobile whip antenna say about 3 to 4 feet long. I need something that can be bent to 90 degrees at a very small radius and still return to reasonable straightness. I think thin piano wire will give the best results. Place a lot of them in a flexible tube to gain some thickness and have them silvered for conductivity - or add a stranded copper wire. Spring metal strip may also work, especially if you can manage some type of hinge at the base that allows it to turn when sideways force is exerted, or if the force is in one plane. Thomas what is a tight bend? music wire comes in diff sizes and the number in the tube and how tightly the tube conforms to it will have an effect on the flexibility. Yeah, sorry chaps, I should have better defined what I meant by 'very small radius'. I compete in radio-controlled model battles, so the model stands to get fipped upside down from time to time in a very bruising environment and it already has a very low ground-clearance, so using a spring as a base mounting won't help much, I'm afraid. We're talking about radiuses of as little as 5mm! How about the specific grade of stainless steel in wire form that springs are made from? I know where I can get hold of some of that.... -- "I believe history will be kind to me, since I intend to write it." - Winston Churchill |
Paul Burridge wrote:
On Sat, 02 Aug 2003 03:25:47 GMT, Active8 wrote: In article vKBWa.20717$KF1.308575@amstwist00, lid says... Paul Burridge wrote: Hi chaps, Can anyone suggest a suitable material from which to make an ultra-flexible mobile whip antenna say about 3 to 4 feet long. I need something that can be bent to 90 degrees at a very small radius and still return to reasonable straightness. I think thin piano wire will give the best results. Place a lot of them in a flexible tube to gain some thickness and have them silvered for conductivity - or add a stranded copper wire. Spring metal strip may also work, especially if you can manage some type of hinge at the base that allows it to turn when sideways force is exerted, or if the force is in one plane. Thomas what is a tight bend? music wire comes in diff sizes and the number in the tube and how tightly the tube conforms to it will have an effect on the flexibility. Yeah, sorry chaps, I should have better defined what I meant by 'very small radius'. I compete in radio-controlled model battles, so the model stands to get fipped upside down from time to time in a very bruising environment and it already has a very low ground-clearance, so using a spring as a base mounting won't help much, I'm afraid. We're talking about radiuses of as little as 5mm! How about the specific grade of stainless steel in wire form that springs are made from? I know where I can get hold of some of that.... "I believe history will be kind to me, since I intend to write it." - Winston Churchill The alloy is Type 301 (17% chromium, 7% nickel stainless steel) hard drawn wire, or even better is a 17/7PH (precipitation hardening) grade that our firm once produced for tank aerials, that also may take a few knocks. ;) Both (especially the PH grade) need a final heat-treatment (420C for a few minutes IIRC) for ultimate spring properties, but to get such a tight bend you'd need quite a thin wire. It's a matter of the proof strain or limit of proportionality, how much the outer skin can stretch without taking a permanent set, compared to the neutral central axis, on the bend. |
Paul Burridge wrote:
On Sat, 02 Aug 2003 03:25:47 GMT, Active8 wrote: In article vKBWa.20717$KF1.308575@amstwist00, lid says... Paul Burridge wrote: Hi chaps, Can anyone suggest a suitable material from which to make an ultra-flexible mobile whip antenna say about 3 to 4 feet long. I need something that can be bent to 90 degrees at a very small radius and still return to reasonable straightness. I think thin piano wire will give the best results. Place a lot of them in a flexible tube to gain some thickness and have them silvered for conductivity - or add a stranded copper wire. Spring metal strip may also work, especially if you can manage some type of hinge at the base that allows it to turn when sideways force is exerted, or if the force is in one plane. Thomas what is a tight bend? music wire comes in diff sizes and the number in the tube and how tightly the tube conforms to it will have an effect on the flexibility. Yeah, sorry chaps, I should have better defined what I meant by 'very small radius'. I compete in radio-controlled model battles, so the model stands to get fipped upside down from time to time in a very bruising environment and it already has a very low ground-clearance, so using a spring as a base mounting won't help much, I'm afraid. We're talking about radiuses of as little as 5mm! How about the specific grade of stainless steel in wire form that springs are made from? I know where I can get hold of some of that.... "I believe history will be kind to me, since I intend to write it." - Winston Churchill The alloy is Type 301 (17% chromium, 7% nickel stainless steel) hard drawn wire, or even better is a 17/7PH (precipitation hardening) grade that our firm once produced for tank aerials, that also may take a few knocks. ;) Both (especially the PH grade) need a final heat-treatment (420C for a few minutes IIRC) for ultimate spring properties, but to get such a tight bend you'd need quite a thin wire. It's a matter of the proof strain or limit of proportionality, how much the outer skin can stretch without taking a permanent set, compared to the neutral central axis, on the bend. |
