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I don't know of any good way to troubleshoot an oscillator without an
oscilloscope and signal generator, except to measure all the voltages. However, the voltages can be right and the oscillator still not oscillate. Or you can find that some voltages are different simply because it's not oscillating. Perhaps someone else has some tips that can help. Your problems with oscillators are possibly caused by poor component choices. Capacitors should be low loss types, like mica, NPO ceramic, or polystyrene plastic, and should be physically small so they don't have much inductance. NPO ceramic has the lowest temperature coefficient so is the best choice for stability. If you have a poorly made inductor, the temperature drift of a polystyrene capacitor might more-or-less cancel it, but that's a poor way to get stability. Inductors also have to be low loss, and that's probably the answer to your question about the toroid. There are just one or two types of ferrite that might be usable for an oscillator inductor, but they're uncommon so you're unlikely to have them in your junk box. All other kinds of ferrite cores are too lossy for this use. You should use only powdered iron cores. In my experience, the best is type 6, which is colored yellow and typically with a glossy finish. Type 7, colored white, should be similar, although it's much less common. I wouldn't use any other type of toroid core except these two types of powdered iron. Ferrite is a good core choice for the RF choke, although you might have trouble with core saturation if you're putting a fair amount of current through it. Chances are you don't really need a choke with a value this high, although you might in some applications. Don't apologize for the questions! We all had to start somewhere, and are glad to see you learning. And you never learn much from circuits that work -- it's the ones that don't which are educational. Roy Lewallen, W7EL Jock Cooper wrote: Hi everyone, I've been interested in radios and how they work since I was a kid -- I had a crystal radio kit and a RF-2200. Recently I started building radios and have been having a blast. Please keep in mind that I am very newbie. After scouring the web for am radio circuit schematics I found quite a few and successfully built several of them (I'm using breadboards). Then I wanted to get a little more sophisticated so I got some NE602s and started to work on a superhet ish type design -- basically cobbling together bits from other circuits. I had some decent success using the NE602 internal oscillator (although getting the oscillator to track the rf input is tricky), then I wanted to use an external oscillator. I tried numerous circuits and numerous types (Hartley, Colpitts etc) I had found but I couldn't get any of them to start up. Finally somehow I got one working reliably: it was a JFET Clapp with a JFET buffer amp. I hooked up my Elenco LCR to it to measure the frequency. I was using a 3 gang 10-500pf air cap and a coil I wound onto a pill bottle. The oscillator was running from 980 khz to 2050 or so. I fed it into the NE602 pin 6. Only problem was (again) I had a hard time getting the main tuning (also on the 3 gang cap) to track the same range (well the same minus 455). I guess I had plenty of stray capacitance or something that was mucking up my calculations. So at say 540 they would line up but tuning to the other end they'd be off by a few 100 (!) khz. So I decided to build a second oscillator to help align the antenna tuning tank. I pulled out one of those little 'mini' breadboards and basically dupicated the working oscillator circuit on it. Only this time no startup. I also moved it to a second breadboard but still no good. Now I'm at a loss as to how to proceed. How do you diagnose a bad oscillator circuit? I thought about measuring the voltages all various points on the working osc while it was running and comparing those, not sure how much that will tell me. Also, a related question. I tried winding a toroid with the same inductance as my pill bottle coil, and hooking it in place of the pill bottle coil in the working oscillator. But it wouldn't start then. Any clue why this might be the case?? Also I have seen some circuits that call for a 1mH RF choke.. Can I wind a toroid for this? I don't have any chokes that high. thanks for any help and apologies for any dumb questions, Jock Cooper --- http://www.fractal-recursions.com |
help building oscillator
I don't know of any good way to troubleshoot an oscillator without an
oscilloscope and signal generator, except to measure all the voltages. However, the voltages can be right and the oscillator still not oscillate. Or you can find that some voltages are different simply because it's not oscillating. Perhaps someone else has some tips that can help. Your problems with oscillators are possibly caused by poor component choices. Capacitors should be low loss types, like mica, NPO ceramic, or polystyrene plastic, and should be physically small so they don't have much inductance. NPO ceramic has the lowest temperature coefficient so is the best choice for stability. If you have a poorly made inductor, the temperature drift of a polystyrene capacitor might more-or-less cancel it, but that's a poor way to get stability. Inductors also have to be low loss, and that's probably the answer to your question about the toroid. There are just one or two types of ferrite that might be usable for an oscillator inductor, but they're uncommon so you're unlikely to have them in your junk box. All other kinds of ferrite cores are too lossy for this use. You should use only powdered iron cores. In my experience, the best is type 6, which is colored yellow and typically with a glossy finish. Type 7, colored white, should be similar, although it's much less common. I wouldn't use any other type of toroid core except these two types of powdered iron. Ferrite is a good core choice for the RF choke, although you might have trouble with core saturation if you're putting a fair amount of current through it. Chances are you don't really need a choke with a value this high, although you might in some applications. Don't apologize for the questions! We all had to start somewhere, and are glad to see you learning. And you never learn much from circuits that work -- it's the ones that don't which are educational. Roy Lewallen, W7EL Jock Cooper wrote: Hi everyone, I've been interested in radios and how they work since I was a kid -- I had a crystal radio kit and a RF-2200. Recently I started building radios and have been having a blast. Please keep in mind that I am very newbie. After scouring the web for am radio circuit schematics I found quite a few and successfully built several of them (I'm using breadboards). Then I wanted to get a little more sophisticated so I got some NE602s and started to work on a superhet ish type design -- basically cobbling together bits from other circuits. I had some decent success using the NE602 internal oscillator (although getting the oscillator to track the rf input is tricky), then I wanted to use an external oscillator. I tried numerous circuits and numerous types (Hartley, Colpitts etc) I had found but I couldn't get any of them to start up. Finally somehow I got one working reliably: it was a JFET Clapp with a JFET buffer amp. I hooked up my Elenco LCR to it to measure the frequency. I was using a 3 gang 10-500pf air cap and a coil I wound onto a pill bottle. The oscillator was running from 980 khz to 2050 or so. I fed it into the NE602 pin 6. Only problem was (again) I had a hard time getting the main tuning (also on the 