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Book recommendation please
On Mon, 28 Aug 2006 23:38:38 GMT, David
wrote: From what I understand so far the bias should should not necessarily be the same and the capacitors will not scale as suggested. The ESR of the crystal would be different for different overtone crystals so therefore the bias should change to provide correct drive and C to ground on the C-Tap would also need to change. According to Matthy the Cap to ground should be 0.5 to 1 x ESR and emitter drive impedance less than ESR. Or have I misinterpreted something here ? The DC bias would be unchanged. The feedback required may need to be altered but thats a product of frequency and transistor(or fet) gain at the target frequency and any change in overtone used. In short if the circuit shown uses a 100mhz crystal in a 7th overtone mode it will scale if a 89mhz 7th overtone crystal is used. Usually for a narrow range of frequencies like that the ERS varies but not greatly. This does not cover the difference between good quality crystal and poor quality crystals, If you going to use poor quality crystals there may be other issues to investigate as well. I am also unsure of whether the tank should be tuned above or below resonance. Rhea's book suggests the tank should be capacitive at Fo indicating the tank itself would be tuned above the operating frequency. Believe it or not, doesn't matter. You'll build it and then have to tune it for proper oscillation. At around 100mhz the circuit parasitics such as coil construction, PC board trace capacitance and inductance, transistor characteristics, transistor, coil and capactior lead length are all in the mix. I would like to learn more about the Butler emitter follower crystal oscillator. If I ask the specific questions about this typology and someone gives me an answer, where did they obtain this information. Have they learned by just playing with the circuit in a hit and miss fashion or have they first obtained fundamental information from some text and using what they have learnt then played with the circuit. If so, what would this text be ? Generally I try to avoid high order oscilators(overtone) as stability and the need for being tuned doesn't suit my needs. I've never seen a in depth analysis in any one book. I apply my EE training plus 30+ years of theory vs what really happens and go from there. Sometimes being an engineer is really more like science where you observe and build or search out theory to explain the observed behavour, or you break out the diddle stick and adjust it and move on to bigger problems. If Ro = Rsource/(beta+1), is Rsource in the oscillator case of the emitter follower Rp of the coil in parallel with the bias resistance or does it also include (Rphi+RE) x Beta. Is Beta used here an approximation calculate by Ft/F ? Thats all first order rule of thumb. However, are you trying to build one working oscillator or flog it to death? I say that as I've found it to be both less than an exact science and that accurate to more than 3 decimal places is excess for operation. For one oscillator it is both easy and practical to dead bug it and see if it meets your needs. If you going to build in quantity something using it that is a whole different set of issues. Allison wrote: On Mon, 28 Aug 2006 13:25:40 GMT, David wrote: Thanks for the feedback. I do not have a ready supply of ferrite cores and do not really want to wind coils. I have surface mountable air fixed coils that provide Q 100 that I expect should be suitable for most applications and use of trimmer capacitors. The only high frequency crystal oscillator I could find in the EMRFD (100MHz) is page 4.15 which is a common base butler. I understand these suffer parasitic effects, the tank is only effective for a limited range of inductance. The butler emitter follower is offered as a more superior typology but this circuit is not found in this book. The circuit values in his example are incorrect as the 25nH inductor in the tank requires over 100pF to resonate at 100MHz. The circuit shown has a net capacitance of around 40pF ? Built as described, it works. However the 25nH is an approximation as distributed C and also lead lengths add significantly. Mine tuned with 33ohms substituted for the crystal from 93 to 122mhz. There is very little design information given with respect to ratio of the C-Tap or emitter bias. Read the test as the concepts are outlined rather than how to design xyz circuit in cookbook fashon. If you need help, the easy way is to calculate the reactances at the shown frequency and then using those numbers scale for the desired frequency. The bias point would be the same at any frequency for a given transistor and power. I also have his book "Introduction to Radio Frequency design". This does go into more depth but is centred mainly around colpitts oscillators (not good for harmonic crystal oscillators). In general oscillators in the 20mhz range are harmonic or overtone designs and more subject to parasitic effects. I've