While I was happy to get the higher-quality PP215s, they don't really offer any performance advantage over the PP510 other than not falling apart.Falling apart ?
FYI there has been a change in Siglent PP510 and PP215 probes only visible that the later have 00 marked on them.
The only change I have noticed is the slightly different compensation range in ones marked 00.
@ozkarah
Possibly a thru-line 50 ohm terminator between the vna and the probe to bnc adapter? It may make a significant difference to the test results in this case.
@Vestom I just noticed the same lack in your first image. I think you both should repeat your tests with a thru-line 50 ohm terminator (or at least use a Tee adapter with a 50 ohm terminator) and compare the result against those of the original test.
[EDIT] Oops! Apologies, Vestom for not realising that you were effectively terminating the connection with CH1 set for DC50.
Now results are close but still Digilent seems to have a better rise time and imaging capability (look at the previous post).
There must be something said about these probe verifications. In order for any characterizations to make sense, they have to be repeatable and comparable to other people's measurements. That is why standards are made.
Passive probes are tested for frequency response with leveled 50Ω generator by making frequency sweep in frequency range in question. Signal has to be sinewave. On output of generator good quality 50Ω pass trough terminator is connected and then passive probe. That makes source impedance 25Ω.
Pulse response is verified with pulse generator. Pulse generator must create signal that has fast edges, but it has to have top of the signal last long enough for all equipment connected to settle. Leo's pulser has 10MHz repetition rate that gives comfortable 50ns low and high for scopes 50-100 MHz or more. For 10-20 MHz scopes it would be better to measure with signal that has 1 MHz repetition rate or slower.
Output of pulse generator should also be loaded with 50Ω pass trough terminator (in line) and then passive probe.
Don't use any "T" connectors with cables going anywhere for any measurements. They create stubs in transmission line, and can influence (distort) the signal that probe sees.
That being said, there are many, many books written about humble passive probes. Input pin of the probe will present as a complex impedance (RLC) to signal node in DUT and will have it's own impedance peaks and lows and resonance (multiple actually with various Q). There will also be resultant complex impedance/resonances when probe internal impedance combines with a node that you are measuring...
That is why people give lot's of money for active probes to minimize parasitic properties of probe inputs..
In short, it is normal for one probe to have "better" behavior compared to other one with one source and worse than same other probe with different signal source.
If you expect that those measurements have merit to show "real life performance", then don't use coax adapter on the tip. Use the probe with a ground clip and see the horror then....
That is why standards are made.
There must be something said about these probe verifications. In order for any characterizations to make sense, they have to be repeatable and comparable to other people's measurements. That is why standards are made.
Passive probes are tested for frequency response with leveled 50Ω generator by making frequency sweep in frequency range in question. Signal has to be sinewave. On output of generator good quality 50Ω pass trough terminator is connected and then passive probe. That makes source impedance 25Ω.
Pulse response is verified with pulse generator. Pulse generator must create signal that has fast edges, but it has to have top of the signal last long enough for all equipment connected to settle. Leo's pulser has 10MHz repetition rate that gives comfortable 50ns low and high for scopes 50-100 MHz or more. For 10-20 MHz scopes it would be better to measure with signal that has 1 MHz repetition rate or slower.
Output of pulse generator should also be loaded with 50Ω pass trough terminator (in line) and then passive probe.
Don't use any "T" connectors with cables going anywhere for any measurements. They create stubs in transmission line, and can influence (distort) the signal that probe sees.
That being said, there are many, many books written about humble passive probes. Input pin of the probe will present as a complex impedance (RLC) to signal node in DUT and will have it's own impedance peaks and lows and resonance (multiple actually with various Q). There will also be resultant complex impedance/resonances when probe internal impedance combines with a node that you are measuring...
That is why people give lot's of money for active probes to minimize parasitic properties of probe inputs..
In short, it is normal for one probe to have "better" behavior compared to other one with one source and worse than same other probe with different signal source.
If you expect that those measurements have merit to show "real life performance", then don't use coax adapter on the tip. Use the probe with a ground clip and see the horror then....
Thank you 2N3055 for the detailed explanations.
Unfortunately, I don't have a proper HF signal source. So I tried to use the LiteVna.
This time tried to follow your suggestions as much as I can.
I have an SDG2042X (upgraded to 120 Mhz). I used it as a signal source. Synchronized the outputs at 50 Ohm load setting. Connected scope's CH1(DC1M) to CH1 of AWG using pass-through 50 Ohm terminator at the output of AWG. CH4 (DC50) of the scope is directly connected to CH2 of the AWG.
(Attachment Link)
Using 1Hz-120MHz sweep setting at 632 mVpp (~0dBm) I created a sweep signal. Analyzed the 3 probes again. The results are below:
(Attachment Link)
There must be something said about these probe verifications. In order for any characterizations to make sense, they have to be repeatable and comparable to other people's measurements. That is why standards are made.
Passive probes are tested for frequency response with leveled 50Ω generator by making frequency sweep in frequency range in question. Signal has to be sinewave. On output of generator good quality 50Ω pass trough terminator is connected and then passive probe. That makes source impedance 25Ω.
