[AMRadio] Side band power with increased carrier/was

[D. Chester]

Some of this seems like a long round about way to travel a short distance. 
Here's the way I have explained it many times to SSBers who are trying for 
the first time to set their  rigs and amps properly for AM.  Works every 
time, if followed exactly.

First, put the rig in CW or TUNE mode, and run the carrier wide open to 
maximum output.  Note the DC current to the final and  rf output.  That 
tells you the maximum PEP output that the rig is capable of running. 
Typically, 100 watts. Now switch to AM mode, and adjust the carrier to about 
25% the maximum output as noted above.  The DC current to the final should 
run close to 50% the figure noted above. Now start speaking into the mic, 
and check the envelope pattern on the scope if you have one, and adjust the 
modulation for 100% without overmodulating in the negative direction or 
flat-topping on positive peaks.

If you don't have a scope, set the carrier to 25% of max, as explained 
above.  Now begin modulating.  Advance  the audio gain until the DC final 
meter just begins to wiggle.  It must not significantly increase or decrease 
in average reading while talking. That should get it close to 100% 
modulation.  Back off the drive to JUST BELOW the point where the ALC begins 
to be tickled.  You DO NOT want the ALC to activate on voice peaks, but 
adjust it until even a slight increase in output level does begin to hit the 
ALC.

Many of the present day  rigs will automatically adjust when simply 
switching to AM mode.

Once you are sure the exciter is working properly on AM,  note all the 
settings, so they can be reproduced easily.

Now fire up the amplifier.  Tune up in normal tune mode, as with SSB.  Again 
drive with full, unmodulated carrier to maximum output, noting meter 
readings of DC to the final and rf output.  Careful! don't over heat the 
final.  Keep the test transmission short, a few seconds max, and allow  the 
tubes to cool down between tests.  Once you have established  the maximum 
output (right at the point where any further increase in rf drive no longer 
produces any increase in rf output), again note the meter readings and rf 
output. Check the tuning and loading to make sure the rf output is right at 
maximum.

Now switch the exciter to AM mode.  Without changing any of the amplifier 
tuning settings, adjust the rf output from the exciter so that the amplifier 
is running 25% of maximum, as described above. The optimum settings for 
"barefoot" operation may not be the same as for the amplifier; this may 
drive the amp too hard, in which case  the exciter must be re-tuned for less 
output @ 100% modulation.

When modulating, the DC to the final should slightly wiggle at most, with no 
significant increase or decrease in plate or anode current.  Note the 
unmodulated rf carrier output and DC input to the final.  The carrier output 
should be somewhere about 1/3 the DC input in watts.  Again, make sure the 
ALC is never even tickled on voice peaks, but any slight increase in drive 
to the amp DOES cause the ALC to activate. As before, the carrier out should 
be about 25% of the maximum dead carrier key-down output.  Make sure the 
plate dissipation of the tubes (DC input - rf output, watts) does not exceed 
the tube manufacturer's rating. The average rf output should just kick up 
slightly under modulation.  It should NEVER deflect downwards while 
speaking.

On-the-air reports may require slight variations in the adjustments for best 
signal.  Again, the best indicator is to monitor with an oscilloscope in 
envelope pattern mode.  I don't think many ricebox manufacturers any longer 
make monitor scopes to go with their rigs (apparently not enough of to-day's 
appliance operators are interested enough in learning  how to use one, so 
there was no longer a demand for the product), but a good used scope made 
for an older rig, or a bench scope properly set up is well worth the trouble 
and expense.

To me, operating phone without a monitor scope is like driving on a country 
road at night with the headlights turned off.

Good luck.

Don k4kyv
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This message was typed using the DVORAK keyboard layout.

http://www.mwbrooks.com/dvorak/
http://gigliwood.com/abcd/