On Sat, 02 Aug 2003 11:11:31 +0100, Paul Burridge hath writ:
Paul Burridge wrote: Can anyone suggest a suitable material from which to make an ultra-flexible mobile whip antenna say about 3 to 4 feet long. I need something that can be bent to 90 degrees at a very small radius and still return to reasonable straightness. Yeah, sorry chaps, I should have better defined what I meant by 'very small radius'. I compete in radio-controlled model battles, so the model stands to get fipped upside down from time to time in a very bruising environment and it already has a very low ground-clearance, so using a spring as a base mounting won't help much, I'm afraid. We're talking about radiuses of as little as 5mm! How about the specific grade of stainless steel in wire form that springs are made from? I know where I can get hold of some of that.... You might try a section from a steel tape measure. (Just don't select one of the cheap, Made-In-China plastic/mylar ones. HI!HI!) Additionally, try to mount the antenna in a "well" on the robot. Even a well of 5-10 mm will help out. HTH, Jonesy -- | Marvin L Jones | jonz | W3DHJ | OS/2 | Gunnison, Colorado | @ | Jonesy | linux __ | 7,703' -- 2,345m | config.com | DM68mn SK |
On Sat, 02 Aug 2003 11:11:31 +0100, Paul Burridge hath writ:
Paul Burridge wrote: Can anyone suggest a suitable material from which to make an ultra-flexible mobile whip antenna say about 3 to 4 feet long. I need something that can be bent to 90 degrees at a very small radius and still return to reasonable straightness. Yeah, sorry chaps, I should have better defined what I meant by 'very small radius'. I compete in radio-controlled model battles, so the model stands to get fipped upside down from time to time in a very bruising environment and it already has a very low ground-clearance, so using a spring as a base mounting won't help much, I'm afraid. We're talking about radiuses of as little as 5mm! How about the specific grade of stainless steel in wire form that springs are made from? I know where I can get hold of some of that.... You might try a section from a steel tape measure. (Just don't select one of the cheap, Made-In-China plastic/mylar ones. HI!HI!) Additionally, try to mount the antenna in a "well" on the robot. Even a well of 5-10 mm will help out. HTH, Jonesy -- | Marvin L Jones | jonz | W3DHJ | OS/2 | Gunnison, Colorado | @ | Jonesy | linux __ | 7,703' -- 2,345m | config.com | DM68mn SK |
In article ,
says... On Sat, 02 Aug 2003 03:25:47 GMT, Active8 wrote: In article vKBWa.20717$KF1.308575@amstwist00, lid says... Paul Burridge wrote: Hi chaps, Can anyone suggest a suitable material from which to make an ultra-flexible mobile whip antenna say about 3 to 4 feet long. I need something that can be bent to 90 degrees at a very small radius and still return to reasonable straightness. I think thin piano wire will give the best results. Place a lot of them in a flexible tube to gain some thickness and have them silvered for conductivity - or add a stranded copper wire. Spring metal strip may also work, especially if you can manage some type of hinge at the base that allows it to turn when sideways force is exerted, or if the force is in one plane. Thomas what is a tight bend? music wire comes in diff sizes and the number in the tube and how tightly the tube conforms to it will have an effect on the flexibility. Yeah, sorry chaps, I should have better defined what I meant by 'very small radius'. I compete in radio-controlled model battles, so the model stands to get fipped upside down from time to time in a very bruising environment and it already has a very low ground-clearance, so using a spring as a base mounting won't help much, I'm afraid. We're talking about radiuses of as little as 5mm! How about the specific grade of stainless steel in wire form that springs are made from? I know where I can get hold of some of that.... -- "I believe history will be kind to me, since I intend to write it." - Winston Churchill oh, hi. it's the battle bot guy. i should have caught that, duh! mike |
In article ,
