I am about to purchase a dual channel scope and would welcome comments from users of either the Owen 25MHz digital colour scope (sold by Saelig for only $349) or the Tenma 20MHz analog scope with built-in function generator (sold by Farnell for £225). They both have their advantages and disadvantages but seem to offer good value for money, if they are reliable.
scope advice please
- Thread starter MFB
- Start date
I'd spend a bit of time looking at eBay for a reputable listing for a reputable (eg Tektronix) second hand one.
I got a 60Mhx twin channel Tektronix 2213A for £100 from a private listing 5 miles from home so I could give it a good look over before actually taking it.
Make sure you get probes with it, or be prepared to pay approx £20 each (I got mine from Rapid)
I got a 60Mhx twin channel Tektronix 2213A for £100 from a private listing 5 miles from home so I could give it a good look over before actually taking it.
Make sure you get probes with it, or be prepared to pay approx £20 each (I got mine from Rapid)
I don't know either of those scopes but if I were buying my choice would be for Digital Storage. It all depends upon what you want to do and need; as you say they al have their advantages and disadvantages. I found DSO's indispensible for looking at serial data where it's non-repetitive or a short burst with a large interval and you want to grab one sample and analyse it. I 'don't do analogue' so I'm not qualified to say what's needed there.
I personally like analog scopes, but I do well more analog than digital stuff (probably 75% to 25%). BUT...and this is a big but, I've also got frequency counters, a logic analyzer, and various other doodads and whatsits that do a lot of the digital work for me.
Also, I really dont think 25 mhz is enough. You can ebay 60-100 mhz scopes for the same price, and if you go with an HP, tektronics, etc. it's going to work jsut fine unless it's seriously jacked up.
The bandwidth ratings are kinda different for digital and analog scopes. With an analog scope, it's generally the -3db bandwidth. This means that you'll get half the response at it's maximum bandwidth. You can actually use a 20mhz analog scope to look at a 40mhz signal, but you wont garner the information from that trace as you would if it were within the bounds of the scopes design. Pretty much, you'd get to look at a general representation of the waveform, but that about it. No accurate measurements at all.
With digital scopes, the bandwidth is generally indicating the response time of the ADC's inside. You cant, for instance, look at a 10 nanosecond pulse with a 25mhz digital scope even if it only repeats at 100hz (there are ways around this, but out of the scope of this post!). The rise times, jitter, etc of digital signals also fall into this category of inability.
For the most bang for your buck int he picaxe world, I'd have to suggest a digital scope. However, I'd also suggest something much higher than 25mhz. I'd look at 50mhz at least. 100mhz would be preferable. It just gives you a ton more information than a lower bandwidth scope would give you and as a tool is much more versatile in the long run for many activities.
--Andy P
Also, I really dont think 25 mhz is enough. You can ebay 60-100 mhz scopes for the same price, and if you go with an HP, tektronics, etc. it's going to work jsut fine unless it's seriously jacked up.
The bandwidth ratings are kinda different for digital and analog scopes. With an analog scope, it's generally the -3db bandwidth. This means that you'll get half the response at it's maximum bandwidth. You can actually use a 20mhz analog scope to look at a 40mhz signal, but you wont garner the information from that trace as you would if it were within the bounds of the scopes design. Pretty much, you'd get to look at a general representation of the waveform, but that about it. No accurate measurements at all.
With digital scopes, the bandwidth is generally indicating the response time of the ADC's inside. You cant, for instance, look at a 10 nanosecond pulse with a 25mhz digital scope even if it only repeats at 100hz (there are ways around this, but out of the scope of this post!). The rise times, jitter, etc of digital signals also fall into this category of inability.
For the most bang for your buck int he picaxe world, I'd have to suggest a digital scope. However, I'd also suggest something much higher than 25mhz. I'd look at 50mhz at least. 100mhz would be preferable. It just gives you a ton more information than a lower bandwidth scope would give you and as a tool is much more versatile in the long run for many activities.
--Andy P
Scopes and cost.
MFB. I'll leave others to discuss the electronics.
Dec. 2006 , I bought an Owon from the USA. (It's still working OK).
Price + shipping. Then, three weeks later, got stung by
Customs + Excise for £48.44 !
(For folks outside the UK, there's only one rule with C+E; you lose!)
I see that Rapid sell the Owon range starting at £179 (£210 inc VAT. Free delivery)
for the 25 MHz model.
e.
