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I read in sci.electronics.design that James Meyer
wrote (in ) about 'A neat and compact way to generate RF harmonics...', on Sat, 17 Apr 2004: IOW, the Q without the probe will be higher than the Q when you insert the probe to measure the Q. Use an inductive current pick-off. That how the Marconi Instruments 1245 series Q-meters work(ed). -- Regards, John Woodgate, OOO - Own Opinions Only. The good news is that nothing is compulsory. The bad news is that everything is prohibited. http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk |
I read in sci.electronics.design that James Meyer
wrote (in ) about 'A neat and compact way to generate RF harmonics...', on Sat, 17 Apr 2004: IOW, the Q without the probe will be higher than the Q when you insert the probe to measure the Q. Use an inductive current pick-off. That how the Marconi Instruments 1245 series Q-meters work(ed). -- Regards, John Woodgate, OOO - Own Opinions Only. The good news is that nothing is compulsory. The bad news is that everything is prohibited. http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk |
On Sat, 17 Apr 2004 15:46:59 GMT, James Meyer
wrote: On Sat, 17 Apr 2004 07:43:49 GMT, Robert Baer posted this: John Larkin wrote: Well, all the usual methods: resonance width, phase shift, ringdown, stuff like that. I work with gadgets with Qs over 1e9, and people measure them without difficulty. John Ringdown is the easist way when Qs are extremely high. You must still account for the energy you extract from the circuit in order to measure the ringdown. Even the energy needed to drive a high impedance probe is significant when the Q gets high. IOW, the Q without the probe will be higher than the Q when you insert the probe to measure the Q. Jim Of course, you can account for the probe loss when you do the math. Or leave the probe disconnected during a ringdown, and add it after some delay to see how much energy is left in the system. John |
On Sat, 17 Apr 2004 15:46:59 GMT, James Meyer
wrote: On Sat, 17 Apr 2004 07:43:49 GMT, Robert Baer posted this: John Larkin wrote: Well, all the usual methods: resonance width, phase shift, ringdown, stuff like that. I work with gadgets with Qs over 1e9, and people measure them without difficulty. John Ringdown is the easist way when Qs are extremely high. You must still account for the energy you extract from the circuit in order to measure the ringdown. Even the energy needed to drive a high impedance probe is significant when the Q gets high. IOW, the Q without the probe will be higher than the Q when you insert the probe to measure the Q. Jim Of course, you can account for the probe loss when you do the math. Or leave the probe disconnected during a ringdown, and add it after some delay to see how much energy is left in the system. John |
Robert Baer wrote in message ...
.... Yes, but the emphasis was on small size, and a helical resonator allows a goodly shrinkage of volume wihout a corresponding loss large of Q. As compared with what? A given coil in a helical resonator will result in lower Qu than that same coil unshielded and simply resonated with a good capacitor. .... Maybe his requirements are not too realistic? Seems to commonly be the case. |
Robert Baer wrote in message ...
