I bought two "oscilloscope+FFT analyzer+logic analyzer" ISA cards recently on eBay without probes. These are my first "'scopes" and I'd like to know what kind of probes I should buy. With these cards, I can either choose to have one single 200MHz channel or two 100MHz channels per card.
But, since they are not linked together, if I put both in 200MHz mode, they act as two separate 'scopes, so comparing between both signals is not possible.
I know absolutely nothing to probes, what should I get?
But, since they are not linked together, if I put both in 200MHz mode, they act as two separate 'scopes, so comparing between both signals is not possible.
I know absolutely nothing to probes, what should I get?
You shold be able to use virtually any scope probe, but best to get them both for 200 Mhz since your cards will go up to 200 Mhz sample rate. This is assuming that the cards or some part of your system have two BNC connectors, one for each probe, one on to each channel input.
There are always loads of Scope probes available on Ebay at about £5- £10 each.
Hope this helps
There are always loads of Scope probes available on Ebay at about £5- £10 each.
Hope this helps
Further to my last regarding Scope probes with BNC connectors, I have realized that there are available scope probes for sound card scopes and these have Phono plug connectors so these should be available also.
There should be no reason why you should not be able to cut off the BNC connectors and fit Phono's instead but the BNC is better at high frequency than Phono. There may be a difficulty with getting suitable plugs to fit the thin wire that is used, definately better to get the correct type in the first place. It all depends on your card input requirements.
There is another post regarding PC sound card scope probes just down the page, click on the link to see Phono connector scope probes.
There should be no reason why you should not be able to cut off the BNC connectors and fit Phono's instead but the BNC is better at high frequency than Phono. There may be a difficulty with getting suitable plugs to fit the thin wire that is used, definately better to get the correct type in the first place. It all depends on your card input requirements.
There is another post regarding PC sound card scope probes just down the page, click on the link to see Phono connector scope probes.
Well, it's not a sound card, it's some real dedicated scopes with BNC connectors.
The thing is, I know I can buy almost any probes out there, but there is also is the fact that there are X1, X10, X100 ones, different coax cables, different connectors, and a big price difference between the probes.
I'd like to narrow the amount of choice to more specific things / what's the most useful, etc.
The thing is, I know I can buy almost any probes out there, but there is also is the fact that there are X1, X10, X100 ones, different coax cables, different connectors, and a big price difference between the probes.
I'd like to narrow the amount of choice to more specific things / what's the most useful, etc.
Probes with phono connectors are definitely not suitable for a 200 MHz sampling scope.
Tektronix has at least one good app note on their web site about choosing scope probes. I suggest you start there.
Decent scope probes have a trimmer capacitor in the little box with the BNC connector. The trimmer is adjusted to match the probe capacitance to the scope's input capacitance using the reference 1 KHz clock on the scope. You typically adjust the capacitance to make the square wave look square. Don't even think about a high frequency measurement without trimming the probe.
I_F
Tektronix has at least one good app note on their web site about choosing scope probes. I suggest you start there.
Decent scope probes have a trimmer capacitor in the little box with the BNC connector. The trimmer is adjusted to match the probe capacitance to the scope's input capacitance using the reference 1 KHz clock on the scope. You typically adjust the capacitance to make the square wave look square. Don't even think about a high frequency measurement without trimming the probe.
I_F
Well, I can't seem to find any interesting info on Tek's site, but I found these:
http://www.ezprobe.com/mm5/merchant...e_Code=E&Product_Code=TEX250&Category_Code=PP
http://www.ezprobe.com/mm5/merchant...e_Code=E&Product_Code=TEX100&Category_Code=PP
Much cheaper than Tektronix's $100+ 200MHz probes!
http://www.ezprobe.com/mm5/merchant...e_Code=E&Product_Code=TEX250&Category_Code=PP
http://www.ezprobe.com/mm5/merchant...e_Code=E&Product_Code=TEX100&Category_Code=PP
Much cheaper than Tektronix's $100+ 200MHz probes!
you can make a phono plug which has decent impedance to 150 MHz or so -- it takes a little bit of 5/32" brass tubing and RG-188 coax -- http://users.easystreet.com/w7zoi/rca_plugs.html
if you aren't going to roll your own connector with an RCA plug and brass tubing -- this is the effect of one RCA phono connector from 100kHz to 200 MHz -- the trace was normalized at 50 ohms -- the vertical scale is 0.05dB/interval.
"A bad probe is worse than a bad wife..."
if you aren't going to roll your own connector with an RCA plug and brass tubing -- this is the effect of one RCA phono connector from 100kHz to 200 MHz -- the trace was normalized at 50 ohms -- the vertical scale is 0.05dB/interval.
"A bad probe is worse than a bad wife..."
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1.get a cheap x10 probe first, you will always need spare probe later on
x10 is good compromise for start, I'll always have at least 2 of those
typical worst case you will get at least 25 mhz bandwith with cheap 10x probe. make sure it has adjustment.
since higher quality probe is prohibitively expensive, In practice I use the cheap much more to prevent damage from overvoltage, or mishandling.
