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AM-10HD / Aug 2008
A M - 1 0 H D G U I
Output Mode
Mono – The two analog outputs are independent and labeled
Analog 1 and Analog 2. In this mode both transmitter outputs have
their own LF Tilt and HF Correct equalizers available, as well as their
own phase inverting controls. Note that the Positive Modulation (see
below) control is common to both outputs.
Stereo – The two outputs of the analog processing chain are Left
and Right channels. There is one output control that sets both channels
simultaneously and there is also just one set of LF Tilt and HF
Correction equalizers and one phase inverter control.
Stereo MS – The two outputs are designated as Sum (L+R)
and Diff (L‑R). There is one output control that sets both chan‑
nels simultaneously and also just one set of LF Tilt and HF
Correction equalizers. This mode is useful for the C‑Quam AM
stereo system, noting that the operator will need to manually
reduce negative modulation to the ‑75% maximum required by
the C‑Quam system. There is only one phase inverter control
available in this output mode.
Positive Modulation
This control adjusts the asymmetry allowed within the mul‑
tiband limiter and the distortion‑masked clipper. The amount of
positive modulation permitted can be adjusted from 100% up to
the 200% limit of the positive modulation control. Peak control
in both polarities is very good at all settings.
The AM‑10HD’s AM mode is capable of providing very
dense modulation up to the 200% (yes, we said 200%!) limit of
its Positive Modulation (Asymmetry) control.
We equipped the AM‑10HD with this capability because (1) not every country
in the world is bound by the United States’ 125% positive modulation limit and (2)
the detectors within the AM‑10HD’s unique multiband limiter allows this magnitude
of asymmetry.
Caveat #1:
We would be remiss if we didn’t mention that unless the transmitter
is either (1) a grossly over designed plate modulated rig, or (2) is of very recent
design and has one of the newer modulation schemes and the power supply and
the RF power stages have the required headroom, positive modulation above
100% should be approached with caution. Trying to force an “inadequate” AM
transmitter to modulate above 100% in the positive direction may cause adjacent
channel interference at the least and possibly expensive transmitter damage at
the other extreme.
Remember also that the Positive Modulation control affects all output channels
simultaneously, regardless of the output configuration!
Caveat #2:
The AM‑10HD’s analog output amplifiers have a maximum peak output
level capability of +24dBu. This means that if you wish to operate with the Posi
‑
tive Modulation control cranked all the way up to 200% then the transmitter input
level required for 100% modulation must be no more than +18.0dBu or there will
be insufficient headroom in the AM‑10HD’s output amplifiers to accommodate the