says... On Sat, 02 Aug 2003 03:25:47 GMT, Active8 wrote: In article vKBWa.20717$KF1.308575@amstwist00, lid says... Paul Burridge wrote: Hi chaps, Can anyone suggest a suitable material from which to make an ultra-flexible mobile whip antenna say about 3 to 4 feet long. I need something that can be bent to 90 degrees at a very small radius and still return to reasonable straightness. I think thin piano wire will give the best results. Place a lot of them in a flexible tube to gain some thickness and have them silvered for conductivity - or add a stranded copper wire. Spring metal strip may also work, especially if you can manage some type of hinge at the base that allows it to turn when sideways force is exerted, or if the force is in one plane. Thomas what is a tight bend? music wire comes in diff sizes and the number in the tube and how tightly the tube conforms to it will have an effect on the flexibility. Yeah, sorry chaps, I should have better defined what I meant by 'very small radius'. I compete in radio-controlled model battles, so the model stands to get fipped upside down from time to time in a very bruising environment and it already has a very low ground-clearance, so using a spring as a base mounting won't help much, I'm afraid. We're talking about radiuses of as little as 5mm! How about the specific grade of stainless steel in wire form that springs are made from? I know where I can get hold of some of that.... -- "I believe history will be kind to me, since I intend to write it." - Winston Churchill oh, hi. it's the battle bot guy. i should have caught that, duh! mike |
On Sat, 2 Aug 2003 16:40:43 +0100, "cpemma"
wrote: The alloy is Type 301 (17% chromium, 7% nickel stainless steel) hard drawn wire, or even better is a 17/7PH (precipitation hardening) grade that our firm once produced for tank aerials, that also may take a few knocks. ;) Both (especially the PH grade) need a final heat-treatment (420C for a few minutes IIRC) for ultimate spring properties, but to get such a tight bend you'd need quite a thin wire. It's a matter of the proof strain or limit of proportionality, how much the outer skin can stretch without taking a permanent set, compared to the neutral central axis, on the bend. There speaks a man who obviously knows what he's talking about. Yes, I believe we can order 301 from our guy in N. London who's very accommodating on such matters. Thanks for a valuable steer! Just one point, though: is stainless steel a reasonable radiator of RF energy? -- "I believe history will be kind to me, since I intend to write it." - Winston Churchill |
On Sat, 2 Aug 2003 16:40:43 +0100, "cpemma"
wrote: The alloy is Type 301 (17% chromium, 7% nickel stainless steel) hard drawn wire, or even better is a 17/7PH (precipitation hardening) grade that our firm once produced for tank aerials, that also may take a few knocks. ;) Both (especially the PH grade) need a final heat-treatment (420C for a few minutes IIRC) for ultimate spring properties, but to get such a tight bend you'd need quite a thin wire. It's a matter of the proof strain or limit of proportionality, how much the outer skin can stretch without taking a permanent set, compared to the neutral central axis, on the bend. There speaks a man who obviously knows what he's talking about. Yes, I believe we can order 301 from our guy in N. London who's very accommodating on such matters. Thanks for a valuable steer! Just one point, though: is stainless steel a reasonable radiator of RF energy? -- "I believe history will be kind to me, since I intend to write it." - Winston Churchill |
On 2 Aug 2003 16:24:24 GMT, Allodoxaphobia
wrote: You might try a section from a steel tape measure. (Just don't select one of the cheap, Made-In-China plastic/mylar ones. HI!HI!) Additionally, try to mount the antenna in a "well" on the robot. Even a well of 5-10 mm will help out. Not sure about the tape measure suggestion, but mounting in a well is something I'd not considered and am most grateful for the idea of! Thanks... -- "I believe history will be kind to me, since I intend to write it." - Winston Churchill |
On 2 Aug 2003 16:24:24 GMT, Allodoxaphobia
wrote: You might try a section from a steel tape measure. (Just don't select one of the cheap, Made-In-China plastic/mylar ones. HI!HI!) Additionally, try to mount the antenna in a "well" on the robot. Even a well of 5-10 mm will help out. Not sure about the tape measure suggestion, but mounting in a well is something I'd not considered and am most grateful for the idea of! Thanks... -- "I believe history will be kind to me, since I intend to write it." - Winston Churchill |
:
The alloy is Type 301 (17% chromium, 7% nickel stainless steel) hard drawn wire, or even better is a 17/7PH (precipitation hardening) grade that our firm once produced for tank aerials, that also may take a few knocks. ;) Both (especially the PH grade) need a final heat-treatment (420C for a few minutes IIRC) for ultimate spring properties, but to get such a tight bend you'd need quite a thin wire. It's a matter of the proof strain or limit of proportionality, how much the outer skin can stretch without taking a permanent set, compared to the neutral central axis, on the bend. There speaks a man who obviously knows what he's talking about. Yes, I believe we can order 301 from our guy in N. London who's very accommodating on such matters. Thanks for a valuable steer! Just one point, though: is stainless steel a reasonable radiator of RF energy? Back years ago (30 or so) there was an ad in a magazine about either a loaded CB or 5/8 two meter whip about 36 inches long bent in a circle made of the 17/7 material. Not sure what the whips are actually made of but most are some kind of steel . |
