Transmit Receive Sequencer
Transmit/Receive Sequencer
Transmit/Receive Sequencer Connections
Sequencer Schematic* NEW
The station sequencer is a simple circuit that provides keying voltages for all station transmitters, as well as the antenna change-over relays and receiver muting circuits. A local or remote PTT switch is used to energize 120VAC and 12VDC outputs, as well as similar outputs with time-delayed deactivation. These outputs are used in conjunction with other interlock circuits to key the transmitter. The interlocks include contacts on the antenna change-over relays that disable these sequencer output voltages when the antenna relays are not yet fully picked up for transmit. The time-delayed outputs are used to provide proper operation when switching the transmitter state from transmit to standby.
The main antenna change-over relay is a large DPDT open frame relay. One relay pole is used to switch the antenna from transmitter to receiver inputs. A small auxiliary DPDT relay is used to apply ground to the receiver input when the main relay is energized (transmit). Contacts on each of the two relays are connected in series to provide the interlock signal to the sequencer. Both relays are mounted in an aluminum enclosure with SO-239 jacks for Antenna, Transmitter and Receiver connections.
Sequencer Inputs:
- 120VAC power in
- PTT 12VDC contact closure (local switch or remote)
- Antenna changeover relay interlock contact closure (closed for transmit).
Sequencer Outputs:
- 120VAC to antenna changeover relay coils (in transmit)
- 120VAC and 12VDC on transmit
- 120VAC and 12VDC on transmit with delayed deactivation (approx. 0.2 sec.)
The sequencer can be used to activate any of the station transmitters without rewiring. Separate switching would be needed to enable individual transmitters and switch the antenna to the active transmitter.
350W Class E Transmitter Sequencer Implementation
Sequencer/Antenna Relay Testing
Transmitter Keying Schematic* NEW
The sequencer is wired to provide TR switching for the 350W transmitter as follows.
120VAC transmit voltage (with delayed deactivation) is provided to the rf amplifier keying relay. This small relay has contacts to energize the driver power supply regulators and provide an output signal to the VFO PTT input (see rf amplifier details).
120VAC transmit voltage (No delayed deactivation) is routed to the PWM modulator via the VFO On interlock contact (provided by the VFO internal relay). This keying voltage is also sequenced by the modulator internal overload trip circuit on the efficiency meter board (see PWM modulator details). These interlocks prevent the modulator from energizing the TR relay in the absence of an active VFO or during an overload trip. This voltage also energizes a small modulator relay that activates the PWM pulse train.
12VDC transmit voltage (with delayed deactivation) is used to energize individual relays which mute the station receivers. This sequencer arrangement allows several active receivers to be connected to the antenna relay simultaneously. They are also protected by a grounded input when the sequencer is in transmit.
Information from WA1QIX on TR switching can be found in “The Transmit/Receive System”