The equation is correct. This is because the capacitive voltage divider works inversely compared to a resistive divider. A larger series resistor creates a smaller voltage at the divider output. A larger series capacitor creates a larger voltage at the divider output.

@@w2aew Thank you! One more question, most scope probes have a capacitor compensation range of roughly 10pF to 30pF, so it would be impossible to reach a 1 to 9 ratio. In fact it seems that you would want to obtain a 1:1 ratio since the probes adjustable capacitor and the scopes internal capacitance are almost the same to begin with. Any thoughts on this too would be very helpful! Thank you

@@joedenny8853 That specification refers to the range of *scope input capacitance* that the probe can be properly compensated for. So, if the probe says its compensation range is 10-30pF, that means at this probe can be used with any scope who's input capacitance is between 10pF and 30pF.

If you are able to properly compensate the probe (get a good, flat squarewave on the comp signal when running at 200us/div), then you should be fine. When properly compensated, response should be good to the 3dB BW of the scope or probe, whichever is less.

The amount of shunt capacitance presented by the probe will be listed in the probe specifications - it doesn't really matter where the adjustment location is.

Linas K The MDO3000 will automatically compensate the new TPPxxxx style of Tek probes. It does this by adjusting filter coefficients in the front end of the scope, and then storing those coefficients internally along with the serial number of the probe. So, each time you plug that probe back in, it recalls those filter coefficients.

+Vasudev Mr It means that the outer shell of the BNC connectors on the two channels are connected to each other, and connected to the scope's ground connection. Thus, be sure that you connect the probe ground clips to the same ground in your circuit, and not to a different voltage. Scope's are not fully floating like a DMM where you can connect the probes anywhere. With a scope, the ground connections are common among all inputs.

Chrismalito Terec Yes, it can! This is because the oscilloscope and with it, the probe, isn’t isolated from mains earth. Dave Jones on the EEVBlog has a video on it: kzfaq.info/get/bejne/rsd1f9Ry1JrPm4U.html

bloodedge If you can adjust to get both overshoot and undershoot, then the primary compensation adjustment is fine - just get it as close as you can. There are internal adjustments in the probe to fine-tune the broadband frequency response, but this generally requires special fixtures and equipment. If the imperfections are small in the resulting square wave, then it is unlikely that you'll be able to even see any detrimental effects when using them in day to day use.

+Vasudev Mr passive

Absolutely! Even a sub-100MHz analog or digital scope can be tremendously useful. I'm fortunate enough to be working for Tektronix, so I have access to some incredible equipment. However, before this, I used my 100MHz analog scope extensively.

Hi Alan - thanks so much for answering my question, especially so quickly as I am considering one right now - Which brings me to another idea - Why don't you do a sort of review of the older tektronix scopes and your recommendations? I purchased a 2465A some years back, and now days you see them in the $200 or less range. I did a lot of reading on the analogue scopes first, so I feel pretty good about that purchase. But why would someone purchase, say a 465B like yours instead? Or would you? What about the 2430A mentioned above - would that be ample for people doing radio repairs on boat anchors and other radios? If you have a 2430A, would it be helpful to have a 465 or 2465? Would it be redundant? If a storage scope from that era be worth spending 200 bux on when you can get digital scopes with LCD displays like the Regol for a little bit more? Anyhow, just some questions - and of course my concerns revolve more around RF and radio repairs. I too am a Ham. Would make a fantastic vid for hobbyists out here, I bet. Anyway, I watch a lot of vids and yours really are good. Very simple, clear instruction.

If it can be properly compensated, there is no performance gain as the BW is limited by the scope.

Thank you for the heads up. I fixed the link.

@@w2aew Thank you very much.

It's tough to say without more info. You could have bad probes. Info that would be helpful is: what scope, what probes, what settings, what signal you're looking at, etc.

+w2aew thank you for your quick reply! the scope I am working with is a teledyne lecroy 1.5GHz input bandwidth scope. the probes i have are lecroy pp006 500MHz 10x probe with a 10M ohm inpedance and 12pf capacitance. the oscilloacope was able to recognize the attenuations of the probes eaisly. the other settings were accordingly on the scope. the calibration waveform was gemerated with the scope itself, which was 2MHz square wave with Vpp of 1 V, 50% duty cycle and 2 ns of rising time.

Not sure what's going on there. Make sure the scope is using its 1M input impedance setting. Do other 10x probes work OK?

***** what insteresting is, i took the probe from my handheld scope, which is a 6 MHz bandwidth 10x 10M probe. And it turned out to be working just fine. I am thinking about I might got bad probes from eBay. I am not very familiar with the new scope I got, so I am not quite sure about whether yhe probes are broken or I have the wrong setting.

The 500MHz probes should work with the same settings that worked for the probes from your handheld.

Yes, this is perfectly reasonable. As you said, be sure that the probe's compensation range is adequate for your scope's input capacitance. And, just beware that the frequency response on the ultra-cheap probes might not be as flat or ideal as a higher quality probe. But, for most applications, this will be fine also.

Indeed, the frequency response is somewhat of an unknown with cheaper probes :-(. I note with some amusement when looking at low-cost probes recently that seemingly identical probes all nominally '100 MHz' were being listed as such, but one company had it listed as '80 MHz', possibly a more honest appraisal.

The main point of a 10x probe is to get the bandwidth, not really about the attenuation. The 10x probe is designed to isolate the ~100pf of the cable and scope input capacitance from the circuit under test - see this video on the topic (kzfaq.info/get/bejne/ib5ke6p_vKjJZYE.html). This scope automatically senses that the 10x probe is attached and adjusts the vertical scale reading appropriately so that it accurately shows the actual signal amplitude.

