Ummm ... several reasons. Resistance component of an incandescent bulb
impedance varies with the temperature [brightness] of the filament.
They are also somewhat reactive. Push-pull vacuum tubes and link
coupling didn't care about SWR, I don't even remember the term in the
ham lexicon until the Pi-network and 50 ohm output was invented.
They're also not very good at the "dummy" part. N6BT, of Force 12 fame,
is fairly famous for his "phased illuminator," 3 300 watt bulbs mounted
on his deck railing in a V arrangement on which he worked all
continents. More than once I made contacts while using a 100 watt bulb
as my dummy load.
If you're going to use the paralleled metal film resistor construction
method, be sure to keep the resistor leads short and spaced them from
each other. Lead inductance will start to become a factor on 6 m and
up. I built mine with 40 2K 2W resistors and it works find at 100W if
used intermittently. It's air cooled. Don't know how much putting it
in oil would improve the dissipation.
73,
Fred K6DGW
- Northern California Contest Club
- CU in the 50th Running of the Cal QSO Party 3-4 Oct 2015
- www.cqp.org
On Mar 25, 2015, at 14:25, Bob Gibson via Elecraft <[email protected]>
wrote:
HOW ABOUT A LAMP WITH 100 WATT BLUB, THATS ALL US OLD GUYS HAD! 73s Bob W5RG
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