Oscilloscope

[Matt_Rowe]

Here you can download service manual for Hitachi V-202F in case you need some more insight or repair.

http://ftb.ko4bb.com/getsimple/index...ipment/Hitachi

hank you
T

[green]

I've been using a Rigol DS1052E. Don't know how it compares with other scopes in it's price range. Works for me. Have used analog and digital scopes at work. One advantage of a digital scope, can see the whole trace when looking at longer record times(looking at integrator noise with 500ms or 1second/division as an example). Analog scope with persistence would work also. I haven't seen a disadvantage using my digital scope playing with metal detector circuits.

Digital scopes can alias. If trace doesn't make sense, change the time base to see if trace changes.

I've been seeing oscillation around 500kHz at amplifier out. Shows better with input shorted(no coil pickup noise). Tried to find why yesterday. Still had oscillation with scope probe and ground lead connected to scope common. Oscillation is 100MHz with low time base. Aliases to about 500kHz when time base is long enough.

[Matt_Rowe]

Im at the point now of tired of asking ebay sellers why they say their scopes are tested but they have no leads or probes, then i ask to hook them up with a probe to the cal test clip and get me a picture of the square wave at .5 volt so i can see it, then they say they cant do that, so i tell them i wont buy it then. They are just selling stuff they get from yard sales or goodwill, and they say tested but doesnt even come with a power cord, i can get a brand new pc scope from amazon as i said in first post for $58 dollars, free shipping, a warranty, and includes cords and probes,and there are youtube videos of people with reviews and peo-le using them for a reference and i get a manual, and i downloaded the full manual already.

[WM6]

..... why they say their scopes are tested but they have no leads or probes, ....

They drop it to 3 years old grandson to play with buttons and switches for some days.

So it is thoroughly tested. They use leads or probes to build baby swing, so its gone.

..... i can get a brand new pc scope from amazon as i said in first post for $58 dollars, free shipping, ....

Here small one, no need PC, but all MD module testing check you need, can be done, even on terrain without all in-house EMI.

For 57 euro is available as DIY kit (all delicate parts already soldered), fully assembled one is about 80 euro.

You even get two channel signal generator with it, for (par example) XY check, without additional AWG:

https://www.banggood.com/Original-JY...r_warehouse=CZ

[Old cart]

I've been seeing oscillation around 500kHz at amplifier out. Shows better with input shorted(no coil pickup noise). Tried to find why yesterday. Still had oscillation with scope probe and ground lead connected to scope common. Oscillation is 100MHz with low time base. Aliases to about 500kHz when time base is long enough.

This is common mode noise probably being picked up in the probe ground lead. It could be coming from a local radio station or other HF appliance in or near the house.
Assuming you are using a scope probe connected directly to your DUT, try using a shorter ground lead. Also try the 20MHz limit on the scope.

[green]

This is common mode noise probably being picked up in the probe ground lead. It could be coming from a local radio station or other HF appliance in or near the house.
Assuming you are using a scope probe connected directly to your DUT, try using a shorter ground lead. Also try the 20MHz limit on the scope.

Not sure what causes the 100MHz. Did a scope calibration and think the 100MHz amplitude reduced in half(should have stored before and after but didn't). Just tried looking at it again. Still have the 100MHz. Scope still aliases down to about 500kHz. Don't need more than 20MHz, so turning 20MHz limit on is probably a good idea. Wondering why I see 100MHz when the scope is rated 50MHz.

See the 100MHz with shorted probe touching scope common also, doesn't need to touch detector circuit. 20MHz limit reduces signal but doesn't eliminate it.

[Old cart]

I tried to respond to this before with a long wordy answer. It somehow got lost in hyperspace.��

Rather than repeat it here I will simply link a couple of documents that will help those that need help understanding the in and outs.
The first one is a compilation of Tektronix documents. Very good, lots of reading but worth your effort to learn the basics.

https://www.testequity.com/tektronix-xyzs-oscilloscopes
this discusses most everything you need to know to make the best use of any oscilloscope.


If you don’t have a scope it gives good hints as to how to select one.
If you do follow through the doc with your scope hooked up to a Calibrator output on the scope.

[Old cart]

Not sure what causes the 100MHz. Did a scope calibration and think the 100MHz amplitude reduced in half(should have stored before and after but didn't). Just tried looking at it again. Still have the 100MHz. Scope still aliases down to about 500kHz. Don't need more than 20MHz, so turning 20MHz limit on is probably a good idea. Wondering why I see 100MHz when the scope is rated 50MHz.

See the 100MHz with shorted probe touching scope common also, doesn't need to touch detector circuit. 20MHz limit reduces signal but doesn't eliminate it.