.... Yes, but the emphasis was on small size, and a helical resonator allows a goodly shrinkage of volume wihout a corresponding loss large of Q. As compared with what? A given coil in a helical resonator will result in lower Qu than that same coil unshielded and simply resonated with a good capacitor. .... Maybe his requirements are not too realistic? Seems to commonly be the case. |
On Sat, 17 Apr 2004 17:26:15 +0100, John Woodgate
posted this: I read in sci.electronics.design that James Meyer wrote (in ) about 'A neat and compact way to generate RF harmonics...', on Sat, 17 Apr 2004: IOW, the Q without the probe will be higher than the Q when you insert the probe to measure the Q. Use an inductive current pick-off. That how the Marconi Instruments 1245 series Q-meters work(ed). Nevertheless, *ANY* method used to probe the field associated with the resonator will load the resonator and degrade the Q. Jim |
On Sat, 17 Apr 2004 17:26:15 +0100, John Woodgate
posted this: I read in sci.electronics.design that James Meyer wrote (in ) about 'A neat and compact way to generate RF harmonics...', on Sat, 17 Apr 2004: IOW, the Q without the probe will be higher than the Q when you insert the probe to measure the Q. Use an inductive current pick-off. That how the Marconi Instruments 1245 series Q-meters work(ed). Nevertheless, *ANY* method used to probe the field associated with the resonator will load the resonator and degrade the Q. Jim |
On Sat, 17 Apr 2004 10:04:36 -0700, John Larkin
posted this: On Sat, 17 Apr 2004 15:46:59 GMT, James Meyer wrote: IOW, the Q without the probe will be higher than the Q when you insert the probe to measure the Q. Jim Of course, you can account for the probe loss when you do the math. Or leave the probe disconnected during a ringdown, and add it after some delay to see how much energy is left in the system. John If you have to "do the math", you might as well just calculate the Q from first principles and forget the "measurement". Jim |
On Sat, 17 Apr 2004 10:04:36 -0700, John Larkin
posted this: On Sat, 17 Apr 2004 15:46:59 GMT, James Meyer wrote: IOW, the Q without the probe will be higher than the Q when you insert the probe to measure the Q. Jim Of course, you can account for the probe loss when you do the math. Or leave the probe disconnected during a ringdown, and add it after some delay to see how much energy is left in the system. John If you have to "do the math", you might as well just calculate the Q from first principles and forget the "measurement". Jim |
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On Sat, 17 Apr 2004 19:07:12 GMT, James Meyer
wrote: On Sat, 17 Apr 2004 10:04:36 -0700, John Larkin posted this: On Sat, 17 Apr 2004 15:46:59 GMT, James Meyer wrote: IOW, the Q without the probe will be higher than the Q when you insert the probe to measure the Q. Jim Of course, you can account for the probe loss when you do the math. Or leave the probe disconnected during a ringdown, and add it after some delay to see how much energy is left in the system. John If you have to "do the math", you might as well just calculate the Q from first principles and forget the "measurement". Jim How can you calculate Q from first principles? 3D EM simulation? Quantum mechanics? John |
On Sat, 17 Apr 2004 19:07:12 GMT, James Meyer
wrote: On Sat, 17 Apr 2004 10:04:36 -0700, John Larkin posted this: On Sat, 17 Apr 2004 15:46:59 GMT, James Meyer wrote: IOW, the Q without the probe will be higher than the Q when you insert the probe to measure the Q. Jim Of course, you can account for the probe loss when you do the math. Or leave the probe disconnected during a ringdown, and add it after some delay to see how much energy is left in the system. John If you have to "do the math", you might as well just calculate the Q from first principles and forget the "measurement". Jim How can you calculate Q from first principles? 3D EM simulation? Quantum mechanics? John |
Ah, just the person I've been waiting for. How do you account for
current bunching on the conductors (that is, non-uniform distribution of current around the conductors)? What reference, equation, or program do you use? Nearly all "first principle" calculations of Q I've seen grossly overestimate Q, and I believe the failure to take this into account is at least part of the reason. I haven't seen a decent analytical method of dealing with it, and an anxious to see how you do it. Then there's surface corrosion and roughness, radiation, and coupling to nearby objects. How do you deal with those? Have you identified some of the other factors that often make a simplistic "first principle" calculation disagree so badly with carefully made measurements? Roy Lewallen, W7EL James Meyer wrote: If you have to "do the math", you might as well just calculate the Q from first principles and forget the "measurement". Jim |