MFB. I'll leave others to discuss the electronics.
Dec. 2006 , I bought an Owon from the USA. (It's still working OK).
Price + shipping. Then, three weeks later, got stung by
Customs + Excise for £48.44 !
(For folks outside the UK, there's only one rule with C+E; you lose!)
I see that Rapid sell the Owon range starting at £179 (£210 inc VAT. Free delivery)
for the 25 MHz model.
e.
Thanks for the helpful comments, especially about that extra VAT payment that makes a purchase from Rapid look much more competitive.
Regarding the digital-v-analog issues, I have used both for many years and agree that the former is more versatile (never needing more that 20 MHz bandwidth when working with microcontrollers). My reason for considering the Farnell offering for private use is that even simple function generators cost over £100 and the Tenma unit has one built-in. Therefore, if you need a function generator anyway, you effectively get a dual scope thrown in for about £120.
One problem with digital scopes is that it is possible to get mislead by effects like aliasing. If your mind is on debugging and your just looking at the scope ‘out of the corner of your eye’ then such effects can waste time (whilst, analog displays just get dimmer if the time base is too slow). If I do go the analog route, then I’ll have to use a cheap (modified Parallax type) logic state analyser for monitoring serial interfaces.
Regarding the digital-v-analog issues, I have used both for many years and agree that the former is more versatile (never needing more that 20 MHz bandwidth when working with microcontrollers). My reason for considering the Farnell offering for private use is that even simple function generators cost over £100 and the Tenma unit has one built-in. Therefore, if you need a function generator anyway, you effectively get a dual scope thrown in for about £120.
One problem with digital scopes is that it is possible to get mislead by effects like aliasing. If your mind is on debugging and your just looking at the scope ‘out of the corner of your eye’ then such effects can waste time (whilst, analog displays just get dimmer if the time base is too slow). If I do go the analog route, then I’ll have to use a cheap (modified Parallax type) logic state analyser for monitoring serial interfaces.
My tuppence worth.
I use a couple of pretty expensive Tektronix digital scopes. Aliasing problems? No way.
(Ive done DSP programming for a scope display using PIC and dsPIC and aliasing problems are removed with good filtering so I know what it looks like. Tektronix shows NO aliasing problems.)
Maybe some of the cheap Beijing Bangers have a problem ? I really don't know.
Obv your decision is based around budget and spending £600 upwards may seem OTT for domestic use, BUT do you trust the calibration on cheaper ones? I'm sure that if you want a pretty picture and reasonable spec then the cheaper ones will be OK, but if you want to be confident then you'll have to open the wallet a bit wider.
Ive just noticed that the latest TDS1000B Tektronix range have FFT built in too which appeals to me. USB connection and a USB flash drive supported appeals too. Prices down as they're now (apparently) made in China (isnt everything? Apart from my Dualit toaster.) Prices in Farnell start t £527+VAT in UK.
My older (USA made) Tektronix TDS210 has been perfect over 10 years. And when there was a technical issue it was taken away and fixed and returned FOC by Tektronix. Will you get that service with a.n.other brand?
Upsides: Storing waveforms, ability to trigger miles off-screen so you can look at a delayed signal shape, sending data to PC with softare free from Tektronix website, FFT - Tektronix gets my (slightly biased) vote. In day2day use you couldn't tell it from analogue except it looks a bit more dotty. And its only a couple of inches 'deep' on the desktop.
Digimess (Grundig) looks quite good too. And the GW Instek GDS820S looks good too.
I'm sure the cheaper ones would be fine for most apps, but the advantages of digital storage would make me think about spending a bit more. Who knows what you may need it for next year? And, of course, with the 'better makes' you'll still be using it (hopefully) in 10 years time too. And the 'better' makes will hold the price should you ever come to sell it.
One final comment when parting with a big wedge is the supplier. Will they give support? Will they exchange faulty items without fuss? Will the 'Cheapest on the Internet Supplier' be there in 6 months time? Ebay? Wouldn't touch it. I know Farnell is not the cheapest but their support/returns policy has been faultless with us.
Good luck, sorry about long drivel.
I use a couple of pretty expensive Tektronix digital scopes. Aliasing problems? No way.
(Ive done DSP programming for a scope display using PIC and dsPIC and aliasing problems are removed with good filtering so I know what it looks like. Tektronix shows NO aliasing problems.)
Maybe some of the cheap Beijing Bangers have a problem ? I really don't know.