:
The alloy is Type 301 (17% chromium, 7% nickel stainless steel) hard drawn wire, or even better is a 17/7PH (precipitation hardening) grade that our firm once produced for tank aerials, that also may take a few knocks. ;) Both (especially the PH grade) need a final heat-treatment (420C for a few minutes IIRC) for ultimate spring properties, but to get such a tight bend you'd need quite a thin wire. It's a matter of the proof strain or limit of proportionality, how much the outer skin can stretch without taking a permanent set, compared to the neutral central axis, on the bend. There speaks a man who obviously knows what he's talking about. Yes, I believe we can order 301 from our guy in N. London who's very accommodating on such matters. Thanks for a valuable steer! Just one point, though: is stainless steel a reasonable radiator of RF energy? Back years ago (30 or so) there was an ad in a magazine about either a loaded CB or 5/8 two meter whip about 36 inches long bent in a circle made of the 17/7 material. Not sure what the whips are actually made of but most are some kind of steel . |
"Paul Burridge" wrote in message ... On 2 Aug 2003 16:24:24 GMT, Allodoxaphobia wrote: You might try a section from a steel tape measure. (Just don't select one of the cheap, Made-In-China plastic/mylar ones. HI!HI!) Additionally, try to mount the antenna in a "well" on the robot. Even a well of 5-10 mm will help out. Not sure about the tape measure suggestion, but mounting in a well is something I'd not considered and am most grateful for the idea of! Thanks... Does it have to be a whip antenna? Why not try a horizontal circular loop? Since you are working line of sight to the robot, the signal loss from going from vertical to horizontal shouldn't matter much unless your transmitter is extremely low power. A loop could be mounted inside a wooden or fiberglas body and be pretty safe from attack. Is there anything in the rules forbidding your installing a jammer transmitter to cause the other bot to lose its command channel? Probobly a poor use of what little electrical capacity the onboard battery holds, but it would be one way of causing the other bot to freeze in place and become like a deer in the headlights. thanks, John. KC5DWD |
"Paul Burridge" wrote in message ... On 2 Aug 2003 16:24:24 GMT, Allodoxaphobia wrote: You might try a section from a steel tape measure. (Just don't select one of the cheap, Made-In-China plastic/mylar ones. HI!HI!) Additionally, try to mount the antenna in a "well" on the robot. Even a well of 5-10 mm will help out. Not sure about the tape measure suggestion, but mounting in a well is something I'd not considered and am most grateful for the idea of! Thanks... Does it have to be a whip antenna? Why not try a horizontal circular loop? Since you are working line of sight to the robot, the signal loss from going from vertical to horizontal shouldn't matter much unless your transmitter is extremely low power. A loop could be mounted inside a wooden or fiberglas body and be pretty safe from attack. Is there anything in the rules forbidding your installing a jammer transmitter to cause the other bot to lose its command channel? Probobly a poor use of what little electrical capacity the onboard battery holds, but it would be one way of causing the other bot to freeze in place and become like a deer in the headlights. thanks, John. KC5DWD |
On Sat, 2 Aug 2003 18:24:44 -0500, "john graesser"
wrote: Does it have to be a whip antenna? Why not try a horizontal circular loop? Since you are working line of sight to the robot, the signal loss from going from vertical to horizontal shouldn't matter much unless your transmitter is extremely low power. A loop could be mounted inside a wooden or fiberglas body and be pretty safe from attack. If I believed this idea was workable I'd have implemented it by now. You need to bear in mind that immediately beneath the polycarbonate surface armor, there's a hulking great metal framework. Consequently, sandwiching the antenna between the armour and the frame is going to lead to unacceptable loss of radiated energy, I'd have thought. Unless anyone knows differently.. Is there anything in the rules forbidding your installing a jammer transmitter to cause the other bot to lose its command channel? Probobly a poor use of what little electrical capacity the onboard battery holds, There's a considerable amount of battery power on board, actually, since the peak current draw is well over 100 Amps at times. A few milliwatts for a local jammer would therefore be a negligable drain on resources. *However* as you've already guessed, jammers are banned, as are EMP pulse type weapons and such like. The reason for this is very sound, when you think about it: it makes for really bad TV. The producers want to see as much *action* as possible. You ain't gonna get that if everybody's disabled everybody else's robot! -- "I believe history will be kind to me, since I intend to write it." - Winston Churchill |
