IP over Ham Radio via New Packet Radio
When I first got into ham radio several years ago, I experimented with transferring webpages via PSK31. I dreamt of a network of amateur radio operators with the ability to browse an internal internet “off grid” via ham radio. I later learned about AREDN/Modified Wifi for Ham radio, and AX25 over IP, but there were some shortcomings for my use.
AX25 Drawbacks
AX25 offers the ability to do IP over amateur radio. But for one, AX25 is limited in general use to 1200 bits/s. This speed is enough to achieve telnet/BBS system connections. You can serve text over the air, and offer the ability to remotely control a station. What appealed to me most was it’s ability to ALMOST be a turn key solution. You need either a software sound modem, or an old fashioned hardware TNC, and running the Linux Kernel. The fact that setup on anything other than Linux would be difficult for the average user, and the lack of speed made me look into a different direction.
Wifi via Ham Radio
Hams also have the ability to modify some WIFI equipment to repurpose for the amateur radio bands. This creates a elegant solution to establishing Point-to-Point links. But that’s where my issues lies. Once you are 1Ghz and above, you basically need a line of sight. This means connecting to others can involve moving an antenna around and coordinating direction finding. This is no good if you are in rough terrain or unknown environment. So I kept looking.
New Packet Radio
The NPR-70 is an open source 70cm, IP over amateur radio modem created by F4HDK. It utilizes a protocol named “New Packet Radio”. The modem hardware and software are both open source. You can find a link to the project here. This modem makes IP over radio as easy as configuring an IP, and plugging in an ethernet cable. A user would need a minimum of 2 of these modems to form a connection, but several can be connected together at a time to form a network. A network consists of at least one master modem, and up to 6 connected client modems. That data rates are impressive, and here in America are actually limited due to FCC regulations. Once can achieve the maximum legal data rate on par with a dial up connection over the 70cm band with one of these modems. The beauty of this device and protocol are that they archive easily over 20 times what is possible with AX25, without the need for a hard line of sight connection between each device that we see with Wifi over ham radio. You can also buy one ready to go here from Elekitsorparts. Because the hardware and software are open source, some users have built their own upgraded versions, such as the NPR-H 2.0 which boasts faster processing speed, and 7 watts of transmit power. If a master is connected to a home router, you can even use it to serve the internet to remote clients.
The Pros and Cons of NPR-70 vs NPR-H 2.0
After buying one of these modems, along with an upgraded version, the NPR-H, I’ve noted a few things each one does worse and better than the other.
NPR-70
First, lets talk about the original model by F4HDK. I ordered an assembled kit of the NPR-70 from Elekitsorparts. The case design in aesthetic, sturdy and a a piece I would feel comfortable adding to my shack as is. It’s all metal which I would assume will be good for blocking EMI. All needed input/output is right there built into the assembly. Just add 12 volts and an ethernet cable and you’re ready to rock and roll. (Well almost). The problem with the base model is the power output. You get about 500mW of power on the antenna jack, and that’s barley enough to even drive the amplifier that you will need to get this thing connected in a real environment. The good news is F4HDK has already done the homework on testing amplifiers and it looks like the BTECH AMP-U25D amplifier is the once of choice to get up and running. But even so, it’s still only advertised to work with at least 2W input. This puts the modem in a strange middle area of being a demo by itself and a full blown tool when you happen to snag an amplifier while they are in stock (which is rare). If the modem itself shipped with at least 5 Watts of output power, it would be the perfect move for someone looking to get into the technology. It would allow you to communicate at a reasonable distance and easily drive an amplifier if needed. This makes the cost rise to around 240 bucks for a system that will work in the real world with real distance including the amplifier.
NPR-H 2.0
This is an upgrade of the original model by F4HDK. It features 7 Watts of transmit power built into the board which already solves the biggest gripe I had with the NPR-70. It also features the SRAM 1024K which speeds up the internal processing. This projects hardware is also open source, and the build can be found here. You can also purchase an assembled version, here. The power alone is enough to make this a decent upgrade. It turns the NPR-70 from a demo project into something that can be used in the wild. 7 Watts of transmit power can get you several miles, and even more with the client station utilizing a yagi antenna. The draw backs here? The lack of enclosure, and fancy power connector. It may not seem like much to some, but the presentation by the NPR-70 with the ability to plug in a barrel connector, throw it in a car and go makes it much faster to deploy. Just as a little bit of power could make the NPR-70 go a long way in turns of “worth”, a proper enclosure assembled with power connectors could make the NPR-H 2.0 go a long way as well. The price hike of +$90 for 7 watts of power, upgraded chip, but minus the enclosure with fancy power input and switches make this deal kind of tough. Shipping from Germany to the US for this product also carried a hefty fee and time as well.
So which one should I buy?
If you are comfortable with creating an enclosure, drilling holes and you are either running a Master+Amplifier, or only need to communicate several miles, the NPR-H 2.0 will do you justice. I say this because the upgraded Chip will make this a better option for handling several clients. And the 7 watts of TX power will be enough with short distance or line of sight.
If you are not conformable with modifying an enclosure and want a system that has a fancy case and either are experimenting, or willing to buy an amplifier, the original NPR-70 is a good option. Without the amplifier, this thing is just a toy for the house. But paired with an amp, this is a great long distance client or master.