Duncan Munro wrote:
On Wed, 24 Nov 2004 20:57:59 +0000, Ian White, G3SEK wrote:

Plugging the number of turns, diameter and length into the usual formula
suggests inductances of less than 0.1uH, even for the larger ones. This
means they have inductive reactances rising up to about 10 ohms at
30MHz.

Ian, I've just measured a couple of resistors bought as spares for the
FL-2100Z, 33 ohm 3W metal film used as a grid stopper, and 22 ohm 3W metal
oxide used on the anode, again as a suppressor, with a coil wound round it
(both of the originals were carbon).

The metal film 33R measures 6.5uH and the oxide 22R measures 4.5uH on the
aade.com meter. Both values (if the readings are correct) would represent
a high ratio of X to R at HF frequencies...

I have quite a surplus of them, so if you wish I can send one of each in
the mail for you to check on your VNA.

Those values seem surprisingly high, so yes, please do and I will
measure them.

Based on the standard inductance formula (and there seems no reason why
that shouldn't apply in this case) it would seem to require very large
numbers of turns to achieve 1uH.

My posting was based on the ones I scraped the paint off in pre-VNA
days, so it would be useful to collect more data on typical 'coil'
dimensions and numbers of turns, together with the actual effective
inductances.


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