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On Sat, 10 Apr 2004 08:22:21 GMT, Robert Baer
wrote: Not a varactor (diode), but a switching diode; fast. Snap-off is lotz better. And they are a *LOT* smaller! Thanks, Robert (and all else) I'd prefer a diode solution as there'd be no power supply requirements for each device. The tiny size is an added bonus, of course. But what's the drawback with superfast switching diodes as against active inverters? I'm sure there must be (at least) one... |
A neat and compact way to generate RF harmonics...
On Sat, 10 Apr 2004 08:22:21 GMT, Robert Baer
wrote: Not a varactor (diode), but a switching diode; fast. Snap-off is lotz better. And they are a *LOT* smaller! Thanks, Robert (and all else) I'd prefer a diode solution as there'd be no power supply requirements for each device. The tiny size is an added bonus, of course. But what's the drawback with superfast switching diodes as against active inverters? I'm sure there must be (at least) one... |
I'd prefer a diode solution as there'd be no power supply requirements for each device. The tiny size is an added bonus, of course. But what's the drawback with superfast switching diodes as against active inverters? I'm sure there must be (at least) one... Well for starters, they often, (VERY often) act as parametric devices and oscillate on their own at the frequency of their choosing. W4ZCB |
I'd prefer a diode solution as there'd be no power supply requirements for each device. The tiny size is an added bonus, of course. But what's the drawback with superfast switching diodes as against active inverters? I'm sure there must be (at least) one... Well for starters, they often, (VERY often) act as parametric devices and oscillate on their own at the frequency of their choosing. W4ZCB |
Paul Burridge wrote:
On Sat, 10 Apr 2004 08:22:21 GMT, Robert Baer wrote: Not a varactor (diode), but a switching diode; fast. Snap-off is lotz better. And they are a *LOT* smaller! Thanks, Robert (and all else) I'd prefer a diode solution as there'd be no power supply requirements for each device. The tiny size is an added bonus, of course. But what's the drawback with superfast switching diodes as against active inverters? I'm sure there must be (at least) one... An active inverter is S L O W by comparison; a good, fast diode can have turnoff times in the tens of picoseconds region. |
Paul Burridge wrote:
On Sat, 10 Apr 2004 08:22:21 GMT, Robert Baer wrote: Not a varactor (diode), but a switching diode; fast. Snap-off is lotz better. And they are a *LOT* smaller! Thanks, Robert (and all else) I'd prefer a diode solution as there'd be no power supply requirements for each device. The tiny size is an added bonus, of course. But what's the drawback with superfast switching diodes as against active inverters? I'm sure there must be (at least) one... An active inverter is S L O W by comparison; a good, fast diode can have turnoff times in the tens of picoseconds region. |
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On Sun, 11 Apr 2004 14:14:56 +0200, "Fred Bartoli"
r_AndThisToo wrote: Don't let Paul dream too much about picoseconds. Well, quite. I wouldn't know what to do with all those extra harmonics, anyway. :-) Diodes sound great, but I'm heavily put off by that comment earlier in the thread that they're prone to self oscillation. :-( What's a "parametric device" anyway? In order to achieve results that good, one have to pay very careful attention to "wiring". There's still a lot of room for Paul to improve his PCB design skills ;-) Fair comment. But I *am* working on it! |
On Sun, 11 Apr 2004 14:14:56 +0200, "Fred Bartoli"
r_AndThisToo wrote: Don't let Paul dream too much about picoseconds. Well, quite. I wouldn't know what to do with all those extra harmonics, anyway. :-) Diodes sound great, but I'm heavily put off by that comment earlier in the thread that they're prone to self oscillation. :-( What's a "parametric device" anyway? In order to achieve results that good, one have to pay very careful attention to "wiring". There's still a lot of room for Paul to improve his PCB design skills ;-) Fair comment. But I *am* working on it! |
