Hi All,
If I may, I'd like to start a "philosophical" thread which arises
from:
i) many of us home-brewing amps
ii) tuning with a string of high-speed (i.e. high-speed
compared to the time constants of our meters) vs.
key-down, vs. whistling or saying "hoooooooola" into
the microphone.
iii) our desire to remain legal.
Here's the situation: (non-US hams, please fill in the appropriate
numbers)
Suppose I tune my home-brew amp to put out the US allowed
maximum of 1500W under key-down conditions. My HV drops from say
3200V (key up) to 3000V (key down). Now if I send CW, my HV doesn't
drop quite as far, so I'm probably putting out more power, say 1600W
for the sake of the example. If I transmit SSB, the HV dops even
less, and I'll actually be putting out maybe 1700W PEP.
Now if I'm able to monitor my output signal with a good oscilloscope,
(and my antenna represents a pure resistive load whose value I know
accurately, but let's not go there right now) then I can just turn
down my drive a bit, and stay legal. The burden of staying below
1500W PEP output power is on me, the designer, builder,
owner-operator of the amp. But suppose I don't have a sure-fire, lab
quality means of measuring my true PEP under all conditions (FM, CW,
SSB, AM etc.) How can I be sure I get maximum output and still
comply? Well, I can tune with a string of fast dits. But the
problem (of exceeding 1500W PEP) still remains; it's just different
in magnitude.
But wait! It doesn't have to be a HB amp! What if I own one of many
1500W output commercially available, type-approved, amplifiers? I
still have the same problem(s)! How does, say, Alpha Power, (to take
a high-quality example) make sure that no more than 1500W goes out?
Did they have to do that to get US FCC type acceptance? How much
"overhead," i.e. how much more than 1500W PEP does the FCC consider
compliant? Are high speed dits satisfactory? Do the manuals include
this as a tuning method? Should they?
These questions came to me in an RF-induced dream after a recent
contest. Maybe I should post this to an FCC part97 reflector! 8>)
All responses are welcome!
73,
George T. Daughters, K6GT
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