|
|
On Wed, 18 Feb 2004 10:05:58 GMT, Active8
,invalid wrote: Gee. I could have sworn Jim was hinting at the math approach. Wouldn'tcha just love to predict that roll-off on paper and *then* see it in real life? Starts with an "F", looks like a number, sounds like a frog. Fourier? I wouldn't trust it. Sounds French. :- -- The BBC: Licensed at public expense to spread lies. |
On Wed, 18 Feb 2004 10:05:58 GMT, Active8
,invalid wrote: Gee. I could have sworn Jim was hinting at the math approach. Wouldn'tcha just love to predict that roll-off on paper and *then* see it in real life? Starts with an "F", looks like a number, sounds like a frog. Fourier? I wouldn't trust it. Sounds French. :- -- The BBC: Licensed at public expense to spread lies. |
|
|
In article ,
Paul Burridge wrote: What's the maximum multiplication factor it's practical and sensible to attempt to achieve in one single stage of multiplication? (Say from a 7Mhz square wave source with 5nS rise/fall times.) Depends on what you call "practical". I know that one type of atomic clock uses a one stage frequency multiplier to go from about 10MHz to about 9.1GHz. A slow edged square wave follows the 1/N rule to about the point where the rise or fall time is equal to half a cycle of the harmonic frequency. From that point up, the spectrum falls off at a rate of at least 1/n^2. Usually it is faster than that. If we assume that the 5nS rise time is the input to a stage, we can use a fast transistor to effectively speed the edge up. -- -- forging knowledge |
In article ,
Paul Burridge wrote: What's the maximum multiplication factor it's practical and sensible to attempt to achieve in one single stage of multiplication? (Say from a 7Mhz square wave source with 5nS rise/fall times.) Depends on what you call "practical". I know that one type of atomic clock uses a one stage frequency multiplier to go from about 10MHz to about 9.1GHz. A slow edged square wave follows the 1/N rule to about the point where the rise or fall time is equal to half a cycle of the harmonic frequency. From that point up, the spectrum falls off at a rate of at least 1/n^2. Usually it is faster than that. If we assume that the 5nS rise time is the input to a stage, we can use a fast transistor to effectively speed the edge up. -- -- forging knowledge |
Avery Fineman wrote:
. . . Making practical, reproducible active multipliers in the home shop is, practically, a trial-and-error process involving playing with cut- off bias of the active device input, energy and harmonic content of the source, and Q of the multiplier's output stage. In the past I've made tripling-in-the-plate pentode crystal oscillators using fundamental frequency quartz but those were highly dependent on getting the highest impedance tuned plate circuit and needed scope viewing to check output waveforms. Not very reproducible. There's no "easy" way to do it that will "work every time" despite the claims of many. :-) . . . While that's certainly true of multipliers in general, I've certainly found it very easy to make repeatable doublers with a two transistor push-push stage. Driving it with about zero bias and a large enough signal to get it to conduct on at least a good fraction of each cycle gives plenty of harmonic energy. A collector circuit with decent Q will take care of most higher harmonics, although a simple filter following the stage is usually adequate for more demanding applications. The fundamental can be nulled out reasonably well with a pot between emitters with a grounded center tap. I'd think a push-pull tripler would be nearly as easy, but I haven't had occasion to make one. Several simple diode and transistor multipliers are described in Chapter 5 of _Experimental Methods in RF Design_, which I heartily recommend for the homebrewer and experimenter. Roy Lewallen, W7EL |
Avery Fineman wrote:
. . . Making practical, reproducible active multipliers in the home shop is, practically, a trial-and-error process involving playing with cut- off bias of the active device input, energy and harmonic content of the source, and Q of the multiplier's output stage. In the past I've made tripling-in-the-plate pentode crystal oscillators using fundamental frequency quartz but those were highly dependent on getting the highest impedance tuned plate circuit and needed scope viewing to check output waveforms. Not very reproducible. There's no "easy" way to do it that will "work every time" despite the claims of many. :-) . . . While that's certainly true of multipliers in general, I've certainly found it very easy to make repeatable doublers with a two transistor push-push stage. Driving it with about zero bias and a large enough signal to get it to conduct on at least a good fraction of each cycle gives plenty of harmonic energy. A collector circuit with decent Q will take care of most higher harmonics, although a simple filter following the stage is usually adequate for more demanding applications. The fundamental can be nulled out reasonably well with a pot between emitters with a grounded center tap. I'd think a push-pull tripler would be nearly as easy, but I haven't had occasion to make one. Several simple diode and transistor multipliers are described in Chapter 5 of _Experimental Methods in RF Design_, which I heartily recommend for the homebrewer and experimenter. Roy Lewallen, W7EL |
In article , Roy Lewallen
writes: Avery Fineman wrote: . . . Making practical, reproducible active multipliers in the home shop is, practically, a trial-and-error process involving playing with cut- off bias of the active device input, energy and harmonic content of the source, and Q of the multiplier's output stage. In the past I've made tripling-in-the-plate pentode crystal oscillators using fundamental frequency quartz but those were highly dependent on getting the highest impedance tuned plate circuit and needed scope viewing to check output waveforms. Not very reproducible. There's no "easy" way to do it that will "work every time" despite the claims of many. :-) . . . While that's certainly true of multipliers in general, I've certainly found it very easy to make repeatable doublers with a two transistor push-push stage. Driving it with about zero bias and a large enough signal to get it to conduct on at least a good fraction of each cycle gives plenty of harmonic energy. A collector circuit with decent Q will take care of most higher harmonics, although a simple filter following the stage is usually adequate for more demanding applications. The fundamental can be nulled out reasonably well with a pot between emitters with a grounded center tap. I'd think a push-pull tripler would be nearly as easy, but I haven't had occasion to make one. Okay. I can't agree that they are "easy" after having enough occasions to make several. :-) Your mileage, of course, varies. Several simple diode and transistor multipliers are described in Chapter 5 of _Experimental Methods in RF Design_, which I heartily recommend for the homebrewer and experimenter. A diode doubler using a toroid transformer, pair of diodes and a tuned circuit in the output works fine right off the paper pad and slide-rule (or calculator) numbers. Typically the source is a distorted sinewave from either another multiplier or an oscillator. Rocket science it ain't. BREADBOARD. A most handy part of the bench tools. Recommended first. Especially for those purist hobbyists who think that digital circuits aren't "real radio." :-) Playing with bias on a transistor multiplier stage is fine for optimizing a multiplication but all it is is play when there's nothing to compare one bias setting with another as to power output at the desired multiple. A spectrum analyzer isn't an absolute need, by the way, there's other ways to measure the harmonic content. Is that in "Experimental Methods..." published by the ARRL? [I'm pushing work-on-the-bench, not books, pardon my attitude that has resulted from years of having to produce hardware results, not paper reports] Len Anderson retired (from regular hours) electronic engineering person |
| All times are GMT +1. The time now is 07:33 PM. |
Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
RadioBanter.com