Oscilliscope advice  - Page 1
Forum section: electronics / beginners

author: daniel123
author_rank: Regular Contributor
timestamp: April 24, 2016, 10:12:56 pm
content: I live in houston TX in the usa and I am new to the hobby and I am trying to find a working oscilliscope for dirt cheap because I can't afford a scope of any kind. I would like an analog scope so I can measure wave forms in quartz crystal and in oscilator circuits. If anyone has one that they dont use anymore or any suggestions please let me know.SincerlyDaniel V

author: tautech
author_rank: Super Contributor
timestamp: April 24, 2016, 10:20:55 pm
content: daniel, disclosing your location might improve your chances as shipping cost could be much more than an old CRO's value.Spelling corrected

author: daniel123
author_rank: Regular Contributor
timestamp: April 24, 2016, 10:23:38 pm
content: I live in Houston TX in the US. from australia that would be a fortune for shipping.

author: uncle_bob
author_rank: Unknown
timestamp: April 25, 2016, 12:49:30 am
content: Quote from: daniel123 on April 24, 2016, 10:23:38 pmHiTo look at a straight quartz crystal you will need a network analyzer (or something similar) rather than a scope.For an oscillator, a scope will show you very limited information. There are other devices you can buy / build that might be of more use.A scope or other gear could easily be frequency specific. What frequency range are you targeting ?Bob

author: daniel123
author_rank: Regular Contributor
timestamp: April 25, 2016, 01:12:45 am
content: im looking for the 100 mhz range

author: daniel123
author_rank: Regular Contributor
timestamp: April 25, 2016, 01:28:10 am
content: 100 to 200 dont want a digital

author: rstofer
author_rank: Super Contributor
timestamp: April 25, 2016, 02:00:22 am
content: I know you are looking for free but this is pretty darn close as long as you don't chase the price too far:http://www.ebay.com/itm/Tektronix-465-100-MHZ-Dual-Channel-Oscilloscope-with-Option-1-and-DM-44/111976336128?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D36499%26meid%3D458fa4cdfab84fd8bb70f5a534fa6eab%26pid%3D100005%26rk%3D1%26rkt%3D6%26sd%3D272221814343&rt=nc$100 including freightThese are great scopes, I have one that cost me about $200 12 years ago.

author: daniel123
author_rank: Regular Contributor
timestamp: April 25, 2016, 02:21:02 am
content: i cant really afford any scope really as in im broke

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: April 25, 2016, 04:47:47 am
content: Call or go around to some local schools (tech schools, community colleges). See if they have any they want to get rid of.Check craigslist as well.

author: uncle_bob
author_rank: Unknown
timestamp: April 25, 2016, 11:16:36 am
content: Quote from: daniel123 on April 25, 2016, 01:12:45 amHiIf you are working on a 100 MHz oscillator, you will need a scope with a bandwidth of at least 300 MHz. That's the only way you will see much of what is going on with the circuit.Bob

author: daniel123
author_rank: Regular Contributor
timestamp: April 25, 2016, 08:58:37 pm
content: Yea I mean 300 mhz

author: danadak
author_rank: Super Contributor
timestamp: April 25, 2016, 09:39:36 pm
content: If you want to see 100 Mhz osc a 100 Mhz analog scope will trigger andshow you the waveform. The 300 Mhz number discussed earlier is morefor a digital oscilloscope, where the sampler must operate at least at Nyquist(2X signal f of interest) to see the waveform without aliasing.Regards, Dana.

author: daniel123
author_rank: Regular Contributor
timestamp: April 25, 2016, 09:43:25 pm
content: Now what brand should I look for and do you know if anyone can give one for free to me?

author: danadak
author_rank: Super Contributor
timestamp: April 25, 2016, 09:45:54 pm
content: You will also need two probes.Can your Mom and Dad help out for purchase/shipping costs ?Regards, Dana.

author: daniel123
author_rank: Regular Contributor
timestamp: April 25, 2016, 09:50:54 pm
content: They might be able to help. I'll ask them. The only problem if it is from overseas it would cost too much I will get back to you when I find out

author: uncle_bob
author_rank: Unknown
timestamp: April 25, 2016, 11:26:52 pm
content: Quote from: danadak on April 25, 2016, 09:39:36 pmHiA 100 MHz scope with a 100 MHz oscillator will simply show you a sine wave. You will not see any distortion issues or be able to check the limiting process. In order to get a valid look at the circuit, you *have* to get some of the higher order harmonics visible on the scope. 300 MHz is indeed the minimum you would want for that sort of thing.Bob

author: danadak
author_rank: Super Contributor
timestamp: April 25, 2016, 11:42:33 pm
content: One thing you can do is call some local businesses that are making electronic products,ask for purchasing, and describe your situation. And ask them if they have any surplusequipment they sell or give away to schools or individuals. If your school has an electronicscalls maybe the teacher could help with suggestions. If purchasing guy does not seem tobe of much help ask if you could talk to an engineer, sometimes they will connect you tosomeone.Another group of people to contact are the radio amateurs in the area. One of their mantrasis to help each other and youngsters get involved. Google "radio amateur club" for yourarea and see if you get any hits. Also look/post here -http://www.arrl.org/Regards, Dana.

