Just a note to let you know that there really is quite a difference between digital radio and packet communications sometimes referred to as digital communications. In digital radios computers are used to analyse incoming information filter and demodulate it and even amplify it at the audio end all using digital techniques. Voice, Morse code, and HF packet can all be managed in this way.
Packet communications, up until now, have used analog technology through the radio and then a TNC (terminal node controller), a radio version of a modem familiar to computer users who used telephone land lines to communicate text, images, and other data between each other. Radio people use TNC's in a similar way. A TNC or modem convert digital information into shifting tones or tones with phase changes or both. That tonal information can be handled easily by analog radios. It's not much different than sending voice.
Receiving packet data is simply done in reverse. The radio receiver outputs tonal information to the TNC and the TNC makes sense of the shifting tone and phase information to produce data which is then applied to a computer. Various forms of packet are done on all bands on FM, and Single Sideband modes.
Having said all that there is a company - AOR, who have created a device that goes between your mic and the mic jack on a conventional SSB HF radio. It converts normal voice into several digitally modulated audio streams at different frequencies. Each stream is very narrow band and so all of the streams fit within the normal audio bandwidth allowed to be transmitted by the radio. At the far end a reverse demodulation of the data takes place and the audio from the output of the AOR device goes out to headphones or speaker. The great thing about this is the quality of transmission, very clear.
See: http://www.aorusa.com/ard9800.html
Icom has also expanded on some digital technology developed by a Japanese consortium. They have a system called D-Star incorporated into several models of hand held and mobile radios VHF/UHF, and 1.2 Gig. Depending on what level of radio you purchase you can communicated with voice or voice and data simultaneously either by simplex or by suitable repeater. The voice is digitized at the transmit end and demodulated at the receive end and there is virtually no noise right up until signal degrades to the point you simply lose the link. The radios can be used to communicate with other analog radios as well.
You will need a computer. In days gone by people simply used older computers that would run in the DOS operating system. They were big and power hungry and required 120VAC to operate. Most people wanting to get onto packet are doing so because they are involved in emergency preparedness. An ability to run off of a 12V battery is an advantage. Many choose to purchase a shiny new net book computer. A net book computer has no floppy drive and no CD/DVD ROM drive in it so the overall package is small and light weight. As far as I am aware of none of the portable computers or even desktop computers have got serial ports built into them. In place of that they all have USB ports.
Here`s a couple of things to know about net books
1) They generally come with a stripped down version of Windows 7. You may want to replace that with Windows XP. There`s more ham software that works with it than Windows 7.
2) New netbooks come with an Atom N450 processor. There are some older stock ones that come with the N270 processor. The N450 is faster. Soon you will be seeing a newer N550 processor in stock coming in within the next couple of months.
3) Get one with a 6 cell battery if you can afford the extra expense. They last up to 9 hours on a charge compared to around 3 or 4. If you intend on running off of a twelve volt supplyyou won’t need the more expensive 6 cell battery pack but you will need some sort of 12V adapter to run your computer from. Before going further see if the store that sells your net book also sells an automobile adapter. If there is no such thing then you will need a 12VDC to 120VAC adapter to run your net book from and it should be one which has a true sine wave output. Some computers don’t work well on some of the cheaper adapters which have a digital step sine output..
4) You can get a net book with Blue Tooth if you want it but realize that is another system that can use up battery charge. You can probably live without it. I have it on my fancy HP laptop/tablet computer and enjoy using a blue tooth mouse with it (no cord). I can turn off the blue tooth and expect that is the case with most other laptops or net books.
5) All net books and laptops come with WIFI ability now and you should also be able to turn that off when it's not required to save batteries.
It plugs into my laptop or desk top (or a net book) right into the USB port. It also plugs into my radio. Pretty straight forward. When buying the Signallink unit you carefully look over the listings and pick a unit with the correct cable to match your radio. If they don’t have a cable that has the right ends on it you get a basic cable and build your own ends to suit. You can even getextra cables in case you have more than one radio you may tie into.All you have to do then is deal with the software. My SignalLink can be used with a whole host of different packet programs and VHF/UHF/and HF radios. Pretty versatile. It acts as a TNC. It has it's own high definition audio card built in so you don't need a newer computer, it could be one like my old laptop with Windows ME. As long as it has a USB port you are good to go. The price is reasonable. Looking at user reviews on eHam the SignalLink looks like a good choice.
The KPC-3 requires a serial port on your computer. Newer computers no longer have the old fashioned serial ports but that is easily solved by using a USB to serial converter cable. You generally have to make up your own cables to go from the TNC to the radio. Not too big a problem and everyone who uses a KPC-3 has had to make their own cables. Using a TNC you don't need to make use of the computer's sound card. All of that digital to audio conversion is taken care of in the TNC box.
This is an interface that can be built which makes use of a computer's sound card. It's pretty simple if you have the parts, the time, and the experience.
MFJ makes an interface that works with sound cards and has a lot of neat features you may never use. Still tempting though. The MFJ-1279 or similar ilk are top of the line interface type cards with a bunch of additional features for rig control. I could imagine one of these more useful with an HF radio, a fancy additional mic and speaker, and a foot switch to control the transmit. Pretty neat but maybe a bit over the wall for you.
There are several versions of the 1279. The guts are all the same but they have different microphone connections. I still think that the Tigertronics USB SignalLink is the way to go. Less cables to worry about but some wiring may be necessary depending on the radio you get. As someone mentioned - don't expect to have your stuff all plug-and-play when dealing with packet systems.
A simple quarter wave antenna with droopy radials is all that many packet users use. It can be a real stealth antenna because it fits nicely in an attic space where no one can see it. Another alternative is a J-Pole or aSlim-Jim mounted on a piece of pipe. You can build one for cheap out of copper water pipe. Lots of plans on the web but before transmitting with any antenna get it checked out using an antenna analyzer. Save yourself from cooking the finals (power transistors) in your transmitter. If you join a radio club either the club will have an antenna analyzer or someone in it will.
Power
I mention 12VDC because in a disaster and the AC power goes out all that is left is some sort of battery power. My favourite is an AGM battery. These are a type of a sealed deep discharge lead acid battery . They are twice the price of conventional auto batteries but there is no external gassing. My home AGM battery is rated at 120 amp hours. To charge it you would normally use a small smart trickle charger that keeps the battery topped up. I run my ham shack on my battery and don`t bother with an expensive power supply. My future wants include a pair of 100 watt solar panels mounted on my roof or fence and connected to my battery/s through an MPPT (maximum power point tracker) charge controller.
There are other batteries which may be making a come back. Nickle Iron batteries were invented in the early 1900's and they have many excellent features newer batteries do not have. One very important one is that they can take deep discharging without going into failure, and likewise can be overcharged. Lead acid batteries quickly sulphate up. Another admirable trait is that they don't contain toxic metals like lead or cadmium. Life span of nickle iron batteries is enormous. No one seems to have come up with a good estimation for life span because batteries that are 50 years old are still being used. The unfortunate thing is that nickle iron batteries are no longer manufactured in North America. You have to order them from Europe or China. From what I have had explained to me they are the ideal battery to use with a photovoltaic system. The only maintenance they seem to require is to be topped up with distilled water as their electrolyte level starts to drop down.
Please advise me if there are any failed links. Thanks!