Ah, just the person I've been waiting for. How do you account for
current bunching on the conductors (that is, non-uniform distribution of current around the conductors)? What reference, equation, or program do you use? Nearly all "first principle" calculations of Q I've seen grossly overestimate Q, and I believe the failure to take this into account is at least part of the reason. I haven't seen a decent analytical method of dealing with it, and an anxious to see how you do it. Then there's surface corrosion and roughness, radiation, and coupling to nearby objects. How do you deal with those? Have you identified some of the other factors that often make a simplistic "first principle" calculation disagree so badly with carefully made measurements? Roy Lewallen, W7EL James Meyer wrote: If you have to "do the math", you might as well just calculate the Q from first principles and forget the "measurement". Jim |
I read in sci.electronics.design that James Meyer
wrote (in ) about 'A neat and compact way to generate RF harmonics...', on Sat, 17 Apr 2004: On Sat, 17 Apr 2004 17:26:15 +0100, John Woodgate posted this: I read in sci.electronics.design that James Meyer wrote (in ) about 'A neat and compact way to generate RF harmonics...', on Sat, 17 Apr 2004: IOW, the Q without the probe will be higher than the Q when you insert the probe to measure the Q. Use an inductive current pick-off. That how the Marconi Instruments 1245 series Q-meters work(ed). Nevertheless, *ANY* method used to probe the field associated with the resonator will load the resonator and degrade the Q. IIRC, the Marconi unit used a 10 nH inductor (maybe less) made of a short length of silver wire, gold-plated to eliminate sulfide attack. The effect on Q would be minimal in the extreme. -- Regards, John Woodgate, OOO - Own Opinions Only. The good news is that nothing is compulsory. The bad news is that everything is prohibited. http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk |
I read in sci.electronics.design that James Meyer
wrote (in ) about 'A neat and compact way to generate RF harmonics...', on Sat, 17 Apr 2004: On Sat, 17 Apr 2004 17:26:15 +0100, John Woodgate posted this: I read in sci.electronics.design that James Meyer wrote (in ) about 'A neat and compact way to generate RF harmonics...', on Sat, 17 Apr 2004: IOW, the Q without the probe will be higher than the Q when you insert the probe to measure the Q. Use an inductive current pick-off. That how the Marconi Instruments 1245 series Q-meters work(ed). Nevertheless, *ANY* method used to probe the field associated with the resonator will load the resonator and degrade the Q. IIRC, the Marconi unit used a 10 nH inductor (maybe less) made of a short length of silver wire, gold-plated to eliminate sulfide attack. The effect on Q would be minimal in the extreme. -- Regards, John Woodgate, OOO - Own Opinions Only. The good news is that nothing is compulsory. The bad news is that everything is prohibited. http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk |
On Sat, 17 Apr 2004 17:26:15 +0100, John Woodgate
wrote: I read in sci.electronics.design that James Meyer wrote (in ) about 'A neat and compact way to generate RF harmonics...', on Sat, 17 Apr 2004: IOW, the Q without the probe will be higher than the Q when you insert the probe to measure the Q. Use an inductive current pick-off. That how the Marconi Instruments 1245 series Q-meters work(ed). I can recall using one of those, some little time back. Anybody have the schematic diagram for it? Barry Lennox |
On Sat, 17 Apr 2004 17:26:15 +0100, John Woodgate
wrote: I read in sci.electronics.design that James Meyer wrote (in ) about 'A neat and compact way to generate RF harmonics...', on Sat, 17 Apr 2004: IOW, the Q without the probe will be higher than the Q when you insert the probe to measure the Q. Use an inductive current pick-off. That how the Marconi Instruments 1245 series Q-meters work(ed). I can recall using one of those, some little time back. Anybody have the schematic diagram for it? Barry Lennox |
On Sat, 17 Apr 2004 12:22:03 -0700, Roy Lewallen posted this:
