Measurements (well) out of 'scope bandwidth

[Cursitor Doom]

Gentlemen,

I need to check two signals, one at just over 2Ghz and the other at just
over 6. Problem is, the fastest scope I have, as far as I'm aware, is an
analogue 350Mhz Tektronix. At the time I bought this (*long* time ago) I
couldn't imagine I'd ever need anything faster than this as for as long
as I lived, but it seems I was wrong.
Anyone know any dodges/work-arounds/wheezes to be able to view signals
that are *much* faster than the stated maximum scope bandwidth?



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Anyone know any dodges/work-arounds/wheezes to be able to view signals
that are *much* faster than the stated maximum scope bandwidth?

Doesn't come up much round here on account of my extensive boat anchor collection, but BITD I'd probably have cobbled together a superhet from a Mini Circuits mixer and a microwave sweeper. That only works for reasonably narrow-band signals, of course.

Cheers

Phil Hobbs

 

[Tom Gardner]

On 08/09/19 13:45, Cursitor Doom wrote:

Gentlemen,

I need to check two signals, one at just over 2Ghz and the other at just
over 6. Problem is, the fastest scope I have, as far as I'm aware, is an
analogue 350Mhz Tektronix. At the time I bought this (*long* time ago) I
couldn't imagine I'd ever need anything faster than this as for as long
as I lived, but it seems I was wrong.
Anyone know any dodges/work-arounds/wheezes to be able to view signals
that are *much* faster than the stated maximum scope bandwidth?

What is this signal?
What are you trying to determine?

If it is a modulated carrier, then:
- you don't need to look at the *carrier* frequency
- the scopes' bandwidth only needs to be that of the
modulating signal
- so downconvert the modulated signal so that it is
below 350MHz

Apart from that, a scope is usually the wrong tool
to observe a modulated RF signal. Usually a spectrum
analyser is better (lower noise, more linear).

 

On Sun, 8 Sep 2019 12:45:11 -0000 (UTC), Cursitor Doom
<curd@notformail.com> wrote:

Gentlemen,

I need to check two signals, one at just over 2Ghz and the other at just
over 6. Problem is, the fastest scope I have, as far as I'm aware, is an
analogue 350Mhz Tektronix. At the time I bought this (*long* time ago) I
couldn't imagine I'd ever need anything faster than this as for as long
as I lived, but it seems I was wrong.
Anyone know any dodges/work-arounds/wheezes to be able to view signals
that are *much* faster than the stated maximum scope bandwidth?

Check? If you want to see the waveforms, no.

If it's some modulated carrier, maybe use a diode detector ahead of
the scope.

Or, as suggested, heterodyne.

 

[mpm]

On Sunday, September 8, 2019 at 8:45:18 AM UTC-4, Cursitor Doom wrote:

Gentlemen,

I need to check two signals, one at just over 2Ghz and the other at just
over 6. Problem is, the fastest scope I have, as far as I'm aware, is an
analogue 350Mhz Tektronix. At the time I bought this (*long* time ago) I
couldn't imagine I'd ever need anything faster than this as for as long
as I lived, but it seems I was wrong.
Anyone know any dodges/work-arounds/wheezes to be able to view signals
that are *much* faster than the stated maximum scope bandwidth?

Ha! For me it was 20 MHz. Then 70 MHz.
I gave away the 20 MHz scope to an engineering student.
And acquired the RIGOL 300 MHz scope because the price was so good.

As others have mentioned, you can either down-convert, or use a spectrum analyzer. Would help to know more about what you're measuring.

I can "thumbs-up" the RIGOL DSA-832E.
Although we use a lot of expensive SA's, sometimes an "el cheap-o" variety is needed for oddball tasks. We picked up one of these (with the tracking generator option) a few months back when they were on-sale. A little weird to program it for "pass/fail", but it gets the job done without breaking the bank.
Might still be more than you want to spend, though.

 

On Sun, 8 Sep 2019 17:22:59 -0000 (UTC), Cursitor Doom
<curd@notformail.com> wrote:

On Sun, 08 Sep 2019 07:35:41 -0700, jlarkin wrote:

Check? If you want to see the waveforms, no.

If it's some modulated carrier, maybe use a diode detector ahead of the
scope.

Or, as suggested, heterodyne.

Someone else suggested I use a spectrum analyser which had not occurred
to me. I do have two spare SAs that more than cover that region of the
spectrum but by now they probably both need recommissioning.
Anyway, John, this is all your fault with your obsession with continually
pushing the BW envelope upwards; "picosecond timing" and all that. Why
couldn't you be satisfied with ~100Mhz?

I like speed. Cars, roller coasters, skiing, EclipsLite gates and GaN
fets. I was born in a moving 1936 Ford.


There once was a time when "VHF"
>- as it was then - was more than enough for everyone.

I don't much care for RF, which is fundamentally narrowband. 5 GHz is
not interesting; DC-to-5GHz is.

Things get interesting at 1 ns. Things get difficult at 100 ps.


And don't forget
>you still owe me a burger and fries.

Sure, any time.

 

[Cursitor Doom]

On Sun, 08 Sep 2019 07:35:41 -0700, jlarkin wrote:

Check? If you want to see the waveforms, no.

If it's some modulated carrier, maybe use a diode detector ahead of the
scope.

Or, as suggested, heterodyne.

Someone else suggested I use a spectrum analyser which had not occurred
to me. I do have two spare SAs that more than cover that region of the
spectrum but by now they probably both need recommissioning.
Anyway, John, this is all your fault with your obsession with continually
pushing the BW envelope upwards; "picosecond timing" and all that. Why
couldn't you be satisfied with ~100Mhz? There once was a time when "VHF"
- as it was then - was more than enough for everyone. And don't forget
you still owe me a burger and fries.