3 gang cap) to track the same range (well the same minus 455). I guess I had plenty of stray capacitance or something that was mucking up my calculations. So at say 540 they would line up but tuning to the other end they'd be off by a few 100 (!) khz. So I decided to build a second oscillator to help align the antenna tuning tank. I pulled out one of those little 'mini' breadboards and basically dupicated the working oscillator circuit on it. Only this time no startup. I also moved it to a second breadboard but still no good. Now I'm at a loss as to how to proceed. How do you diagnose a bad oscillator circuit? I thought about measuring the voltages all various points on the working osc while it was running and comparing those, not sure how much that will tell me. Also, a related question. I tried winding a toroid with the same inductance as my pill bottle coil, and hooking it in place of the pill bottle coil in the working oscillator. But it wouldn't start then. Any clue why this might be the case?? Also I have seen some circuits that call for a 1mH RF choke.. Can I wind a toroid for this? I don't have any chokes that high. thanks for any help and apologies for any dumb questions, Jock Cooper --- http://www.fractal-recursions.com |
"Roy Lewallen" wrote in message
... I don't know of any good way to troubleshoot an oscillator without an oscilloscope and signal generator, except to measure all the voltages. However, the voltages can be right and the oscillator still not oscillate. Or you can find that some voltages are different simply because it's not oscillating. Perhaps someone else has some tips that can help. Your problems with oscillators are possibly caused by poor component choices. Capacitors should be low loss types, like mica, NPO ceramic, or polystyrene plastic, and should be physically small so they don't have much inductance. NPO ceramic has the lowest temperature coefficient so is the best choice for stability. If you have a poorly made inductor, the temperature drift of a polystyrene capacitor might more-or-less cancel it, but that's a poor way to get stability. Inductors also have to be low loss, and that's probably the answer to your question about the toroid. There are just one or two types of ferrite that might be usable for an oscillator inductor, but they're uncommon so you're unlikely to have them in your junk box. All other kinds of ferrite cores are too lossy for this use. You should use only powdered iron cores. In my experience, the best is type 6, which is colored yellow and typically with a glossy finish. Type 7, colored white, should be similar, although it's much less common. I wouldn't use any other type of toroid core except these two types of powdered iron. Ferrite is a good core choice for the RF choke, although you might have trouble with core saturation if you're putting a fair amount of current through it. Chances are you don't really need a choke with a value this high, although you might in some applications. Don't apologize for the questions! We all had to start somewhere, and are glad to see you learning. And you never learn much from circuits that work -- it's the ones that don't which are educational. Roy Lewallen, W7EL Jock Cooper wrote: Hi everyone, I've been interested in radios and how they work since I was a kid -- I had a crystal radio kit and a RF-2200. Recently I started building radios and have been having a blast. Please keep in mind that I am very newbie. After scouring the web for am radio circuit schematics I found quite a few and successfully built several of them (I'm using breadboards). Then I wanted to get a little more sophisticated so I got some NE602s and started to work on a superhet ish type design -- basically cobbling together bits from other circuits. I had some decent success using the NE602 internal oscillator (although getting the oscillator to track the rf input is tricky), then I wanted to use an external oscillator. I tried numerous circuits and numerous types (Hartley, Colpitts etc) I had found but I couldn't get any of them to start up. Finally somehow I got one working reliably: it was a JFET Clapp with a JFET buffer amp. I hooked up my Elenco LCR to it to measure the frequency. I was using a 3 gang 10-500pf air cap and a coil I wound onto a pill bottle. The oscillator was running from 980 khz to 2050 or so. I fed it into the NE602 pin 6. Only problem was (again) I had a hard time getting the main tuning (also on the 3 gang cap) to track the same range (well the same minus 455). I guess I had plenty of stray capacitance or something that was mucking up my calculations. So at say 540 they would line up but tuning to the other end they'd be off by a few 100 (!) khz. So I decided to build a second oscillator to help align the antenna tuning tank. I pulled out one of those little 'mini' breadboards and basically dupicated the working oscillator circuit on it. Only this time no startup. I also moved it to a second breadboard but still no good. Now I'm at a loss as to how to proceed. How do you diagnose a bad oscillator circuit? I thought about measuring the voltages all various points on the working osc while it was running and comparing those, not sure how much that will tell me. Also, a related question. I tried winding a toroid with the same inductance as my pill bottle coil, and hooking it in place of the pill bottle coil in the working oscillator. But it wouldn't start then. Any clue why this might be the case?? Also I have seen some circuits that call for a 1mH RF choke.. Can I wind a toroid for this? I don't have any chokes that high. thanks for any help and apologies for any dumb questions, Jock Cooper --- http://www.fractal-recursions.com Yup to everything that Roy said, and I'll add a couple comments of my own. Depending on the type of breadboard that you're using, the capacitance between the rows of contacts can upset RF tuning. At the relatively low frequencies that you're using, that shouldn't be having that much of an effect,but you can't rule it out entirely. I assume, that since you're trying to build a superhet radio, that you're tuning the oscillator and RF with a multi-section variable capacitor. I'll bet that you're using a variable with equal capacitance on each section. Wrong!! Since the frequencies that the oscillator needs to tune is different from the RF tuning, then you need to select a variable with a high capacity section for the RF side, and a lower capacity section for tuning the oscillator. Take a look inside an old tube superhet radio and look at the tuning capacitor. Notice that one section has very large plates on the rotor and the other section has plates that are about 1/2 to 2/3 the size of the large (high capacity) section. That's probably why the oscillator isn't tracking the RF tuning. Now, to get the oscillator to run reliably, you may need to separate the connections on the breadboard a little more. Instead of connecting somponents to adjacent rows, separate them by two rows. That will reduce the capacitance somewhat. Are you using a suggested circuit from the data sheet of the NE602? If so, be sure you use suggested types of components, especially capacitors. They can be notoriously problematic if they are the wrong type for the application. -- Tweetldee Tweetldee at att dot net (Just subsitute the appropriate characters in the address) Time is what keeps everything from happening all at once. |
"Roy Lewallen" wrote in message
