by David VA7SZ


During the February business meeting, NORAC membership approved a one month trial of the Rattlegram app on the EGO VHF repeater (147.38+).

This open source app is available for Android phones (an old phone may work). With the app running, the phone is placed next to a VHF/UHF FM transceiver, where it listens for the incoming hash of a text message. The phone hears the hash and magically turns it into a text message on the phone’s screen. To send a message, you type it into the phone, key the radio and then hit send on the phone. You can also test this with two Android phones, running Rattlegram side by side.

So how useful is this technology? Well, I could see it being helpful in emergency situations as messages can be received and stored without the operator being present. Sometimes written information is valuable as it can be viewed or printed later. It could also be used to send alerts, possibly to supplement voice. Then there is general chit-chat, alerts for coffee meetings and other reminders.

The app has a “parrot” mode; received texts can be automatically rebroadcast using a radio with VOX - making it possible to cover a much larger area, and also to let the original sender know the message was correctly received. Of course, messages can be rebroadcast manually too.

The app comes from Germany and is currently in beta. It’s currently free to download. There are no real instructions but the menus are simple. There is a version for sending images too. The system is based on coded orthogonal frequency-division multiplexing, used in amateur TV and commercial data communications. For more information check out the developers site and check YouTube for videos.

I’m sure the system would be more robust with a cable interface, but that adds complexity. How it performs in an acoustically noisy environment isn’t known (to me), and likewise in a noisy RF environment - more experimentation is required.

I’m sure the same thing can be achieved with other, more refined protocols, but the advantage of Rattlegram, for me, was not having to go out and purchase widgets, cables or even new radios. Note there are also APRS apps available for Android phones but those rely on a wired interface.

If you want to experiment with Rattlegram on EGO VHF, please identify yourself by voice and announce your intentions before sending the data - that way other users will know that it is not random interference or a repeater issue. You may receive your message “parroted” back to you by another user. For extended use you will need to supply your phone and radio with external power, especially as currently the screen remains on when the phone is listening. Some of us are hardwiring our old Android phones to the radio to obtain cleaner signals.

Those of us already experimenting are using receive/transmit sampling rates of 16kHz and a 2 second noise burst at the start of the transmission. Our call signs are entered into the app for on-air identification.

Remember, this is an experiment, and things may not always go smoothly or work as intended. Please respect other users and stay within recommended band plans.

If the app gains traction, no doubt developers will tweak it and provide additional features.