Author Topic: Buying a scope for measuring RF waveforms  (Read 1111 times)

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Offline Mike99Topic starter

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Buying a scope for measuring RF waveforms
« on: November 01, 2023, 10:37:14 am »
Dear experts

I'm a radio amateur and my main use for a scope is to measure AF and RF waveforms up to 50MHz. I rarely need to examine logic waveforms.

I currently have a venerable Tektronix 2340A which does the job but is big, heavy and noisy and I'd like to replace it with something new.

I'm only a couple of miles from a major UK supplier of test equipment, including Siglent, Rigol and Micsig scopes, and the Siglent SDS 1202X-E is looking attractive. I only need 2 channels and don't want to spend more than £400.

Not being a scope expert I'd like to hear your opinions on whether this will suit my requirements.

Thanks!

Mike
 

Offline tszaboo

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Re: Buying a scope for measuring RF waveforms
« Reply #1 on: November 01, 2023, 10:48:27 am »
What's the reason you would want an oscilloscope for such a job, instead of a spectrum analyzer? That's usually not the right job for that task, even if it has FFT, the signal levels for a scope is much higher, the dynamic range is much lower, you don't have 50 Ohm termination on the low frequency scopes, the input capacitance is high and so on. I would guess even an SDR would be better, or a low cost spectrum analyzer.
 

Offline tggzzz

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Re: Buying a scope for measuring RF waveforms
« Reply #2 on: November 01, 2023, 10:59:56 am »
I'm a radio amateur and my main use for a scope is to measure AF and RF waveforms up to 50MHz. I rarely need to examine logic waveforms.

Measure what, exactly?
  • frequency? A frequency counter will give more accurate results faster
  • amplitude? Scopes are only 2% vertical linearity, at best. To that add the effects of the scope's frequency response, the probing technique (especially resonance), scope VSWR (probably 1:1.3, i.e. >2dB) Better to use a power meter or spectrum analyser
  • power? See amplitude, especially for low powers
  • harmonics? Not a chance with a scope due to non-linearity and/or ADC resolution. A spectrum analyser is much more appropriate.
  • modulation? What type, e.g. amplitude, phase, frequency? FM/PM better with a modulation domain analyser which showing frequency vs time. Or an SDR
Summary: a scope is a time-domain instrument. RF measurements are usually frequency domain and lower power. Choose the right tool for the job.

Personally, if I had a working scope that does the job, I would spend my money on something that gave me new and different and interesting capabilities.
« Last Edit: November 01, 2023, 12:42:54 pm by tggzzz »
There are lies, damned lies, statistics - and ADC/DAC specs.
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Offline Mike99Topic starter

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Re: Buying a scope for measuring RF waveforms
« Reply #3 on: November 01, 2023, 01:12:39 pm »
I already have an SDR with spectrum analyser software, frequency counter, modulation meter, RF millivoltmeter and a power meter. I'm interested in every day general measurements of peak-to-peak amplitude, noisy waveforms, 2-tone tests of SSB transmitter linearity etc. Nothing fancy.

Mike
« Last Edit: November 01, 2023, 01:14:14 pm by Mike99 »
 

Online nctnico

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Re: Buying a scope for measuring RF waveforms
« Reply #4 on: November 01, 2023, 01:13:50 pm »
AFAIK the SDS1202 gives you the most bandwidth for your money.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline tszaboo

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Re: Buying a scope for measuring RF waveforms
« Reply #5 on: November 01, 2023, 02:26:14 pm »
I already have an SDR with spectrum analyser software, frequency counter, modulation meter, RF millivoltmeter and a power meter. I'm interested in every day general measurements of peak-to-peak amplitude, noisy waveforms, 2-tone tests of SSB transmitter linearity etc. Nothing fancy.

Mike
All these are typically measured on a spectrum analyzer. Try to borrow a TinySA or a used SA to see how it does it. Or the TinySA is like 70 EUR, hard to go wrong with that.
 


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