... I don't know of any good way to troubleshoot an oscillator without an oscilloscope and signal generator, except to measure all the voltages. However, the voltages can be right and the oscillator still not oscillate. Or you can find that some voltages are different simply because it's not oscillating. Perhaps someone else has some tips that can help. Your problems with oscillators are possibly caused by poor component choices. Capacitors should be low loss types, like mica, NPO ceramic, or polystyrene plastic, and should be physically small so they don't have much inductance. NPO ceramic has the lowest temperature coefficient so is the best choice for stability. If you have a poorly made inductor, the temperature drift of a polystyrene capacitor might more-or-less cancel it, but that's a poor way to get stability. Inductors also have to be low loss, and that's probably the answer to your question about the toroid. There are just one or two types of ferrite that might be usable for an oscillator inductor, but they're uncommon so you're unlikely to have them in your junk box. All other kinds of ferrite cores are too lossy for this use. You should use only powdered iron cores. In my experience, the best is type 6, which is colored yellow and typically with a glossy finish. Type 7, colored white, should be similar, although it's much less common. I wouldn't use any other type of toroid core except these two types of powdered iron. Ferrite is a good core choice for the RF choke, although you might have trouble with core saturation if you're putting a fair amount of current through it. Chances are you don't really need a choke with a value this high, although you might in some applications. Don't apologize for the questions! We all had to start somewhere, and are glad to see you learning. And you never learn much from circuits that work -- it's the ones that don't which are educational. Roy Lewallen, W7EL Jock Cooper wrote: Hi everyone, I've been interested in radios and how they work since I was a kid -- I had a crystal radio kit and a RF-2200. Recently I started building radios and have been having a blast. Please keep in mind that I am very newbie. After scouring the web for am radio circuit schematics I found quite a few and successfully built several of them (I'm using breadboards). Then I wanted to get a little more sophisticated so I got some NE602s and started to work on a superhet ish type design -- basically cobbling together bits from other circuits. I had some decent success using the NE602 internal oscillator (although getting the oscillator to track the rf input is tricky), then I wanted to use an external oscillator. I tried numerous circuits and numerous types (Hartley, Colpitts etc) I had found but I couldn't get any of them to start up. Finally somehow I got one working reliably: it was a JFET Clapp with a JFET buffer amp. I hooked up my Elenco LCR to it to measure the frequency. I was using a 3 gang 10-500pf air cap and a coil I wound onto a pill bottle. The oscillator was running from 980 khz to 2050 or so. I fed it into the NE602 pin 6. Only problem was (again) I had a hard time getting the main tuning (also on the 3 gang cap) to track the same range (well the same minus 455). I guess I had plenty of stray capacitance or something that was mucking up my calculations. So at say 540 they would line up but tuning to the other end they'd be off by a few 100 (!) khz. So I decided to build a second oscillator to help align the antenna tuning tank. I pulled out one of those little 'mini' breadboards and basically dupicated the working oscillator circuit on it. Only this time no startup. I also moved it to a second breadboard but still no good. Now I'm at a loss as to how to proceed. How do you diagnose a bad oscillator circuit? I thought about measuring the voltages all various points on the working osc while it was running and comparing those, not sure how much that will tell me. Also, a related question. I tried winding a toroid with the same inductance as my pill bottle coil, and hooking it in place of the pill bottle coil in the working oscillator. But it wouldn't start then. Any clue why this might be the case?? Also I have seen some circuits that call for a 1mH RF choke.. Can I wind a toroid for this? I don't have any chokes that high. thanks for any help and apologies for any dumb questions, Jock Cooper --- http://www.fractal-recursions.com Yup to everything that Roy said, and I'll add a couple comments of my own. Depending on the type of breadboard that you're using, the capacitance between the rows of contacts can upset RF tuning. At the relatively low frequencies that you're using, that shouldn't be having that much of an effect,but you can't rule it out entirely. I assume, that since you're trying to build a superhet radio, that you're tuning the oscillator and RF with a multi-section variable capacitor. I'll bet that you're using a variable with equal capacitance on each section. Wrong!! Since the frequencies that the oscillator needs to tune is different from the RF tuning, then you need to select a variable with a high capacity section for the RF side, and a lower capacity section for tuning the oscillator. Take a look inside an old tube superhet radio and look at the tuning capacitor. Notice that one section has very large plates on the rotor and the other section has plates that are about 1/2 to 2/3 the size of the large (high capacity) section. That's probably why the oscillator isn't tracking the RF tuning. Now, to get the oscillator to run reliably, you may need to separate the connections on the breadboard a little more. Instead of connecting somponents to adjacent rows, separate them by two rows. That will reduce the capacitance somewhat. Are you using a suggested circuit from the data sheet of the NE602? If so, be sure you use suggested types of components, especially capacitors. They can be notoriously problematic if they are the wrong type for the application. -- Tweetldee Tweetldee at att dot net (Just subsitute the appropriate characters in the address) Time is what keeps everything from happening all at once. |
A general coverage receiver is a good piece of test eqpt. Tune the rx to
the approx frequency of one that works to get a good idea of how to couple and how loud it should be. CW or SSB is easier to use than AM. You can also couple the LO of a receiver to use it as a test LO or signal gen. good luck hank wd5jfr "Tweetldee" wrote in message ... "Roy Lewallen" wrote in message ... I don't know of any good way to troubleshoot an oscillator without an oscilloscope and signal generator, except to measure all the voltages. However, the voltages can be right and the oscillator still not oscillate. Or you can find that some voltages are different simply because it's not oscillating. Perhaps someone else has some tips that can help. Your problems with oscillators are possibly caused by poor component choices. Capacitors should be low loss types, like mica, NPO ceramic, or polystyrene plastic, and should be physically small so they don't have much inductance. NPO ceramic has the lowest temperature coefficient so is the best choice for stability. If you have a poorly made inductor, the temperature drift of a polystyrene capacitor might more-or-less cancel it, but that's a poor way to get stability. Inductors also have to be low loss, and that's probably the answer to your question about the toroid. There are just one or two types of ferrite that might be usable for an oscillator inductor, but they're uncommon so you're unlikely to have them in your junk box. All other kinds of ferrite cores are too lossy for this use. You should use only powdered iron cores. In my experience, the best is type 6, which is colored yellow and typically with a glossy finish. Type 7, colored white, should be similar, although it's much less common. I wouldn't use