On Sat, 2 Aug 2003 18:24:44 -0500, "john graesser"
wrote: Does it have to be a whip antenna? Why not try a horizontal circular loop? Since you are working line of sight to the robot, the signal loss from going from vertical to horizontal shouldn't matter much unless your transmitter is extremely low power. A loop could be mounted inside a wooden or fiberglas body and be pretty safe from attack. If I believed this idea was workable I'd have implemented it by now. You need to bear in mind that immediately beneath the polycarbonate surface armor, there's a hulking great metal framework. Consequently, sandwiching the antenna between the armour and the frame is going to lead to unacceptable loss of radiated energy, I'd have thought. Unless anyone knows differently.. Is there anything in the rules forbidding your installing a jammer transmitter to cause the other bot to lose its command channel? Probobly a poor use of what little electrical capacity the onboard battery holds, There's a considerable amount of battery power on board, actually, since the peak current draw is well over 100 Amps at times. A few milliwatts for a local jammer would therefore be a negligable drain on resources. *However* as you've already guessed, jammers are banned, as are EMP pulse type weapons and such like. The reason for this is very sound, when you think about it: it makes for really bad TV. The producers want to see as much *action* as possible. You ain't gonna get that if everybody's disabled everybody else's robot! -- "I believe history will be kind to me, since I intend to write it." - Winston Churchill |
Zak wrote:
Paul Burridge wrote: Just one point, though: is stainless steel a reasonable radiator of RF energy? Stainless steel is awful at conducting electricity - so it won't make a very efficient antenna. But how much it really matters, I don't know. So's my body, but I get a decent TV picture if I touch the aerial input ;-) |
Zak wrote:
Paul Burridge wrote: Just one point, though: is stainless steel a reasonable radiator of RF energy? Stainless steel is awful at conducting electricity - so it won't make a very efficient antenna. But how much it really matters, I don't know. So's my body, but I get a decent TV picture if I touch the aerial input ;-) |
"Active8" wrote in message k.net... In article , says... "Paul Burridge" wrote in message ... On 2 Aug 2003 16:24:24 GMT, Allodoxaphobia wrote: You might try a section from a steel tape measure. (Just don't select one of the cheap, Made-In-China plastic/mylar ones. HI!HI!) Additionally, try to mount the antenna in a "well" on the robot. Even a well of 5-10 mm will help out. Not sure about the tape measure suggestion, but mounting in a well is something I'd not considered and am most grateful for the idea of! Thanks... Does it have to be a whip antenna? Why not try a horizontal circular loop? Since you are working line of sight to the robot, the signal loss from going from vertical to horizontal shouldn't matter much unless your transmitter is extremely low power. A loop could be mounted inside a wooden or fiberglas body and be pretty safe from attack. Is there anything in the rules forbidding your installing a jammer transmitter to cause the other bot to lose its command channel? Probobly a poor use of what little electrical capacity the onboard battery holds, but it would be one way of causing the other bot to freeze in place and become like a deer in the headlights. thanks, John. KC5DWD i always thought jamming would be a great weapon, but i bet it's illegal. i'd like to see the rules for some of those competitions. i'd think it would be fun to try sometime. i wan't to smash jay leno's bot. come on. "chinkilla"? who writes his lines? Paul's restricted to two bands, which i think stinks. he's probably not allowed to jam. The band restriction i really don't like since it's a bot competition not a DX contest. I have a friend who competes. I suggested jamming to him; he said it was not allowed. Besides, they're not really robots. All of them are just RC toys. I'll be more impressed when they are autonomous. |
