I was planning on getting a RIGOL DS1052E oscilloscope for some radio work. I will be working with the 400Mhz and 900Mhz bands using Amplitude-shift keying (ASK). I know the scope is 100Mhz: 1GS/s. but is this enough for the bands I will be using?
Ediit:
The system I am working with is using AM and no other modulation. I need to look at the the RF output to see that the packets are correct. Is a spectrum analzyer better than a scope for this?
Best Answer
The simple answer is no, it won't be anywhere near enough.
The reason:
Digital Storage Oscilloscopes (DSO) are limited bandwidth wise by two things: the sampling rate, and the analogue bandwidth. Generally one dictates the other depending on the desired operation of the scope.
For sampling, Nyquist tells us that we cannot detect signals unambiguously above half of the sample rate (i.e. we get aliasing). However, for a scope we want to do more than just detect, we want to see the waveform, so generally a bandwidth of around 1/10th of the sampling rate is used. Also, since a filter starting close to the Nyquist frequency that (e.g. >400MHz) would roll off enough to prevent aliasing is much harder and more expensive to design than a simple one or two pole filter rolling off from further back.
So the analogue bandwidth is usually dictated by these factors, and of course it doesn't make sense to waste money on bandwidth you are not going to use. An exception to this might be if aliasing was desired (i.e undersampling, often used for RF applications) or if the scope is capable of equivalent time sampling (ETS). If most of the stuff you want to observe is repetitive, then ETS may be of use to you - make sure the scope has the required analogue bandwidth as well though.
Some scope product pages are a bit misleading with specs, making it hard for a new user to figure out what is what.
Generally though, a decent scope will advertise the usable bandwidth along with the model number, like for your Rigol, which is advertised as "Rigol DS1052E 50MHz Digital Oscilloscope".
So the bandwidth is 50MHz, and signals above this be be attenuated, more as you get higher in frequency.
Relevant to the above discussion about sampling rate and analogue bandwidth, note that there is no physical difference between the DS1052E 50MHz, and the DS1102E 100MHz. They both have the same sampling rate and front end, but the bandwidth is intentionally limited for the DS1052E using a varicap that can be set in the firmware. It can be hacked to 100MHz, or at least the old model could) by setting the firmware accordingly (using RS232 IIRC)
So for real time observation of signals up to a GHz, you are talking at least 5GHz sampling rate, a front end to match, and a pretty expensive scope (>£5k at least)