any other type of toroid core except these two types of powdered iron. Ferrite is a good core choice for the RF choke, although you might have trouble with core saturation if you're putting a fair amount of current through it. Chances are you don't really need a choke with a value this high, although you might in some applications. Don't apologize for the questions! We all had to start somewhere, and are glad to see you learning. And you never learn much from circuits that work -- it's the ones that don't which are educational. Roy Lewallen, W7EL Jock Cooper wrote: Hi everyone, I've been interested in radios and how they work since I was a kid -- I had a crystal radio kit and a RF-2200. Recently I started building radios and have been having a blast. Please keep in mind that I am very newbie. After scouring the web for am radio circuit schematics I found quite a few and successfully built several of them (I'm using breadboards). Then I wanted to get a little more sophisticated so I got some NE602s and started to work on a superhet ish type design -- basically cobbling together bits from other circuits. I had some decent success using the NE602 internal oscillator (although getting the oscillator to track the rf input is tricky), then I wanted to use an external oscillator. I tried numerous circuits and numerous types (Hartley, Colpitts etc) I had found but I couldn't get any of them to start up. Finally somehow I got one working reliably: it was a JFET Clapp with a JFET buffer amp. I hooked up my Elenco LCR to it to measure the frequency. I was using a 3 gang 10-500pf air cap and a coil I wound onto a pill bottle. The oscillator was running from 980 khz to 2050 or so. I fed it into the NE602 pin 6. Only problem was (again) I had a hard time getting the main tuning (also on the 3 gang cap) to track the same range (well the same minus 455). I guess I had plenty of stray capacitance or something that was mucking up my calculations. So at say 540 they would line up but tuning to the other end they'd be off by a few 100 (!) khz. So I decided to build a second oscillator to help align the antenna tuning tank. I pulled out one of those little 'mini' breadboards and basically dupicated the working oscillator circuit on it. Only this time no startup. I also moved it to a second breadboard but still no good. Now I'm at a loss as to how to proceed. How do you diagnose a bad oscillator circuit? I thought about measuring the voltages all various points on the working osc while it was running and comparing those, not sure how much that will tell me. Also, a related question. I tried winding a toroid with the same inductance as my pill bottle coil, and hooking it in place of the pill bottle coil in the working oscillator. But it wouldn't start then. Any clue why this might be the case?? Also I have seen some circuits that call for a 1mH RF choke.. Can I wind a toroid for this? I don't have any chokes that high. thanks for any help and apologies for any dumb questions, Jock Cooper --- http://www.fractal-recursions.com Yup to everything that Roy said, and I'll add a couple comments of my own. Depending on the type of breadboard that you're using, the capacitance between the rows of contacts can upset RF tuning. At the relatively low frequencies that you're using, that shouldn't be having that much of an effect,but you can't rule it out entirely. I assume, that since you're trying to build a superhet radio, that you're tuning the oscillator and RF with a multi-section variable capacitor. I'll bet that you're using a variable with equal capacitance on each section. Wrong!! Since the frequencies that the oscillator needs to tune is different from the RF tuning, then you need to select a variable with a high capacity section for the RF side, and a lower capacity section for tuning the oscillator. Take a look inside an old tube superhet radio and look at the tuning capacitor. Notice that one section has very large plates on the rotor and the other section has plates that are about 1/2 to 2/3 the size of the large (high capacity) section. That's probably why the oscillator isn't tracking the RF tuning. Now, to get the oscillator to run reliably, you may need to separate the connections on the breadboard a little more. Instead of connecting somponents to adjacent rows, separate them by two rows. That will reduce the capacitance somewhat. Are you using a suggested circuit from the data sheet of the NE602? If so, be sure you use suggested types of components, especially capacitors. They can be notoriously problematic if they are the wrong type for the application. -- Tweetldee Tweetldee at att dot net (Just subsitute the appropriate characters in the address) Time is what keeps everything from happening all at once. |
A general coverage receiver is a good piece of test eqpt. Tune the rx to
the approx frequency of one that works to get a good idea of how to couple and how loud it should be. CW or SSB is easier to use than AM. You can also couple the LO of a receiver to use it as a test LO or signal gen. good luck hank wd5jfr "Tweetldee" wrote in message ... "Roy Lewallen" wrote in message ... I don't know of any good way to troubleshoot an oscillator without an oscilloscope and signal generator, except to measure all the voltages. However, the voltages can be right and the oscillator still not oscillate. Or you can find that some voltages are different simply because it's not oscillating. Perhaps someone else has some tips that can help. Your problems with oscillators are possibly caused by poor component choices. Capacitors should be low loss types, like mica, NPO ceramic, or polystyrene plastic, and should be physically small so they don't have much inductance. NPO ceramic has the lowest temperature coefficient so is the best choice for stability. If you have a poorly made inductor, the temperature drift of a polystyrene capacitor might more-or-less cancel it, but that's a poor way to get stability. Inductors also have to be low loss, and that's probably the answer to your question about the toroid. There are just one or two types of ferrite that might be usable for an oscillator inductor, but they're uncommon so you're unlikely to have them in your junk box. All other kinds of ferrite cores are too lossy for this use. You should use only powdered iron cores. In my experience, the best is type 6, which is colored yellow and typically with a glossy finish. Type 7, colored white, should be similar, although it's much less common. I wouldn't use any other type of toroid core except these two types of powdered iron. Ferrite is a good core choice for the RF choke, although you might have trouble with core saturation if you're putting a fair amount of current through it. Chances are you don't really need a choke with a value this high, although you might in some applications. Don't apologize for the questions! We all had to start somewhere, and are glad to see you learning. And you never learn much from circuits that work -- it's the ones that don't which are educational. Roy Lewallen, W7EL Jock Cooper wrote: Hi everyone, I've been interested in radios and how they work since I was a kid -- I had a crystal radio kit and a RF-2200. Recently I started building radios and have been having a blast. Please keep in mind that I am very newbie. After scouring the web for am radio circuit schematics I found quite a few and successfully built several of them (I'm using breadboards). Then I wanted to get a little more sophisticated so I got some NE602s and started to work on a superhet ish type design -- basically cobbling together bits from other circuits. I had some decent success using the NE602 