Forums

ADC limitations for bandpass/IF sampling

Started by clam December 13, 2005
Hello Jerry,
> > Back in 1962 interviewed for a position at RCA Labs. One question was > about making 10 watts of square wave at 100 MHz. All I could do was tick > off all the tube types that couldn't do it and profess ignorance of any > semiconductors that might. The interviewer agreed that those avenues > were closed, but added, "I need it, so what should I do?" A said that > the only way I could think of was to synthesize is by generating the > components separately. I said it would be a dog to tweak the phases, but > that it could be made stable enough in the lab. He told me "That's what > we did" and I got the job. Sometimes the hard way is the only way. >
Synthesizing is a cool method. It's interesting to think about problems while having to limit the parts to what was around in the early 60's. Depending on what transition time was needed maybe it could have been done with tubes. A couple of 2C39 come to mind which were pretty cheap, at least as mil surplus. The output transformer would be quite challenging and in those days you could not get that designed with CAD like today. The noise from the air cooling might also have been considered a nuisance by the interviewer. Regards, Joerg http://www.analogconsultants.com
Joerg wrote:
> Hello Jerry, > >> >> Back in 1962 interviewed for a position at RCA Labs. One question was >> about making 10 watts of square wave at 100 MHz. All I could do was >> tick off all the tube types that couldn't do it and profess ignorance >> of any semiconductors that might. The interviewer agreed that those >> avenues were closed, but added, "I need it, so what should I do?" A >> said that the only way I could think of was to synthesize is by >> generating the components separately. I said it would be a dog to >> tweak the phases, but that it could be made stable enough in the lab. >> He told me "That's what we did" and I got the job. Sometimes the hard >> way is the only way. >> > > Synthesizing is a cool method. It's interesting to think about problems > while having to limit the parts to what was around in the early 60's. > > Depending on what transition time was needed maybe it could have been > done with tubes. A couple of 2C39 come to mind which were pretty cheap, > at least as mil surplus. The output transformer would be quite > challenging and in those days you could not get that designed with CAD > like today. The noise from the air cooling might also have been > considered a nuisance by the interviewer.
It was a power supply for a then classified computer using tunnel diodes. Since square-wave current into a low impedance was needed, they used a capacitative ballast impedance. The resulting differentiation reduced the necessary amplitude the higher harmonics from 1/n to 1/n^2. The 7th harmonic was overkill. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Hello Jerry,
> > It was a power supply for a then classified computer using tunnel > diodes. Since square-wave current into a low impedance was needed, they > used a capacitative ballast impedance. The resulting differentiation > reduced the necessary amplitude the higher harmonics from 1/n to 1/n^2. > The 7th harmonic was overkill. >
That would have been tough with a tube. Did they ever de-classify it and put some info on the web? > Engineering is the art of making what you want from things you can get. < That's why engineering was more fun in the old days. It was tougher. There was no Digikey and you had to make do with whatever the radio or TV industry used. I remember concocting state registers and ring counters with Ge transistor because they wanted over $5 for one RTL chip which exceeded my allowance. And even at that price they probably were from a 're-labeler'. Bulk waste days were field days because one could harvest tons of tubes for free and create cool stuff with them. Regards, Joerg http://www.analogconsultants.com
Joerg wrote:
> Hello Jerry,
...
> That would have been tough with a tube. Did they ever de-classify it and > put some info on the web?
Not that I know. I don't think I'm talking out of turn by giving the name: Project Lightning. ... Jerry -- Engineering is the art of making what you want from things you can get. &#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;
Joerg <notthisjoergsch@removethispacbell.net> wrote in
news:vkoof.41470$D13.20408@newssvr11.news.prodigy.com: 