Pulse response is verified with pulse generator. Pulse generator must create signal that has fast edges, but it has to have top of the signal last long enough for all equipment connected to settle. Leo's pulser has 10MHz repetition rate that gives comfortable 50ns low and high for scopes 50-100 MHz or more. For 10-20 MHz scopes it would be better to measure with signal that has 1 MHz repetition rate or slower.
Output of pulse generator should also be loaded with 50Ω pass trough terminator (in line) and then passive probe.
Don't use any "T" connectors with cables going anywhere for any measurements. They create stubs in transmission line, and can influence (distort) the signal that probe sees.
That being said, there are many, many books written about humble passive probes. Input pin of the probe will present as a complex impedance (RLC) to signal node in DUT and will have it's own impedance peaks and lows and resonance (multiple actually with various Q). There will also be resultant complex impedance/resonances when probe internal impedance combines with a node that you are measuring...
That is why people give lot's of money for active probes to minimize parasitic properties of probe inputs..
In short, it is normal for one probe to have "better" behavior compared to other one with one source and worse than same other probe with different signal source.
If you expect that those measurements have merit to show "real life performance", then don't use coax adapter on the tip. Use the probe with a ground clip and see the horror then....
Thank you 2N3055 for the detailed explanations.
Unfortunately, I don't have a proper HF signal source. So I tried to use the LiteVna.
This time tried to follow your suggestions as much as I can.
I have an SDG2042X (upgraded to 120 Mhz). I used it as a signal source. Synchronized the outputs at 50 Ohm load setting. Connected scope's CH1(DC1M) to CH1 of AWG using pass-through 50 Ohm terminator at the output of AWG. CH4 (DC50) of the scope is directly connected to CH2 of the AWG.
(Attachment Link)
Using 1Hz-120MHz sweep setting at 632 mVpp (~0dBm) I created a sweep signal. Analyzed the 3 probes again. The results are below:
(Attachment Link)
That is nice work!
And now you can see that all probes tested have amplitude flatness inside 1 dB. And that particular Digilent probe has very good flatness up to 100MHz at that source and load impedance...
But in reality they are all good enough, because signal as seen will be more influenced by source than anything else... As I said, try probes with a grounding clip...
If someone here has the same setup I would love to see the results.
I have an SDG2042X (upgraded to 120 Mhz). I used it as a signal source. Synchronized the outputs at 50 Ohm load setting. Connected scope's CH1(DC1M) to CH1 of AWG using pass-through 50 Ohm terminator at the output of AWG. CH4 (DC50) of the scope is directly connected to CH2 of the AWG.
...
Using 1Hz-120MHz sweep setting at 632 mVpp (~0dBm) I created a sweep signal. Analyzed the 3 probes again.
All this is just an academic discussion, because in any real-world scenario a passive high impedance probe like the ones discussed here isn’t going to be very useful for high frequencies anyway. Input impedances in the realm of 10 pF mean that any probing above 100 MHz requires a source impedance below 160 ohms, just to keep the measurement error below 50%. Once you’re at source impedances that low, a passive low impedance probe (which essentially is just a resistive match to a 50 ohms coax line) usually is the much better solution.
Once had to find a troublesome glitch on a 16 MHz clock signal (AC logic), which disappeared when attaching the venerable P6139A 8pF 500MHz probe. Had to use a 50 Ohm BNC cable with a resistor in series at the tip to see it (remember to put the scope in 50 Ohm mode). That was before we got the hugely expensive active differential probes good for several GHz
I can highly recommend making your own cheap Lo-Z probe, if you need to see signals beyond 100 MHz. I should probably myself make some small PCBs with a 2.5k in series, a 51R in parallel and SMA connector for cheap high speed x100 Lo-Z probes...
There's no need to add a 50 ohm resistor across the co-ax at the Lo-Z probe end if it's terminated in a matching impedance at the scope end. You'll be halving your already attenuated signal voltage for no real benefit otherwise. A 50 ohm transmission line, terminated with a purely resistive 50 ohm load will look just like a 50 ohm resistor
the tricky bit is dealing with keeping the probe's ground connection as short as possible to minimise 'ground bounce' and the effective area of the ground loop minimised to reduce stray noise ingress.
However, the scope is not a perfect 50 ohm termination but is typically slightly capacitive (specified to 17pF for SD2kX+) yielding a slight mismatch and a small reflection, ...
It is still true that the 50 ohms input mode is not perfect. Yet the VSWR stays below 1:1.5 at the specified bandwidth (500 MHz in case of the SDS2000X Plus).
Is that "good enough" for a Z0 probe without additional 50 Ohm termination of the cable's source end?
Thankfully not true. If the input capacitance of 17 pF would still be present even in 50 ohms mode, it could hardly be useful at frequencies above 100 MHz.
This is also the reason why an external terminator on a high-Z scope input can never replace the genuine 50 ohms input mode.
It is still true that the 50 ohms input mode is not perfect. Yet the VSWR stays below 1:1.5 at the specified bandwidth (500 MHz in case of the SDS2000X Plus).