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AM-55 / Sep 2015
A M - 5 5 G U I
4. Turn on the AM‑55 test oscillator Tilt Test by clicking its check box. Using an
oscilloscope connected to a low level RF sample of the transmitter output observe
the resulting RF waveform. It should appear like waveform A or waveform C below,
or somewhere in between the two exteremes, depending on the response flatness of
the transmitter’s low frequency performance.
5.
If the response of the transmitter does not resemble Figure C, alternatively adjust
the LF Tilt EQ’s F(Frequqncy), Q (Bandwidth) and L (Level) controls in order to
achieve the flattest top and bottom of the waveform. It is not recommended to run
older transmitters that cannot be fully corrected with gross amounts of final clipping
or bass equalization. Doing so can cause stress on internal components and lead to
failure (or worse).
HF Correction
The performance of all AM transmission systems is constrained to varying degrees by
less than infinite bandwidth. Whether or not this limited bandwidth creates a modulation
control problem at high frequencies is usually a matter of degree.
Many transmitter/antenna system combinations will not require correction in their
High frequency overshoot response. However, if the transmitter is operating into a fairly
high ‑Q antenna system or common point, then some correction of the overall response at
high frequencies may be beneficial.
When bandwidth restrictions cause modulation overshoot, the best way to minimize it
is to (1) reduce the bandwidth of the signal entering the transmission system, (2) reduce
the rise time of the waveforms exiting the audio processor, or (3) a combination of both.