--
This message may be freely reproduced without limit or charge only via
the Usenet protocol. Reproduction in whole or part through other
protocols, whether for profit or not, is conditional upon a charge of
GBP10.00 per reproduction. Publication in this manner via non-Usenet
protocols constitutes acceptance of this condition.

 

On Sun, 8 Sep 2019 12:45:11 -0000 (UTC), Cursitor Doom
<curd@notformail.com> wrote:

Gentlemen,

I need to check two signals, one at just over 2Ghz and the other at just
over 6. Problem is, the fastest scope I have, as far as I'm aware, is an
analogue 350Mhz Tektronix. At the time I bought this (*long* time ago) I
couldn't imagine I'd ever need anything faster than this as for as long
as I lived, but it seems I was wrong.
Anyone know any dodges/work-arounds/wheezes to be able to view signals
that are *much* faster than the stated maximum scope bandwidth?

Is the waveform of interest periodic ?

If so, the classical trick was to use a sampling scope, i.e. take only
one sample from each cycle and reconstruct a full cycle display by
slightly varying the sampling point relative to the RF cycle.

Apparently many digital scopes use this trick to claim huge bandwidths
while still using mediocre speed ADCs (conversion time of one or
multiple RF cycles). Of course such bandwidths are possible only for
periodic waveforms, not for a single shot capture.

 

[Cursitor Doom]

On Sun, 08 Sep 2019 19:53:03 +0300, upsidedown wrote:

> Is the waveform of interest periodic ?

Yup, just a plain ol' unmodulated sine wave in both cases.

If so, the classical trick was to use a sampling scope, i.e. take only
one sample from each cycle and reconstruct a full cycle display by
slightly varying the sampling point relative to the RF cycle.

I've got one of those somewhere among my collection; a Philips one I
believe. I dislike such contrivances and won't use it on account of its
loathsome artifice in this respect.

Apparently many digital scopes use this trick to claim huge bandwidths
while still using mediocre speed ADCs (conversion time of one or
multiple RF cycles). Of course such bandwidths are possible only for
periodic waveforms, not for a single shot capture.

This is why I avoid anything other than good old analogue methods if at
all possible. I do have some digital scopes but avoid using them at all
costs if an analogue will suffice.


--
This message may be freely reproduced without limit or charge only via
the Usenet protocol. Reproduction in whole or part through other
protocols, whether for profit or not, is conditional upon a charge of
GBP10.00 per reproduction. Publication in this manner via non-Usenet
protocols constitutes acceptance of this condition.

 

On Sunday, 8 September 2019 13:45:18 UTC+1, Cursitor Doom wrote:

Gentlemen,

I need to check two signals, one at just over 2Ghz and the other at just
over 6. Problem is, the fastest scope I have, as far as I'm aware, is an
analogue 350Mhz Tektronix. At the time I bought this (*long* time ago) I
couldn't imagine I'd ever need anything faster than this as for as long
as I lived, but it seems I was wrong.
Anyone know any dodges/work-arounds/wheezes to be able to view signals
that are *much* faster than the stated maximum scope bandwidth?

Envelope detect it, diode & cap.


NT

 

[Sjouke Burry]

On 08.09.19 14:45, Cursitor Doom wrote:

Gentlemen,

I need to check two signals, one at just over 2Ghz and the other at just
over 6. Problem is, the fastest scope I have, as far as I'm aware, is an
analogue 350Mhz Tektronix. At the time I bought this (*long* time ago) I
couldn't imagine I'd ever need anything faster than this as for as long
as I lived, but it seems I was wrong.
Anyone know any dodges/work-arounds/wheezes to be able to view signals
that are *much* faster than the stated maximum scope bandwidth?

If intermittent , rectify with a fast diode, and view the result on your
scope.

 

[whit3rd]

On Sunday, September 8, 2019 at 10:15:46 AM UTC-7, Cursitor Doom wrote:

On Sun, 08 Sep 2019 19:53:03 +0300, upsidedown wrote:

Is the waveform of interest periodic ?

Yup, just a plain ol' unmodulated sine wave in both cases.

The crudest possibility would be an attenuator and frequency counter.
With minimum attenuation, you get an indication of the frequency.
Crank up the attenuation until the frequency drops, and that tells
you the amplitude (at which the counter loses signal).

As long as it IS an umnodulated sine wave, there's no more useful information than
frequency and amplitude, because phase is gonna be different in
each inch of space...

Calibration is left as an exercise for the operator...

 

[George Herold]

On Sunday, September 8, 2019 at 9:23:13 PM UTC-4, whit3rd wrote:

On Sunday, September 8, 2019 at 10:15:46 AM UTC-7, Cursitor Doom wrote:
On Sun, 08 Sep 2019 19:53:03 +0300, upsidedown wrote:

Is the waveform of interest periodic ?

Yup, just a plain ol' unmodulated sine wave in both cases.

The crudest possibility would be an attenuator and frequency counter.
With minimum attenuation, you get an indication of the frequency.
Crank up the attenuation until the frequency drops, and that tells
you the amplitude (at which the counter loses signal).

As long as it IS an umnodulated sine wave, there's no more useful information than
frequency and amplitude, because phase is gonna be different in
each inch of space...

Calibration is left as an exercise for the operator...

Maybe one of the old HP frequency meters?
HP 536a. And a diode detector.

George H.