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How to measure RF carriers

K

Klem

Jan 1, 1970
0
Hello Everyone,

An Engineer at my work told me that I should use an oscilloscope to
measure RF signals (60-400MHz)

I have never heard of such thing other then back in the days of tubes.
Our current designs consist of LNA's and Rf amps with any of their
specs in dB, I have always done troubleshooting/testing with means of
a Spectrum analyzer and a powered probe.


What are your ideas on this?

I appreciate any comments,

Thanks
 
J

Joerg

Jan 1, 1970
0
Hello Klem,

An Engineer at my work told me that I should use an oscilloscope to
measure RF signals (60-400MHz)

I have never heard of such thing other then back in the days of tubes.
Our current designs consist of LNA's and Rf amps with any of their
specs in dB, I have always done troubleshooting/testing with means of
a Spectrum analyzer and a powered probe.


What are your ideas on this?

A spectrum analyzer is the usual instrument here. Unless you are chasing
non-linearities in large amplifiers.
 
J

John Larkin

Jan 1, 1970
0
Hello Everyone,

An Engineer at my work told me that I should use an oscilloscope to
measure RF signals (60-400MHz)

I have never heard of such thing other then back in the days of tubes.
Our current designs consist of LNA's and Rf amps with any of their
specs in dB, I have always done troubleshooting/testing with means of
a Spectrum analyzer and a powered probe.


What are your ideas on this?

I appreciate any comments,

Thanks

We're designing some wideband RF power amps, and we plan to do all the
testing with sampling oscilloscopes. We're concerned with time-domain
stuff like phase shift versus time, rf envelope amplitude droop over
long bursts, things that would be hard to measure in the frequency
domain.

John
 
J

Joerg

Jan 1, 1970
0
Hello John,
We're designing some wideband RF power amps, and we plan to do all the
testing with sampling oscilloscopes. We're concerned with time-domain
stuff like phase shift versus time, rf envelope amplitude droop over
long bursts, things that would be hard to measure in the frequency
domain.

But AFAIR you guys have some >10GHz scopes. The stuff with a high drool
factor among RF engineers and where you have to talk to the bank before
signing the P.O. Although, sometimes one can luck out. When I bid on an
older HP 1GHz scope I was totally surprised when they called me to pay
and pick it up. Turns out there was only one bid ;-)
 
E

EE123

Jan 1, 1970
0
Klem said:
Hello Everyone,

An Engineer at my work told me that I should use an oscilloscope to
measure RF signals (60-400MHz)

I have never heard of such thing other then back in the days of tubes.
Our current designs consist of LNA's and Rf amps with any of their
specs in dB, I have always done troubleshooting/testing with means of
a Spectrum analyzer and a powered probe.


What are your ideas on this?

I appreciate any comments,

Thanks



What is the carrier frequemcy that you
are working at?
RF can mean a lot of different
things to different people.

Dave
 
P

Phil Allison

Jan 1, 1970
0
** Groper alert !
What is the carrier frequemcy that you
are working at?


** See the numbers in brackets ??




........ Phil
 
G

Genome

Jan 1, 1970
0
Phil Allison said:
** Groper alert !



** See the numbers in brackets ??




....... Phil

Yes!!! Radio 2 used to be on the Long Wave at 200KHz so that makes no sense
at all.

I would be inclined to ask the Engineer how he does it. Either he will tell
you or look fairly stupid.

DNA
 
J

John Larkin

Jan 1, 1970
0
Hello John,


But AFAIR you guys have some >10GHz scopes. The stuff with a high drool
factor among RF engineers and where you have to talk to the bank before
signing the P.O. Although, sometimes one can luck out. When I bid on an
older HP 1GHz scope I was totally surprised when they called me to pay
and pick it up. Turns out there was only one bid ;-)

A Tek 11801 or equivalent mainframe is usually under $1K on ebay, less
if you know a trick. 12 or 20 GHz dual-channel sampling heads are
typically about $700 or so, although TDR runs more. They are
phenomenally precise instruments.

