None of these apply!
All these resistors are meant to do is lower the Q of the suppressor
inductance and dissipate the harmonic energy involved. Their stability is of
no concern, since the circuit is not so critical as some believe.
On the other hand, composition resistors have the lowest parasitic
inductance of the generally available resistors and this is definitely an
important characteristic, since this inductance can easily hamper proper
suppressor operation.
BTW, your inductance measurement is off: a piece of wire one inch long is
approximately 25-30 nH, not 2-3nH. You have to add it to the resistor's
inductance. You simply can't connect it with zero length wire!
Alex 4Z5KS
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
Behalf Of Steve Thompson
Sent: Tuesday, July 27, 2010 8:36 AM
To: amps@contesting.com
Subject: Re: [Amps] More parasitic choke questions
> It does seem though as
> if the preferred carbon composition resistors are no longer easily found.
What is preferred about carbon comp? Given the heat and the need
for long term stability in value they're the least suitable
component you could choose.
Some years ago I measured some different suppressors(results in a
posting on 30 Aug 06), subsequently I swapped the carbon comp
resistors for MOX on a couple of them, and couldn't measure the
difference. Whenever I measure 2 or 3W MOX resistors in the 20-100
ohms range, the inductance is in the regions of 2-3nH, which has
minimal impact in a suppressor. Inductance is higher in the 5W
ones I've tried.
Steve
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