Ah, just the person I've been waiting for. How do you account for current bunching on the conductors (that is, non-uniform distribution of current around the conductors)? What reference, equation, or program do you use? Nearly all "first principle" calculations of Q I've seen grossly overestimate Q, and I believe the failure to take this into account is at least part of the reason. I haven't seen a decent analytical method of dealing with it, and an anxious to see how you do it. Then there's surface corrosion and roughness, radiation, and coupling to nearby objects. How do you deal with those? Have you identified some of the other factors that often make a simplistic "first principle" calculation disagree so badly with carefully made measurements? Roy Lewallen, W7EL James Meyer wrote: If you have to "do the math", you might as well just calculate the Q from first principles and forget the "measurement". Jim I was responding to a suggestion that one could do the math to calculate what the Q would have been if you hadn't tried to measure it. I was pointing out that if you could do that math, and get it correct, that you could do the whole exercise with math and forget measuring anything. And how do you know for sure that calculations overestimate Q when measuring Q to verify the calculations disturbs the very thing you're measuring? An engineer knows when to say "close enough". A mathematician is never satisfied. Jim |
On Sat, 17 Apr 2004 12:22:03 -0700, Roy Lewallen posted this:
Ah, just the person I've been waiting for. How do you account for current bunching on the conductors (that is, non-uniform distribution of current around the conductors)? What reference, equation, or program do you use? Nearly all "first principle" calculations of Q I've seen grossly overestimate Q, and I believe the failure to take this into account is at least part of the reason. I haven't seen a decent analytical method of dealing with it, and an anxious to see how you do it. Then there's surface corrosion and roughness, radiation, and coupling to nearby objects. How do you deal with those? Have you identified some of the other factors that often make a simplistic "first principle" calculation disagree so badly with carefully made measurements? Roy Lewallen, W7EL James Meyer wrote: If you have to "do the math", you might as well just calculate the Q from first principles and forget the "measurement". Jim I was responding to a suggestion that one could do the math to calculate what the Q would have been if you hadn't tried to measure it. I was pointing out that if you could do that math, and get it correct, that you could do the whole exercise with math and forget measuring anything. And how do you know for sure that calculations overestimate Q when measuring Q to verify the calculations disturbs the very thing you're measuring? An engineer knows when to say "close enough". A mathematician is never satisfied. Jim |
On Sat, 17 Apr 2004 21:05:34 +0100, John Woodgate
posted this: I read in sci.electronics.design that James Meyer wrote (in ) about 'A neat and compact way to generate RF harmonics...', on Sat, 17 Apr 2004: On Sat, 17 Apr 2004 17:26:15 +0100, John Woodgate posted this: I read in sci.electronics.design that James Meyer wrote (in ) about 'A neat and compact way to generate RF harmonics...', on Sat, 17 Apr 2004: IOW, the Q without the probe will be higher than the Q when you insert the probe to measure the Q. Use an inductive current pick-off. That how the Marconi Instruments 1245 series Q-meters work(ed). Nevertheless, *ANY* method used to probe the field associated with the resonator will load the resonator and degrade the Q. IIRC, the Marconi unit used a 10 nH inductor (maybe less) made of a short length of silver wire, gold-plated to eliminate sulfide attack. The effect on Q would be minimal in the extreme. But what about the energy extracted from the probe to make the measurement? Any load on the probe is transformed into a load on the resonator. Compensating for that load requires a very small number be divided by another very small number. Any error in either number makes a much larger error in the result of the calculation. Jim |
On Sat, 17 Apr 2004 21:05:34 +0100, John Woodgate
