This system may be used to protect any transceiver and any external amplifier from damage due to high s.w.r. operation. You can reduce replacement costs and increase your rig's operating life.
A long with the fun of operating a modern transceiver, one often experiences the following troubles with the power amplifier stage.

● When operation is attempted with a high s.w.r., damage often occurs to the loading padder capacitors. This can happen even when the transmitter is operated for only a second; for example, if a few dits are accidentally keyed into the wrong antenna. The problem is especially serious when the transmitter is equipped with broadband circuits.
● When tetrode tubes are used, there is a special problem. Under high s.w.r. conditions, or during tune-up while loading adjustments are being made, the screen current often rises far beyond the maximum allowable limit. This causes tube failure, internal arcing, and driver and power supply damage.
● Even under normal operation into a proper load, there is often a spike in the r.f. output, occuring at the beginning of a transmission, which causes arcing in the PA circuit components. This arcing can cause burnt contacts in the bandswitch, requiring extensive repairs.

● When used as a driver for a linear amplifier, the amplifier relay is often slower than the transceiver circuits. This means that while the amplifier is switching, the transceiver operates into an open circuit, causing all the above problems associated with high s.w.r. This problem is especially likely to occur when the transceiver incorporates break-in.

System Performance
With this system, the transceiver may be used with any antenna, or even no antenna (signal reports may be low!), with no damage to the radio, in either the broadband or the manual mode. It allows on-the-air operation with high s.w.r., at automatically reduced input. Tuning is greatly simplified; instead of the usual method of gradually increasing the drive while constantly monitoring the screen current and adjusting the loading, the drive may be turned up and the PA controls quickly adjusted for maximum output, while the new circuit automatically keeps the screen current under control.
This system, while developed for the Signal/One CX7, will function as well in any modern transceiver. The circuits shown need no changes; the installation and connection to the existing transceiver circuitry will of course be adapted to the particular model.

The system is presently in use in more than a dozen transceivers, with uniformly excellent results.

Theory of Operation

The system consists of the following three components:

● A d.c. amplifier added to the a.l.c. circuits.
● An r.f. level detector added to the power amplifier manual and broadband tuning capacitors.

● An r.f. level detector added to the power amplifier manual and broadband loading capacitor

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High S.W.R. protection for transceivers and amplifiers

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