Re: [TCML] newbie question rsg

[Mddeming@xxxxxxx]

In a message dated 11/15/07 8:53:54 A.M. Eastern Standard Time,  
kc5gym@xxxxxxx writes:

if a  rotary spark gap is to allow the tank to charge at full potential of 
the  60 hz sine wave, then how does a spark gap of over 120 bps offer any  
advantage?

_______________________________________________


Dear KC5GYM,
 
   With an Asynchronous rotary gap, as the bps is increased,  you will reach 
points where occasionally there will be two charges/discharges of  the cap for 
a half cycle of the supply voltage. While these take place  at less than full 
voltage, two pulses per half cycle at say,  75% voltage,  will put more 
average power into the secondary than one pulse at full voltage.  At certain ratios 
of gap speed to line frequency, enough sub-optimal pulses  occur that there 
is an increase in the average power throughput to the streamer  per second. 
Added to this is the fact that a spark gap is not a precision  switching device. 
It's on and off times tend to wander slightly over the space  of a 
second,(heat, air currents, oxidation, residual ions, etc.) which is a  long time at TC 
frequencies. If this happens enough times per second, you get  some advantage 
from the more frequently recurring double pulses. The net  result will be 
occasional longer discharges, occurring somewhat less frequently.  Here again, we 
are talking "more and less" on very short time scales. Some folks  like it that 
way, some don't. If you look at the discharge frequency of a  static gap, you 
will find that its average is close to, but slightly  above line frequency. 
With a DC coil, of course, the pulses can be  fine-tuned with a variable speed 
gap to match the exact capacitor charging time,  and this is where, IMO, they 
are most useful. I believe that a majority of the  AC-powered coils that do 
use rotaries, use Synchronized ones.
 
Hope this helps,
 
Matt D.
 
"If two engineers agree, fire one of them - Don't pay twice for the same  
idea" 
--Old Bell Telephone Labs internal slogan



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