[sdiy] TB-303 smps interference

[Neil Johnson]

Hi,

cheater00  wrote:
> I've improvised a small E/H field probe. It's made from one strand of
> UTP cable (with stranded core, not wire), and one of those rings that
> stay on the neck of a water bottle when you remove the cap. About 40
> turns all around (I think the cable was ~50 cm).

Umm, that's neither an E nor an H field probe.  That's a toroid.  Not
very good at picking up external magnetic fields (that's why toroidal
mains transformers are preferred as they have very low magnetic
leakage).  You're most likely seeing signals picked up by parasitic
inductance and/or capacitance - where is the termination resistor?

H-field probe construction looks like this:

http://www.compliance-club.com/archive/old_archive/030718.htm

And E-field probes look like this:

http://books.google.co.uk/books?id=tpwrKfeyEV8C&pg=PA139&lpg=PA139&dq=e+field+probe+construction&source=bl&ots=Su4tHzfAk5&sig=GVGsWWsvq-u-OlkvzBPbIU8XORo&hl=en&sa=X&ei=D4CSUqf8NJKJhQeKjoGoAw&ved=0CDEQ6AEwAg#v=onepage&q=e%20field%20probe%20construction&f=false

Cheers,
Neil
--
http://www.njohnson.co.uk