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TX/RX sequencer

Proper changing from receive to transmit operation is vital for the receive pre-amplifiers as well as the used coax relays. Especially it becomes important with 1 Kilowatt power levels, mistakes will almost certain mean the immediate death of the pre-amplifier! To prevent including sequence control circuitry in every amplifier a standalone sequencer has built.


3 level sequence. Multi level sequence is needed to make sure all parts of the TX and RX chain are switched in a well manor

Stable timing. This seems straightforward, but most of the existing designs use analog or discrete components for timing. This leads to variations in the timing as a result of temperature of power supply voltage change. This design uses a crystal oscillator as the timing element and is virtual 100% stable.

Flexible timing. Although the basic timing is hard coded in the microprocessor firmware (could be changed easily with a new firmware update) the break-in time for CW can be set by a 16 step switch from the outside.

Multiple outputs. As we envisage using this sequencer also with multiply antenna/transmitter systems most of the sequenced output are more than once available. Multiply outputs are isolated from each other to prevent unwanted interaction.

Winkey ready. Sequencer is optimal when used with a CW interface such as Winkey. For that reason a Winkey circuit is fitted in the box. At the moment a Winkey version 10 is used including the serial connection toward the host computer for control.

Detailed timing description

Sequencer consists of 3 functional blocks and winkey as an internal module:

Input provides I/O to external CW in, Winkey CW in, external PTT in and Winkey PTT in. The controller Block is sampling those signals and generates the correct timing before output the signal to CW out, PTT out, PA out and Coax out.

SSB Timing

Sequence Diagram (13K)

Upon activating the footswitch, first the coax relais and pre-amplifier will be switched on. Secondly the power amplifier will be enabled and the transceiver will be PTT-ed.

CW timing, with Winkey

Sequence Diagram cw winkey (5K)

Due to the internal timing of Winkey, it will first activate the (internal) Winkey PTT. This will trigger the sequence. After a (configurable in Winkey) time the actual CW will be transmitted. This has one big advantage that no "first" letter of CW is missed as will be the case when using an external CW-keyer.

CW timing, external (non Winkey) keyer.

Sequence Diagram cw external (6K)

As soon as CW is detected the sequence will be triggered. Sequence will be stopped i.e. go to receive when during a certain amount of time no CW input is detected (T-hold). This time can be set via the "Hold switch". As can been see the first part of the CW will not be aired, because the PTT transceiver needs to be hold of for the power amplifier and coax relais circuits are settled.

Tune timing

Sequence Diagram tune (4K)

To be able to tune the e.g. the amplifier in a save way a tune mode is available. Upon applying the tune button the correct sequence will be initiated and a CW signal (continues key down) is output. Off course the transceiver should be in CW mode for proper function.

External input and outputs

CW in. Main CW signal from an external keyer. Internal the Winkey CW is connected separate.

Footswitch PTT. Main PTT input used in SSB operation. Normally this is connected to a footswitch PTT paddle. Use in CW for overriding the "hold time" and setting the transceiver in "transmit" preventing excessive switching in low speed operation.

CW out. Main CW going to the CW input of the transceiver. As this has the same timing as the CW input, it is vital hat the transceiver should be switched to NO-Break in operation i.e. the transceiver should NOT transmit RF when CW input is activated. Normally only the side tone will be heard.

PTT out (2).Main PTT towards the transceiver. This will signal the transceiver to go into transmit mode and generate SSB or CW modulated RF.

PA out (5). These 5 separate outputs will set the power amplifier(s) in transmit operation.

Coax out (2).These 2 output are controlling the coax relay i.e. the final relay just before the antenna system where also the receive pre-amplifier is connected.


CW hold time.This control will set the CW hold time

Tune.Will generate a CW key down situation

Speed.Set Winkey speed

Circuit description

Open circuit diagram as .pdf in new browser window

On the left are the active low outputs. For the Coax relays outputs (2) and the Power amplifier outputs (5) high current FET's are used, capable of sinking large current in excess of 1A. CW and PTT output (2 each) are comfigured around medium current FET's. Sinking current is approx. 100 mA each. Outputs are driven by a 89C2051 microprocessor with on chip ram and flash program memory. All timing is derived from the stable crystal oscillator. Inputs from the Winkey module, footswitch and tune are level shifted to +5V/GND by the NPN- transistors. Small signal diodes are added to accommodate a wide range of input signals. Inputs are active low. Hold time can be adjusted by the binary switch encoder and read in realtime by the microprocessor. Circuit is completed with some LED's indicated the state of the sequencer. Sequencer is power by an external poweradapter in the range of +12VDC. Current drain is approx… mA. Sequencer firmware was developed in C. Source code is compiled with the (freeware) Keil compiler. TX/RX timing is fixed within the source code, but can be easily adapted for other values.