RF Ping

[Carter Shore]

Using the knock sensor as a 'microphone', connect an
audio spectrum analyzer. Run the motor without knock
as a baseline, recording the output. Now induce the
knock, and record the output. There will probably be
several spikes due to the knock. Choose the strongest
spike (frequency) that is distinct from the rest of
the normal engine noise. That is the one that you want
to keep, filtering out everything else.

Don't have an audio spectrum anaylyzer laying around?
There is off the shelf PC software that will use a
sound card to perform exactly that function.

Now, as for modifying the ESC to filter out everything
else, I cannot help. You could build an external
filter with an op-amp and some precision resistors and
caps. 

If you knew what frequency the ESC was currently tuned
for, you could:
1) Have an oscillator running at the old frequency
which would be triggered by in-band signals at the new
frequency, feeding the ESC.
2) Calculate the frequency difference, then inject and
mix the IF with the knock sensor to produce in-band
signals at the old frequency (superheterodyne anyone?)

OK, OK, you get the idea, I'm laughing too hard now to
continue ....



--- Dave Zug <dzug at delanet.com> wrote:
> 
> > since the ESC filters out everything except the
> specific frequency of 
> > signal it wants, unless the RFI was at the knock
> frequency, it would either 
> > do nothing, or maybe reduce sensitivity.
> 
> and not all knock sensors are tuned for the same
> frequency correct?  
> I get barely any knock on a boosted 5.7l with a
> stock prom and 89 
> octane ..I'm wondering if the new alum heads require
> a different 
> frequency detection range ?
>  
> ~~~
> Dave Z. www.delanet.com/~tgp
> 

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