"Active8" wrote in message k.net... In article , says... "Paul Burridge" wrote in message ... On 2 Aug 2003 16:24:24 GMT, Allodoxaphobia wrote: You might try a section from a steel tape measure. (Just don't select one of the cheap, Made-In-China plastic/mylar ones. HI!HI!) Additionally, try to mount the antenna in a "well" on the robot. Even a well of 5-10 mm will help out. Not sure about the tape measure suggestion, but mounting in a well is something I'd not considered and am most grateful for the idea of! Thanks... Does it have to be a whip antenna? Why not try a horizontal circular loop? Since you are working line of sight to the robot, the signal loss from going from vertical to horizontal shouldn't matter much unless your transmitter is extremely low power. A loop could be mounted inside a wooden or fiberglas body and be pretty safe from attack. Is there anything in the rules forbidding your installing a jammer transmitter to cause the other bot to lose its command channel? Probobly a poor use of what little electrical capacity the onboard battery holds, but it would be one way of causing the other bot to freeze in place and become like a deer in the headlights. thanks, John. KC5DWD i always thought jamming would be a great weapon, but i bet it's illegal. i'd like to see the rules for some of those competitions. i'd think it would be fun to try sometime. i wan't to smash jay leno's bot. come on. "chinkilla"? who writes his lines? Paul's restricted to two bands, which i think stinks. he's probably not allowed to jam. The band restriction i really don't like since it's a bot competition not a DX contest. I have a friend who competes. I suggested jamming to him; he said it was not allowed. Besides, they're not really robots. All of them are just RC toys. I'll be more impressed when they are autonomous. |
On Sun, 3 Aug 2003 11:40:55 -0400, "Bob Lewis \(AA4PB\)"
wrote: Stainless steel is awful at conducting electricity - so it won't make a very efficient antenna. I doubt that the difference in resistance between stainless and copper is going to cause any significant additional losses in a whip antenna. That difference will be small compared to the other losses. Stainless is often used for whip antennas because of its mechanical properties. Yes, I've several proprietory s/steel whip antennas that give excellent results. But a question springs to mind. If a s/steel antenna has slightly higher resistance, does that appreciably lower its Q? -- "I believe history will be kind to me, since I intend to write it." - Winston Churchill |
On Sun, 3 Aug 2003 11:40:55 -0400, "Bob Lewis \(AA4PB\)"
wrote: Stainless steel is awful at conducting electricity - so it won't make a very efficient antenna. I doubt that the difference in resistance between stainless and copper is going to cause any significant additional losses in a whip antenna. That difference will be small compared to the other losses. Stainless is often used for whip antennas because of its mechanical properties. Yes, I've several proprietory s/steel whip antennas that give excellent results. But a question springs to mind. If a s/steel antenna has slightly higher resistance, does that appreciably lower its Q? -- "I believe history will be kind to me, since I intend to write it." - Winston Churchill |
On Sun, 3 Aug 2003 10:19:55 -0700, "Richard Henry"
wrote: Besides, they're not really robots. All of them are just RC toys. I'll be more impressed when they are autonomous. That's not entirely true these days. Autonomy in certain areas of control is becoming increasingly prevalent. It'll be interesting to see how this particular aspect of design develops over the coming years... -- "I believe history will be kind to me, since I intend to write it." - Winston Churchill |
On Sun, 3 Aug 2003 10:19:55 -0700, "Richard Henry"
wrote: Besides, they're not really robots. All of them are just RC toys. I'll be more impressed when they are autonomous. That's not entirely true these days. Autonomy in certain areas of control is becoming increasingly prevalent. It'll be interesting to see how this particular aspect of design develops over the coming years... -- "I believe history will be kind to me, since I intend to write it." - Winston Churchill |
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If a s/steel antenna has slightly higher resistance, does that
appreciably lower its Q? I don't have any figures available but I wouldn't think so. The difference between the resistance of a 2-foot piece of copper and a 2-foot piece of stainless is going to be pretty small. |
If a s/steel antenna has slightly higher resistance, does that
appreciably lower its Q? I don't have any figures available but I wouldn't think so. The difference between the resistance of a 2-foot piece of copper and a 2-foot piece of stainless is going to be pretty small. |
The short answer is that stainless probably won't make a noticeable