posted this: I read in sci.electronics.design that James Meyer wrote (in ) about 'A neat and compact way to generate RF harmonics...', on Sat, 17 Apr 2004: On Sat, 17 Apr 2004 17:26:15 +0100, John Woodgate posted this: I read in sci.electronics.design that James Meyer wrote (in ) about 'A neat and compact way to generate RF harmonics...', on Sat, 17 Apr 2004: IOW, the Q without the probe will be higher than the Q when you insert the probe to measure the Q. Use an inductive current pick-off. That how the Marconi Instruments 1245 series Q-meters work(ed). Nevertheless, *ANY* method used to probe the field associated with the resonator will load the resonator and degrade the Q. IIRC, the Marconi unit used a 10 nH inductor (maybe less) made of a short length of silver wire, gold-plated to eliminate sulfide attack. The effect on Q would be minimal in the extreme. But what about the energy extracted from the probe to make the measurement? Any load on the probe is transformed into a load on the resonator. Compensating for that load requires a very small number be divided by another very small number. Any error in either number makes a much larger error in the result of the calculation. Jim |
James Meyer wrote:
. . . And how do you know for sure that calculations overestimate Q when measuring Q to verify the calculations disturbs the very thing you're measuring? An engineer knows when to say "close enough". A mathematician is never satisfied. I've measured quite a number of inductors both with a homebrew setup, in which I account for the losses in the input and output networks, and with an HP Q meter of specified accuracy. With simple input and output networks consisting of a small series C and shunt R, the effect on Q is predictable and easy to calculate. Results from the two methods agree quite closely, even though they use somewhat different methods to arrive at the Q, giving a fair amount of confidence in both results. And both disagree quite dramatically in some cases to Q calculated simply from theoretical calculations which include only conductor resistance (including skin effect, of course), inductance, and shunt capacitance. This is with inductors of only moderate Q -- calculation of very high Q inductors, which is being discussed here, would require more attention to second order effects -- as would measurement. Thanks for the profound observation about mathematicians and engineers. In which category does one put a person who's satisfied with calculations made without thinking about, caring about, or considering the errors caused by ignoring fundamental effects? Certainly not an engineer as I use the term. Roy Lewallen, W7EL |
James Meyer wrote:
. . . And how do you know for sure that calculations overestimate Q when measuring Q to verify the calculations disturbs the very thing you're measuring? An engineer knows when to say "close enough". A mathematician is never satisfied. I've measured quite a number of inductors both with a homebrew setup, in which I account for the losses in the input and output networks, and with an HP Q meter of specified accuracy. With simple input and output networks consisting of a small series C and shunt R, the effect on Q is predictable and easy to calculate. Results from the two methods agree quite closely, even though they use somewhat different methods to arrive at the Q, giving a fair amount of confidence in both results. And both disagree quite dramatically in some cases to Q calculated simply from theoretical calculations which include only conductor resistance (including skin effect, of course), inductance, and shunt capacitance. This is with inductors of only moderate Q -- calculation of very high Q inductors, which is being discussed here, would require more attention to second order effects -- as would measurement. Thanks for the profound observation about mathematicians and engineers. In which category does one put a person who's satisfied with calculations made without thinking about, caring about, or considering the errors caused by ignoring fundamental effects? Certainly not an engineer as I use the term. Roy Lewallen, W7EL |
I read in sci.electronics.design that James Meyer
wrote (in ) about 'A neat and compact way to generate RF harmonics...', on Sat, 17 Apr 2004: On Sat, 17 Apr 2004 21:05:34 +0100, John Woodgate posted this: I read in sci.electronics.design that James Meyer wrote (in ) about 'A neat and compact way to generate RF harmonics...', on Sat, 17 Apr 2004: On Sat, 17 Apr 2004 17:26:15 +0100, John Woodgate posted this: I read in sci.electronics.design that James Meyer wrote (in ) about 'A neat and compact way to generate RF harmonics...', on Sat, 17 Apr 2004: IOW, the Q without the probe will be higher than the Q when you insert the probe to measure the Q. Use an inductive current pick-off. That how the Marconi Instruments 1245 series Q-meters work(ed). Nevertheless, *ANY* method