Because it's correct. 1 / ( 2 * 3.14 * 10,000 * 15E-12) is equal to 1.06Mohm.

Yes, you are correct. Thanks for your reply.

+Vasudev Mr That would make the most sense - and probe CAREFULLY!

+w2aew probe carefully??,will it harm the scope?

+Vasudev Mr I was referring to the fact that those voltages can easily harm *you*.

+w2aew oh ok, that's true

Assuming the information you have on the probe is correct, then it should be able to compensate the 25pF input capacitance of the 2225 scope. Have you made sure to connect the ground lead when doing the compensation? Are you sure about that part number for the probe? It's very unusual that Keysight doesn't have any datasheet or documentation on their website about that particular model number.

@@w2aew I did find documents within keysight site. There is a note saying: "These probes have been designed and calibrated for use with instruments having an input impedance of 1M Ω paralleled by 20pF. However, these may be recalibrated for use with instruments having an input capacitance of 15 to 30pF." I went through the process one more time and recorded a video showing the scope settings and the process. Maybe I am doing something wrong. kzfaq.info/get/bejne/hdScpNljv66ceZs.html

@@carentanbr Looks like you've got everything about right. I would push in the x10 multiplier on the Vertical scale knob (it looks like you have it pulled out) and then adjust the vertical scale setting as needed, then do the compensation. As long as you can make it flat, don't worry if you can't get reach the overcompensation condition.

​@@w2aew Thanks for replying! That is one interesting point. Yes, I did pull the 10x mag. If I push it back, i cant get any decent reading. It gets all blurred. I think it has to do with the quality of the internal signal generator. So I get a sharper image if I pull the 10x mag up.

@@carentanbr Push in the 10x mag, then rotate the vertical scale down to a lower value. The 10x mag is really only used when looking at very small signals. There is a procedure for doing the compensation in the user manual. www.tek.com/manual/2225-operators-manual. Starting setup on page 2-5, probe comp on page 4-1.

It depends on the probe. The voltage ratings are typically listed right on the probe itself. A few hundred volts is typical.

+John Floyd Tektronix, HP, Agilent, Fluke, etc. are basically the leaders in the general test and measurement industry. There are many others that make equipment that I would say are "second tier", but still very good - these would be companies like Leader, BK Precision, Kenwood, Philips, Hitachi, etc. and I think that Sperry would fit into this category. They're still around, but don't make oscilloscopes anymore. I'm assuming that you found the User manual for your scope on their website: www.sperryinstruments.com/en/resources/legacy

+w2aew Yes. I found the manual beforehand(Thank you Google!). I was just reading through it because after just watching your video I'm trying to find some reasonable price probes that will work well with the scope. Since I'm completely new to oscilloscopes it's a bit of a learning curve for me. It would have been nice if like your scopes the picofarrads would have been listed above the BNC connector. This is not the case for this scope. The manual states this though, " The input of this oscilloscope is 1MOhm shunted by 20pF capacitance. When the probe is used 10:1 attenuation, the impedance becomes 10MOhm shunted by 15pF. Then the voltage must be multiplied by 10". If I understand this correctly then as long as a set of probes has 15pF in it's compensation range then it should work ok with this 20MHz scope (provided you actually compensate it)?

+John Floyd Almost... You'll need to find probes that can compensate the 20pF input capacitance. The 15pF they mention is the input impedance of the PROBE that they sold. The probes you find might have a different input capacitance, and that's OK, as long as the compensation range encompasses 20pF.

+w2aew Excellent. I appreciate all your help so far! What advice would you give about buying probes. I've seen a few comments and videos warning against cheap probes. I'm assuming they meant passive ones. I haven't been looking for active ones since those seem to be geared toward measurements well above what this scope is capable of (I think). Other than cheaper probes having narrower compensation ranges can you give me an idea of anything else to avoid when buying? Should I be looking for name brand probes for a second tier low MHz scope like this? Right now I have two that I'm looking at www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_2189880_-1 & www.amazon.com/gp/product/B0030KWM30?keywords=oscilloscope%20probe&qid=1444917794&ref_=sr_1_1&sr=8-1#descriptionAndDetails . If you had a scope like this would you consider either of these for general testing?

+John Floyd The two links you provided look like they'd be perfectly adequate for your scope. No need to go to the name brand route, especially for hobbyist use. The very cheap no-name probes will often be made of inferior materials which may fit poorly, be less durable or flexible, etc. or have limited accessories. I'd be comfortable with either of these for hobby use with a 20MHz scope like you have.

In the old school analog scopes, the input capacitance was generally a consequence of of the input attenuator circuitry. In modern scopes, where the BW is software controlled, this is generally done deeper in the channel front end, or even in DSP.

***** I just recently got a shiny new rigol D1054Z, it is really nice, though having it less than a week I have already found some limitations to it compared to nice analog scopes. :/ Have you heard of oscillofun? it is a stereo soundtrack that can be fed into the XY mode of a scope to make cool cube shapes! It works much better on the old analog scope than it does on my DSO though.

Nothing beat the nice green glow with the perfectly "intensity grated display!"

Power Max Yes, there are definitely applications where an old CRT based analog scope is superior - and that XY example is a good one. I've never seen a digital scope that does an acceptable job on things like that, or looking at RF envelopes, etc.