Well, let me see. 2m/70cm D-star radios can communicate with each other without a repeater. These radios can send audio and slow speed data simultaneously. The slow speed data can be displayed on the radio's screen or on a laptop connected to the radio.
The call-sign squelch should work without a repeater. When call-sign squelch is enabled, no voice transmissions or data transmissions will be received unless it is address to that radio's call-sign. Of course the radio must be constantly turned on. The power consumption will be very low because o it is not transmitting while waiting for a message with its callsign o The speaker is off/squelched until a message arrives with its callsign Disadvantages of d-star are: o It is overpriced compared to similar FM only non-Dstar radios. Compared to digital P25 radios that government bodies buy, it is low cost. But most Amateurs are not going to spend their own money on D- star until the prices drop and it becomes only $100 more than a similar FM only dual bander. ICOM's IC91AD handheld was reasonably priced without the d-star board, and not too much extra for d-star. But the other dual band d-star radios have been priced much higher than Icom's FM only radios. o When the signal is not strong enough voice gets very squeally sounding. Most would rather listen to weak FM signals than the D- star squeal. o You simply can not assume your volunteer workforce will have these radios unless your organization purchases them. As I mentioned earlier, one can get similar functionality - a radio that is quiet unless VOICE is received with that radio's squelch code. You can divy out a dozen or so squelch codes for your teams to use in their FM radios. The prevailing radio-email systems require receivers to routinely check into a radio email server to check for mail. This can be automated to be every X minutes (for example every 10 minutes) with Paclink software. So you keep an email server up - like RMS Packet with RMS Relay software, and the field units use Paclink software. If your email server has its internet down, the email capabilities will be limited to sending and receiving email messages among your email server and Paclink stations that directly connect to it via radio. Error-free delivery of the emails is guaranteed with retransmissions if necessary. Another option is 1200 baud packet. I have not played with this very much, but on HF there are several programs where one Amateur radio "connects" to another Amateur's radio using his callsign, then typed messages are delivered and acknowledged. Automatic retransmissions are performed if necessary to guarantee error-free delivery. The receiving radio transmits - telling the other radio it has received the message without errors. This would require every radio to also have a laptop with the appropriate software. On HF I have used programs such as XPWare and WinPTC. There is also Alpha, but it is not free. I bet the free WINPACK software has similar functionality. It would also be nice if the software will automatically accept a connection call and save the message to a file, so the operator does not need to be intently watching his screen ready to click to accept a connection. Some HF digital modes work under conditions where voice would be unrecognizable. Keep in mind there exists the capability for radios to listen in on digital communications not addressed to them. I am thinking Email server is the best way for you to get your functionality - though the field stations will be polling the email server every 10 minutes or so. Or FM packet digital radio would not require the 10 minute polling intervals - (or some other VHF digital mode) might be what you want. Radio and laptop on all the time. NO need to sit there listening or watching intently IF some kind of auto-accept-connections feature exists. Your message is saved on his laptop for him to read after he returns to his vehicle, or wakes up if sleeping. I am not sure this auto-accept-connection and save the message to a file features exist in existing software. Since I am not very experienced on VHF digital modes, someone else would need to guide you to hardware and software choices. If VHF does not give the range/distance you require, then a digipeater with generator, solar power, or other backup power would expand that range. And then there is also the HF digital option. Howard