It is likely a local FM around 104 Mhz station. Even though the scope has bandwidth of 50 MHz the roll of is not brick wall. Since this same model is offered in high bandwidths they likely just limit it to 50 MHz with a single cap so it will only be down about 9dB at 100 MHz. Slowing the sweep speed does NOT reduce the bandwidth. Because it reduces only the sample rate it just introduces false aliases into the signal caused by UNDER sampling the signal fewer than 2 times per cycle. See post 82 for more detail.
Shorting the probe tip to the ground lead still has a short unshielded wire which acts as an antenna. Try removing the probe tip and see if you can short between the tip itself and the ground point on the probe. Better yet if you have a BNC shorting cap put that on the input of the scope or otherwise short from the BNC center to the outer ring with an exacto knife or similar.
If you still see the 100 MHz if could be.
1. Poor common mode rejection of the input amp.
2. Poorly shielded probe cable.
3. Conducted emissions entering via the power cable.
4. Internal oscillations or noise pickup within the scope.

For a Pi you should always leave the bandwidth limiter on.

[Matt_Rowe]

Thanks wm6 and old cart, i download the pdf from the website on basics, looking for the scope in usa now wm6

[green]

It is likely a local FM around 104 Mhz station. Even though the scope has bandwidth of 50 MHz the roll of is not brick wall. Since this same model is offered in high bandwidths they likely just limit it to 50 MHz with a single cap so it will only be down about 9dB at 100 MHz. Slowing the sweep speed does NOT reduce the bandwidth. Because it reduces only the sample rate it just introduces false aliases into the signal caused by UNDER sampling the signal fewer than 2 times per cycle. See post 82 for more detail.
Shorting the probe tip to the ground lead still has a short unshielded wire which acts as an antenna. Try removing the probe tip and see if you can short between the tip itself and the ground point on the probe. Better yet if you have a BNC shorting cap put that on the input of the scope or otherwise short from the BNC center to the outer ring with an exacto knife or similar.
If you still see the 100 MHz if could be.
1. Poor common mode rejection of the input amp.
2. Poorly shielded probe cable.
3. Conducted emissions entering via the power cable.
4. Internal oscillations or noise pickup within the scope.

For a Pi you should always leave the bandwidth limiter on.

Don't see the oscillation when I short the probe with the ground lead. Need to touch the shorted probe to scope ground to see about 2mV p-p oscillation at about 100MHz. There is a 100.5MHz FM station in the area, not sure where the antenna is located. 100.5MHz aliasing at 500kHz would match what I see.

The problem started when I saw 500kHz at amplifier out. 500kHz at amplifier out is possible. 100MHz when scope is switched to shorter time base at amplifier out not likely. Wondering why.

[Old cart]

What ground, the PI ground? That is not really ground, that is an antenna!
To be fair even earth ground is not really a good ground. Earth ground is there for safety purposes, not EMI reduction.
While ferrite beads on the leads properly applied may reduce this interference the best solution would be differential amp with high CMRR at high frequencies. Such a solution, while available, is very expensive.

One solution you could try, which will probably not work, is to use pseudo differential.
Ideally you use 2 x1 probes or possibly 2 pieces of coax with BNC's on one end and bare leads on the other. Solder the cable shields together at the DUT end and apply the signal between probe ch1 and probe channel 2. GROUND IS NOT USED at the probe end. Bandwidth limit BOTH scope channels. Put the scope in add and invert mode so the trace display is CH1-Ch2. you may find, if your signal is repetitive, that signal averaging will help.

One last alternative is to repeat the above with Z0 probes. to do this you must have the scope inputs terminated into 50ohms. The easiest way to do this if the scope does not have 50 ohm selection is to use BNC terminators.
DIY z0 probes are shown here:

http://paulorenato.com/index.php/ele...the-lo-z-probe

[green]

What ground, the PI ground? That is not really ground, that is an antenna!


Don't need to connect shorted probe to PI circuit. Connecting shorted probe to scope ground is all that's needed(scope calibration common terminal, scope input common at scope as examples). Now that I know it's there I can live with it but would like to know why and if the 100.5MHz FM station is the source. Before I found the 100MHz I was spending a lot of time trying to figure out where the 500kHz was coming from.

[WM6]

DIY z0 probes are shown here:

http://paulorenato.com/index.php/ele...the-lo-z-probe

Hi Old cart,

Assume that blog from above link is yours.

Nice journey trough your creativity on those site.

Great knowledge and commendable willingness to share ideas with others.

Unfortunately all photos / illustrations on some project pages disappeared already.

Like here:

http://paulorenato.com/index.php/ele...ligator-probes

and here:

http://paulorenato.com/index.php/ele...ht-multimeters

Is this photo vanishing reversible?

[Old cart]

Hi Old cart,

Assume that blog from above link is yours.

Nice journey trough your creativity on those site.

Great knowledge and commendable willingness to share ideas with others.

Unfortunately all photos / illustrations on some project pages disappeared already.

Like here:

http://paulorenato.com/index.php/ele...ligator-probes

and here:

http://paulorenato.com/index.php/ele...ht-multimeters

Is this photo vanishing reversible?

Sorrythat is Not my site or blog. I just found the link and it was good for the z0 probe so I provided it.

[Old cart]

Green sorry the response is the same. The scope chassis is not super quiet.
Try this. Connect a 36" piece of wire to the probe center conductor and place it well away from any device , including the scope, does the noise increase? Also try the other solutions. The Z0 probe may well work because it has a low input impedance. It does require that your device be able to drive a 450 ohm load though.