09-02-2021, 05:34 PM
In many applications at anything more than pretty low frequencies the capacitance of a scope probe usually matters more than the resistance. The 40k source should keep the loading on the circuit pretty low.
If your scope has enough sensitivity you might like to try a low resistance passive probe. This is often a 4k7 resistor soldered directly to the point under test, with the signal fed back to the scope via 50R co-ax and terminated in 50R at the scope. This method works well to beyond 1GHz and is excellent for probing high speed logic. Of course you're getting 100:1 attenuation. If you can stand even more attenuation than that you can use higher value resistors. There's no point in going that high resistance for very high frequencies but it might just give a good result in your application.
If your scope has enough sensitivity you might like to try a low resistance passive probe. This is often a 4k7 resistor soldered directly to the point under test, with the signal fed back to the scope via 50R co-ax and terminated in 50R at the scope. This method works well to beyond 1GHz and is excellent for probing high speed logic. Of course you're getting 100:1 attenuation. If you can stand even more attenuation than that you can use higher value resistors. There's no point in going that high resistance for very high frequencies but it might just give a good result in your application.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