I have 8 or 10 of the mainframes by now, and maybe 20 heads, $600k or
so at last catalog price!

A guy could equip a basement lab with everything needed to go into the
picosecond products business for the price of a used Harley.

John
 
T

Tom Bruhns

Jan 1, 1970
0
John Larkin wrote:
....
We're designing some wideband RF power amps, and we plan to do all the
testing with sampling oscilloscopes. We're concerned with time-domain
stuff like phase shift versus time, rf envelope amplitude droop over
long bursts, things that would be hard to measure in the frequency
domain.

John

Things like that don't seem difficult at all to measure with modern
frequency domain instruments like we build here. I don't know that
you'd find them on ebay quite as cheap as the scopes you mentioned in a
followup posting, though.

Cheers,
Tom
 
J

Joerg

Jan 1, 1970
0
Hello Tom,
Things like that don't seem difficult at all to measure with modern
frequency domain instruments like we build here. I don't know that
you'd find them on ebay quite as cheap as the scopes you mentioned in a
followup posting, though.

Phase shift versus time can be tough (meaning expensive) in frequency
domain if you are looking at just a couple degrees or so. But for droop
you are right, we measure that with spectrum analyzers. That stuff is a
serious concern when designing pulsed Dopplers for ultrasound. Spectrum
analyzers just don't like to trigger that well, mostly they provide a
BNC jack in the back for this and you have to concoct some circuitry to
drive it (but only once).
 
V

vasile

Jan 1, 1970
0
Klem said:
Hello Everyone,

An Engineer at my work told me that I should use an oscilloscope to
measure RF signals (60-400MHz)


What are your ideas on this?

I appreciate any comments,


Your engineer knows what it said. If you have no money for a spectrum
analyzer then a good oscilloscope is the next affordable tool for that.
Knowing the frequency is not enough if you are his boss and you don't
know to answer him why you'll not buy one.
You must also ask him which would be the amplitude levels and if will
be much happy if the scope will also have a good FFT and an analogic
bandwidtth twice than 400MHz.

greetings,
Vasile
 
T

Tom Bruhns

Jan 1, 1970
0
Joerg said:
Hello Tom,


Phase shift versus time can be tough (meaning expensive) in frequency
domain if you are looking at just a couple degrees or so. But for droop
you are right, we measure that with spectrum analyzers. That stuff is a
serious concern when designing pulsed Dopplers for ultrasound. Spectrum
analyzers just don't like to trigger that well, mostly they provide a
BNC jack in the back for this and you have to concoct some circuitry to
drive it (but only once).
....
Well, like I said, it doesn't seem all that difficult with modern
frequency domain instruments like we build here. They can trigger on
all sorts of things, including things that scopes can have lots of
difficulty with--like triggering on energy above a particular level in
a particular frequency band. If you calibrate out cable lengths
properly, you can get phase accuracy to a fraction of a degree. How,
with a scope, do you detect signals at -90dBc and determine that they
are or are not harmonically related to the fundamental? How do you
analyze phase noise versus frequency with a scope? How do you plot a
color map of amplitude versus frequency versus time with a scope, and
then display a trace of amplitude versus time for any particular
frequency? I'm not aware of any scopes that digitize with the required
spurious free dynamic range to do that as well as modern spectral
analyzers, and I don't believe they come with software that does as
good a job as what you get with spectral analyzers for frequency-domain
applications. On the other hand, if you need really wide instantaneous
bandwidth (perhaps greater than 100MHz), you probably ARE better off
with a scope--for now.

In general, I'd say that if you are analyzing a signal and want to know
its time-domain behaviour, like rise time, overshoot and the like,
you're better off with a scope; but if you want frequency domain
information like phase, harmonic content, accurate frequency
information, and spurious versus frequency, and even the time
progression of any of those things, you are better off with the proper
frequency domain analyzer.

Cheers,
Tom
 
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