HFpager Demo

A tool for text message radio communication via IFSK modulation on HF using low power (QRP).

This application together with HF radio will ensure a possibility to transmit text messages on low frequency HF radio bands 1.8-7 MHz at a distance up to 300 km (~200 miles) using powers lower than 5 Watt without blind spots in the NVIS (near vertical incident sky-wave) mode of radiation.

Such a significant reserve (usual transceivers can provide a power up to 100 Watt) in radiated power allow to use text communications with pedestrian portable or mobile operators in the field conditions. In places without cell coverage it could be the most optimal mean of regular and rapid communication for travelers, fishermen, hunters, forest rangers, geologists, and other professions.

Using HFPager you can send short by important messages:

- We arrived to the cabin, everything is in place;

- Start in the morning to the base, next communication in a day;

- Let us know when the next delivery is planned;

- Here are coordinates of our camp.

Software

HFPager is an application, which can be installed on a smartphone, tablet, laptop, netbook or a stationary PC. It works through generation of an audio signal, containing information encoded as changing sound tone. Decoding of received messages works through processing of an input audio signal resulting in text messages.

These audio signals can be transmitted using any professional or amateur radio with SSB capability and audio input and output lines (if specialized connectors are not available, microphone and external speaker connectors can be used).

The application HFPager can be install on a smartphone with Android version 4.4.4 and newer, which in turn is connected to the HF radio (transceiver).

Switching between receive and transmission modes (PTT) is realized through VOX system, which turns transmission on if audio IFSK signal is present at an input line.

Audio volume level can be adjusted by both the standard computer audio mixer interface and through application.

If for a standard voice message in phone mode even 100 Watts of power can be not enough, for IFSK encoded text message even 5 Watts is plenty. There are many situations when a short message is all you need. Sometimes short message can be critical in life and death situation or just to save some gas and time.

The used encoding protocol utilizes low transmission rate of 18 tones IFSK signal augmented by forward error correction based on Reed-Solomon approach.

Availability of two different transmission rates: 1.46 and 5.86 Baud, allows to choose optimal regime of operation. Reception automatically chooses the right baud rate.

Modulating audio signal can be chosen in a wide range from 400 tо 2600 Hz, which allows a dozen op HFPagers to work in one radio channel.

Available functions:

- Waterfall, visual method of control of receiving signal.

- Personal ID, issued after licensing.

- confirmation request will allow to be sure, that your message was received.

- Channel control allows to ensure that you setup is in a working condition.

- Day history demonstrates the work of your respondent beacon.

- Ham radio call sign in CW is included at the end of every beacon transmission.

- Geolocation, reception/transmission of geographical coordinates obtained by smartphone’s GPS receiver. The position of respondent shown on a map.

- Message sorting by “Inbox” and “Sent” folders allows to keep message history in order.

- Modulating audio frequency can be chosen in a range between 400 and 2600 Hz.

- Automatic frequency adjustment can be done by a simple push of button in application menu.

- Transmission rate can be chosen depending on the quality of the radio channel between 1.46 and 5.86 Baud.

- Either upper (USB) or lower (LSB) side band signals can be used.