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Re: Frequency Counter

Subject:  Re: Frequency Counter
  Date:   Fri, 9 May 1997 11:02:44 -0500
  From:   "Robert W. Stephens" <rwstephens-at-headwaters-dot-com>
    To:   Tesla List <tesla-at-pupman-dot-com>


> Date:          Thu, 08 May 1997 01:21:43 -0500
> To:            tesla-at-poodle.pupman-dot-com
> Subject:       Frequency Counter
> From:          Tesla List <tesla-at-pupman-dot-com>

> Subject:   Frequency Counter
>   Date:    Thu, 8 May 1997 00:59:51 -0400 (EDT)
>   From:    SSNSanders-at-aol-dot-com
>     To:    Tesla-at-pupman-dot-com
> 
> 
> I bought a freq. counter from radio shack that seems to be a pretty good
> unit. It uses an antenna or a cable hookup and will check up to 1.3 Ghz.
> Not
> very expensive and so far functions well on plasma globes and induction
> coils. I have yet to try it on a Tesla coil but I just finished up my
> medium
> size coil tonight and will fire it up tomorrow if I can get the RQ gap
> to
> fire. I can stick a large screwdriver into the gap and get it to fire
> but its
> too close to be if it throws an arc so Im going to try to rig a trigger
>  voltage setup.     Stephen Sanders
> 
> 
Stephen,

I don't recall where this thread started but I wish to comment.

Electronic frequency counters rely on a precision timing circuit opening
a gate 
and then counting the number of input cycles of the waveform being 
measured during the precise time the gate is open to give an answer.
For this answer to be correct the input 
wave being sampled has to exist as a continuous CW waveform.  Tesla 
coils are disrupted wave devices.  They bang a few potent RF cycles 
of ringing at the RF resonant frequency and then shut down for long 
periods of time in between bursts.  An ordinary frequency counter will
not 
read correctly under these conditions.  Best instrument here is a 
'Wavemeter'.  These are basically a hi-Q tuneable tank circuit 
(tuning fork) which can be made to ring when excited by a RF pulse 
train, continuous or not, at the frequency to which they are tuned.  
A mechanical dial pre-calibrated at the factory then tells you the 
frequency, you just tune the dial like tuning a radio receiver and 
peak up on the highest meter reading.  If you do not have a wavemeter 
you can use a communications receiver with the RF gain turned way 
down low and a very short, or no antenna wire connected.  A portable 
battery operated receiver is best as it cannot be confused by RFI on 
the local AC mains which will also be there from the Tesla coil 
device.

I was actually stumped by this for a while when a quality frequency 
counter refused to read the operating frequency of a vacuum tube TC
a long time ago.  I figured this out when I realized that the 
oscillator was off more than 50% of the time during the negative 
swing of the 60 Hz mains and there were no RF cycles for the 
frequency counter to count while it's gate was open.

Hope this helps someone.

rwstephens