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Re: Unexplained arcing current

Hi Gary,

	Hmmmmmmm....  I "thought" I had it figured out...

I have suspected that some resistors have poor high frequency
characteristics that contribute to heating.  But you are using low
inductance types that I assume have good high frequency performance.
Probably ceramic cores with a thick film resistive past that is similar to
those used in water cooled high power RF loads.  You resistors are probably
still perfectly good at high frequencies...  I doubt if very high frequency
noise is causing the problem but...

If you have a MicroSim model (the *.sch file) for your circuit I would like
you to send it to me at terrellf-at-uswest-dot-net so I can check it out.  We
really need to get to the bottom of this problem.  Many people have
reported this unusual heating but apparently the cause is still a mystery.
It does not seem to affect my system but it does others.  Something is
going on here I don't think we understand...

I will visit your web site tonight to get as much info on your components
as I can.  I would be especially curious as to what type of gap are you
using.  Your page mentions two.  I wonder if the heating changes with the
type of gap used?

Cheers,

	Terry


At 04:19 PM 5/23/99 -0400, you wrote:
>Hi Terry:
>
>I ran a simulation on my system, observing the current through the series
>resistors.  I did observe the large current spikes each time the gap
>closed, close to 2 Amps.  This was due to the charge in the bypass caps
>being dumped into the series resistors.  The magnitude of the spikes were
>the same regardless of the bypass cap value, and this makes sense.  The
>initial magnitude of the spike is just a function of the bypass cap
>voltage divided by the resistor value.  The duration of the spikes were
>related to the cap value, of course.
>
>But this additional power burned in the resistors due to the bypass caps
>discharging is not that much, since the pulse widths are so brief.  The
>RMS current through the resistors was just over 100 mA, pretty much
>regardless of reasonable bypass cap values.
>
>On your model, I get an RMS current through RF2 of between 75-90mA with
>your 2700pF bypass cap.  Changing the cap to 0.27pF reduced the current
>only slightly.
>
>I don't think this explains my heating observation.  
>
>Regards, Gary Lau
>Waltham, MA USA
>
>
snip.....