"Paul Burridge" wrote in message ... On Sun, 11 Apr 2004 14:14:56 +0200, "Fred Bartoli" r_AndThisToo wrote: Don't let Paul dream too much about picoseconds. Well, quite. I wouldn't know what to do with all those extra harmonics, anyway. :-) Diodes sound great, but I'm heavily put off by that comment earlier in the thread that they're prone to self oscillation. :-( What's a "parametric device" anyway? Parametric operation is when you have a parameter such as diode capacitance that varies with voltage. The non-linearity of the parameter makes it act as a multiplier, mixer or an amplifier. Parametric amplifiers (they need to be 'pumped' with an oscilllator) used to be very popular for microwave use. If you have inadvertently make yourself a parametric amplifier with your diode it could oscillate given the right conditions and do all sorts of strange things. In your hands, this is a strong possibility. 8-) Leon |
"Paul Burridge" wrote in message ... On Sun, 11 Apr 2004 14:14:56 +0200, "Fred Bartoli" r_AndThisToo wrote: Don't let Paul dream too much about picoseconds. Well, quite. I wouldn't know what to do with all those extra harmonics, anyway. :-) Diodes sound great, but I'm heavily put off by that comment earlier in the thread that they're prone to self oscillation. :-( What's a "parametric device" anyway? Parametric operation is when you have a parameter such as diode capacitance that varies with voltage. The non-linearity of the parameter makes it act as a multiplier, mixer or an amplifier. Parametric amplifiers (they need to be 'pumped' with an oscilllator) used to be very popular for microwave use. If you have inadvertently make yourself a parametric amplifier with your diode it could oscillate given the right conditions and do all sorts of strange things. In your hands, this is a strong possibility. 8-) Leon |
Parametric operation is when you have a parameter such as diode capacitance that varies with voltage. The non-linearity of the parameter makes it act as a multiplier, mixer or an amplifier. Parametric amplifiers (they need to be 'pumped' with an oscilllator) used to be very popular for microwave use. If you have inadvertently make yourself a parametric amplifier with your diode it could oscillate given the right conditions and do all sorts of strange things. In your hands, this is a strong possibility. 8-) I think you have a point Leon. Paul, use a Schottky diode, (HP 5082-2835 or similar), use ZERO lead lengths. Make your PCBoard for the multiplier double sided, drill a hole the diameter of the diode length, wrap a copper tape ground from top to bottom on one edge of the hole, and drop the diode in the hole and solder both ends. One end to the ground tape, the other to the land to the filter for the harmonic you want. Then, drive with not more than +10 dBm of fundamental and hope a lot. It may STILL oscillate, but you've maximized your chances. When you start getting output from the filter (on the desired frequency which ought to be the only output you can get with the filter in place) you can start matching the input to the diode with "L" networks to maximize the output. Generally, the diode looks like a quite low impedance so the capacitor used, ought to wind up on the side of the inductor AWAY from the diode. You can use an MMIC in the same manner to generate harmonics. Overdrive it and under feed it with DC. More output, more chance of self oscillation if you don't pay attention to detail. A superior (less touchy) method of harmonic generation is just a full wave diode rectifier. Using signal diodes and a center tapped transformer, make a full wave doubler. Ground the DC out with an RF choke and you have 2F the input frequency with good suppression of the fundamental and odd harmonics built in. It's then a lot easier to filter the rest of the undesired out. Do two of those to get 4F out rather than trying to do it all in one stage. LOTS more efficiency. W4ZCB |
Parametric operation is when you have a parameter such as diode capacitance that varies with voltage. The non-linearity of the parameter makes it act as a multiplier, mixer or an amplifier. Parametric amplifiers (they need to be 'pumped' with an oscilllator) used to be very popular for microwave use. If you have inadvertently make yourself a parametric amplifier with your diode it could oscillate given the right conditions and do all sorts of strange things. In your hands, this is a strong possibility. 