1x fixed scope probe

[jfsimon]

Hi,

After seeing the quite interesting video regarding scope, I realized the probes I had were 1/10x hence bandwith approx 6 MHz [edit: at 1x].

I'd like the flexibility of 1x for best sensitivity and bandwith but I can't seem to find them on marker, could you please suggest one or a few manufacturer and references ?

Thanks & Regards,

Jean-François

[bob91343]

If you want a 1:1 probe you have some options.  You can dispense with a probe by using a piece of shielded wire with clips on the free end.  You can also use a switchable probe that can be used either as 10:1 or 1:1.  And finally you can buy a standard 1:1 probe.  The best ones seem to come from the scope companies but they are expensive.

I have had decent luck with Chinese cheap probes.  You can buy several so if one breaks you have others.

[jfsimon]

Thanks, I'll check this in more detail, I'm a bit lost in terms or termination resistor.

Would a 0 Ohm cable o n1 Meg input impedence scope be perfect, or need a 50 Ohm termination with low impedence cable, or both equal ?

I'll check, Eevblog has also interesting videos.

Thanks for the tips, indeed just a coax cable with clips seems a cheap solution, I got to figure out the correct impedance and how this matters.

See you regards
Jean-François

[bob91343]

It can get complex.  You have to visualize the circuit.  You have a signal source you want to measure.  If you put a load on it you will change it.  So you want to put as little load on as possible.  The scope probably has 1 Megohm input resistance shunted by maybe 20 pF.  If you put a shielded cable across that you increase the capacitance considerably.  That may not matter at low frequencies but you have to decide that.

The source impedance of the signal is important to decide how heavy a load it will tolerate before your measurement error becomes too great.  A small amount of error could be compensated for but some circuits will stop working properly with too much load.

If you try to make the load less by adding a resistor, you have created a low pass filter so that will eliminate high frequencies from your display.  How much so will depend on the specific situation.

So the answer to your question, as so often happens, is that it depends on what you are doing and what results you seek.

[ogden]

After seeing the quite interesting video regarding scope, I realized the probes I had were 1/10x hence bandwith approx 6 MHz.

Please provide info about video and probes you mention. I am afraid that video or you got it backwards. 1:1x probes usually have lower bandwidth than 1:10x. Examples:

https://www.keysight.com/zz/en/product/10070D/passive-probe-1-1-20-mhz-1-5-m.html
https://www.keysight.com/zz/en/product/N2843A/passive-probe-10-1-500-mhz-1-2-m.html

[edit] If you really needs low voltage and high bandwidth (like SMPS ripple) measurements - then get scope with 50Ohms input native impedance and use quality coax cables.

[jfsimon]

Hi,

I see thank you, it really matter the capacitance of the cable, it seems also why I saw a "poor man's HF probe" with just a coax and two equal resistors doing as probe.

Regards

Jean-François

[jfsimon]

Hi

This is the video I mentionned



Rgd

Jean-François

[ogden]

Screenshot from video

[jfsimon]

Hello Odgen,

Yep reduced bandwith at 1x when using a dual 1x/10x probe at its 1x range.

Looking the 1x for sensitivity without lossy cable specifically used for the 10x
range, as fitted in the dual range probe.

Got your Keysight ref thank you (10070D).

JF

[tooki]

Hi,

After seeing the quite interesting video regarding scope, I realized the probes I had were 1/10x hence bandwith approx 6 MHz [edit: at 1x].

I'd like the flexibility of 1x for best sensitivity and bandwith but I can't seem to find them on marker, could you please suggest one or a few manufacturer and references ?

Testec is a German manufacturer of nice probes at very reasonable prices. Their standard 1x probe is the TT-LF 112.

€17 at Reichelt: https://www.reichelt.com/fr/fr/modular-probe-25-mhz-x1-testec-lf-112-p32414.html

[jfsimon]

Thank you,

  Indeed that'll fit the budget.

Jean-François

[ogden]

Suggested probe looks like good deal. Meanwhile you may consider to read Analog appnote AN-1144. Note that "poor man's hi-speed probe" or straight connection of coax to 50 Ohm scope or SA input require DC blocking capacitor.

[alm]

Since the majority of capacitance of a 1x probe comes from the cable capacitance without any attenuation, a shorter probe cable will have a larger bandwidth. Old Tektronix probe used to come in 6 feet, 9 feet and 12 feet options with decreasing bandwidth. Their dedicated 1x probes were labeled P6101, P6101A and P6101B.

[Fungus]

A 12-foot oscilloscope probe?? 

Even 6-foot is pretty darn long.

[BrokenYugo]

A 12-foot oscilloscope probe?? 

Even 6-foot is pretty darn long.

Assuming "old Tektronix" means "back when the good scope weighed 100+ lbs and lived on a cart" I can see how a 12ft probe cable could be required from time to time.

[alm]

I remembered wrong, it was 3.3 ft, 6.6 ft and 9.9 ft (aka 1 m / 2 m / 3 m): https://w140.com/tekwiki/images/f/f4/P6101.pdf

[David Hess]

Tektronix did not make a whole lot of x1 only probes.  In 1984, so well into the integrated circuits age:

P6101   1.0M   32.0pF   34.0MHz
P6101   2.0M   54.0pF   15.5MHz
P6101   3.0M   78.0pF   08.0MHz

P6028   03.5ft   050.0pF   17.0MHz
P6028   06.0ft   067.0pF   10.0MHz
P6028   09.0ft   090.0pF   07.0MHz
P6028   12.0ft   112.0pF   04.0MHz

Switched x1/x10 probes were even slower for the same length when set to x1.

[jasonRF]

I realize this is an old thread.  But for kicks was looking at fixed x1 probes on Digikey.  Cal Test makes a couple

ge2501, 1.2m, 45pF, 55 MHz
ge2502, 2m, 65pF, 35 MHz

I believe the capacitances assume scope input is 1MOhm//13pF, so the 13pF is included in those numbers.  They each run about $30.  I realize that circuit loading could of course be an issue with these, but I’m tempted to try one out.   Anyone have experience with them? 

Jason

Update: picked up the ge2501 in my last digikey order.   Using a tinySA transmitter, 50 Ohm pass-through and the supplied probe-tip-to-BNC adapter, I find that I get about 35 MHz 3-dB bandwidth.   At 55 MHz it was more like 6 dB down.   This was measured by my Picoscope 5244B 200 MHz scope with nominal 1 M Ohm||13 pF input - just what the probe was designed for.  I like the probe but it will have niche uses.

[vk6zgo]

A 12-foot oscilloscope probe?? 

Even 6-foot is pretty darn long.

Some Techs use a 'scope for any voltage they are looking for, instead of swapping back & forth to a DMM, so a lot of the time it will be used just to see if say, a DC supply voltage is present, in which case, frequency response is immaterial.
If they are looking at a large, rack based or standalone unit, the long probe lead may be very handy.
As always, use the appropriate length lead, (or find a workaround).