VHF Twist-Shift Keying Rotation-Shift Keying Orthogonal BPSK Twist Modulation Motorola SyntorX

Posted on Feb 5, 2014

The material in this section shows how we built the Twist-Shift system for VHF using commonly available (and cheap) surplus land mobile VHF transceivers modified to operate on the 2-meter ham band. The radios we used were the 100-watt Motorola SyntorX model. The radios were additionally modified for the Twist-Shift experiments as described below.

VHF Twist-Shift Keying Rotation-Shift Keying Orthogonal BPSK Twist Modulation Motorola SyntorX
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This section also describes the auxiliary circuitry needed to implement the system and the test setup for the experiments we ran to prove that the concept works and to quantify just how well it works. This page describes the VHF Twist-Shift Keying setup using the SyntorX radios. The material is presented, not as a hard and fast specification of equipment and circuitry, but as an example of how Twist-Shift can be implemented. A method for driving the transmitting antenna elements `in quadrature`, that is, with two precisely synchronized sources of RF energy offset in phase by 90 degrees. A dual synchronized receiving system that provides separate paths for the orthogonal signals picked off from the receiving antenna. Synchronization requires that injection sources for all mixers in the system be driven from a common source. The receiving system must also be "normalized", that is, the two signal paths must be brought back into zero-degree phase synchronicity. The cross-polarized antennas we used for feasability testing are shown here. They consist simply of two j-pole type elements cut for a resonant frequency of 146 MHz mounted orthogonally. The transmit antenna was suspended from the rafters of an outbuilding on my property 50 meters distant from my shop where an identical receive antenna was likewise suspended from the ceiling. Calculated path loss from the transmit end to the receive end was 50 dB. Later, the j-pole...

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