internal oscillator (although getting the oscillator to track the rf input is tricky), then I wanted to use an external oscillator. I tried numerous circuits and numerous types (Hartley, Colpitts etc) I had found but I couldn't get any of them to start up. Finally somehow I got one working reliably: it was a JFET Clapp with a JFET buffer amp. I hooked up my Elenco LCR to it to measure the frequency. I was using a 3 gang 10-500pf air cap and a coil I wound onto a pill bottle. The oscillator was running from 980 khz to 2050 or so. I fed it into the NE602 pin 6. Only problem was (again) I had a hard time getting the main tuning (also on the 3 gang cap) to track the same range (well the same minus 455). I guess I had plenty of stray capacitance or something that was mucking up my calculations. So at say 540 they would line up but tuning to the other end they'd be off by a few 100 (!) khz. So I decided to build a second oscillator to help align the antenna tuning tank. I pulled out one of those little 'mini' breadboards and basically dupicated the working oscillator circuit on it. Only this time no startup. I also moved it to a second breadboard but still no good. Now I'm at a loss as to how to proceed. How do you diagnose a bad oscillator circuit? I thought about measuring the voltages all various points on the working osc while it was running and comparing those, not sure how much that will tell me. Also, a related question. I tried winding a toroid with the same inductance as my pill bottle coil, and hooking it in place of the pill bottle coil in the working oscillator. But it wouldn't start then. Any clue why this might be the case?? Also I have seen some circuits that call for a 1mH RF choke.. Can I wind a toroid for this? I don't have any chokes that high. thanks for any help and apologies for any dumb questions, Jock Cooper --- http://www.fractal-recursions.com Yup to everything that Roy said, and I'll add a couple comments of my own. Depending on the type of breadboard that you're using, the capacitance between the rows of contacts can upset RF tuning. At the relatively low frequencies that you're using, that shouldn't be having that much of an effect,but you can't rule it out entirely. I assume, that since you're trying to build a superhet radio, that you're tuning the oscillator and RF with a multi-section variable capacitor. I'll bet that you're using a variable with equal capacitance on each section. Wrong!! Since the frequencies that the oscillator needs to tune is different from the RF tuning, then you need to select a variable with a high capacity section for the RF side, and a lower capacity section for tuning the oscillator. Take a look inside an old tube superhet radio and look at the tuning capacitor. Notice that one section has very large plates on the rotor and the other section has plates that are about 1/2 to 2/3 the size of the large (high capacity) section. That's probably why the oscillator isn't tracking the RF tuning. Now, to get the oscillator to run reliably, you may need to separate the connections on the breadboard a little more. Instead of connecting somponents to adjacent rows, separate them by two rows. That will reduce the capacitance somewhat. Are you using a suggested circuit from the data sheet of the NE602? If so, be sure you use suggested types of components, especially capacitors. They can be notoriously problematic if they are the wrong type for the application. -- Tweetldee Tweetldee at att dot net (Just subsitute the appropriate characters in the address) Time is what keeps everything from happening all at once. |
Jock Cooper wrote in message ...
Hi everyone, ... How do you diagnose a bad oscillator circuit? Roy offered some good advice. No need for me to try to duplicate it! But I know there can be a lot of times you just don't see something that would be obvious to someone else who has more experience. If you can find someone locally to have a look at things, the answers might come a lot quicker. Failing that, if there's a place you could put up some pictures on the web, that might help. Are you using known-good circuits? Sounds like you probably are, given that you understand the differences among the various types of circuits. But it might be good to get your hands on a book with a bunch of circuit ideas in it, if you don't already have one (or more). Cheers, Tom |
Jock Cooper wrote in message ...
Hi everyone, ... How do you diagnose a bad oscillator circuit? Roy offered some good advice. No need for me to try to duplicate it! But I know there can be a lot of times you just don't see something that would be obvious to someone else who has more experience. If you can find someone locally to have a look at things, the answers might come a lot quicker. Failing that, if there's a place you could put up some pictures on the web, that might help. Are you using known-good circuits? Sounds like you probably are, given that you understand the differences among the various types of circuits. But it might be good to get your hands on a book with a bunch of circuit ideas in it, if you don't already have one (or more). Cheers, Tom |
I highly recommend _Experimental Methods in RF Design_, by Hayward,
Campbell, and Larkin, available from the ARRL or your favorite book seller. All the circuits in the book have actually been built with the component values shown, and have been designed by people who know what they're doing. My personal favorite oscillator is the one shown in fig. 4.4 on p. 4.3. It's a dead-simple Hartley, is very stable, and just about bulletproof. I've made versions from 2 to over 100 MHz, and they always oscillate. The authors say in the book that they've made versions from 1 MHz to 3 GHz. You'll also find equations so you can calculate the capacitors you need for a given tuning range, and a wealth of other information. Although it's a terrific bargain at the price, some people balk at spending the money for it. If you're one of those, check your local library. They might not have it yet -- if not, ask them to order it if they haven't already. Roy Lewallen, W7EL Tom Bruhns wrote: . . . Are you using known-good circuits? Sounds like you probably are, given that you understand the differences among the various types of circuits. But it might be good to get your hands on a book with a bunch of circuit ideas in it, if you don't already have one (or more). |
I highly recommend _Experimental Methods in RF Design_, by Hayward,
Campbell, and Larkin, available from the ARRL or your favorite book seller. All the circuits in the book have actually been built with the component values shown, and have been designed by people who know what they're doing. My personal favorite oscillator is the one shown in fig. 4.4 on p. 4.3. It's a dead-simple Hartley, is very stable, and just about bulletproof. I've made versions from 2 to over 100 MHz, and they always oscillate. The authors say in the book that they've made versions from 1 MHz to 3 GHz. You'll also find equations so you can calculate the capacitors you need for a given tuning range, and a wealth of other information. Although it's a terrific bargain at the price, some people balk at spending the money for it. If you're one of those, check your local library. They might not have it yet -- if not, ask them to order it if they haven't already. Roy Lewallen, W7EL Tom Bruhns wrote: . . . Are you using known-good circuits? Sounds like you probably are, given that you understand the differences among the various types of circuits. But it might be good to get your hands on a book with a bunch of circuit ideas in it, if you don't already have one (or more). |
