I should have mentioned that this will work without a 50ohm load on the scope, with the normal 1Mohm input impedence the signal will need about x8 probe compensation - i.e. on x10 the signal will be a bit bigger than intended - but you could tthen add a series resistor on the probe output to scale it so you can use x10, I think off the top of my head you would need about 220k - but use a multiturn trimmer to find out then replace with surface mount fixed resistor. Of course not all probes wll be anything like the same!

I have been using the one with the multiple first stage capacitors with great results when probing VFO and VCO circuits. But, the first thing I did with mine was to encase it into a small aluminium tube from a chunky old Biro. Totally usable upto high 100s of MHz. For what they cost to purchase, they are a bit of a no brainer for anyone probing around RF circuits. Very interesting video. Also, I second the Diff probe design idea. Would make a nice development project. Karl

@MakeOrRepair

5 ай бұрын

It performed a lot better than I expected, handy as long as you don't expect too much, but given the price of a 2nd hand agilent probe, I'll also be putting it in a case and using it quite a lot.

Also... It would be very interesting, if you would do a DIY Diff Probe development project for us. I, for one, would be glad to build it out and test it. Something with decent performance, but at a much lower price point than a MicSig.

@MakeOrRepair

5 ай бұрын

I too have a diff probe project sitting on the shelf but if I recall I did something very wrong. I was aiming at a 1GHz x1/x10 probe (By which I mean gain) aimed only at low power circuits because at the time I was working on a lot of rf signal generators. It might resurface at some point but things are still disrupted by dealing with several bereavements last year, so for the moment only small jobs are getting done.

Good video. I'm surprised if capacitor measured 8pF at 10kHz and 2pF at 100kHz, FR4 dielectric constant does vary but shouldn't be much more than 10 or 20% I think. Maybe something else is having an effect. The main issue is losses in the FR4 once you get to 1GHz+.

@MakeOrRepair

5 ай бұрын

Yes, it was tricky to measure and i suspect that may be the reason for the big difference, although there is a bit of scope for inductance to fool the lcr calculation, I would have been better setting up a proper vna measurement but I was just curious.

As a coincidence, I am also revisiting a log-shelved diff probe project. An open source design offered by Linear Technologies, based on their LTC6268 op amp. These testing techniques will prove quite useful. Thank you. Are your DMM probes Probe Master 9000 series? If so, what do you think of them? If not, what are they and do you like them?

@BusyElectrons

6 ай бұрын

They appear to be the same ones I use (Pomona 6275). Pros: Very good for probing SMD (sharp tips, thin yet strong). Cons: Somewhat fragile leads; Handle gently.

@MakeOrRepair

6 ай бұрын

​@BusyElectrons yes, Pomona is the type. Very strong replacable sharp tips but light leads, the leads have not been a problem but after about 1 year of constant use I find the replaceable tips have worked slightly loose in the socket, they make good contact but when probing sockets the top sometimes gets pulled out.