The TRS04VD is a transmit/receive control circuit designed primarily for use with vhf/uhf transverter or transceiver, power amplifier and mast mounted preamplifiers. Sequentially keyed outputs from the TRS04VD accurately control the timing of all system transmit/receive changeovers eliminating coaxial relay and preamplifier failure. Such failures are common in systems where all relays are keyed simultaneously. In these systems rf is applied while relay contacts are bouncing and not fully closed arcing the relay contacts and causing permanent damage. Also, if the relay is not fully closed, excessive power can be applied to the receive side of the relay causing preamplifier failure. Ruining a good coaxial relay and GaAsFET preamplifier can be an expensive proposition! The TRS04VD eliminates these problems by preventing the flow of rf until all system relays have had ample time to settle.
A timing diagram best illustrates the operation of the TRS04VD. Applying a control signal from the transceiver initiates the RX to TX transition. Eight milliseconds after the control signal is received by the TRS04VD, circuit A is activated - normally used to switch the mast mounted relay/preamplifier to the transmit position. Thirty milliseconds later circuit B is activated - normally used to remove cutoff bias from the high power amplifier. Thirty milliseconds after that circuit C is activated allowing the transverter to switch to the transmit mode. A fourth circuit, D, is provided for those systems that require the switching of an additional system component such as another relay or driver amplifier. TX to RX transition occurs when the control signal is removed and the whole sequence is reversed. Circuit D opens first, followed by C, B and A at 30 millisecond intervals. Since coaxial relays require from 10 - 25 milliseconds for complete contact closure the TRS04VD allows each relay to fully close before activating the following circuit. TRS04VD outputs are SPST reed relay contacts isolated from ground. Consequently, positive or negative polarity switching may be accomplished. Output A is a normally closed contact and outputs B, C and D are normally open. The reed relay contacts are rated for 10VA at 0.5 amp max./200V max. Optional normally open mercury wetted relays are available with a 25 VA at 1.0 amp max/1000V max. rating. TRS04VD is sold as an assembled and tested 2-1/2" X 3-1/2" circuit board module. Price $74.95.