8-) I think you have a point Leon. Paul, use a Schottky diode, (HP 5082-2835 or similar), use ZERO lead lengths. Make your PCBoard for the multiplier double sided, drill a hole the diameter of the diode length, wrap a copper tape ground from top to bottom on one edge of the hole, and drop the diode in the hole and solder both ends. One end to the ground tape, the other to the land to the filter for the harmonic you want. Then, drive with not more than +10 dBm of fundamental and hope a lot. It may STILL oscillate, but you've maximized your chances. When you start getting output from the filter (on the desired frequency which ought to be the only output you can get with the filter in place) you can start matching the input to the diode with "L" networks to maximize the output. Generally, the diode looks like a quite low impedance so the capacitor used, ought to wind up on the side of the inductor AWAY from the diode. You can use an MMIC in the same manner to generate harmonics. Overdrive it and under feed it with DC. More output, more chance of self oscillation if you don't pay attention to detail. A superior (less touchy) method of harmonic generation is just a full wave diode rectifier. Using signal diodes and a center tapped transformer, make a full wave doubler. Ground the DC out with an RF choke and you have 2F the input frequency with good suppression of the fundamental and odd harmonics built in. It's then a lot easier to filter the rest of the undesired out. Do two of those to get 4F out rather than trying to do it all in one stage. LOTS more efficiency. W4ZCB |
If I understand correctly, you're interested in harmonics up in the
70MHz region. To me it seems silly to use diodes capable of generating a comb of harmonics out to 20GHz for that. An advantage--a big advantage--of the tiny logic is that you get considerable power gain in the stage, and the sot-23 package is likely no larger than the diode you might have used anyway. The edges, as others have pointed out, are PLENTY fast enough for what I believe you want to do. Whether you use diodes or gates, your size problem will be the harmonic-selection filter. As you've learned (and I trust not forgotten already), you need either multiple poles in your filter or a rather high Q. You _could_ get the high Q with crystals, but of course then you're locked down to particular frequencies. For high multiplication factors to low-VHF frequencies, it's probably hard to beat a PLL for (potentially) small size. In offering suggestions, it would also be helpful to us to know your actual needs for signal purity, both close-in (phase noise) and broadband (other harmonics, etc.) 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. Cheers, Tom Paul Burridge wrote in message . .. On Sun, 11 Apr 2004 14:14:56 +0200, "Fred Bartoli" r_AndThisToo wrote: Don't let Paul dream too much about picoseconds. Well, quite. I wouldn't know what to do with all those extra harmonics, anyway. :-) Diodes sound great, but I'm heavily put off by that comment earlier in the thread that they're prone to self oscillation. :-( What's a "parametric device" anyway? In order to achieve results that good, one have to pay very careful attention to "wiring". There's still a lot of room for Paul to improve his PCB design skills ;-) Fair comment. But I *am* working on it! |
If I understand correctly, you're interested in harmonics up in the
70MHz region. To me it seems silly to use diodes capable of generating a comb of harmonics out to 20GHz for that. An advantage--a big advantage--of the tiny logic is that you get considerable power gain in the stage, and the sot-23 package is likely no larger than the diode you might have used anyway. The edges, as others have pointed out, are PLENTY fast enough for what I believe you want to do. Whether you use diodes or gates, your size problem will be the harmonic-selection filter. As you've learned (and I trust not forgotten already), you need either multiple poles in your filter or a rather high Q. You _could_ get the high Q with crystals, but of course then you're locked down to particular frequencies. For high multiplication factors to low-VHF frequencies, it's probably hard to beat a PLL for (potentially) small size. In offering suggestions, it would also be helpful to us to know your actual needs for signal purity, both close-in (phase noise) and broadband (other harmonics, etc.) 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. Cheers, Tom Paul Burridge wrote in message . .. On Sun, 11 Apr 2004 14:14:56 +0200, "Fred Bartoli" r_AndThisToo wrote: Don't let Paul dream too much about picoseconds. Well, quite. I wouldn't know what to do with all those extra harmonics, anyway. :-) Diodes sound great, but I'm heavily put off by that comment earlier in the thread that they're prone to self oscillation. :-( What's a "parametric device" anyway? In order to achieve results that good, one have to pay very careful attention to "wiring". There's still a lot of room for Paul to improve his PCB design skills ;-) Fair comment. But I *am* working on it! |
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 |
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 |
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 |
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 |