bult the 100mhz design and it worked fine for me within the limits of the crystal used though after a x4 multiplication the thermal drift was unacceptable and the crystal was the first order contributor. The oscillator otherwise behaved well. My solution for the whole mess was a lower frequency osc and using low order harmonics. The lower frequency crystale proved both less fussy to oscilate and more stable in fundemental mode. Note: I was interested in sufficient stability to copy SSB at ~1296mhz so even a few dozen Hz drift is noticeable.. Allison wrote: On Mon, 28 Aug 2006 05:59:39 GMT, David wrote: Dave, I do have EMIRFD but find almost all the circuits are based around rf transformers for matching and most of them are low frequency (3MHz etc). Up to around 200mhz thats not a big issue if properly scaled and the right ferrite used. I've used a lot of ideas from that book at 6 and 2m. The book list presented is one I'd have suggested and added the venerable handbook both current and a few older copies. Allison Regards David Dave Platt wrote: Anyone recommend a "decent" book that would cover oscillators, small signal RF amps and matching techniques sufficiently to enable a novice to start experimenting with circuits and have enough detail in the text to tweak the circuits to get them running properly ? "Experimental Methods in RF Design" by Hayward, Campbell, and Larkin, available from the ARRL, would be a good place to start. It's the successor to the classic "Solid-State Design for the Radio Amateur" from back in 1977. If you can find copies of Doug Demaw's "Design notebook" and "QRP notebook", there's some good reading there as well. Not as advanced as "Experimental Methods" but perhaps a bit more accessible. Buying a bunch of back issues of QRPp might also be helpful. In a lot of the articles which discuss QRP receiver and transmitters, the authors go into detail about their own particular circuit preferences, tweaks, construction and debugging techniques, etc. For a slightly deeper background, I'd recommend "Troubleshooting Analog Circuits" by Robert Pease. It's not specific to RF but is full of useful tricks and ideas. |
#13
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Book recommendation please
Thanks for the information.
The book example uses a 5th OT 100MHz crystal. My application uses a 7th OT 151 MHz crystal. I suspect the ESR jumps from around 60-70 in the 5th OT to a max. of 120R for the 7th OT. Something I find a little confusing though in in Matthys book at the beginning he explains that in series mode, the lower the impedances driving and loading the crystal - the better as this ensures the crystal has maximum control of the feedback path. But during his explanation of the butler emitter follower, he mentions the load cannot be "too" small and suggests optimal load of 1/2 to 1 x ESR. Can you shed some light on this for me please. I realise another option is to build a 3rd OT oscillator followed by a tripler and filtering but I find when I do this that I have trouble getting rid of harmonics. Also each tank circuit ends up adding lots of cost to the circuit as I usually use a fixed air-wound SMD format coil and SMD trimmer cap and these are expensive. Another option was I could use a PLL as I have a heap of the LMX1602. Then the trouble is that the microcontroller overhead goes.(Having to set frequency each time the system boots). I also looked at other PLL ICs like the motorola devices that can be pre-programmed with pin settings but these seem to be hard to obtain now. Thanks again. I appreciate the time people have taken to consider my questions and provide me with some valuable insight that I have not yet gained from experience. (I suppose that is the power of such a forum as this anyway). regards David wrote: On Mon, 28 Aug 2006 23:38:38 GMT, David wrote: From what I understand so far the bias should should not necessarily be the same and the capacitors will not scale as suggested. The ESR of the crystal would be different for different overtone crystals so therefore the bias should change to provide correct drive and C to ground on the C-Tap would also need to change. According to Matthy the Cap to ground should be 0.5 to 1 x ESR and emitter drive impedance less than ESR. Or have I misinterpreted something here ? The DC bias would be unchanged. The feedback required may need to be altered but thats a product of frequency and transistor(or fet) gain at the target frequency and any change in overtone used. In short if the circuit shown uses a 100mhz crystal in a 7th overtone mode it will scale if a 89mhz 7th overtone crystal is used. Usually for a narrow range of frequencies like that the ERS varies but not greatly. This does not cover the difference between good quality crystal and poor quality crystals, If you going to use poor quality crystals there may be other issues to investigate as well. I am also unsure of whether the tank should be tuned above or below resonance. Rhea's book suggests the tank should be capacitive at Fo indicating the tank