> Hello Jerry, >> >> It was a power supply for a then classified computer using tunnel >> diodes. Since square-wave current into a low impedance was needed, >> they used a capacitative ballast impedance. The resulting >> differentiation reduced the necessary amplitude the higher harmonics >> from 1/n to 1/n^2. The 7th harmonic was overkill. >> > > That would have been tough with a tube. Did they ever de-classify it > and put some info on the web? > > > > Engineering is the art of making what you want from things you can > > get. < > > That's why engineering was more fun in the old days. It was tougher.
Its wasn't tougher, just different. One of the changes that I think will affect our profession is that it is very difficult for a kid to get started if he wants to build hardware. You probably need several thousand dollars of used equipment to start (microscope, good soldering iron, etc.) This is a lot of money for a 16 year old kid. Of course, we didn't have personal computers.....
> There was no Digikey and you had to make do with whatever the radio or > TV industry used.
I used to go to the local shop for parts, then Radio Shack.... I remember concocting state registers and ring
> counters with Ge transistor because they wanted over $5 for one RTL > chip which exceeded my allowance. And even at that price they probably > were from a 're-labeler'. Bulk waste days were field days because one > could harvest tons of tubes for free and create cool stuff with them. > > Regards, Joerg > > http://www.analogconsultants.com
-- Al Clark Danville Signal Processing, Inc. -------------------------------------------------------------------- Purveyors of Fine DSP Hardware and other Cool Stuff Available at http://www.danvillesignal.com
Al Clark wrote:
> Joerg <notthisjoergsch@removethispacbell.net> wrote in > news:vkoof.41470$D13.20408@newssvr11.news.prodigy.com: > > >>Hello Jerry, >> >>>It was a power supply for a then classified computer using tunnel >>>diodes. Since square-wave current into a low impedance was needed, >>>they used a capacitative ballast impedance. The resulting >>>differentiation reduced the necessary amplitude the higher harmonics >>>from 1/n to 1/n^2. The 7th harmonic was overkill. >>> >> >>That would have been tough with a tube. Did they ever de-classify it >>and put some info on the web? >> >> >> >>>Engineering is the art of making what you want from things you can >>>get. < >> >>That's why engineering was more fun in the old days. It was tougher. > > > Its wasn't tougher, just different. > > One of the changes that I think will affect our profession is that it is > very difficult for a kid to get started if he wants to build hardware. > > You probably need several thousand dollars of used equipment to start > (microscope, good soldering iron, etc.) This is a lot of money for a 16 > year old kid. > > Of course, we didn't have personal computers.....
Its very hard for any of us to prototype now. BGA, QFN, everything else new seems like a "get your hands off" kinda device. Professionally this forces us to use simulations of one sort or another to a high degree. Any school kid can do the same on their PC. There are a number of free tools (e.g. Octave) to keep the cost really low. They all have PCs, so that's a non-issue. So..... at a hands on level what you say is kind of true. However, the wealth of things they can do with a PC these days I think allows them to go much farther in interesting engineering than I could when I was young. One practical consideration: When I was 12, my father let me build valve/tube equipment running on 400V to 500V. He was an electro-mechanical engineer, so he fully understood what he was letting me do. There is *absolutely* *no* *way* my two kids are going to do that when they are 12 :-) [...] Steve
Steve Underwood wrote:

   ...

