[Elecraft] K2 Resistor Question...

[David F. Reed]

David,

I am not sure how best to put this...

Imagine you put a resistor of infinite value in parallel with your 100 
ohm resistor and measured it at the ends of the 100 ohm resistor; of 
course, you would see the 100 ohms; what if the two resistors were 100 
ohms each? well, being in parallel, you would see 50 ohms; if you put a 
0 ohm resistor in parallel with the 100 ohm, what would you see?

so anything with some resistance to it, a resistor, a trace, a relay 
coil, will affect the resistance you measure.

A nice mental exercise you can do with a handful of resistors is to tack 
solder them together into a  cube, and start measuring across different 
points; maybe even make it simple, and do just a square first (4 
resistors); you might start to develop some intuition about how this 
works. try it with same value resistors first...

I think you will find your resistors are fine; when you get to a test 
sequence in the manual, you will see they tell you what to look for in 
resistance that is quite different and that this intuition gained will 
help you feel more comfortable.

Alternatively, if you are more accustomed to math, you might just learn 
some of the associated applications of Ohm's law, or do both what the 
heck...

dking at vcn.com wrote:
> R6 and R8 are both listed as 100 ohm resistors (BRN-BLK-BRN), but 
> after installation, both show 61.6 ohms on three different 
> DMM's..while R7 which is a 68 ohm resistor is showing 50.1
>
> I recognize all of them read slightly lower than their "listed" 
> values...but these seemed at such wide variance I didn't want to 
> continue until I knew whether I should be replacing them or not.
>
> These three resistors all form a U around relay K12...so I didn't know 
> if the relay would be sucking down my readings...but I'm placing the 
> probe on the resistor wire on either side of the body of the 
> resistor...so I can't see how something else could be causing that 
> great of a difference....

the rest of the circuit that is in parallel with the resistor is 
responsible for that variation.

> Another identical 100 ohm resister still in the paper ladder to be 
> installed later in the sequence is giving me a 97 ohm reading...
>

And if you removed the ones you already soldered in, they would measure 
close to the same 100 ohms (or 97 in your case.

> Any advice would be appreciated.
>
> David King
> KE7EKA
> K2 #6048 


73 de Dave, W5SV