[RFI] Touch Light Update #3

Jon Ogden Jon Ogden <jon.ogden@cain-forlaw.com>
Tue, 26 Jun 2001 10:23:11 -0500


> 	Have you tried a "micro" Henry choke on the sense line? 
>  Something
> from 1-10 micro Henries is what is recommended.  I don't 
> think the resistor
> is really needed since this is a very low current application 
> (high current
> would be bad for the human contact!).  

No I have not.  I had assumed that the sense line wrapped around the torroid
would end up looking similar to using a choke in series in the line.
Perhaps I am mistaken.  Ten turns of the wire around an FT-50B-77 (half inch
torroid using the 77 material) didn't do much to solve the problem.  Maybe
it's not the same as a choke actually in series with the line.

>> So far, I have found no good way to RF bypass the sensing 
>>line.  What I want to do is basically shunt all HF energy to ground on
that 
>>line, but I can't load down the line otherwise the sensing circuitry won't
help.
>  
> 	Perhaps you could use a capacitor to pass the 14Mhz on 
> the hood to
> ground while, at the right value could look like a higher 
> reactance to the
> sensing line's capacitance.  Cap of 0.01 microF would give 
> 1.1 ohms at 14
> Mhz & 93 ohms at 170Khz.  So connect the cap to the hood 
> somewhere or at a
> couple of places, then gorund the other end of the cap(s).

Tried that.  The .01 uF cap prevents things from working correctly. That's
93 Ohms at 170 KHz and I think that it pulls the circuit to ground too much.
I think a much, much smaller cap will need to be used.
> 
> 	The problem is that the sensing line is operating on a
> "Change-of-Capacitance" to change the operating state.  The 
> 14Mhz bypass to
> ground might desense the "sensing line" enough to kill it.  I 
> think that's
> what you've found already.  So we're back to getting the RF 
> choke right.
> This all depends alot on the free running oscillator's 
> operating frequency.
> Is it spec'ed anywhere?

Exactly.  No, I don't have a spec on the oscillator frequency.  I think I
will finally puy my O-scope to a useful purpose and try to measure it.  Then
I can try to make some useful sense out of things.  

UGH!  There has got to be a solution though.  So close!

73,

Jon
NA9D

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