used to probe the field associated with the resonator will load the resonator and degrade the Q. IIRC, the Marconi unit used a 10 nH inductor (maybe less) made of a short length of silver wire, gold-plated to eliminate sulfide attack. The effect on Q would be minimal in the extreme. But what about the energy extracted from the probe to make the measurement? The sensing inductor was connected to the grid of a triode tube, with, IIRC, a 1 Mohm grid leak. With 1 mV across the sensor, that's a whole 1 uJ/s of energy extraction. Any load on the probe is transformed into a load on the resonator. Compensating for that load requires a very small number be divided by another very small number. Any error in either number makes a much larger error in the result of the calculation. Check your math. It's small errors in *differences*, not in ratios, that result in large errors in results. -- Regards, John Woodgate, OOO - Own Opinions Only. The good news is that nothing is compulsory. The bad news is that everything is prohibited. http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk |
I read in sci.electronics.design that James Meyer
wrote (in ) about 'A neat and compact way to generate RF harmonics...', on Sat, 17 Apr 2004: On Sat, 17 Apr 2004 21:05:34 +0100, John Woodgate posted this: I read in sci.electronics.design that James Meyer wrote (in ) about 'A neat and compact way to generate RF harmonics...', on Sat, 17 Apr 2004: On Sat, 17 Apr 2004 17:26:15 +0100, John Woodgate posted this: I read in sci.electronics.design that James Meyer wrote (in ) about 'A neat and compact way to generate RF harmonics...', on Sat, 17 Apr 2004: IOW, the Q without the probe will be higher than the Q when you insert the probe to measure the Q. Use an inductive current pick-off. That how the Marconi Instruments 1245 series Q-meters work(ed). Nevertheless, *ANY* method used to probe the field associated with the resonator will load the resonator and degrade the Q. IIRC, the Marconi unit used a 10 nH inductor (maybe less) made of a short length of silver wire, gold-plated to eliminate sulfide attack. The effect on Q would be minimal in the extreme. But what about the energy extracted from the probe to make the measurement? The sensing inductor was connected to the grid of a triode tube, with, IIRC, a 1 Mohm grid leak. With 1 mV across the sensor, that's a whole 1 uJ/s of energy extraction. Any load on the probe is transformed into a load on the resonator. Compensating for that load requires a very small number be divided by another very small number. Any error in either number makes a much larger error in the result of the calculation. Check your math. It's small errors in *differences*, not in ratios, that result in large errors in results. -- Regards, John Woodgate, OOO - Own Opinions Only. The good news is that nothing is compulsory. The bad news is that everything is prohibited. http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk |
James Meyer wrote:
On Sat, 17 Apr 2004 07:43:49 GMT, Robert Baer posted this: John Larkin wrote: Well, all the usual methods: resonance width, phase shift, ringdown, stuff like that. I work with gadgets with Qs over 1e9, and people measure them without difficulty. John Ringdown is the easist way when Qs are extremely high. You must still account for the energy you extract from the circuit in order to measure the ringdown. Even the energy needed to drive a high impedance probe is significant when the Q gets high. IOW, the Q without the probe will be higher than the Q when you insert the probe to measure the Q. Jim Not a problem; use two different loads. Just like measuring the internal resistance of a battery or a curent meter... ...Never done directly. |
James Meyer wrote:
On Sat, 17 Apr 2004 07:43:49 GMT, Robert Baer posted this: John Larkin wrote: Well, all the usual methods: resonance width, phase shift, ringdown, stuff like that. I work with gadgets with Qs over 1e9, and people measure them without difficulty. John Ringdown is the easist way when Qs are extremely high. You must still account for the energy you extract from the circuit in order to measure the ringdown. Even the energy needed to drive a high impedance probe is significant when the Q gets high. IOW, the Q without the probe will be higher than the Q when you insert the probe to measure the Q. Jim Not a problem; use two different loads. Just like measuring the internal resistance of a battery or a curent meter... ...Never done directly. |
James Meyer wrote in message . ..
