| Author |
Message |
Jerry Avins
Guest
|
 Posted:
Thu Dec 15, 2005 9:09 am Post subject:
Re: I'm confused ;) was[Re: ADC limitations for bandpass/IF |
|
|
Joerg wrote:
| Quote: | Hello Bhaskar,
Neat! I know of a few who've done this although I'm not masochistic
enough
(sounds like you are :-))
I am not a masochist, at least I hope not. We just didn't have any other
choice back then to get to 12 bits. But I have to confess that I really
like those challenges. And when some folks say that it cannot be done
it's even more fun to get it done :-)
Regards, Joerg
http://www.analogconsultants.com
|
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.
Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ |
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Steve Underwood
Guest
|
| Posted:
Thu Dec 15, 2005 9:16 am Post subject:
Re: I'm confused ;) was[Re: ADC limitations for bandpass/IF |
|
|
Jerry Avins wrote:
| Quote: | Joerg wrote:
Hello Bhaskar,
Neat! I know of a few who've done this although I'm not masochistic
enough
(sounds like you are :-))
I am not a masochist, at least I hope not. We just didn't have any
other choice back then to get to 12 bits. But I have to confess that
I really like those challenges. And when some folks say that it
cannot be done it's even more fun to get it done :-)
Regards, Joerg
http://www.analogconsultants.com
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.
Jerry
|
I remember getting to 12 bits at 3M samples/second in the 1970s, using
four 750k sample/second Philbrick ADCs polyphased. In those days using a
processor to manage them wasn't on (though there were dead times in
their operation, every few seconds, where we could have done some kind
of calibration). Being large bricks, with several chips inside, making
them thermally track wasn't easy. Yeah, sometimes the hard way is the
only way. However, it sucks up so much of your time trying to deal with
this stuff, it seriously detracts from doing the interesting stuff with
the digitised data. I've never been big on brute force solutions.
The next system used a form of pipelined ADC, with each chip handling 2
bits of the final result. These were made by Quantel (the TV effects
people). They were dramatically better (though still somewhat
problematic) without really using devices that were inherently faster.
Maybe the smart way was better than the hard way? :-)
Regards,
Steve |
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Joerg
Guest
|
| Posted:
Fri Dec 16, 2005 1:16 am Post subject:
Re: I'm confused ;) was[Re: ADC limitations for bandpass/IF |
|
|
Hello Jerry,
| Quote: |
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?
| Quote: | 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 |
|
| Back to top |
|
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Jerry Avins
Guest
|
| Posted:
Fri Dec 16, 2005 1:16 am Post subject:
Re: I'm confused ;) was[Re: ADC limitations for bandpass/IF |
|
|
Joerg wrote:
| Quote: | 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.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ |
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Joerg
Guest
|
| Posted:
Fri Dec 16, 2005 1:16 am Post subject:
Re: I'm confused ;) was[Re: ADC limitations for bandpass/IF |
|
|
Hello Jerry,
| Quote: |
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 |
|
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|
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Jerry Avins
Guest
|
| Posted:
Fri Dec 16, 2005 1:16 am Post subject:
Re: I'm confused ;) was[Re: ADC limitations for bandpass/IF |
|
|
Richard Owlett wrote:
...
| Quote: | I assume you mean "Sampling Bandpass Signals" in Chapter 2.
I "understood" each of his math steps but I still miss big picture.
Math seems to clash with my concept of physical reality.
[part of reason I never got my EE degree? ;]
|
I'm with you there: math is useful to me for quantifying, but not very
much for conceptualizing. I always have a niggling doubt about my
understanding of things I can explain only with math. I think I
understand sampling subband signals.
Shannon tells you that you need at a bit more than two samples per cycle
to nail down a frequency component, and that the smaller that bit is,
the more samples it takes for it to come clear.* Believe him. (He didn't
need to tell me because I learned how to extract Fourier components by
hand.) The penalty for not sampling fast enough is aliasing.
Aliasing isn't necessarily bad; there are times when it doesn't bother
us at all. Consider a sampler running at 10 KHz. Frequencies in the
sampled signal from 0 to 5 KHz will be sampled just fine. Those from 5
to 10 KHz will alias and end up looking like they ran from 5 to 0 kHz --
an inversion. Frequencies from 10 to 15 KHz will look like (be aliases
of) the frequencies from 0 to 5 KHz. A mess? Only maybe.
Normally, before the signal is sampled. it will be run through a lowpass
filter to cut off everything above, say, 4.5 KHz, and the reconstruction
filter will be similar. Suppose instead that we use bandpass filters
that pass 5.5 to 9.5 KHz. Can you see that the signal /in that band/
will be faithfully reproduced? If "yes", I don't have to write more. If
"no", tell me what eludes you.
...
Jerry
__________________________________________
* We're talking obtainable samples here. I'll give up on you if you
argue from infinite precision just to be ornery.
