diy IF transformers: first attempt.

[Amie]

Good explanation but unfortuantely the probe tip capacitance doesn't directly scale with attenuation.  This is mainly due to the capacitance of the probe cable. A x10 probe usually presents 8 to 10pF at the tip. x100 probes (which are quite rare and often expensive) can get down to 2pF or so. Active FET probes can go even lower but they are electrically fragile and horribly expensive.

The capacitance at the tip of a x1 probe is often about 100pF, again mainly due to the cable. For almost all purposes x1 (and switchable x1/x10) probes should be banned. Nasty things that will mislead those who don't understand.

I'd thought I had got my head round the early anomalous results I was getting.... But of course I hadn't.

If.... I'd have simply measured the capacitance of the probes the penny would have dropped. I spent some time yesterday trying to arrange a local oscillator coil, but getting nowhere with the practical testing then turned the scope off in disgust and stuck the results into an online calculator to check my maths. The error was consistent.

I've now measured the probes.

I know he doesn't need it from me, but to validate Jeffrey....
Basic ×1 probe = 103pF
Switchable ×1-10 probe =  15pF × 10  1nanofarad ×1 

The technique with the axial chokes is valid, but be careful with the test and measurements.....

Going to go away now and take up crochet.

Amie.