The idea was to measure the coated resistor under exactly the same
conditions as the regular one, so couldn't you just use exactly the same
setup as before?

Roy Lewallen, W7EL

Ian White, G3SEK wrote:
Roy Lewallen wrote:

Ian, if it's not too much trouble, I'd be very interested in how the
measured inductance compares to that of the resistor body/leads only.
I'd think that could be done by coating a similar-size resistor with
conductive paint or foil and measuring with the same method. The
difference between this measurement and the one you made would then
show how much inductance is due to the spiral element, and would
represent the minimum possible inductance for that resistor body type
and lead length.

I could certainly do that, because Duncan has supplied pairs of
resistors: one in original condition, and the other with the coating
cleaned off, just ready for painting.

However, the difference in inductance is going to be very small, and I'd
need to build a test jig that can keep other stray inductances under
control.

Over the weekend, maybe...

Roy Lewallen wrote:
The idea was to measure the coated resistor under exactly the same
conditions as the regular one, so couldn't you just use exactly the
same setup as before?

Afraid not... In the present setup, the main contribution to the total
inductance comes from the long, floppy resistor wires, and I couldn't
guarantee not to disturb their configuration while applying conductive
paint to the resistor.

To get a reliable answer, I'd need to reduce the lead length and make
the whole thing mechanically more stable.


Ian White, G3SEK wrote:
Roy Lewallen wrote:

Ian, if it's not too much trouble, I'd be very interested in how the
measured inductance compares to that of the resistor body/leads only.
I'd think that could be done by coating a similar-size resistor with
conductive paint or foil and measuring with the same method. The
difference between this measurement and the one you made would then
show how much inductance is due to the spiral element, and would
represent the minimum possible inductance for that resistor body type


I could certainly do that, because Duncan has supplied pairs of
resistors: one in original condition, and the other with the coating
cleaned off, just ready for painting.
However, the difference in inductance is going to be very small, and
I'd need to build a test jig that can keep other stray inductances
under control.
Over the weekend, maybe...


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek