View Full Version : How much power for APRS?

12-07-2013, 07:17 AM
So, I'm toying with the idea of building a stand-alone APRS system for my truck. The loose concept I'm thinking about would be to have a TinyTrak 4 and a dedicated 2m radio hidden behind the dash. The GPS receiver would be mounted on the dash. Eventually (but not anytime soon) I'd probably hook up something like an AVMap for a display. I am thinking I'll power the whole thing via a splice from the cig lighter so it'll be on anytime the ignition is on (but I'll put in a kill switch in case I am someplace that I don't want anyone to know about).

So, my question is… Will a 5W radio (with a good external antenna) be enough to reach digipeaters when I'm in remote areas?

12-07-2013, 07:26 AM
To ask my question another way: Can I just get a BaoFeng UV3R and a DC power adapter ($40 total on Amazon) to use as my radio for this setup?

12-07-2013, 07:43 AM
I wouldn't count on 5W getting you a whole lot of packets from remote locations to digipeaters. But honestly the bigger issue would be location rather than power. IOW, 5W from a hill top is ten times better than 500W in a valley. So I guess my response is really more like that would be fine.

What you're proposing is probably the second most common APRS type installation and the most common dumb beacon: cheap Chinese radio + small TNC.

Realize that the AvMap is very expensive and only fully useful with a Kenwood TM-D700/710 or the TH-D72. It'll work with any regular TNC to display waypoints but the fancy stuff like the messaging extend the Kenwood specific protocol. With other radios most of the functionality doesn't extend, mainly the ability to receive and send messages on it. So it's really just a very expensive display for APRS stations in that case.

IMHO I'd avoid unless you have a Kenwood radio. You can duplicate the functions using APRSdroid with a tablet and the Tinytrak4 for a lot less cash. Nice thing about going this route is you can link the TinyTrak and the tablet via Bluetooth so there's less mess of cabling. In fact you can rig up the radio to talk to a tablet using the mic and headphones and not even need a dedicated TNC to run APRSdroid.


Truth is a tablet (or maybe you already have an Android phone) isn't much more than a TinyTrak. APRSdroid leverages the built-in GPS of the device, so no extra stuff hanging around.

But I have a TinyTrak4 and it's a handy little bugger. I have a Garmin GPS 18 puck I run with it and it's reliable and works well for a beacon with any radio. I have a little hacked display that shows raw packets and can interface a PS/2 keyboard, so it can do messages. It's not very portable, no case and trying to deal with a keyboard is a PITA. But it's fun to mess with it.

12-07-2013, 08:17 AM
The Byonics website says you can now use AVMap and TT4 to send texts. They even have a video on it from W6GPS.

Of course… He's doing it with the Kenwood D-710 as his radio, so I'm not totally sure it would work with something else.

But, yeah, the price of the AVMap is ludicrous. Will look into the droid tablet as an alternative… Though I'm pretty well married to the Apple ecosystem.

So, yeah, I guess I'll try it out with a BaoFeng. I can always change it to something like a FT 1900 or even add an amplifier if I need to. I'll keep you posted. Probably will be a couple months before I start building it.

12-07-2013, 08:24 AM
OpenAPRS, PocketPacket and iAPRS work in iOS.




Couldn't tell you how any of them work I'm still married to the Nokia flip phone 'ecosystem'. Hi-hi.

I also stand corrected, apparently the G6 does work with TinyTrak4 TNCs (and maybe others). It actually sounds as though the G6 needs the TT4 to work fully even with Kenwood radios.


Adding Capability with the Byonics Tiny Tracker 4
The Byonics Tiny Tracker 4 (TT4) is an APRS capable TNC available as a kit or built and tested. It is supported by a host of available interface cables for computer and radio, free downloadable firmware, keyboard and display options, and downloadable documentation. The TT4 is a relatively inexpensive way to turn any 2 meter radio into an APRS station.

While the AvMap GeoSat 6 APRS is designed to work with all Kenwood APRS capable radios, Kenwood does not support all of the messaging capabilities of the G6. Kenwood does support message sending via the mic keypad, only. With a capable TNC such as the TT4 connected between the G6 and your radio, it is possible to select a received station from the G6 APRS contact list and send that station a message. When such a station is selected a soft key board appears on the screen. The “keys” are about the size of my finger tips and make message creation as easy as one could imagine. The G6 keeps a log of messages sent, received, and pending, much like an email application.

12-08-2013, 05:44 AM
Maybe this is useful, Keith?

(http://www.expeditionportal.com/forum/threads/114535-iPhone-PocketPacket-Baofeng-UV5R-and-APRS)ExPo Forum: iPhone, PocketPacket, Baofeng UV5R and APRS

12-08-2013, 01:50 PM
Yes. I've done a lot of searching. Seems like a lot of people are doing it with a HT. Seems like that gets you pretty spotty coverage… But also seems like going up to 50W doesn't really help that much.

I think I'm gonna go ahead and build one with a BaoFeng, TinyTracker 4, and a good external 2m antenna. We'll see how well it works in the Spring…

Right now my time, mind, and money are occupied with building a "battery box" that I'll use to run HAM stuff at home and potentially in the field. I just got a screaming deal on a couple of AGM batteries: http://www.batterystuff.com/batteries/mobility-scooter-wheelchair/UB12500-45977.html

12-08-2013, 02:04 PM
Do you need a maintainer/supply? I have a IOTA DLS-45 that a Group 27 AGM just sits on 24/7. I'd like to put the battery in the truck somehow but in the interim I'm probably reconfiguring to sit the battery on stand-by float with an external controller using my regular power supply. So the switch over is automatic and I can eliminate the IOTA.

FWIW, I run my APRS beacons at low power all the time, which is 5W. You're either going to get packets in or you're not. Using Friis Equation the difference in going up an order on the power is 3 times the range, all things being equal (unity gain antennas, -65dBm received signal strength at 145MHz). But in real life you can figure 5W to 50W will get you roughly twice as much effective range safely in most any condition since simplfied Friis doesn't account for true path loss. It can, but the formula is more complex and I'd have to stick it into a spreadsheet.

A lot of hams do the numbers game with mobiles and buy 75W radios. The difference in range between a 50W and 75W radio is a bit more than 20%. IOW, the 50W would be reliable to say 65 miles the 75W would get you the same signal strength at 79 miles on VHF. As you go down in frequency the power differences become quite a bit more significant. At 7MHz the difference in 50W and 75W is 350 miles, 5W gets you 435 miles and 50W would go 1,400 miles (for the same received strength).

12-08-2013, 08:40 PM
Dave, all of your posts make one thing clear: I need to take a class from you.

Starting a new thread to discuss plans for a battery box.