Measurements (well) out of 'scope bandwidth

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?

--
This message may be freely reproduced without limit or charge only via  
the Usenet protocol. Reproduction in whole or part through other  
 Click to see the full signature
Reply to
Cursitor Doom
Loading thread data ...

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

Reply to
pcdhobbs

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).

Reply to
Tom Gardner

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 an alyzer. 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 weir d 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.

Reply to
mpm

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.

Reply to
jlarkin

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.

Reply to
upsidedown

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

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.

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  
 Click to see the full signature
Reply to
Cursitor Doom

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  
 Click to see the full signature
Reply to
Cursitor Doom

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"

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

Sure, any time.

Reply to
jlarkin

Envelope detect it, diode & cap.

NT

Reply to
tabbypurr

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

Reply to
Sjouke Burry

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...

Reply to
whit3rd

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

George H.

Reply to
George Herold

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.