I used to use the non-inductive resistive T pads between the T4 and amp
(a tetrode amp--low drive). Also used that for a little QRP. But
recently have been really loving the Anaren monolithic 50 ohm
attenuators. They can be had in many ratings and values. I use 10dB
100W. Mounted on a heat sink, small fan if you really want to, and they
are magic. Super small also. 1/2" x 3/4 by about 3/16 thick. You can
often find them on the e&*y for cheap.
Light bulbs are usable but they change value as they light up. 50 ohm
dummy loads work too but if you connect an antenna to it with a T, the
impedance that the Tx sees is now only 25ohms.
I used the Anaren unit to get the TR7 down into the 50mW range last year
for the SKCC QRP challenge--lowest cumulative power used to work all
districts with bonus for HI and AK. My cum was way less than 5W and I
managed AK with 75mW. And all the 10 continentals were non-scheduled.
Measurement becomes a bit of an issue below a few watts.
Have fun! Happy Holidays!
FWIW
Curt
KU8L.
On 12/17/2011 12:41 PM, Don Cunningham wrote:
Ron,
I would think that the only "reliable" way to accomplish QRP with the
Drake rigs (assuming the 4 line tube rigs mostly) would be to build up
a good transmitting attenuator pad and "use up" the wattage in that
pad. Many examples can be found in old Johnson literature designed to
let their many transmitters feed the "kilowatt desk" amp they built.
I'm planning to do that to feed some of my transmitters into my Alpha
amp which needs a low drive level. You do need to watch for
"overshoot" upon initial keying, I am told in some literature.
Otherwise, the old dummy load (light bulb if you want to see your
keying) on the end of a coax "tee", then use the small sampling used
normally to "see" the signal on an oscilloscope, might be just enough
power to suit your needs. Either way "wastes" the power, but could
heat and briefly light your shack, hi hi. (Tongue firmly in cheek).
73,
Don, WB5HAK
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