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. I'd like to talk you out of a couple, and thanks for the supplier info. Wonder what MaCom's min order is? Anything you need in trade or a few green stamps? W4ZCB Call Book Address. |
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. I'd like to talk you out of a couple, and thanks for the supplier info. Wonder what MaCom's min order is? Anything you need in trade or a few green stamps? W4ZCB Call Book Address. |
On Mon, 12 Apr 2004 22:16:01 GMT, "Harold E. Johnson"
wrote: 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. I'd like to talk you out of a couple, and thanks for the supplier info. Wonder what MaCom's min order is? Anything you need in trade or a few green stamps? W4ZCB Call Book Address. ^^^^^^^^^^^^^^^^^^ don't have one. Email me, with hopefully obvious despam. John |
On Mon, 12 Apr 2004 22:16:01 GMT, "Harold E. Johnson"
wrote: 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. I'd like to talk you out of a couple, and thanks for the supplier info. Wonder what MaCom's min order is? Anything you need in trade or a few green stamps? W4ZCB Call Book Address. ^^^^^^^^^^^^^^^^^^ don't have one. Email me, with hopefully obvious despam. John |
"John Larkin" wrote in message ... W4ZCB Call Book Address. ^^^^^^^^^^^^^^^^^^ don't have one. Email me, with hopefully obvious despam. http://qrz.com/callsign/w4zcb "PM" |
"John Larkin" wrote in message ... W4ZCB Call Book Address. ^^^^^^^^^^^^^^^^^^ don't have one. Email me, with hopefully obvious despam. http://qrz.com/callsign/w4zcb "PM" |
Hi Harold,
Nice of John to make that offer! As for background and theory, I'll make copies of an artcile or two to send you, about the discovery of the effect and the optimization of diode structure to enhance it. I suppose that the effect you're seeing with the Schottkys is almost entirely capacitive stored charge, and that won't "sweep out" of the diode with the sharp step you get with a step-recovery diode. The articles I'll send have info about efficiency, which can be surprisingly high considering the high order of multiplication. Cheers, Tom "Harold E. Johnson" wrote in message news:3QBec.21137$_K3.55643@attbi_s53... If you do use diodes for higher-order harmonic generation, and not just a simple full-wave-rectifier type frequency doubler, I suppose you want something of the nature of a step recovery diode. That implies minority carrier stored charge in the diode, and that would preclude using a Schottky diode (which would work great in the full-wave-rectifier type doubler). If you get into actually wanting to generate harmonic combs out to microwave frequencies, it's probably worthwhile looking for diodes actually characterized for step recovery service. But I really think that's way beyond what you are trying to accomplish right now. My turn to learn something here. Tom, would you elaborate a bit on the above please? I know SRD's are comb generators out to visible light, but they're also 50 percent hard to find and 50 percent magic. I've been using Schottky's for X16 multipliers to 2 GHz, am I doing something wrong? (I keep promising myself that I'm gonna substitute an MMIC for that one day, I DID find the "Filter Gain" in the line length from generator to filter), THAT was both impressive AND helpful. If I go with the MMIC, any preference of Silicon over GaAs? Regards W4ZCB |
Hi Harold,
Nice of John to make that offer! As for background and theory, I'll make copies of an artcile or two to send you, about the discovery of the effect and the optimization of diode structure to enhance it. I suppose that the effect you're seeing with the Schottkys is almost entirely capacitive stored charge, and that won't "sweep out" of the diode with the sharp step you get with a step-recovery diode. The articles I'll send have info about efficiency, which can be surprisingly high considering the high order of multiplication. Cheers, Tom "Harold E. Johnson" wrote in message news:3QBec.21137$_K3.55643@attbi_s53... 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 |
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Nice of John to make that offer! You bet! MaCom is no HP however, and their "data sheets" are awfully skimpy. I can almost put money on losing at least one finding out how sturdy they are. As for background and theory, I'll make copies of an artcile or two to send you, about the discovery of the effect and the optimization of diode structure to enhance it. Will appreciate that as well Tom. I don't have to know the physics to make use of the device, but it's helpful to have that insight when you're trying to optimize the circuitry. W4ZCB |