author: danadak
author_rank: Super Contributor
timestamp: April 26, 2016, 12:03:30 am
content: If you need a scope, here is a PC based freebee that handles AC coupling only, but very usefull. Note in themanual you have to limit input to sound card on the order of a volt, but still application, with FFT and Sig Genmakes a very usable freebee instrument. Build an interface for the signal gen, a simple opamp buffer would do,to buffer sound card output, and an attenuator/clamp on sound card input and you should be good to go. Acouple diodes paralled should work as a clamp.https://www.zeitnitz.eu/scope_enhttp://www.daqarta.com/dw_0all.htmhttp://homediyelectronics.com/projects/howtomakeafreesoundcardpcoscilloscope/?p=3http://www.build-electronic-circuits.com/sound-card-oscilloscope/After you build the protective interface to sound card check it first by placing a higher Von input to protective circuit and look at output of circuit that would connect to soundcard input.Note this scope is only good for audio type frequencies.Regards, Dana.

author: danadak
author_rank: Super Contributor
timestamp: April 26, 2016, 12:56:11 am
content: Uncle_Bob is right, I kept thinking oscillator as a sine osc, not a clock osc whereharmonics very much a part of waveform character. So his 300 Mhz is minimumyou want, that only picks up 1 odd harmonic which will still yield a fairly distortedsquare wave.Try this applet out -http://www.falstad.com/fourier/https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwiWsPy7j6vMAhUF4yYKHQ6tC9cQjRwIBw&url=https%3A%2F%2Fsites.google.com%2Fsite%2Fpsychoacousticssoundperception%2Fwaveform-and-superposition&psig=AFQjCNG5pHqqX85S82REPGEMTPP9K4dreg&ust=1461719308813292Regards, Dana.

author: vk6zgo
author_rank: Super Contributor
timestamp: April 27, 2016, 03:01:51 am
content: Quote from: uncle_bob on April 25, 2016, 11:26:52 pmUnc,it is easy to see things through the prism of one's own advanced technical level.I don't think the OP is at a level where he is going to be much concerned with 100MHzsquarewaves.A 100MHz analog 'scope will happily display a sine wave at that frequency,even if itis3dB down.Granted,you won't see any distortion,but again,he is not at that level.It sounds like he has a bunch of odd crystals,& wants to make oscillators & see if they work.It is unlikely they will be 100MHz ones.VHF crystals will be "overtone" devices,so they could be induced to operate on their lower "fundamental" frequency.Any "freebie" 'scopes he may get will be well short of 100MHz bandwidth,let alone 300MHz.To the OP---"Freebies" are pretty thin on the ground,for various reasons:-(1) Most of us don't live near you---the USA is a big place,& the World much bigger!(2)Some of us have been "bitten" before---you won't believe this,but there are unscrupulous folks who spin a "sob story",get a free device then sell it for a profit!(3)You are quite young----this in itself present difficulties.We need to know your Parents are on board,before sending you anything.A parcel from "some weirdo on the Internet" might end up being the subject of a "controlled explosion" by the Bomb Squad!On one occasion,a rather younger chap than you was looking for a free Oscilloscope.I had a little 10MHz one,& nearly sent it to him,but he was a bit "cagey" about getting his Parents to PM me,so he didn't get his 'scope.If you decide to buy,instead,I would suggest you attend a local "Hamfest".Amateur Radio enthusiasts usually have at least one of these per year,where they buy & sell,mostly Amateur Radio equipment,but there is usually a fair assortment of secondhand instruments,as well as some parts,books on Electronics & so on.Just Google for "Hamfests near Houston TX".

author: GreyWoolfe
author_rank: Unknown
timestamp: April 27, 2016, 12:08:58 pm
content: I will add my 2 cents on hamfests. I got a Tektronics 2235 100 MHz scope for $45 at a local hamfest here in Florida. I dickered the price down a little at the end of the day and all it really needed was a cleaning of the horizontal and vertical controls and an inexpensive set of probes. All in-$60.

author: Apollyon25_
author_rank: Regular Contributor
timestamp: April 29, 2016, 02:54:44 am
content: I'd offer to let you use one of our work scopes at lunchtime or after work, or one of my personal scopes at home if you were closer...Ask local electronics places - talk to the engineers directly if possible. We are all a helpful lot.I worked at a local amplifier design company helping out with odd jobs in the weekends (I was 9 or 10 from memory). Then, many years later, I designed a product for them.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: April 29, 2016, 03:41:30 am
content: I would (almost) be willing to bet that this one actually works fine, and might only need controls cleaned.https://houston.craigslist.org/ele/5510847666.htmlIt might be worth a site visit to see if it will display its probe compensator signal.Borrow the 'rent's lawnmower and go mow two big Houston lawns for the 50 bucks.Or mow lawns for a week and buy a _real_ oscilloscope:https://houston.craigslist.org/ele/5523036149.html