It's normal for power to deflect downward on AM during modulation. You have to have a peak reading wattmeter to see the peaks..... Sounds like you have good modulation.
With an average-reading wattmeter, theoretically the power should shift upwards 50% with 100% modulation with a sinewave tone. An rf ammeter in line should kick upwards about 22%. A field strength meter should show no change, since it reads average voltage output.
With voice modulation, the upward shift in power will be much less, since the duty cycle of a voice signal is much less than that of a pure sine wave. The rf ammeter will show little, if any deflection with voice modulation. Whistle into the mic or play some music, and the meters will show more positive deflection.
If the carrier level (field strength) meter, rf ammeter or wattmeter show any downward deflection during modulation (voice, tone or music), something is wrong. The transmitter is showing poor modulation linearity.
There may be a slight downward shift in carrier strength due to less than perfect voltage regulation of the power supply, especially with plate modulation. This should be no more than 5 percent. The power and rf line current should still kick upwards.
Don K4KYV
