On Wed, 10 Mar 2004 16:59:43 +0100, Toni wrote:

En nick smith va escriure en Wed, 10 Mar 2004 15:38:45 -0000:

To stop the arcing, why not put a condenser across
the points, like on my old Morris Minor contact breaker points ?

Kevin
i
M3 TW T

Not that bad an idea. Had already thought so for a rotable 10/15
rigid dipole. With a 15 pF capacitor / short at 50% on each leg
you get both a good 10 and 15 meters dipole with a little (very
little) extra gain for 10 meters. Operation voltage on capacitor
with 100W is only 170V - No arcing. SWR is about 2 for 28-30 and
1.7 for 15m


(Sorry - couldn't resist that)

(Sorry I couldn't resist either)

Toni - EA3FYA

(I can resist it)

Hi All,

The reason for the condenser in the breakers contacts was to RESONATE
the system so that current dumped through the (this time I will call
it by its more modern name) capacitor. Given this dump was a damped
one cycle wave (the spark current) it both enhanced the boost to the
ignition coil and opened the circuit effectively in the DC path. If
you chose the wrong value, it snubbed the spark and eroded the contact
faces: in other words, worse than useless.

You should take stock of the terms RESONATE and DC, two situations
that are antithetical to the application. If you want to open an AC
circuit path, the addition of this capacitor is counter-intuitive. It
is also a tuning complexity: too big a value, it makes the switch
useless; too small a value, it retains the arc potential. Any value,
it causes a shift of the operating frequency - you are back in trap
city, without the necessary inductor, with an added switch, and
nothing seems to be gained.

Much simpler to not key-down while changing the switch.

73's
Richard Clark, KB7QHC