Cheap RF scope? - Page 1
Forum section: electronics / general

author: sempjam
author_rank: Newbie
timestamp: August 11, 2015, 11:35:41 am
content: Looking for an oscilloscope (bandwidth~4 GHz) that isn't going to break the bank. Can anyone suggest a good model/brand/second hand dealer?

author: BravoV
author_rank: Super Contributor
timestamp: August 11, 2015, 01:10:08 pm
content: Budget ?

author: KJDS
author_rank: Super Contributor
timestamp: August 11, 2015, 01:14:42 pm
content: I'd previously thought that the very definition of oxymoron what "military intelligence." Now it seems we have a new contender.Using a scope to see RF does have it's uses, but a spec ana or signal analyzer, or even a modulation domain analyzer all provide more cost effective ways to peruse more than a couple of hundred MHz

author: tggzzz
author_rank: Super Contributor
timestamp: August 11, 2015, 03:04:19 pm
content: Quote from: sempjam on August 11, 2015, 11:35:41 amIf you tell us yourproblem(as opposed to yoursolution), then we might be able to offer useful advice.For many "RF" problems, any scope would be a bad starting point.

author: nctnico
author_rank: Super Contributor
timestamp: August 11, 2015, 03:10:59 pm
content: If you can get away with a sampling scope there are several cheap options. Perhaps one of the old Tektronix CSA series. They have sampling heads to several GHz. Shipping is going to cost money due to size & weight and the sampling heads could be hard to come by. A Tektronix TDS820 is another option but can have leaking capacitors and it will only trigger up to 2GHz so you'll need a prescaler to derive a trigger signal from signals over 2GHz.

author: Zucca
author_rank: Unknown
timestamp: August 11, 2015, 04:07:31 pm
content: Quote from: tggzzz on August 11, 2015, 03:04:19 pm+1

author: sempjam
author_rank: Newbie
timestamp: August 11, 2015, 04:25:20 pm
content: Thanks for the suggestionsYes, something on the problem may actually be more useful.I'm building and testing various rf dc rectifiers. Specifically looking at the cutoff frequency. Up until now I have been using a fn generator and scope (up to 40 MHz). Now I'm looking to go to higher frequencies. I'd thought to just use the same components. Granted as what I am really concerned with is a 'dc' output, the measurements should be doable without any high frequency measurement kit. But I want to keep an eye on the ref signal and the ripple. Is there a smarter way? Admittedly not much of an expert on any of this but I'm learningCheers!

author: tggzzz
author_rank: Super Contributor
timestamp: August 11, 2015, 04:53:51 pm
content: I'm not sure what you mean by an "rf dc rectifier".If you interested in measuring power, then have a look at Analog Devices chips designed for that purpose.If you are interested in "energy harvesting", then I suggest you do some calculations and measurements of the powers that are likely (and unlikely) to be available. There's a lot of bovine excrement in that topic.Don't forget that you will rapidly become very interested in resonant circuits and transmission line theory and practice since it is essential to match impedances throughout the system.In general RF components are very different to "ordinary" analogue components, e.g. carefully shaped strips of copper on a PCB act as bandpass/reject filters, and wires simply don't exist (all that exists are inductors and capacitors), and parasitic effects are dominantHave a look at the MiniCircuits website to get an idea of the components that are available; you probably won't recognise many of them!

author: KJDS
author_rank: Super Contributor
timestamp: August 11, 2015, 04:58:54 pm
content: If you want to accurately measure RF power, then a power meter is the most accurate way. HP/Agilent, Marconi Instruments, R&S and Gigatronics all make decent ones.If you want to see the frequency at the same time, then a spectrum analyzer can be used. These will measure power, but nowhere near as accurately as a power meter. A signal analyzer can also be used for this purpose but with only a narrow sweep.