[Elecraft] K2 RF board part C72 Identity

[G3VVT at aol.com]

In a message dated 23/01/05 12:19:41 GMT Standard Time,  
johnlon at sbcglobal.net writes:

The  really confusing aspect of it all is a 270 pfd capacitor 
should be  labelled "271", so you have the case where something marked 
"270" isn't a  270 pfd capacitor.


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The problem with marking small capacitors is providing the value on them so  
that it is more easily readable. What the manufacturers of the bulk of the  
capacitors now used by Elecraft is that the last digit of the three  provided is 
the multiplier. This is just the same as with resistor color  codes.
 
Following this a capacitor marked 271 is 27 with a multiplier of 10 = 270  pF 
(27 x 10 = 270). For a 27pF capacitor this would be marked  270 = 27 with a 
multiplier of 1. (27 x 1 = 27)
This can be useful when higher values of capacitor are used. For example  
0.1uF = 100nF = 100,000pF and would be marked 104. This is 10 with a  multiplier 
of 10,000 (10 x 10000 = 100,000pF).
 
After a while reading the capacitor values becomes automatic just as one  
learns to read the resistor color code. Not really sure which way I read the  
values of resistors, but suspect I look at the last digit first to see the  
multiplier and then the value within that multiplier. Now do the same with the  
capacitors that Elecraft use.
 
The problem arises with this capacitor marking system with values below  10pF 
cannot be accommodated and manufacturers either resort to just providing  the 
value direct or adding a *p* where the decimal point should be. Philips use  
the *p* or the *n* for marking their capacitors. This means a 2.7pF  capacitor 
would be marked 2p7 and a 0.1uF or 100nF capacitor would be marked  100n.To 
be sure I check all the values of the capacitors in doubt with the  capacitance 
measuring facility in my DVM. A large proportion of the DVM seem to  have 
this facility provided even down to the low cost versions and at  least my $50 
DVM will measure down to single digit pF values with reasonable  accuracy.
 
Bob, G3VVT