[AMRadio] B&W 5100B

Donald Chester k4kyv at hotmail.com
Mon Oct 11 13:32:29 EDT 2004

>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.


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