[Central-Electronics] 100V Power Control, was Vintage Ham Shack for Sale - Includes 100V

[Radra]

Hi Jim,

Thought I would take another quick look at the 100V as it won't be around
here much longer.

Output power can be adjusted via front panel controls in two places: the
audio/modulator circuits (i.e. CW, AM, SPEECH LEVEL) and just prior to the
first mixer (i.e. POWER CONTROL). I think a typical user would set the POWER
CONTROL to maximum and adjust the other controls to their proper values.
>From that point forward, changes to the desired power output level would be
made by adjusting only the POWER CONTROL.

I found the adjustment range of the POWER CONTROL to be about 17 dB at 80 m
and about 15 dB at 10 m. This means you can reduce output power by  factors
of about 50 and 33 at 80 m and 10 m respectively. That range should be more
than adequate for most situations.

The POWER CONTROL adjusts all power output, including modulation, desired or
residual carrier, hum, noise, etc. thus maintaining the initial
signal-to-carrier ratio. Too high an adjustment of the SPEECH LEVEL control
was observed to degrade the sideband-to-suppressed carrier ratio when in SSB
mode.

Since the POWER CONTROL does not impact the sideband-to-suppressed carrier
ratio, it is reasonable to assume the residual RF carrier I observe on the
spectrum analyzer [and that measured by the front panel meter when in used
to display the null depth] when in SSB mode is being generated within the
modulator itself. The panel meter does properly display the nulled carrier
level but I question the calibration of the null scale e.g. -20 to -70 dB.
The question relates to what carrier level is referenced, meaning what
carrier level is equal to 0 dB. I suspect the designer was referencing the
level of the CW carrier at maximum output. If that is the case, then the
meter calibration makes sense.

Thus when I observe the suppressed carrier to be only 45 dB below the
sideband, perhaps I should have noted that the suppressed carrier level is
about 60 dB below the maximum CW output level. I should also point out that
the sideband level I used as a reference is variable since by increasing the
audio input level or SPEECH LEVEL setting, a larger value of sideband can
then serve as a reference resulting in a larger suppression number.

Also took a quick look at audio linearity and found the 3 dB compression
range to be a quite respectable 70 dB at 2 kHz.

I hope the foregoing clarifies this matter. It is not well written as I am
anxious to go outdoors to enjoy our fine Sunday weather.

Lyman K7LH