itself would be tuned above the operating frequency. Believe it or not, doesn't matter. You'll build it and then have to tune it for proper oscillation. At around 100mhz the circuit parasitics such as coil construction, PC board trace capacitance and inductance, transistor characteristics, transistor, coil and capactior lead length are all in the mix. I would like to learn more about the Butler emitter follower crystal oscillator. If I ask the specific questions about this typology and someone gives me an answer, where did they obtain this information. Have they learned by just playing with the circuit in a hit and miss fashion or have they first obtained fundamental information from some text and using what they have learnt then played with the circuit. If so, what would this text be ? Generally I try to avoid high order oscilators(overtone) as stability and the need for being tuned doesn't suit my needs. I've never seen a in depth analysis in any one book. I apply my EE training plus 30+ years of theory vs what really happens and go from there. Sometimes being an engineer is really more like science where you observe and build or search out theory to explain the observed behavour, or you break out the diddle stick and adjust it and move on to bigger problems. If Ro = Rsource/(beta+1), is Rsource in the oscillator case of the emitter follower Rp of the coil in parallel with the bias resistance or does it also include (Rphi+RE) x Beta. Is Beta used here an approximation calculate by Ft/F ? Thats all first order rule of thumb. However, are you trying to build one working oscillator or flog it to death? I say that as I've found it to be both less than an exact science and that accurate to more than 3 decimal places is excess for operation. For one oscillator it is both easy and practical to dead bug it and see if it meets your needs. If you going to build in quantity something using it that is a whole different set of issues. Allison wrote: On Mon, 28 Aug 2006 13:25:40 GMT, David wrote: Thanks for the feedback. I do not have a ready supply of ferrite cores and do not really want to wind coils. I have surface mountable air fixed coils that provide Q 100 that I expect should be suitable for most applications and use of trimmer capacitors. The only high frequency crystal oscillator I could find in the EMRFD (100MHz) is page 4.15 which is a common base butler. I understand these suffer parasitic effects, the tank is only effective for a limited range of inductance. The butler emitter follower is offered as a more superior typology but this circuit is not found in this book. The circuit values in his example are incorrect as the 25nH inductor in the tank requires over 100pF to resonate at 100MHz. The circuit shown has a net capacitance of around 40pF ? Built as described, it works. However the 25nH is an approximation as distributed C and also lead lengths add significantly. Mine tuned with 33ohms substituted for the crystal from 93 to 122mhz. There is very little design information given with respect to ratio of the C-Tap or emitter bias. Read the test as the concepts are outlined rather than how to design xyz circuit in cookbook fashon. If you need help, the easy way is to calculate the reactances at the shown frequency and then using those numbers scale for the desired frequency. The bias point would be the same at any frequency for a given transistor and power. I also have his book "Introduction to Radio Frequency design". This does go into more depth but is centred mainly around colpitts oscillators (not good for harmonic crystal oscillators). In general oscillators in the 20mhz range are harmonic or overtone designs and more subject to parasitic effects. I've bult the 100mhz design and it worked fine for me within the limits of the crystal used though after a x4 multiplication the thermal drift was unacceptable and the crystal was the first order contributor. The oscillator otherwise behaved well. My solution for the whole mess was a lower frequency osc and using low order harmonics. The lower frequency crystale proved both less fussy to oscilate and more stable in fundemental mode. Note: I was interested in sufficient stability to copy SSB at ~1296mhz so even a few dozen Hz drift is noticeable.. Allison wrote: On Mon, 28 Aug 2006 05:59:39 GMT, David wrote: Dave, I do have EMIRFD but find almost all the circuits are based around rf transformers for matching and most of them are low frequency (3MHz etc). Up to around 200mhz thats not a big issue if properly scaled and the right ferrite used. I've used a lot of ideas from that book at 6 and 2m. The book list presented is one I'd have suggested and added the venerable handbook both current and a few older copies. Allison Regards David Dave Platt wrote: Anyone recommend a "decent" book that would cover oscillators, small signal RF amps and matching techniques sufficiently to enable a novice to start experimenting with circuits and have enough detail in the text to tweak the circuits to get them running properly ? "Experimental