"Jock Cooper" wrote in message ... Hi everyone, I've been interested in radios and how they work since I was a kid -- I had a crystal radio kit and a RF-2200. Recently I started building radios and have been having a blast. Please keep in mind that I am very newbie. [tale of woe deleted] I'd start again with a simple Hartley oscillator using a tapped toroid (you don't need a choke). Get the basic oscillator working (a scope helps) then add a buffer stage. Forget about getting the oscillator and front end tuning to track properly at this stage, use separate capacitors. When you get the thing working properly you can sort out the tracking. 73, Leon -- Leon Heller, G1HSM http://www.geocities.com/leon_heller |
"Jock Cooper" wrote in message ... Hi everyone, I've been interested in radios and how they work since I was a kid -- I had a crystal radio kit and a RF-2200. Recently I started building radios and have been having a blast. Please keep in mind that I am very newbie. [tale of woe deleted] I'd start again with a simple Hartley oscillator using a tapped toroid (you don't need a choke). Get the basic oscillator working (a scope helps) then add a buffer stage. Forget about getting the oscillator and front end tuning to track properly at this stage, use separate capacitors. When you get the thing working properly you can sort out the tracking. 73, Leon -- Leon Heller, G1HSM http://www.geocities.com/leon_heller |
Hi Jock,
there is nothing you should apologize for. My recommendations: 1/ Do not use breadboards for RF. They are perfect for AF, good for digital citcuits, but RF circuits sometimes work, more often not. And keep the groundplane as big as possible. The "ugly", "rats-nest", "dead bug" or "manhattan" style really seem to be far the best for RF prototyping. Look at http://w1.859.telia.com/~u85920178/blocks/deadbug_0.htm for more info. 2/ Get an oscilloscope covering at least three times your frequency range. An add-on unit for your PC can turn it into an oscillscope and spectrum analyzer for a fair price. 3/ Use the necessary tuning capacitors and their configuration to keep the oscillator and input frequency near to each other at more than one point. The configuration and formulae can be found in many books. 4/ Try the oscillator from http://w1.859.telia.com/~u85920178/blocks/osc7m00.htm ,it should work reliably in a wide frequency band. BR from Ivan OK1SIP |
Hi Jock,
there is nothing you should apologize for. My recommendations: 1/ Do not use breadboards for RF. They are perfect for AF, good for digital citcuits, but RF circuits sometimes work, more often not. And keep the groundplane as big as possible. The "ugly", "rats-nest", "dead bug" or "manhattan" style really seem to be far the best for RF prototyping. Look at http://w1.859.telia.com/~u85920178/blocks/deadbug_0.htm for more info. 2/ Get an oscilloscope covering at least three times your frequency range. An add-on unit for your PC can turn it into an oscillscope and spectrum analyzer for a fair price. 3/ Use the necessary tuning capacitors and their configuration to keep the oscillator and input frequency near to each other at more than one point. The configuration and formulae can be found in many books. 4/ Try the oscillator from http://w1.859.telia.com/~u85920178/blocks/osc7m00.htm ,it should work reliably in a wide frequency band. BR from Ivan OK1SIP |
Jock Cooper writes:
Hi everyone, [snip] Thanks to everyone for the great and helpful suggestions. This sure is a friendly group. Since I just recently started all this tinkering, my junkbox is a little low in some areas, notably NP0 capacitors.. I have a few in values from 3.9 up to 47 and a few 100s but not else. So I've used various other types when higher values are called for.. I'm planning on picking up an assortment soon. Also I have some copper clad non drilled pc boards, I'm going to try to rebuild the oscillator (and radio) using the 'ugly' method; although I'm a little afraid I'll make myself a tangled mess of useless and stuck together parts. The main reason I use breadboards is so that I can take parts in and out of the circuit quickly (ie I'm at the stage where I'm curious about what happens when I take such and such part out, or change its value etc). I'd love to get a oscilloscope but my 'play' budget is mostly spent for awhile. So I've been making due with an LCR and a little cheapo DMM. I did order the book _Experimental Methods in RF Design_ .. I've also got a lot of good info from an old (well 1998) ARRL handbook I got on Ebay. Jock |
Jock Cooper writes:
Hi everyone, [snip] Thanks to everyone for the great and helpful suggestions. This sure is a friendly group. Since I just recently started all this tinkering, my junkbox is a little low in some areas, notably NP0 capacitors.. I have a few in values from 3.9 up to 47 and a few 100s but not else. So I've used various other types when higher values are called for.. I'm planning on picking up an assortment soon. Also I have some copper clad non drilled pc boards, I'm going to try to rebuild the oscillator (and radio) using the 'ugly' method; although I'm a little afraid I'll make myself a tangled mess of useless and stuck together parts. The main reason I use breadboards is so that I can take parts in and out of the circuit quickly (ie I'm at the stage where I'm curious about what happens when I take such and such part out, or change its value etc). I'd love to get a oscilloscope but my 'play' budget is mostly spent for awhile. So I've been making due with an LCR and a little cheapo DMM. I did order the book _Experimental Methods in RF Design_ .. I've also got a lot of good info from an old (well 1998) ARRL handbook I got on Ebay. Jock |
You can series and parallel any number of capacitors to get the right
value. A given oscillator type works best within some range of reactance values for L and C. If you go too far outside the ideal range, stability will suffer, noise might increase, and if too extreme, it might not oscillate. The ideal range depends on the oscillator design. That being said, you can often vary L and C quite a great deal and still get adequate operation. Real inductors are, in general, a lot more different from their theoretical ideal counterparts than capacitors are. Real inductors have considerable loss and stray capacitance, as well as being temperature sensitive. So you'll often find that a circuit works quite a bit differently if you substitute an inductor for one with different physical construction. For a VFO tank, I use only toroids wound on type 6 powdered iron material. (As I mentioned earlier, type 7 is probably as good, but I've never used it.) For VFO tank capacitors, I use only NPO ceramic. The combination produces low drift, dominated by the inductor. If desired, the drift can be compensated by replacing part of the C with negative temperature coefficient parts. Most other types of L and C have substantially greater temperature sensitivity. You might get lucky and have poor parts drift in opposite directions and more-or-less cancel, but that's poor practice and hard to duplicate. Better to design for minimal inherent drift, then compensate what's left if necessary. Toroids have the big advantage of producing a relatively small external field. That makes them much less sensitive to mounting, the influence of nearby objects, and microphonics. Jock Cooper wrote: . . . I wasn't sure if this was even OK to do (if it is too lossy or someting), I figured I could experiment around with the result and find out :) But maybe now I can just ask.. how much mucking around can I do by adding in parallel and serial caps to tweak the variable cap range? Also, Can I just find any old values of L and C that when plugged in would give me the F I'm looking for? Or are there only certain values of L and C that are appropriate for certain ranges of Freq. . . . Roy Lewallen, W7EL |