Nice of John to make that offer! You bet! MaCom is no HP however, and their "data sheets" are awfully skimpy. I can almost put money on losing at least one finding out how sturdy they are. As for background and theory, I'll make copies of an artcile or two to send you, about the discovery of the effect and the optimization of diode structure to enhance it. Will appreciate that as well Tom. I don't have to know the physics to make use of the device, but it's helpful to have that insight when you're trying to optimize the circuitry. W4ZCB |
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What's a sensible target for the multiplication factor using diodes from say a 4Mhz source? I'd be nice to go straight to say 20X on account of the large physical size of the filters at lower HF., not to mention the savings on intermediate stages. An 8 MHz filter doesn't have to be physically large Paul, and efficiency drops pretty fast (Think like a rock) as the multiplication factor goes up. Have you ever actually defined what it is you're trying to do? Some control thing in your 70 MHz band? Or real power for some application? Hard to hit a moving target. Or is that the idea? W4ZCB |
What's a sensible target for the multiplication factor using diodes from say a 4Mhz source? I'd be nice to go straight to say 20X on account of the large physical size of the filters at lower HF., not to mention the savings on intermediate stages. An 8 MHz filter doesn't have to be physically large Paul, and efficiency drops pretty fast (Think like a rock) as the multiplication factor goes up. Have you ever actually defined what it is you're trying to do? Some control thing in your 70 MHz band? Or real power for some application? Hard to hit a moving target. Or is that the idea? W4ZCB |
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Paul Burridge wrote in message . ..
What's a sensible target for the multiplication factor using diodes from say a 4Mhz source? I'd be nice to go straight to say 20X on account of the large physical size of the filters at lower HF., not to mention the savings on intermediate stages. Well, somewhat counter to what Harold wrote, the old HP Journal article I've dredged out to copy says a step recovery diode can do 20X at 30% efficiency. But that's guys who really understood what they were doing! (Just coincidentally, the one table they have is for 20X!) He's right...the filters don't have to be huge. But I'd think of them as large compared with a SOT-23. The tradeoff is that if you do it all in one step, you have to have a filter sharp enough to take the 19x and 21x down to your desired level, whatever that is. But with a 5x and a 4x, you can use a couple filters with wider percentage bandwidths, since for the 5x you'll be using a square-wave input which has practically no 4th and 6th anyway, and the 3rd and 7th are a big percentage removed from the 5th...and the 4x can similarly avoid the 3rd and 5th if you do it right. But again, a PLL can be very small indeed. And I never did see an answer to the question about does it really need to be locked to your low freq, or can it be a separate xtal at 70MHz or whatever? Cheers, Tom |
Paul Burridge wrote in message . ..
What's a sensible target for the multiplication factor using diodes from say a 4Mhz source? I'd be nice to go straight to say 20X on account of the large physical size of the filters at lower HF., not to mention the savings on intermediate stages. Well, somewhat counter to what Harold wrote, the old HP Journal article I've dredged out to copy says a step recovery diode can do 20X at 30% efficiency. But that's guys who really understood what they were doing! (Just coincidentally, the one table they have is for 20X!) He's right...the filters don't have to be huge. But I'd think of them as large compared with a SOT-23. The tradeoff is that if you do it all in one step, you have to have a filter sharp enough to take the 19x and 21x down to your desired level, whatever that is. But with a 5x and a 4x, you can use a couple filters with wider percentage bandwidths, since for the 5x you'll be using a square-wave input which has practically no 4th and 6th anyway, and the 3rd and 7th are a big percentage removed from the 5th...and the 4x can similarly avoid the 3rd and 5th if you do it right. But again, a PLL can be very small indeed. And I never did see an answer to the question about does it really need to be locked to your low freq, or can it be a separate xtal at 70MHz or whatever? Cheers, Tom |
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