Topband: beverage termination

Brad Rehm brehm at
Thu Dec 15 15:58:57 EST 2005

"Anybody out there ever think of using spark plug wires
as beverage termination resistors? I just measured one
about 12 inches long and checked in at 590 ohms. Certainly
more weather-worthy than a 2-Watt Carbon.....
"Mike WA3TTS"


This is an interesting idea, but there are some problems with it.  With the
cooperation of my favorite auto parts emporium, I've measured the resistance
of every brand of plug wire they had on the shelf--several of 'em.  The
resistance of 18-inch hunks of this wire varied from a few thousand Ohms to
as much as 40k Ohms.  It's surprising, at first, that ignition systems will
tolerate this range of resistances and still work properly.  A these
voltages and currents, though, resistance actually doesn't matter.  It's
only important that the wires have enough resistance to reduce the rise time
of the spark current when a plug fires.  This is why some wires are much
better than others for reducing radio noise.

So it could be tough to find two wires of the same resistance, and if you
tried to cut the longer wires, you would run into the problem of how to
terminate them.  These "wires" usually use some kind of cloth fiber that is
impregnated with carbon.  You would probably have to use those little brass
clips we used to be able to buy at every auto parts store (but can't any
more).  So there would be reliability problems because of the terminations.

I'd also wonder about the current ratings of the wires.  The peak spark
currents are high, but they're nothing like the long-duration ground
currents that can develop during a lightning strike.  I didn't terminate my
Beverages with single 2 Watt resistors.  I used four or five in parallel for
each antenna.

Brad KV5V

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