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ |
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Joerg
Guest
|
| Posted:
Fri Dec 16, 2005 1:16 am Post subject:
Re: I'm confused ;) was[Re: ADC limitations for bandpass/IF |
|
|
Hello Steve,
| Quote: | I remember getting to 12 bits at 3M samples/second in the 1970s, using
four 750k sample/second Philbrick ADCs polyphased. In those days using a
processor to manage them wasn't on (though there were dead times in
their operation, every few seconds, where we could have done some kind
of calibration). Being large bricks, with several chips inside, making
them thermally track wasn't easy. Yeah, sometimes the hard way is the
only way. However, it sucks up so much of your time trying to deal with
this stuff, it seriously detracts from doing the interesting stuff with
the digitised data. I've never been big on brute force solutions.
|
We could have done it without a micro because all it did was regulate
out the deviations while applying a test signal, one function at a time.
So a three bit shift register and some analog "glue" would have worked.
But we used a DSP because they had already parked one on the board, it
was there when I came and they didn't want to take it back out. IIRC it
already had one rather mundane job like a slow RS232 comm. Yawn. It was
like using a Ferrari to go grocery shopping.
Regards, Joerg
http://www.analogconsultants.com |
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Richard Owlett
Guest
|
| Posted:
Fri Dec 16, 2005 1:16 am Post subject:
Re: I'm confused ;) was[Re: ADC limitations for bandpass/IF |
|
|
Jerry Avins wrote:
| Quote: | Richard Owlett wrote:
Bhaskar Thiagarajan wrote:
You need to be sure that the analog bandwidth of the ADC is higher than
1MHz. You should find this as a parameter in the data sheet.
Also, I'm assuming your BW of the RF signal is not much more than about
5kHz.
Cheers
Bhaskar
I assume Bhaskar means at least the sample acquisition time is less
than .5 microsecond [ That's how I would apply Nyquist to the
situation. ]
No. He means that the electronics between the analog input and the
sampler will pass 1 MHz without significant attenuation or phase shift.
(It's also important that the aperture uncertainty be as good as would
be needed to sample at the full (2 MHz) rate.)
Given that assumption and assuming the 20kHz sampling rate is not
locked to the 1 MHz carrier, I can not see what information could be
obtained.
Obviously I'm missing something.
Yes. Read the chapter on sub-band sampling in Rick's book.
|
I assume you mean "Sampling Bandpass Signals" in Chapter 2.
I "understood" each of his math steps but I still miss big picture.
Math seems to clash with my concept of physical reality.
[part of reason I never got my EE degree? ;]
| Quote: | (You located it on the shelf behind you.)
|
It moved next to recliner.
|
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Jerry Avins
Guest
|
| Posted:
Fri Dec 16, 2005 7:44 am Post subject:
Re: I'm confused ;) was[Re: ADC limitations for bandpass/IF |
|
|
Joerg wrote:
...
| Quote: | 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.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ |
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Spehro Pefhany
Guest
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Jerry Avins
Guest
|
| Posted:
Fri Dec 16, 2005 5:16 pm Post subject:
Re: I'm confused ;) was[Re: ADC limitations for bandpass/IF |
|
|
Steve Underwood wrote:
...
| Quote: | 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.
| Quote: | 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.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ |
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Rocky
Guest
|
| Posted:
Fri Dec 16, 2005 5:16 pm Post subject:
Re: I'm confused ;) was[Re: ADC limitations for bandpass/IF |
|
|
Steve Underwood wrote:
| Quote: | 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 |
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Al Clark
Guest
|
| Posted:
Fri Dec 16, 2005 5:16 pm Post subject:
Re: I'm confused ;) was[Re: ADC limitations for bandpass/IF |
|
|
Joerg <notthisjoergsch@removethispacbell.net> wrote in
news:vkoof.41470$D13.20408@newssvr11.news.prodigy.com:
| Quote: | 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.....
| Quote: | 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
| Quote: | counters with Ge transistor because they wanted over $5 for one RTL
chip which exceeded my allowance. And even at that price they probably
were from a 're-labeler'. Bulk waste days were field days because one
could harvest tons of tubes for free and create cool stuff with them.
Regards, Joerg
http://www.analogconsultants.com
|
--
Al Clark
Danville Signal Processing, Inc.
--------------------------------------------------------------------
Purveyors of Fine DSP Hardware and other Cool Stuff
Available at http://www.danvillesignal.com |
|
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Steve Underwood
Guest
|
| Posted:
Fri Dec 16, 2005 5:16 pm Post subject:
Re: I'm confused ;) was[Re: ADC limitations for bandpass/IF |
|
|
Al Clark wrote:
| Quote: | Joerg <notthisjoergsch@removethispacbell.net> wrote in
news:vkoof.41470$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 |
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| Back to top |
|
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Al Clark
Guest
|
| Posted:
Fri Dec 16, 2005 11:35 pm Post subject:
Re: I'm confused ;) was[Re: ADC limitations for bandpass/IF |
|
|
"Rocky" <robert@suesound.co.za> wrote in news:1134751225.596897.33290
@g47g2000cwa.googlegroups.com:
| Quote: | 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 |
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