TX/RX SEQUENCER LDMOS SDR LPF


TX/RX SEQUENCER LDMOS SDR LPF

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TX/RX SEQUENCER LDMOS SDR LPF:
$30.00


TX/RX SEQUENCER

Generating precise timedsequence signal upon transition from

receive to transmit and viceversa


1 Description

The sequencer has 3 input sources: PTT, ERROR and RESET. PTT is theinput which need to be asserted when transmission should start. When PTT is pulled low the sequencer startsthe predefined timed sequence of activating the 3 outputs: RADIO PTT, PA ENABLEand TX/RX. Subsequently if PTT is released the sequence will be halted and

reversed. An ERROR input is providedto signal an ERROR situation to the sequencer,for instance this can be a high SWR situation or a separate signal fromthe TX/RX coaxswitch that this switch is for sure in the TX position. To resumenormal operation when this ERROR has occurred the sequencer should be reset viapulling the RESET input low or via a full power cycle.

The 3 output signals are used to signal the transceiver between receiveand transmit state (RADIO PTT), togglingthe external power amplifier (PA ENABLE) and commanding the transmit/receive RFswitch (TX/RX).

Inputs are high impedance and active state (TX , RESET or ERROR active) is low/ground. Outputs are open drain active low signals, pulling theoutput low/ to ground when in TX position. In additions 3 LED’s can beconnected (anode to output, cathode to ground) for state indication.

1.1 Use and connecting

SSB operation

PTT input will be connected to a footswitch or microphone switch.Microphone element connected to the radio in the normal manor. VOX should beswitched off. When PTT is asserted the sequence is started (see chapter 1.2 fordetailed information on the

sequences).

CW operation

To be able to use this sequencer for CW operation the radio should beable to work in no “break-in” or vox mode, i.e. upon activating the CW KEYinput of the radio it should NOT go into transmit (preferable only sidetoneshould be activated). A separate radio PTT input must be available forcommanding the radio to go into transmit and only then RF

power should be output following the CW KEY input. In addition the CWkeyer should provide an outgoing PTT signal (low active) signaling start of CWmessage with sufficient “tail/hang” time such it wouldn’t go inactive betweenCW characters. For instance the Winkey device from k1el is perfectlysuited. CW output of the keyer needs tobe connected to the KEY input of the radio and PTT keyer output to the PTTinput of the sequencer. When PTT is asserted (start of CW) the sequence is started.

For both mode of operation a DC power supply should be connected and ifapplicable 3 LED’s can be connected toprovide an indication if the corresponding output is active. These LED’s shouldbe connected with the anode to the pin and cathode to ground.

1.2 “Go to RX” and “Go to TX” Sequences:

During receive when PTT is brought LOW the “go to TX” sequence willstart and will continue as long as PTT is LOW. In case PTT goes inactive duringthe sequence the “go to TX” sequence will be stopped immediately and revertedonwards.



Go to TX sequence:


When transmitting and PTT is released the “go to RX” sequence will startand will continue as long as PTT is released. In case PTT goes active duringthe sequence the “go to RX” sequence will be stopped and the “go to TX”sequence is started onwards.






4 Design implementation

CAD developed using Eagle 5.6. Board is double clad FR4 with componentsilkscreen. For a good RF immunity the top plane is almost fully copper/ground.Inputs are well decoupled, but for optimal RF immunity it is advised to mountthe PCB in a shielded box and use small valued (100pF) feedthrough capacitors.


TX/RX SEQUENCER LDMOS SDR LPF:
$30.00

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