You can series and parallel any number of capacitors to get the right
value. A given oscillator type works best within some range of reactance values for L and C. If you go too far outside the ideal range, stability will suffer, noise might increase, and if too extreme, it might not oscillate. The ideal range depends on the oscillator design. That being said, you can often vary L and C quite a great deal and still get adequate operation. Real inductors are, in general, a lot more different from their theoretical ideal counterparts than capacitors are. Real inductors have considerable loss and stray capacitance, as well as being temperature sensitive. So you'll often find that a circuit works quite a bit differently if you substitute an inductor for one with different physical construction. For a VFO tank, I use only toroids wound on type 6 powdered iron material. (As I mentioned earlier, type 7 is probably as good, but I've never used it.) For VFO tank capacitors, I use only NPO ceramic. The combination produces low drift, dominated by the inductor. If desired, the drift can be compensated by replacing part of the C with negative temperature coefficient parts. Most other types of L and C have substantially greater temperature sensitivity. You might get lucky and have poor parts drift in opposite directions and more-or-less cancel, but that's poor practice and hard to duplicate. Better to design for minimal inherent drift, then compensate what's left if necessary. Toroids have the big advantage of producing a relatively small external field. That makes them much less sensitive to mounting, the influence of nearby objects, and microphonics. Jock Cooper wrote: . . . I wasn't sure if this was even OK to do (if it is too lossy or someting), I figured I could experiment around with the result and find out :) But maybe now I can just ask.. how much mucking around can I do by adding in parallel and serial caps to tweak the variable cap range? Also, Can I just find any old values of L and C that when plugged in would give me the F I'm looking for? Or are there only certain values of L and C that are appropriate for certain ranges of Freq. . . . Roy Lewallen, W7EL |
Roy Lewallen writes:
When you get _Experimental Methods. . _, look at the very first few pages -- "Getting Started". You'll find a nice drawing and some other information about "ugly construction". Incidentally, the method was first described and the term coined in the article "The Ugly Weekender" by Roger and Wes Hayward, in August 1981 QST. If you can get hold of a copy of this article, it has more about the method, as well as some other good information. If and when you do eventually decide to get a scope -- I've been surprised to see Tek 465 scopes going on eBay for about $200. That's an awful lot of bang for the buck. Roy Lewallen, W7EL Well last night I took some double sided copper clab board and cut off a small square. (By the way, what is the best way to cut this stuff?) I rebuilt the oscillator on there in 'ugly' style. And it was in fact quite ugly. It looked like something I would have done as a kid. But it worked! Now I'm sold on it. Hopefully I can get some pointers on improving my technique from the book. Now I have a new question though. The circuit is a Clapp based on the MPF102 JFET. When I compute the frequency range, it is close to the measured range but not the same; but there appears to be some capacitance that I can't account for, and its value seems higher than would be 'stray'. The circuit I'm using is basically like the one at http://www.electronics-tutorials.com...scillators.htm in figure 2, but without the extra parallel stuff on the variable cap. So I calculate the cap value by adding the var cap value in series with the caps labelled on that website as cfb-a and cfb-b. (By the way, what happens if those two aren't the same value?) Do any of the other capacitors in the circuit factor in? How much capacitance could my 'pill bottle inductor' be contributing? I was careful, but not extra careful when winding it. |
Roy Lewallen writes:
When you get _Experimental Methods. . _, look at the very first few pages -- "Getting Started". You'll find a nice drawing and some other information about "ugly construction". Incidentally, the method was first described and the term coined in the article "The Ugly Weekender" by Roger and Wes Hayward, in August 1981 QST. If you can get hold of a copy of this article, it has more about the method, as well as some other good information. If and when you do eventually decide to get a scope -- I've been surprised to see Tek 465 scopes going on eBay for about $200. That's an awful lot of bang for the buck. Roy Lewallen, W7EL Well last night I took some double sided copper clab board and cut off a small square. (By the way, what is the best way to cut this stuff?) I rebuilt the oscillator on there in 'ugly' style. And it was in fact quite ugly. It looked like something I would have done as a kid. But it worked! Now I'm sold on it. Hopefully I can get some pointers on improving my technique from the book. Now I have a new question though. The circuit is a Clapp based on the MPF102 JFET. When I compute the frequency range, it is close to the measured range but not the same; but there appears to be some capacitance that I can't account for, and its value seems higher than would be 'stray'. The circuit I'm using is basically like the one at http://www.electronics-tutorials.com...scillators.htm in figure 2, but without the extra parallel stuff on the variable cap. So I calculate the cap value by adding the var cap value in series with the caps labelled on that website as cfb-a and cfb-b. (By the way, what happens if those two aren't the same value?) Do any of the other capacitors in the circuit factor in? How much capacitance could my 'pill bottle inductor' be contributing? I was careful, but not extra careful when winding it. |
I usually cut PC board material with tin snips. A hacksaw also works,
but it makes a lot of irritating dust. In the schematic you mention, the "a" and "b" capacitors form a voltage divider to control the amount of signal that's fed back to the active device. If there's too much (a/b ratio too large), the waveform will be distorted and the temperature drift will probably increase. If there's too little, the oscillator will be slow to start or won't start reliably or at all. I don't want to answer your question about calculating the oscillation frequency without some detailed thought, which I don't have time for just now. But I believe you're doing the right calculation. Note that the oscillator output is in parallel with the "b" capacitor, so any capacitive loading on the oscillator will lower the frequency. The RFC and your inductor will both present some stray C. It's nearly impossible to tell how much C your inductor will contribute. There are a couple of ways to measure it, but if you've got the other capacitances under control, you've already made yourself a test fixture for determining inductor capacitance (assuming you know its inductance) -- it's the oscillator. Roy Lewallen, W7EL Jock Cooper wrote: Roy Lewallen writes: When you get _Experimental Methods. . _, look at the very first few pages -- "Getting Started". You'll find a nice drawing and some other information about "ugly construction". Incidentally, the method was first described and the term coined in the article "The Ugly Weekender" by Roger and Wes Hayward, in August 1981 QST. If