On 17 Apr 2004 10:09:22 -0700, (Tom Bruhns) posted this: Robert Baer wrote in message ... ... Yes, but the emphasis was on small size, and a helical resonator allows a goodly shrinkage of volume wihout a corresponding loss large of Q. As compared with what? A given coil in a helical resonator will result in lower Qu than that same coil unshielded and simply resonated with a good capacitor. Not so. And others have pointed that out. If you take an unshielded coil to it's ultimate configuration you are confronted with a resonant antenna that is loaded by its radiation resistance and that results in a *lower* Q than a properly shielded resonator. ONLY if it's really big. See Reg's posting in this thread on that subject. We're talking about making things small here, like smaller than a 1 inch diameter coil at 18MHz. The cavity for a standard helical resonator design will ding the Q by 15% or more; for such a small unshielded coil do you expect that much radiation? I don't. Not even close. Cheers, Tom |
On Sat, 17 Apr 2004 18:56:14 -0700, Roy Lewallen posted this:
Thanks for the profound observation about mathematicians and engineers. In which category does one put a person who's satisfied with calculations made without thinking about, caring about, or considering the errors caused by ignoring fundamental effects? Certainly not an engineer as I use the term. Roy Lewallen, W7EL Such a person as you describe is commonly known as a physicist. I have had to work with several. That some of them are still alive is a testament to my degree of self control. Jim |
On Sat, 17 Apr 2004 18:56:14 -0700, Roy Lewallen posted this:
Thanks for the profound observation about mathematicians and engineers. In which category does one put a person who's satisfied with calculations made without thinking about, caring about, or considering the errors caused by ignoring fundamental effects? Certainly not an engineer as I use the term. Roy Lewallen, W7EL Such a person as you describe is commonly known as a physicist. I have had to work with several. That some of them are still alive is a testament to my degree of self control. Jim |
I read in sci.electronics.design that James Meyer
wrote (in ) about 'A neat and compact way to generate RF harmonics...', on Sun, 18 Apr 2004: On Sat, 17 Apr 2004 18:56:14 -0700, Roy Lewallen posted this: Thanks for the profound observation about mathematicians and engineers. In which category does one put a person who's satisfied with calculations made without thinking about, caring about, or considering the errors caused by ignoring fundamental effects? Certainly not an engineer as I use the term. Roy Lewallen, W7EL Such a person as you describe is commonly known as a physicist. I have had to work with several. That some of them are still alive is a testament to my degree of self control. LOL! But physicists are usually *preoccupied* with fundamental effects and tend to ignore others. In my brief skirmish with aeronautical engineering, I formed the opinion that most of the calculations were as pragmatic as RL suggests; the only consolation is that they seem to work. -- Regards, John Woodgate, OOO - Own Opinions Only. The good news is that nothing is compulsory. The bad news is that everything is prohibited. http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk |
I read in sci.electronics.design that James Meyer
wrote (in ) about 'A neat and compact way to generate RF harmonics...', on Sun, 18 Apr 2004: On Sat, 17 Apr 2004 18:56:14 -0700, Roy Lewallen posted this: Thanks for the profound observation about mathematicians and engineers. In which category does one put a person who's satisfied with calculations made without thinking about, caring about, or considering the errors caused by ignoring fundamental effects? Certainly not an engineer as I use the term. Roy Lewallen, W7EL Such a person as you describe is commonly known as a physicist. I have had to work with several. That some of them are still alive is a testament to my degree of self control. LOL! But physicists are usually *preoccupied* with fundamental effects and tend to ignore others. In my brief skirmish with aeronautical engineering, I formed the opinion that most of the calculations were as pragmatic as RL suggests; the only consolation is that they seem to work. -- Regards, John Woodgate, OOO - Own Opinions Only. The good news is that nothing is compulsory. The bad news is that everything is prohibited. http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk |
On Sat, 17 Apr 2004 23:48:01 GMT, James Meyer