Methods in RF Design" by Hayward, Campbell, and Larkin, available from the ARRL, would be a good place to start. It's the successor to the classic "Solid-State Design for the Radio Amateur" from back in 1977. If you can find copies of Doug Demaw's "Design notebook" and "QRP notebook", there's some good reading there as well. Not as advanced as "Experimental Methods" but perhaps a bit more accessible. Buying a bunch of back issues of QRPp might also be helpful. In a lot of the articles which discuss QRP receiver and transmitters, the authors go into detail about their own particular circuit preferences, tweaks, construction and debugging techniques, etc. For a slightly deeper background, I'd recommend "Troubleshooting Analog Circuits" by Robert Pease. It's not specific to RF but is full of useful tricks and ideas. |
#14
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Book recommendation please
On Tue, 29 Aug 2006 20:41:09 GMT, David
wrote: Thanks for the information. The book example uses a 5th OT 100MHz crystal. My application uses a 7th OT 151 MHz crystal. I suspect the ESR jumps from around 60-70 in the 5th OT to a max. of 120R for the 7th OT. I dont consider that a huge jump, considering the amount of tolereance there is in that kind of thing. Something I find a little confusing though in in Matthys book at the beginning he explains that in series mode, the lower the impedances driving and loading the crystal - the better as this ensures the crystal has maximum control of the feedback path. if the crystal feedbak path loads the crystal too greatly the problems of mode jumping and poor starting are present. But during his explanation of the butler emitter follower, he mentions the load cannot be "too" small and suggests optimal load of 1/2 to 1 x ESR. Can you shed some light on this for me please. too low the osc will not start (low effective gain) and too high allows for possible mode shifts. I realise another option is to build a 3rd OT oscillator followed by a tripler and filtering but I find when I do this that I have trouble getting rid of harmonics. Also each tank circuit ends up adding lots of cost to the circuit as I usually use a fixed air-wound SMD format coil and SMD trimmer cap and these are expensive. I would think using double tuned and properly coupled the undesired harmonics should easily be more than 70db down. Requires some care in layout and grounding. Another option was I could use a PLL as I have a heap of the LMX1602. Then the trouble is that the microcontroller overhead goes.(Having to set frequency each time the system boots). I also looked at other PLL ICs like the motorola devices that can be pre-programmed with pin settings but these seem to be hard to obtain now. Those headaches and also sidebands that are not well surpressed if care is not taken make it potentially worse than 3rd OT and tripler. build and test is my suggestion. Allison wrote: On Mon, 28 Aug 2006 23:38:38 GMT, David wrote: From what I understand so far the bias should should not necessarily be the same and the capacitors will not scale as suggested. The ESR of the crystal would be different for different overtone crystals so therefore the bias should change to provide correct drive and C to ground on the C-Tap would also need to change. According to Matthy the Cap to ground should be 0.5 to 1 x ESR and emitter drive impedance less than ESR. Or have I misinterpreted something here ? The DC bias would be unchanged. The feedback required may need to be altered but thats a product of frequency and transistor(or fet) gain at the target frequency and any change in overtone used. In short if the circuit shown uses a 100mhz crystal in a 7th overtone mode it will scale if a 89mhz 7th overtone crystal is used. Usually for a narrow range of frequencies like that the ERS varies but not greatly. This does not cover the difference between good quality crystal and poor quality crystals, If you going to use poor quality crystals there may be other issues to investigate as well. I am also unsure of whether the tank should be tuned above or below resonance. Rhea's book suggests the tank should be capacitive at Fo indicating the tank itself would be tuned above the operating frequency. Believe it or not, doesn't matter. You'll build it and then have to tune it for proper oscillation. At around 100mhz the circuit parasitics such as coil construction, PC board trace capacitance and inductance, transistor characteristics, transistor, coil and capactior lead length are all in the mix. I would like to learn more about the Butler emitter follower crystal oscillator. If I ask the specific questions about this typology and someone gives me an answer, where did they obtain this information. Have they learned by just playing with the circuit in a hit and miss fashion or have they first obtained fundamental information from some text and using what they have learnt then played with the circuit. If so, what would this text be ? Generally I try to avoid high order oscilators(overtone) as stability and the