APRS IGate Built Using A Raspberry Pi

The hardware seen above is used to bridge a local RF radio network to the APRS-IS network. The APRS-IS is an Internet Service that uses a web connection to communicate between APRS networks in different parts of the world. The Raspberry Pi is perfect for this application because of its ability to connect to a network, and its native use of Linux.

On the software side the majority of the work is done by a Python script. It is responsible for setting up and monitoring a connection with an APRS-IS server. To connect to the handheld radio unit a USB sound card was used. The Multimon package is used to send and receive audio packets through this hardware.

[Sunny] has a few upgrades planned for the system. The device needs to report its location to the APRS-IS server and the plan is to add functionality that will look of the WiFi AP’s location automatically. It may also be possible to get rid of the radio all together and use a DVB dongle as a software defined radio.

28 thoughts on “APRS IGate Built Using A Raspberry Pi

  1. YES!!!! Keep them coming!
    Also note that the RTL2832u (RTLSDR) SDR receiver works with Raspi too. In other words we could use the USB based RTL DVB stick to do the receive and actually have the receiver and Raspi in one box (Free up your HT for other fun projects?). You could even receive on many APRS frequencies at once with an SDR approach. with that said I like your project!

    1. Actually the packet encapsulation decoding already works with the TV decoders, but the Pi resources are too limited for real time decoding.

      We are working on getting the GPU to do the FFT though… damn closed binaries will be opened soon… ;-)

  2. Nice little box for sure, an RTLSDR would drop the need for an external receiver, but the computation required for demodulation is pretty high (narrowband FM takes 65% on both cores of the OMAP4460-based Pandaboard ES). rPi might suffer a little there, which the external transceiver alleviates somewhat.
    You could just go with a non-transmitting receiver, which would be a little cheaper, and probably even tap the radio’s battery as a backup power source in a pinch.
    All that said, this is a fine little build. Very clean. I may have to keep my eyes open for a Singstar dongle.

  3. With the sounds card/HT approach, there doesn’t seem to be much holding this back from being a full Digipeater, other than triggering the radios PTT to transmit. I do like the idea of the RTL2832u SDR though for an iGate in a box. Love to see some weather station integration as well.

    1. Most PTT’s “TNC” connectors work this way:

      Neutral – is obvious
      Speaker – is also obvious
      Mic – this is where it gets fun…

      Apply +Xv DC to the Mic line to hold the PTT. The voltage might vary by radio.

      Apply +/-v AC to the Mic line to send audio. The voltage delta here is significantly smaller than that of the DC signal for the PTT.

      Example hookup (with a Yaesu VX-7)

  4. can someone explain the uses of this? im not an radio guy but this does make me say: this looks cool , anyway can someone explain what it does. good job tho looks clean and professional.

    1. An iGate is a radio and TNC (Terminal node controller) connected to a computer with internet. Packet radio traffic can be routed from the air onto the internet, and put back on the air at another location. APRS is a system that uses packet radio to allow for position reporting, status messages, and weather reports (among other things) to be collected and disseminated. There are internet databases filled with this, often useful, data.

      1. So its like a messaging system to get important data out where its needed without relying on cell towers or other means of sending data?

        So you cant use this to get free internet right? (just kidding)

      2. @riycou it was done at a moment (1990s), but the speed was so slow (1200/9600 bps) that it was superseded by wifi acces points when these became common.

        And it’s forbidden to connect internet to amateur radio networks in some countries, such as france.

        aprs is a survivor of this epoch, you can understand it as a short-message service based on amateur radio technology. aprs igate are “legal” because they don’t route general internet traffic but dedicated “positionning” messages.

      3. @openmakersdaily

        It does make me disheartened that civilians can’t use airwaves for things that companies can.

        Meaning, specifically, generic data services cannot run on open spectrum that are good long range carriers due to various legislative laws rather than physical ones.

      4. @reginald bartlesby : IIRC, it was argued that an experimentation hobby [amateur radio] had nothing to do with a commercial networking service [internet]. That sucks, but it’s the law.

        Given the disaster recovery ability that amateur radio operators are able to deploy, a generic amateur packet service would be a good thing, at least aprs is still there and could be quickly converted into something else if need be…

        Near Paris, the aprs traffic is quite intense, meaning this technology is well alive.

      1. yes, its still $35 for the Baofing or something.
        RTLSRD dongles start at $10 (RTL2832U+R820T)

        but instead of $10 SRD + $35 Rasppi + a lot of optimizing to make it work

        you could go with

        $35 radio + %5 usb sound + $5 USB rs232 + $22 TL-WR703N

        and get both receiving and transmitting, including scanning

  5. This is a receive-only iGate. It’s not particularly useful.

    It would be very easy to make it bidirectional. I recommend APRX software and a simple transistor with a 2k2 resistor to pull down the mic. line for PTT. Use the Pi audio-out to drive the radio mic. in.

    Alternatively use a different USB dongle which has audio out as well as mic. in. If you get one with a CM108 chip there are GPIO lines on the chip which can be programmed to drive PTT.

  6. A dongle with SDR is great for receive, but I don’t see how you could dispense with the larger radio for transmit. Is there an equivalently cheap radio for SDR transmit?

    1. in one word: nope. Here is a quote from SM5BSZ, author of the great Linrad software:

      I have looked at the spectra from available SDR transmitters, just one of them, but the quality is so poor that I do not want it to be possible to use Linrad to produce band pollution to that degree.

      I think SDR transmitting is in the future. Probably the near future, but personally I have not yet seen anything acceptable except for the TX I made for myself by modifying WSE RX converters.
      That solution is clearly unrealistic from a cost perspective.

      At least that’s for general HF/VHF coverage.

      Digital modulation is of course generated in software in GSM,3G and LTE phones, but the hardware is assisting the transmission, the RF bands are limited, and there are specific DSP with complex algorithms in the loop.

      So, nothing like a hacked usb dongle.

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