Sunday, September 21, 2008

APRS station: shopping list

So the more I think about it the more I'm thinking that an APRS station is going to be this winter's project.

Initially I'm just going to listen. The next step is going to be transmitting WX info from our Oregon Scientific PWS. My location won't allow me a very high antenna, but we're a mile and a half from the Tri-State (at closest approach) and so we ought to be able to hear at least some data from mobiles.

APRS is a variation on AX.25 packet, and historically APRS stations have used modified TNCs to do their work. However, I'm not really interested in buying a TNC, and thankfully I really don't need to. It's perfectly feasible, from what I'm reading, to use a computer for this role, using the computer's soundcard to process the signal from the radio, and software to demodulate the "modem noise" into digital signals. Computers are more expensive than TNCs, but I have several spare computers and no spare TNCs, so computer is the direction we'll be going. "Soundmodem" software already exists for Linux, so that's an easy step.

I already have a radio, an ADI-146 that I picked up cheap off eBay a while back. This is a 50 watt 2m mobile rig, and was sold to me without a microphone. No big deal, don't need a microphone for this anyway as the rig controller will replace the microphone anyway. As a mobile rig, the transmitter has no internal power supply, so I'll also need a 12V (or 13.8V) supply. To round things out, I'll also need an antenna and feedline to connect the antenna to the radio. For good measure, it would probably be a good idea to get a VHF SWR meter before transmitting with this rig at 50W; don't want to blow out the finals, after all. Also, most commercial 2m antennas are tuned to peak around 146 MHz; APRS uses 144.390, which is pretty far downband from the 146 center point, and with most commercial antennas likely to require retuning to get a good match. For that I will need either an analyzer or a SWR meter.

So, this means I need to buy the following:
  • Antenna (I'm thinking something like the Diamond F22A, priced at $89.95)
  • Feedline (about 60 feet required with prices that range between 30 cents and $1.20 a foot, plus connectors and short cables, for a total of between $50 and $125)
  • Rig controller (the Rigblaster Plus at $149.95 should suffice)
  • Power supply (probably somewhere around $100)
  • KVM switch (around $30)
  • SWR meter (MFJ has a cheap one for $15.95)
That puts the total budget in the range of $440 to $515, with probably another $25 for incidentals.  Maybe I can find some cheaper alternatives or get some stuff used or something; I'm not sure I'm ready to spend that much right now.

4 comments:

  1. I am also interested in setting up an APRS station on the cheap. I'm currently collecting materials to set this up. I also have an overabundance of computers so I'm hoping to use one of those as the TNC with a rigblaster. I've got a G4 cube I'm hoping to use MacAPRS with but if I have to I'll use a Windows/Linux box.

    I've got an Icom IC-28H that I'm probably going to use for this purpose and antenna wise it's probably going to get a copper j-pole or mag mount on a sheet of metal in the attic (because I already have these items and we're on a budget aren't we?!)

    I'll be interested to see how your setup comes along. I'll probably update my blog with information @ alexkaltsas.com when I get closer to setting this up.

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  2. Do you suppose one could use the AGW Packet Engine and not have to use a rigblaster at all?

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  3. AGWTracker appears to be a "soft TNC". Linux has had AX.25 built into the kernel (as an option) for years, which provides basically the same functionality as AGWTracker. AGWTracker, as a software package, doesn't replace the RIGBlaster, which is the hardware needed to actually connect the radio to the computer so that the radio's audio channels are fed into the computer's sound card with appropriate level adjustments, and also so that the computer can control the radio's transmitter. You need some sort of device for this; the RIGBlaster is one of the better ones but it is pricy. There are less expensive options, but you can't do away with them entirely, unless (of course) your radio has a built-in TNC interface.

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  4. I realized the same thing after I started sketching out a basic setup on paper. Methinks we stayed up too late playing munchkin last night and got too little sleep.

    My concern is that for the price of the needed hardware I almost might as well go pick up a Kenwood TM-710D with built in APRS support and I believe it has a built in TNC as well.

    On the other hand the Rigblaster might be useful in other endeavors in the future.

    Decisions decisions, the govt should send me some Radiobailiout funds and I'll just get all of the above.

    Do you know of any preferred linux/Mac APRS software. packages? I've been looking at Xastir, I'm also looking at macAPRS which still runs in its current carbon form but doesn't appear to have plans for updates in the future (hasn't been updated since 2003). Xastir can be compiled on the Mac as well. More decisions, thanks for your input.

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