wrote: On Sat, 17 Apr 2004 12:22:03 -0700, Roy Lewallen posted this: Ah, just the person I've been waiting for. How do you account for current bunching on the conductors (that is, non-uniform distribution of current around the conductors)? What reference, equation, or program do you use? Nearly all "first principle" calculations of Q I've seen grossly overestimate Q, and I believe the failure to take this into account is at least part of the reason. I haven't seen a decent analytical method of dealing with it, and an anxious to see how you do it. Then there's surface corrosion and roughness, radiation, and coupling to nearby objects. How do you deal with those? Have you identified some of the other factors that often make a simplistic "first principle" calculation disagree so badly with carefully made measurements? Roy Lewallen, W7EL James Meyer wrote: If you have to "do the math", you might as well just calculate the Q from first principles and forget the "measurement". Jim I was responding to a suggestion that one could do the math to calculate what the Q would have been if you hadn't tried to measure it. I was pointing out that if you could do that math, and get it correct, that you could do the whole exercise with math and forget measuring anything. The math in question is trivial. Qs from 1 to 1e9 can be measured accurately without difficulty. An engineer knows when to say "close enough". A mathematician is never satisfied. But then, mathematicians don't measure things, do they? John |
On Sat, 17 Apr 2004 23:48:01 GMT, James Meyer
wrote: On Sat, 17 Apr 2004 12:22:03 -0700, Roy Lewallen posted this: Ah, just the person I've been waiting for. How do you account for current bunching on the conductors (that is, non-uniform distribution of current around the conductors)? What reference, equation, or program do you use? Nearly all "first principle" calculations of Q I've seen grossly overestimate Q, and I believe the failure to take this into account is at least part of the reason. I haven't seen a decent analytical method of dealing with it, and an anxious to see how you do it. Then there's surface corrosion and roughness, radiation, and coupling to nearby objects. How do you deal with those? Have you identified some of the other factors that often make a simplistic "first principle" calculation disagree so badly with carefully made measurements? Roy Lewallen, W7EL James Meyer wrote: If you have to "do the math", you might as well just calculate the Q from first principles and forget the "measurement". Jim I was responding to a suggestion that one could do the math to calculate what the Q would have been if you hadn't tried to measure it. I was pointing out that if you could do that math, and get it correct, that you could do the whole exercise with math and forget measuring anything. The math in question is trivial. Qs from 1 to 1e9 can be measured accurately without difficulty. An engineer knows when to say "close enough". A mathematician is never satisfied. But then, mathematicians don't measure things, do they? John |
John,
Are you saying you have some SRDs available? I could use a couple in a GPR I'm working on. Part of the Sample pulse generator. Don John Larkin wrote: On Mon, 12 Apr 2004 19:09:51 GMT, "Harold E. Johnson" wrote: If you do use diodes for higher-order harmonic generation, and not just a simple full-wave-rectifier type frequency doubler, I suppose you want something of the nature of a step recovery diode. That implies minority carrier stored charge in the diode, and that would preclude using a Schottky diode (which would work great in the full-wave-rectifier type doubler). If you get into actually wanting to generate harmonic combs out to microwave frequencies, it's probably worthwhile looking for diodes actually characterized for step recovery service. But I really think that's way beyond what you are trying to accomplish right now. My turn to learn something here. Tom, would you elaborate a bit on the above please? I know SRD's are comb generators out to visible light, but they're also 50 percent hard to find and 50 percent magic. I've been using Schottky's for X16 multipliers to 2 GHz, am I doing something wrong? (I keep promising myself that I'm gonna substitute an MMIC for that one day, I DID find the "Filter Gain" in the line length from generator to filter), THAT was both impressive AND helpful. If I go with the MMIC, any preference of Silicon over GaAs? Regards W4ZCB The only distributor-stock SRDs I know of are the M/Acom MA44767, MA44768, MA44769 parts, all SOT-23 and dirt cheap. I think Penstock carries them. The '68 or '69 should be good for multiplication to 2 GHz. For high ratios, an SRD will beat a plain diode by a huge amount. There are lots of appnotes around about using them as multipliers. I have a bunch in stock and can send a few to anybody who wants to play. John -- My web pages ....................VVVVVVVV................. Window to My World: http://home.comcast.net/~dcyoung9/fpa/ Faux-Oro, Remove SPAM to E-Mail, Have Cesium Mag. Will Travel |
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