SEQUENCER IZ6NNH

Per questo articolo in Italiano lo puoi scaricare facendo click qui –> manuale
Per l’app SequencerQT di configurazione / for SequencerQT configuration application –> Windows: SequencerQT
STM32 MCU firmware complete source code, Licence GNU GPL V2.0 –> sequencer_qt_fw

1. Introduction

A radio sequencer, often referred to as a PTT sequencer, is an electronic device designed to manage in a safe
and orderly manner the activation and deactivation of the various pieces of equipment connected to a radio station,
especially when using LNAs (Low Noise Amplifiers) and PAs (Power Amplifiers).

1.1 Why It Is Needed

During transmission or reception, the various units of the RF chain must be powered on and off in a precise order
to avoid damage:

In reception:
1. First, the LNA must be enabled and powered to amplify weak received signals.
2. The PA must remain turned off to avoid injecting RF power into the chain.
In transmission:
1. The LNA must be switched off first (if left connected, it risks being destroyed by high RF power).
2. Then the antenna is switched and the PA is enabled.
3. Finally, the radio can be switched to TX.

If the sequence were incorrect, for example with the PA enabled while the LNA is still connected,
the LNA would receive the full transmitter power and be damaged immediately.

1.2 What the Sequencer Does

The sequencer automates this process. It receives a PTT command from the radio and activates a series of outputs
with programmable delays in order to respect the correct activation sequence. At the end, it releases the PTT
towards the radio.

Example – TX sequence:

Disables the LNA by removing its power supply
Depending on the station configuration, switches the antenna relay towards the PA
Enables the PA for transmission
Finally enables the radio PTT

Return to RX sequence:

Releases the radio PTT
Turns off the PA
Switches the antenna relay back to the receiver
Re-enables the LNA

2. The “Sequencer IZ6NNH”

This sequencer was developed out of the need for a reliable unit to be used in the radio station of
Papadopol Lucian-Ioan IZ6NNH, as well as during portable V/UHF contest activities together with
my friend Germano Gabucci IK6FHG.
The original idea and the definition of the main features were suggested by Costantino Cerrotta IC8TEM.

2.1 Features

The sequencer is implemented as an electronic board measuring 50×105 mm, equipped with four 3.3 mm mounting
holes located at the four corners.

The board communicates with a PC via a USB connection. The USB connector mounted on the board is of the Mini-USB type,
chosen as a good compromise between compact size and mechanical robustness.

Connections for PTT input/output, audio signals, and LNA power supply are provided via 2.54 mm pin headers.
These can be used either by directly soldering wires or by using female “Dupont” connectors.

2.2 Functionalities

The sequencer offers the following functionalities:

Power supply from USB or stand-alone operation using a +12/24 V external supply
Two PTT lines active to ground, with 3 V bias and maximum 10 mA, suitable for microphone and foot-switch PTT
Third PTT line driven by the RTS signal of the serial interface
Three sequentially activated outputs
Programmable activation delays for the three outputs
ON/OFF controlled LNA power supply with programmable delay
Integrated audio interface with isolation transformers,
balanced audio input and output, 600 Ohm impedance

2.3 Connection Diagram

For wiring and connections, refer to the following diagram.

2.4 Connection Characteristics

Input / Output	Characteristics	Signal Type	Function
Audio IN	600 Ohm balanced	Audio modulation 100 Hz–3 kHz	Audio from radio
Audio OUT	600 Ohm balanced	Audio modulation 100 Hz–3 kHz	Audio to radio
PTT IN I–II	3 V bias, 10 mA	Active when pulled to ground	User TX request
RTS	LVTTL (UART)	Active low	PC TX control
PTT OUT I–II–III	Closes to ground when active	Digital control	PA and radio TX activation
+12–24V IN	DC max 24 V	DC	Main power input
LNA Supply	Same voltage as input	DC 12–24 V, max 1 A	LNA power supply

Each unit is individually tested, also under load.
To simulate the LNA, a 100 Ohm load resistor is powered with an input voltage of 13.8 V.

2.4.1 Schematic

This is the electronic schematic of the sequencer itself at the newest release, with an accessory UART port added, nothing revolutionary compared to the first revision.
You cannot copy it to make your own sequencer and sell it, this schematic, this post, the source code of the firmware are provided with different licenses, ask me at l.i.papadopol@gmail.com prior to talk with my legal assistants. You can copy to make your own sequencer IF AND ONLY IF for your personal use and for learning.
PDF of the schematic is here –> schema_elettrico

2.5 Delays and Programming Software

The four programmable delays are:

Delay A: from pressing the physical PTT or RTS line, and LNA power-off,
to activation of PTT Out I
Delay B: from activation of PTT Out I to activation of PTT Out II
Delay C: from activation of PTT Out II to activation of PTT Out III
LNA ON Delay: from releasing the physical PTT or RTS line to re-enabling LNA power

The following oscillograms show example measurements with A=20 ms, B=20 ms,
C=20 ms, and LNA_ON_DELAY=100 ms.

Yellow trace: PTT Out I. Pink trace: PTT Out II. Light blue trace: PTT Out III. We can see that, following the activation of any PTT In, the sequence of the three delayed activations is executed correctly. Releasing the PTT immediately brings all three PTT Out lines to the deactivated state simultaneously.

In this image we can see that there is an actual 100 ms delay before the LNA power supply is re-enabled.

Here it can be seen that delay A spans from the moment the PTT is pressed and the LNA power supply is switched off to the activation of PTT Out I.

Delays can be programmed using the SequencerQT application available for Windows and Linux.
The software is distributed as a ZIP archive containing the “SequencerQT” folder.
Simply extract it to any location (e.g. Documents or Desktop) and launch sequencer_qt.exe.

Fields A, B, C, and LNA_ON_DELAY contain delay values in milliseconds
At startup, ensure the sequencer is connected via USB and identify its COM port
Select the correct COM port
Press Read to retrieve current values from the sequencer
Modify the delays and press Write to save them
Values are stored in non-volatile memory and persist after power-off
Exit closes the application

2.6 RTS PTT Usage with WSJT-X & Command Line Interface

The sequencer can be controlled by WSJT-X and similar software.
Typically, it is sufficient to select the correct COM port and enable “PTT via RTS” in the software.

The sequencer also provides a command-line interface via a serial terminal.
By connecting to the sequencer COM port at 115200 baud, it is possible to configure, read,
and reset the device.

Warning:
When using the serial command-line interface, disconnect the sequencer from connected equipment,
as the serial communication activates the RTS line!