[ARC5] Resistor Excursions

[Jacques Fortin]

I agree with Richard comments.
I also measured a lot of CC resistors with Impedance Analyser equipment and I do not agree with what KB8TQ states.
The CC resistors turns capacitive at high frequency and the phase angle do not stay close to 0 degree (they did not stay "resistive").
Depending on the part value, it progresses thru -90 degrees when the frequency increases.
Those who are sceptical about this should take a look at the Allen Bradley resistors catalog for the year 1994.
The behavior of CF, MF and MOF resistors is better, as they stay purely resistive way higher in frequency than the CC.
Test wise, a MF resistor does not exhibit more inductance at RF frequencies than the equivalent length of straight wire.

73, Jacques, VE2JFE in Montreal

What is the source of your information?  I have measured many CC resistors using a Boonton RX-Meter and found they become more reactive at RF. While many think film resistors become inductive I have not found that true. Curiously enough the examples in the Boonton handbook show the same thing.
I was taught the same thing about CC resistors but it seems not to be true.

Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998

On 4/19/2024 4:23 PM, Bob kb8tq wrote:
> Hi
> 
> If you *do* decide to replace CC’s with a different type of resistors, do a deep dive into just how weird CC’s are at RF. Unlike pretty much all other resistors, they drop value, but stay resistive as frequency goes up. While that sounds a lot like a resistor model that includes a cap, it’s not. The phase shift with “pure resistive” is not the same ….
> 
> How much does this matter? It very much depends on how tricky the circuit happens to be. In many cases … not a big deal.
> 
> Bob
> 

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