by Adam M. Farson, VA7OJ/AB4OJ

In the course of using the Icom IC-781 HF transceiver, I have discovered two "hidden" features which are by-products of normal functions of the radio. The first of these is the ability to switch in the Audio Peak Filter in the LSB mode; the second is a means of temporarily restoring full IF bandwidth whilst Twin PBT is engaged, without disturbing Twin PBT settings.

1. The IC-781's APF (Audio Peak Filter) operates only in CW mode. However, it is sufficiently broad to be useful for cleaning up SSB audio without severe loss of fidelity. I have found that the APF can be enabled for LSB signals (not USB) as follows: Select CW WIDE, then offset the VFO by -800 Hz to tune in the LSB signal. Now press the APF button to enable the Audio Peak Filter, and tune the filter using the APF knob (concentric with the NOTCH knob) for best audio quality. TWIN PBT and NOTCH can be used in conjunction with APF, if desired.

To transmit LSB and receive with the APF enabled, set up VFO A as described above, and VFO B on the nominal receive frequency (without -800 Hz offset). Then press SPLIT. The radio will now transmit and receive LSB on the same carrier frequency. Example: To transmit and receive on 14180.00 MHz, tune VFO A to 14.179.20 CW WIDE and VFO B to 14.180.00 LSB.

Note that as the IC-781 demodulates the lower sideband in the CW mode, this feature will not work with USB signals.

2. To temporarily restore full IF bandwidth with one or both Twin PBT (Twin Passband Tuning) controls engaged, without disturbing the settings of these controls, simply press the XFC (Transmit Frequency Check) button. This permits easy "previewing" of the received signal with no bandwidth reduction.

If other IC-781 users have discovered interesting "tricks" that the radio can perform, please e-mail me.

Copyright  1994 - 2002 A. Farson VA7OJ/AB4OJ. All rights reserved.
Page last updated: 11/27/15

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