Summer 2004 Issue

The JWM Engineering SEQ-1.

Recently, JWM Engineering Group introduced the Model SEQ-1 Microprocessor-Controlled Transmit/Receive Sequencer, which maximizes flexibility and safety with programmable time-delay values (http:// jwmeng.com/seq1.html). The SEQ-1 is the first microprocessor-controlled sequencer on the market to provide one “heartbeat” and four visual outputs for confirmation of operation and the ability to program a variable time delay value for the control outputs.

The one-second heartbeat indicator verifies proper operation and provides an error status during the programming phase. The four status LEDs provide visual indication of the sequence and step operation.

“Today’s transverters use very low-noise front ends for the best possible signal-to-noise ratio, but low-noise front ends will not survive the high transmit power levels found in most competitive transverter systems,” said Jerry Mulchin, N7EME, President of JWM Engineering Group. “The solution is sequencing. Controlling the power-on sequence and transmit-receive changeover time will minimize or eliminate damage to the receiver circuits,” Mulchin concluded.

In addition, normal relay contact bounce found in every RF antenna changeover relay can induce unwanted transients that could damage sensitive devices in the receive chain.

The transmit-receive sequence can be initiated with either Low-Enable (ground to transmit) or High-Enable (positive voltage to transmit) input. The High-Enable input requires a positive input voltage from 2.0 volts to 14 volts.

The SEQ-1 provides four sequenced, open-collector outputs to control system switching. Open-collector outputs enable direct control of relay coils. Each output is capable of switching up to 35 volts at 600 mA continuously. Also provided is the ability to invert the active output state of any of the four outputs.

The SEQ-1 time-delay values default to 32 milliseconds for each step, but are programmable from 4 milliseconds to 128 milliseconds per step. This allows the user to fine-tune the delay time for the environment being controlled. For example, if RF switching is all solid-state using PIN diodes, then a small time-delay value would be appropriate. If circuits use electro-mechanical relays, a longer time delay would be required to allow contacts to settle.
 

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