2.Next step will be high impedance active probe,. you will get at least 100Mhz bandwith for decent price + high impedance input, or you can even make it yourself if you can find a schematic/guide.
3.Differential probe is nice, but expensive.
4.DC+AC current probe is nice to have but extremely expensive.
get number 1 first and study to use it maximally, higher speed probe is useless if not properly used, learn how to use grounding near the tip to get best measurement result at high speed circuit ( 20Mhz ++).
x10 is good compromise for start, I'll always have at least 2 of those
typical worst case you will get at least 25 mhz bandwith with cheap 10x probe. make sure it has adjustment.
since higher quality probe is prohibitively expensive, In practice I use the cheap much more to prevent damage from overvoltage, or mishandling.
2.Next step will be high impedance active probe,. you will get at least 100Mhz bandwith for decent price + high impedance input, or you can even make it yourself if you can find a schematic/guide.
3.Differential probe is nice, but expensive.
4.DC+AC current probe is nice to have but extremely expensive.
get number 1 first and study to use it maximally, higher speed probe is useless if not properly used, learn how to use grounding near the tip to get best measurement result at high speed circuit ( 20Mhz ++).
Decent 100MHz probes are cheap. As has been pointed out, it's essential to calibrate them. Avoid switched x1, x10 probes like the plague. Most x10 probes have a voltage limit of only 300V, sometimes less. Worse, there are some x100 probes with the same voltage limit. Only buy a x100 probe if it is good for 2.5kV or more.
trimmer capacitor is not required for x1 range.
only for x10 or x100.
For Audio I'd just use good quality RG58 BNC cables cut in half and make my own ends to suit the job. My favourite is a cheap Ballpoint pen housing with half a sewing needle. Don't forget a ground wire out the back and run the shield all the way down close to the tip.
If you find you are running out of vertical range on your CRO then use a x10 or a x100 probe.
FWIW as an radio electronics tech I have needed a X100 probe three times in 15 years.
only for x10 or x100.
For Audio I'd just use good quality RG58 BNC cables cut in half and make my own ends to suit the job. My favourite is a cheap Ballpoint pen housing with half a sewing needle. Don't forget a ground wire out the back and run the shield all the way down close to the tip.
If you find you are running out of vertical range on your CRO then use a x10 or a x100 probe.
FWIW as an radio electronics tech I have needed a X100 probe three times in 15 years.
Audio you really only need about 200kHz bandwidth.
You are absolutely correct in what you are saying, Important with radio but at audio frequencies in normal circuits the difference is negligible.
A CRO has a 1 Million ohm input impedance and capacitance on AC range is typically 20pF.
Buy a cheap probe for audio, stay away from measuring mains, when it breaks buy a better one.
You are absolutely correct in what you are saying, Important with radio but at audio frequencies in normal circuits the difference is negligible.
A CRO has a 1 Million ohm input impedance and capacitance on AC range is typically 20pF.
Buy a cheap probe for audio, stay away from measuring mains, when it breaks buy a better one.
Yeah, but what is audio? Maybe you'll want to look at the clock in your CD player... Want to see what the data looks like on that SPDIF port? Want to know the rise or fall times of current pulses in that uC circuit you put together?
Audio is squiggley lines on the screen that you can see with the visualizers that come with winamp, etc. If you actually want to measure things you'll find that having BW just adequate for audio turns out to be pretty close to useless. Most of what is interesting happens at much higher than audio speeds.
I_F
Audio is squiggley lines on the screen that you can see with the visualizers that come with winamp, etc. If you actually want to measure things you'll find that having BW just adequate for audio turns out to be pretty close to useless. Most of what is interesting happens at much higher than audio speeds.
I_F
In fact I want to look for oscillation in audio circuits, align some FM tuners, and probably in a near future, start playing with Microchip PICmicros (Fortunately, both cards each have an 8-channel logic analyzer module, which means I don't "necessarily" need probes for this task, unless I start to find some trouble).
But, again, what is the problem with X1-X10 probes? Some say they don't have problems, some say that they're totally crappy.
But, again, what is the problem with X1-X10 probes? Some say they don't have problems, some say that they're totally crappy.
no real problem just as long as you can recognise when it is broken so you donlt chase a fault that isnt there. Check it occasionally with the cal output of your CRO.
The most common failure I get with any cro lead is the wires breaking from use, Once I fried a 100x probe with 4kV (dumb!) but never broke a switch.
The trimmer cap is to match the probe to a particular socket.
If plugging it into you other card you will need to re-trim it.
A good idea to buy one probe for each card and mark which is which.
The most common failure I get with any cro lead is the wires breaking from use, Once I fried a 100x probe with 4kV (dumb!) but never broke a switch.
The trimmer cap is to match the probe to a particular socket.
If plugging it into you other card you will need to re-trim it.
A good idea to buy one probe for each card and mark which is which.
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