Howard, Good discussion. For public service/emergency, we need to keep things simple and ideally self contained. D-Star's selective calling feature could be useful and avoids some of the shortcomings of other selcal systems such as DCS. My wife and I were very early adopters of the DCS technology, but it never worked out well, annoying others openly monitoring and repeaters may not pass the tones. D-Star avoids those issues. I admit that if all the participants cooperated with using DCS, then this could work quite well.
In public service events/emergencies, you will find that most operators will want to know everything that is unfolding as they are mobile and are likely to be listening to the traffic on the frequencies they are monitoring. This also helps them determine if they are staying in range of the other station(s). If message traffic needs to be passed to them or from them, then phone is one of the safest and most practical methods when in motion unless they have another operator aboard. The big question is how to get increased range for both distance and shaded areas. D-Star is going to have slightly shorter range and has difficulty with multipath, assuming the local hams have this equipment, so it may not be the best choice. The strongest point about D-Star is for those operators who want to link through the internet and needless to say, you don't want to include the internet as a requirement for your emergency communications to function properly. SSB phone is currently the best voice mode available by far, when it comes to increased simplex range, but is more expensive than FM only rigs, since you can only get this technology in a combined HF/VHF/UHF transceiver . But some of these rigs are actually no more expensive than D-Star ($700) and give you tremendous value. When you get to your destination, you may have more options, depending on the equipment you brought or is set up for you. Even HF could be used, although not very likely for most locations. HF is normally reserved for a central point that may need to forward traffic out of an affected area and you would not want local tactical traffic on wider area HF nets. At almost any location, you should be able to erect some kind of short mast, fixed direction 2 meter gain antenna to get back to your HQ station. This will give you the 24/7 kind of communication that is not available on HF. Then you could use packet, phone, or other modes that have been decided by your group. Could you comment further on your experiences with RFSM? 73, Rick, KV9U Howard Z. wrote: > 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 > >