need for being tuned doesn't suit my needs. I've never seen a in depth analysis in any one book. I apply my EE training plus 30+ years of theory vs what really happens and go from there. Sometimes being an engineer is really more like science where you observe and build or search out theory to explain the observed behavour, or you break out the diddle stick and adjust it and move on to bigger problems. If Ro = Rsource/(beta+1), is Rsource in the oscillator case of the emitter follower Rp of the coil in parallel with the bias resistance or does it also include (Rphi+RE) x Beta. Is Beta used here an approximation calculate by Ft/F ? Thats all first order rule of thumb. However, are you trying to build one working oscillator or flog it to death? I say that as I've found it to be both less than an exact science and that accurate to more than 3 decimal places is excess for operation. For one oscillator it is both easy and practical to dead bug it and see if it meets your needs. If you going to build in quantity something using it that is a whole different set of issues. Allison wrote: On Mon, 28 Aug 2006 13:25:40 GMT, David wrote: Thanks for the feedback. I do not have a ready supply of ferrite cores and do not really want to wind coils. I have surface mountable air fixed coils that provide Q 100 that I expect should be suitable for most applications and use of trimmer capacitors. The only high frequency crystal oscillator I could find in the EMRFD (100MHz) is page 4.15 which is a common base butler. I understand these suffer parasitic effects, the tank is only effective for a limited range of inductance. The butler emitter follower is offered as a more superior typology but this circuit is not found in this book. The circuit values in his example are incorrect as the 25nH inductor in the tank requires over 100pF to resonate at 100MHz. The circuit shown has a net capacitance of around 40pF ? Built as described, it works. However the 25nH is an approximation as distributed C and also lead lengths add significantly. Mine tuned with 33ohms substituted for the crystal from 93 to 122mhz. There is very little design information given with respect to ratio of the C-Tap or emitter bias. Read the test as the concepts are outlined rather than how to design xyz circuit in cookbook fashon. If you need help, the easy way is to calculate the reactances at the shown frequency and then using those numbers scale for the desired frequency. The bias point would be the same at any frequency for a given transistor and power. I also have his book "Introduction to Radio Frequency design". This does go into more depth but is centred mainly around colpitts oscillators (not good for harmonic crystal oscillators). In general oscillators in the 20mhz range are harmonic or overtone designs and more subject to parasitic effects. I've bult the 100mhz design and it worked fine for me within the limits of the crystal used though after a x4 multiplication the thermal drift was unacceptable and the crystal was the first order contributor. The oscillator otherwise behaved well. My solution for the whole mess was a lower frequency osc and using low order harmonics. The lower frequency crystale proved both less fussy to oscilate and more stable in fundemental mode. Note: I was interested in sufficient stability to copy SSB at ~1296mhz so even a few dozen Hz drift is noticeable.. Allison wrote: On Mon, 28 Aug 2006 05:59:39 GMT, David wrote: Dave, I do have EMIRFD but find almost all the circuits are based around rf transformers for matching and most of them are low frequency (3MHz etc). Up to around 200mhz thats not a big issue if properly scaled and the right ferrite used. I've used a lot of ideas from that book at 6 and 2m. The book list presented is one I'd have suggested and added the venerable handbook both current and a few older copies. Allison Regards David Dave Platt wrote: Anyone recommend a "decent" book that would cover oscillators, small signal RF amps and matching techniques sufficiently to enable a novice to start experimenting with circuits and have enough detail in the text to tweak the circuits to get them running properly ? "Experimental Methods in RF Design" by Hayward, Campbell, and Larkin, available from the ARRL, would be a good place to start. It's the successor to the classic "Solid-State Design for the Radio Amateur" from back in 1977. If you can find copies of Doug Demaw's "Design notebook" and "QRP notebook", there's some good reading there as well. Not as advanced as "Experimental Methods" but perhaps a bit more accessible. Buying a bunch of back issues of QRPp might also be helpful. In a lot of the articles which discuss QRP receiver and transmitters, the authors go into detail about their own particular circuit preferences, tweaks, construction and debugging techniques, etc. For a slightly deeper background, I'd recommend "Troubleshooting Analog Circuits" by Robert Pease. It's not specific to RF but is full of useful tricks and ideas. |
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