difference in loss, and therefore won't make a significant difference in Q. The conductor loss of an antenna of a given wavelength size gets less as the frequency gets higher. That's because the antenna length decreases in inverse proportion to the frequency, while the loss per unit length increases only as the square root of the frequency. So for a given wire diameter, a half wavelength dipole at, say, 10 MHz has half the loss of a half wavelength dipole at 2.5 MHz. Stainless steel whips are fine at 2 meters. But an 80 meter dipole made from small or moderate gauge stainless wire could be pretty lossy -- almost certainly so, if the stainless is a magnetic alloy. (Being magnetic greatly increases the RF loss -- by a factor of the square root of the permeability.) Loss becomes very important when a whip is a lot shorter than a quarter wavelength. However, in many or most cases (like an HF mobile whip), the whip typically has a fairly large diameter where the current is high, and the whip loss is swamped by other losses, so the whip loss isn't objectionable. It's always possible to come up with a combination of whip diameter, length, and frequency where stainless could be a poor choice -- but it's uncommon in typical applications. Roy Lewallen, W7EL Paul Burridge wrote: On Sun, 3 Aug 2003 11:40:55 -0400, "Bob Lewis \(AA4PB\)" wrote: Stainless steel is awful at conducting electricity - so it won't make a very efficient antenna. I doubt that the difference in resistance between stainless and copper is going to cause any significant additional losses in a whip antenna. That difference will be small compared to the other losses. Stainless is often used for whip antennas because of its mechanical properties. Yes, I've several proprietory s/steel whip antennas that give excellent results. But a question springs to mind. If a s/steel antenna has slightly higher resistance, does that appreciably lower its Q? -- "I believe history will be kind to me, since I intend to write it." - Winston Churchill |
The short answer is that stainless probably won't make a noticeable
difference in loss, and therefore won't make a significant difference in Q. The conductor loss of an antenna of a given wavelength size gets less as the frequency gets higher. That's because the antenna length decreases in inverse proportion to the frequency, while the loss per unit length increases only as the square root of the frequency. So for a given wire diameter, a half wavelength dipole at, say, 10 MHz has half the loss of a half wavelength dipole at 2.5 MHz. Stainless steel whips are fine at 2 meters. But an 80 meter dipole made from small or moderate gauge stainless wire could be pretty lossy -- almost certainly so, if the stainless is a magnetic alloy. (Being magnetic greatly increases the RF loss -- by a factor of the square root of the permeability.) Loss becomes very important when a whip is a lot shorter than a quarter wavelength. However, in many or most cases (like an HF mobile whip), the whip typically has a fairly large diameter where the current is high, and the whip loss is swamped by other losses, so the whip loss isn't objectionable. It's always possible to come up with a combination of whip diameter, length, and frequency where stainless could be a poor choice -- but it's uncommon in typical applications. Roy Lewallen, W7EL Paul Burridge wrote: On Sun, 3 Aug 2003 11:40:55 -0400, "Bob Lewis \(AA4PB\)" wrote: Stainless steel is awful at conducting electricity - so it won't make a very efficient antenna. I doubt that the difference in resistance between stainless and copper is going to cause any significant additional losses in a whip antenna. That difference will be small compared to the other losses. Stainless is often used for whip antennas because of its mechanical properties. Yes, I've several proprietory s/steel whip antennas that give excellent results. But a question springs to mind. If a s/steel antenna has slightly higher resistance, does that appreciably lower its Q? -- "I believe history will be kind to me, since I intend to write it." - Winston Churchill |
surface armor, there's a hulking great metal framework. Consequently,
sandwiching the antenna between the armour and the frame is going to lead to unacceptable loss of radiated energy, I'd have thought. Unless anyone knows differently.. I do not know the frequencies, but if they are high enough, one could think of a slot or a patch antenna Is there anything in the rules forbidding your installing a jammer If jamming would be allowed, it would be a totally different sport (but interesting as well). In that case you may as well omit the robots See all the military history about ECM, ECCM, ECCCM (Electronic Counter(*n) Measures) etc. Wim |
surface armor, there's a hulking great metal framework. Consequently,
sandwiching the antenna between the armour and the frame is going to lead to unacceptable loss of radiated energy, I'd have thought. Unless anyone knows differently.. I do not know the frequencies, but if they are high enough, one could think of a slot or a patch antenna Is there anything in the rules forbidding your installing a jammer If jamming would be allowed, it would be a totally different sport (but interesting as well). In that case you may as well omit the robots See all the military history about ECM, ECCM, ECCCM (Electronic Counter(*n) Measures) etc. Wim |
Stainless steel is awful at conducting electricity - so it won't make a
very efficient antenna. But how much it really matters, I don't know. You can coat it with silver or copper, only the outer few microns conduct HF (skin-effect) Wim |
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