Obv your decision is based around budget and spending £600 upwards may seem OTT for domestic use, BUT do you trust the calibration on cheaper ones? I'm sure that if you want a pretty picture and reasonable spec then the cheaper ones will be OK, but if you want to be confident then you'll have to open the wallet a bit wider.
Ive just noticed that the latest TDS1000B Tektronix range have FFT built in too which appeals to me. USB connection and a USB flash drive supported appeals too. Prices down as they're now (apparently) made in China (isnt everything? Apart from my Dualit toaster.) Prices in Farnell start t £527+VAT in UK.
My older (USA made) Tektronix TDS210 has been perfect over 10 years. And when there was a technical issue it was taken away and fixed and returned FOC by Tektronix. Will you get that service with a.n.other brand?
Upsides: Storing waveforms, ability to trigger miles off-screen so you can look at a delayed signal shape, sending data to PC with softare free from Tektronix website, FFT - Tektronix gets my (slightly biased) vote. In day2day use you couldn't tell it from analogue except it looks a bit more dotty. And its only a couple of inches 'deep' on the desktop.
Digimess (Grundig) looks quite good too. And the GW Instek GDS820S looks good too.
I'm sure the cheaper ones would be fine for most apps, but the advantages of digital storage would make me think about spending a bit more. Who knows what you may need it for next year? And, of course, with the 'better makes' you'll still be using it (hopefully) in 10 years time too. And the 'better' makes will hold the price should you ever come to sell it.
One final comment when parting with a big wedge is the supplier. Will they give support? Will they exchange faulty items without fuss? Will the 'Cheapest on the Internet Supplier' be there in 6 months time? Ebay? Wouldn't touch it. I know Farnell is not the cheapest but their support/returns policy has been faultless with us.
Good luck, sorry about long drivel.
Bandwidth : Thinking back on the 16 years when I had both DSO and analogue scopes sitting on my desk, the fastest signals I ever looked at were in the uS Range ( customer was bitterly complaining that a 4uS pulse wasn't 4uS and threatening legal action, until we asked if his scope was calibarted ). More frequently I did a lot of watching DSO on very slow 10 second-plus timebases to watch output DAC ramps go up and down, or audio levels coming in. So while high bandwidth is generally desirable, how desirable depends on what you're doing.
ebay scopes
I have to disagree. On the advice of a friend of mine who had picked up a couple of great pieces of test equipment off ebay I purchased my now beloved HP1631D for <$100 delivered. I love it, it works great, calibration is great. From what I understand the used test equipment market has a huge surplus right now so there are amazing deals! I have stuck with HP/Agilent equipment because it is what I know, but the electronics folks at work swear by Tektronix equipment.
A digital scope lets you do projects that would be really hard to do with an Analog scope IMHO. My digital scope has a minimum sample size of 5 ns (Which corresponds to 200Mhz) which has been ok for most of the things I want to do. This doesn't mean it is really a 200 Mhz scope (All this sampling theorem business)
Here is some sample output:
http://profmason.com/?p=517
BTW, when I first got the digital scope, I was really tempted to bring the analog scope back on the desk a couple of times, but once I got up the learning curve, I took the analog scope in for the students to use and haven't missed it.
have fun!
I have to disagree. On the advice of a friend of mine who had picked up a couple of great pieces of test equipment off ebay I purchased my now beloved HP1631D for <$100 delivered. I love it, it works great, calibration is great. From what I understand the used test equipment market has a huge surplus right now so there are amazing deals! I have stuck with HP/Agilent equipment because it is what I know, but the electronics folks at work swear by Tektronix equipment.
A digital scope lets you do projects that would be really hard to do with an Analog scope IMHO. My digital scope has a minimum sample size of 5 ns (Which corresponds to 200Mhz) which has been ok for most of the things I want to do. This doesn't mean it is really a 200 Mhz scope (All this sampling theorem business)
Here is some sample output:
http://profmason.com/?p=517
BTW, when I first got the digital scope, I was really tempted to bring the analog scope back on the desk a couple of times, but once I got up the learning curve, I took the analog scope in for the students to use and haven't missed it.
have fun!
Phew - that was a bit close....Farnell are doing 10% off all large web orders, but luckily I looked at the small print and it doesn't apply to Tektronix test equipmentTDS2014B...hmmmm...want one.....
Dippy - I hope your post isn't going to cost me a lot of money