you can get hold of a copy of this article, it has more about the method, as well as some other good information. If and when you do eventually decide to get a scope -- I've been surprised to see Tek 465 scopes going on eBay for about $200. That's an awful lot of bang for the buck. Roy Lewallen, W7EL Well last night I took some double sided copper clab board and cut off a small square. (By the way, what is the best way to cut this stuff?) I rebuilt the oscillator on there in 'ugly' style. And it was in fact quite ugly. It looked like something I would have done as a kid. But it worked! Now I'm sold on it. Hopefully I can get some pointers on improving my technique from the book. Now I have a new question though. The circuit is a Clapp based on the MPF102 JFET. When I compute the frequency range, it is close to the measured range but not the same; but there appears to be some capacitance that I can't account for, and its value seems higher than would be 'stray'. The circuit I'm using is basically like the one at http://www.electronics-tutorials.com...scillators.htm in figure 2, but without the extra parallel stuff on the variable cap. So I calculate the cap value by adding the var cap value in series with the caps labelled on that website as cfb-a and cfb-b. (By the way, what happens if those two aren't the same value?) Do any of the other capacitors in the circuit factor in? How much capacitance could my 'pill bottle inductor' be contributing? I was careful, but not extra careful when winding it. |
I usually cut PC board material with tin snips. A hacksaw also works,
but it makes a lot of irritating dust. In the schematic you mention, the "a" and "b" capacitors form a voltage divider to control the amount of signal that's fed back to the active device. If there's too much (a/b ratio too large), the waveform will be distorted and the temperature drift will probably increase. If there's too little, the oscillator will be slow to start or won't start reliably or at all. I don't want to answer your question about calculating the oscillation frequency without some detailed thought, which I don't have time for just now. But I believe you're doing the right calculation. Note that the oscillator output is in parallel with the "b" capacitor, so any capacitive loading on the oscillator will lower the frequency. The RFC and your inductor will both present some stray C. It's nearly impossible to tell how much C your inductor will contribute. There are a couple of ways to measure it, but if you've got the other capacitances under control, you've already made yourself a test fixture for determining inductor capacitance (assuming you know its inductance) -- it's the oscillator. Roy Lewallen, W7EL Jock Cooper wrote: Roy Lewallen writes: When you get _Experimental Methods. . _, look at the very first few pages -- "Getting Started". You'll find a nice drawing and some other information about "ugly construction". Incidentally, the method was first described and the term coined in the article "The Ugly Weekender" by Roger and Wes Hayward, in August 1981 QST. If you can get hold of a copy of this article, it has more about the method, as well as some other good information. If and when you do eventually decide to get a scope -- I've been surprised to see Tek 465 scopes going on eBay for about $200. That's an awful lot of bang for the buck. Roy Lewallen, W7EL Well last night I took some double sided copper clab board and cut off a small square. (By the way, what is the best way to cut this stuff?) I rebuilt the oscillator on there in 'ugly' style. And it was in fact quite ugly. It looked like something I would have done as a kid. But it worked! Now I'm sold on it. Hopefully I can get some pointers on improving my technique from the book. Now I have a new question though. The circuit is a Clapp based on the MPF102 JFET. When I compute the frequency range, it is close to the measured range but not the same; but there appears to be some capacitance that I can't account for, and its value seems higher than would be 'stray'. The circuit I'm using is basically like the one at http://www.electronics-tutorials.com...scillators.htm in figure 2, but without the extra parallel stuff on the variable cap. So I calculate the cap value by adding the var cap value in series with the caps labelled on that website as cfb-a and cfb-b. (By the way, what happens if those two aren't the same value?) Do any of the other capacitors in the circuit factor in? How much capacitance could my 'pill bottle inductor' be contributing? I was careful, but not extra careful when winding it. |
Jock Cooper wrote: I tried numerous circuits and numerous types (Hartley, Colpitts etc) I had found but I couldn't get any of them to start up. Oh, that's easy. You're *trying* to build an oscillator; give up on that goal and choose an easier one: try to build an amplifier. I mean, really *want* to build a stable amplifier. Voila! An oscillator!! Dana K6JQ |
I tried numerous circuits and numerous types (Hartley, Colpitts etc) I
had found but I couldn't get any of them to start up. Oh, that's easy. You're *trying* to build an oscillator; give up on that goal and choose an easier one: try to build an amplifier. I mean, really *want* to build a stable amplifier. Voila! An oscillator!! I once built a power supply that oscillated above 150 MHz. Unfortunately, I could never drop it into the 2-meter band. --Myron. -- Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge PhD EE (retired). "Barbershop" tenor. CDL(PTX). W0PBV. (785) 539-4448 NRA Life Member and Certified Instructor (Home Firearm Safety, Rifle, Pistol) |
I tried numerous circuits and numerous types (Hartley, Colpitts etc) I
had found but I couldn't get any of them to start up. Oh, that's easy. You're *trying* to build an oscillator; give up on that goal and choose an easier one: try to build an amplifier. I mean, really *want* to build a stable amplifier. Voila! An oscillator!! I once built a power supply that oscillated above 150 MHz. Unfortunately, I could never drop it into the 2-meter band. --Myron. -- Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge PhD EE (retired). "Barbershop" tenor. CDL(PTX). W0PBV. (785) 539-4448 NRA Life Member and Certified Instructor (Home Firearm Safety, Rifle, Pistol) |
mcalhoun wrote: I tried numerous circuits and numerous types (Hartley, Colpitts etc) I had found but I couldn't get any of them to start up. Oh, that's easy. You're *trying* to build an oscillator; give up on that goal and choose an easier one: try to build an amplifier. I mean, really *want* to build a stable amplifier. Voila! An oscillator!! I once built a power supply that oscillated above 150 MHz. Unfortunately, I could never drop it into the 2-meter band. Heh. Of course a DC power supply is indistinguishable for a 0Hz oscillator under the best of circumstances, right? But, 150MHz. That's pretty special. What were you using for a pass element(s) ? Dana |
mcalhoun wrote: I tried numerous circuits and numerous types (Hartley, Colpitts etc) I had found but I couldn't get any of them to start up. Oh, that's easy. You're *trying* to build an oscillator; give up on that goal and choose an easier one: try to build an amplifier. I mean, really *want* to build a stable amplifier. Voila! An oscillator!! I once built a power supply that oscillated above 150 MHz. Unfortunately, I could never drop it into the 2-meter band. Heh. Of course a DC power supply is indistinguishable for a 0Hz oscillator under the best of circumstances, right? But, 150MHz. That's pretty special. What were you using for a pass element(s) ? Dana |
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