[hpsdr] ALEX - Non Linear Capacitors

[Hollingsworth, Tommy]

 Team:
Graham Haddock supplied links to curves on several NIC capacitor types.  I
felt from the conversations that followed that some people really did not
get a good understanding of the phenomenon involved.  Below is a link that
has a detailed description of the issues and what you can conclude from
them.  For those of you who already know this, please just ignore it.

http://my.execpc.com/~endlr/ceramic.html

In addition to this I wanted to point out that all components suffer from
these same anomolies to some degree.  Beginners should be aware that
resistors also have a voltage coefficient of resistance.  

The rate of change in resistance value per 1 volt in the prescribed voltage
range is expressed by the following formula:
VCR (ppm/V) = (R0-R)/ R0 X 1/(V0-V) X 106
* R: Measured resistance (Ω) at base voltage
* R0: Measured resistance (Ω) at upper voltage
* V: Base voltage
* V0: Upper voltage

This is mostly a concern in high resistance value and high applied voltage
applications.  In addition most resistors have parasitic values that cause
the resistance to drop at high frequencies.  The lower the resistance the
lower the drop.  In general for most SMT resistors:

Resistance		% Drop at 1 Gigahertz
10				2
100				5
1K				20
10K				50
100K				70
1Meg				80

This is valid for most inexpensive SMT resistors.  Some second generation
resistors are better, but you have to check each vendor for their curves.
There are many RF component manufacturers that have resistors that are flat
to 10 and even 100 Gigahertz.  BC Components is one vender that I have used
for termination resistors on high speed data links.  My bit error rates
dropped dramatically with a good RF termination resistor.  Do not forget
that many of the high speed data lines are operating at  RF frequencies
these days.  Please take my advice and never assume.  All vendors will give
you their curves.  Some make the data easy to find, others you have to ask,


73
Tommy Hollingsworth KE5LFR (currently awaiting KV5T assignment)


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