One of my oldest friends asked me about a text based chat or messaging system which could work over radio. If radio is your thing, that is a fairly basic thing to do.
The modern militia would like to have some sort of message handling system for base-field-base communications. Naturally this would be command and intelligence communications to and from ops in the field. Once again I say there is no reason to reinvent the wheel! Amateur radio has or will provide the answer for you. In this case, we are talking about PSK!
Although many digital modes in radio are aviable, I prefer to use PSK31 or PSK63 as an effective means of medium to long range text based communications of radio. PSK allows you a half-duplex continuous stream of text between radio operators, Many different signals can take up a very small amount of bandwidth, or we can say many tens of signals can occupy the same frequency on your radio. Each “streams” (slightly broken glowing lines) you see in the image above is a different conversation taking place on a single channel (frequency) 14.070Mhz USB. They could be happening on any frequency provided they are on SSB.
The image you see is my bench setup for testing from the comms room in my home. Once I have this setup effectively and consistently sending and receiving PSK messages between radio operators at will, i will transfer this concept to the field, for a man-portable setup which can be used anywhere, where your radio can be deployed.
PSK on the bands
Under special circumstances, or if it is legal in your country to do so, you could even use PSK on non-amateur bands. The only real requirements for PSK31 is an SSB radio. It will not work and was not designed for AM or FM radios, so please dont even ask. So yes it is possible to use PSK on CB radio, Business VHF, …provided you do so with an SSB radio. For you CB radio guys, that band is just the same as any other HF band. Its the equipment which differs slightly. However, if you were using one of the SSB CB radios, there would be no reason why you could not use that for PSK31 (other than the law)!
The typical PSK setup includes:
Software to send and receive PSK
In my setup, I use either a Samsung Galaxy S4, or my Samsung Galaxy Tab, DroidPSK from Wolphi LLC and my Yaesu FT-817ND radio with WolphiLink Interface.
Android or Windows
I prefer android over windows or a laptop for a couple of reasons. Firstly, when I am offline, I don’t want windows screwing around with my machine, even if I have a mobile data connection. While Android respects more the users wishes by making a difference because a mobile data connection and a Wifi connection. Finally, with an Android device, there is a much smaller footprint when operating portable or mobile. Certainly Windows has its advantages, but for me, there are no worthy ones when operating man-portable!
Many people ask if its possible to send encrypted text over PSK. I’ll answer like this. There is no technical challenge preventing you from encrypting the text you send over PSK! It is after all just text. What order the text is transmitted in, is not important!
The best comms guru is a well experienced amateur radio operator who gets outside and tries all sorts of things. He keeps on tryuing until he is an expert at it, then he shares what he knows, then tries something new! Support the curiosity and learning of your comms people. In turn, they will bring new and exciting ideas back to your group.