> Its very hard for any of us to prototype now. BGA, QFN, everything else > new seems like a "get your hands off" kinda device. Professionally this > forces us to use simulations of one sort or another to a high degree. > Any school kid can do the same on their PC. There are a number of free > tools (e.g. Octave) to keep the cost really low. They all have PCs, so > that's a non-issue. > > So..... at a hands on level what you say is kind of true. However, the > wealth of things they can do with a PC these days I think allows them to > go much farther in interesting engineering than I could when I was young.
Hands-on matters. Today we have college students and beyond who glibly compute complex baseband signals on a single twisted pair, and wonder how to proceed with their simulations. It's east to forget that no matter how small things become, they're still made up of parts that interact.
> One practical consideration: > > When I was 12, my father let me build valve/tube equipment running on > 400V to 500V. He was an electro-mechanical engineer, so he fully > understood what he was letting me do. There is *absolutely* *no* *way* > my two kids are going to do that when they are 12 :-)
Acquaintances and neighbors were aghast that I let my kids use tools like saws and chisels before first grade. I explained that I was careful to teach them how to use such tools -- in general and specifically -- without hurting themselves. I too drew a line. I allowed them to use tools that could cut a finger, but not one that could cut a finger off. Jerry -- Engineering is the art of making what you want from things you can get. &#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;
Steve Underwood wrote:
> When I was 12, my father let me build valve/tube equipment running on > 400V to 500V. He was an electro-mechanical engineer, so he fully > understood what he was letting me do. There is *absolutely* *no* *way* > my two kids are going to do that when they are 12 :-)
I think it can be one of the best ways to really learn. It's hard to get a heart-stopping shock in the base of a biscuit tin. Maybe a few white spots on the fingers from touching the HT line. Kids will experiment and do far more life threatening things that that. My biggest scare building a 4 tube radio was when a second-hand HT smoothing cap exploded, covering the ceiling with black spots and other goo while we were fault finding. Regards Rocky
"Rocky" <robert@suesound.co.za> wrote in news:1134751225.596897.33290
@g47g2000cwa.googlegroups.com:

> Steve Underwood wrote: >> When I was 12, my father let me build valve/tube equipment running on >> 400V to 500V. He was an electro-mechanical engineer, so he fully >> understood what he was letting me do. There is *absolutely* *no* *way* >> my two kids are going to do that when they are 12 :-) > > I think it can be one of the best ways to really learn. It's hard to > get a heart-stopping shock in the base of a biscuit tin. Maybe a few > white spots on the fingers from touching the HT line. > > Kids will experiment and do far more life threatening things that that. > > My biggest scare building a 4 tube radio was when a second-hand HT > smoothing cap exploded, covering the ceiling with black spots and other > goo while we were fault finding. > > Regards > Rocky > >
I still call powering up a circuit the first time, the smoke test. Its been a long time since one actually smoked (they don't always work, but they tend to be a lot more benign). When I was a kid, they usually smoked. I think that about half the kids in my EE class were reasonably competent technicians. This is rarely the case today. OTOH, most of the students are C programmers. I'm not criticizing, young techies. I think they are not very different than us grey beards (or female equivalents) when we were their age. They just have different resources and opportunities. I do think that most of them lack good hardware skills, which is unfortunate. Sometimes the best software is code and sometimes its solder. -- Al Clark Danville Signal Processing, Inc. -------------------------------------------------------------------- Purveyors of Fine DSP Hardware and other Cool Stuff Available at http://www.danvillesignal.com
Al Clark wrote:
[*SNIP*]
>>>Engineering is the art of making what you want from things you can >>>get. < >> >>That's why engineering was more fun in the old days. It was tougher. > > > Its wasn't tougher, just different. > > One of the changes that I think will affect our profession is that it is > very difficult for a kid to get started if he wants to build hardware. > > You probably need several thousand dollars of used equipment to start > (microscope, good soldering iron, etc.) This is a lot of money for a 16 > year old kid. > > Of course, we didn't have personal computers..... >
*WHAT* ? just how do you justify that monetary outlay? I'll use myself as an example ;} I am routinely giving grief to regulars on comp.dsp comp.speech.research comp.speech.users comp.lang.forth sci.geo.satellite-nav alt.satellite.gps comp.arch.embedded I have not expended dollars, but I've made some *THINK* ;)
> > >>There was no Digikey and you had to make do with whatever the radio or >>TV industry used. > > > I used to go to the local shop for parts, then Radio Shack.... > > > I remember concocting state registers and ring > >>counters with Ge transistor because they wanted over $5 for one RTL >>chip which exceeded my allowance. And even at that price they probably >>were from a 're-labeler'. Bulk waste days were field days because one >>could harvest tons of tubes for free and create cool stuff with them. >> >>Regards, Joerg >> >>http://www.analogconsultants.com > > > > > > > > >