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APRS on aprs.fi
Stefan Helander

Analog vs digital APRS

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There is actually no such thing as “analog” APRS. The traditional APRS over AX.25 on 144.800 MHz (or 145.390 MHz in other parts of the word) is actually defined as a digital mode.

However, Anytone has a possibility in their radios choose wether to send APRS over AX.25 or as position data over the DMR channel. This settings can be found in MENU -> APRS -> Upload Type, “A -Aprs” for APRS over AX.25 or “D – Aprs” for using the DMR. In Anytone they call these modes “Analog APRS” and “Digital APRS”.

APRS over AX.25 – “analog” APRS

In this mode positions are transmitted on a simplex channel (144.800 MHz in IARU region 1) and can be received by anyone in range. The packets can be repeated by digitpeaters (WIDE1 for local “fill in” digitpeaters and WIDE2 for wide coverage digipeaters). If the packet hits a digitpeater with an I-gate it is transported into the APRS-IS system and can be seen in aprs.fi.

The traditional APRS over AX.25 packet radio has many more functions than just position reporting, such as telemetry, weather reports, messaging etc etc. If your radio is capable of receiving APRS you can also see other hams in the area (position, distance, direction etc).

APRS over DMR – “digital” APRS

In this mode, the radio uses the built in function in the DMR specfication to transmit position data. When this position data reaches the Brandmeister servers it is converted to APRS and fed into the APRS-IS system and can be seen on aprs.fi.

APRS over DMR is limited to only position data so if your goal is to just show up on aprs.fi, this can be the mode of choice for you. You miss out on all other features of APRS when using DMR or “digital” APRS.

If you look at the APRS menu on the Anytone for example, the APRS SMS function is only availible for “Analog APRS”.

APRS SMS only in
APRS SMS not availible in “Digital APRS” (over DMR)

For me, I choose the “old school” APRS over AX.25 all days in the week 🙂

Stefan Helander

APRS (packet radio) – FM wide or FM narrow?

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Looking at many how-to guides for the Anytone AT-D878UV / AT-D578UV and APRS, it can be hard to determine if APRS should be transmitted as FM (20 kHz bandwidth) or FM narrow (12 kHz bandwidth). Some guides show WIDE while others show NARROW.

The answer is clear in the IARU region 1 VHF band plan – APRS on 144.800 MHz should be transmitted using FM narrow.

Anytone AT-D878UV analog APRS TX not working
Stefan Helander

Anytone AT-D878UV analog APRS transmissions not working

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My analog APRS transmissions with the AT-D878UV was not received by any other stations. The problem was that when the codeplug is created (using New in the CPS), the values for Transmit delay and Prewave Time is set to 0 (zero) for APRS and this will not work (probably to battery saving as this is not a problem with the AT-D578UV for example, which will work with much lower values for Transmit Delay and Prewave Time).

Solution:

In the CPS -> APRS -> set Transmit Delay to 600 ms and Prewave time to 600 ms.

Anytone AT-D878UV analog APRS TX not working
Anytone AT-D878UV analog APRS TX not working – solution

Source: https://www.reddit.com/r/AnyTone/comments/han0y5/aprs_problems_the_solution_anytone_atd878uv/

Ana Aprs Tx should be set to “Narrow” according to IARU region 1 bandplan.

What is Transmit Delay and Prewave Time?

I’ve tried to find an explanation to these values online but haven’t found anything closer than “it controls the time after activating the transmitter until data is being sent”. So I tried setting each value, one at a time to it’s maximum and this is what I think it does:

  • Transmit Delay: The radio starts transmitting a packet but it sounds like it waits “Transmit Delay” milliseconds before it starts transmitting any valuebla data. During this time my guess it is filling the packet with zeroes.
  • Prewave Time: The radio pulls the PTT but waits “Prewave Time” milliseconds before it starts to send the packet. During this time, the radio just sends carrier.

If I set the Prewave Time too high, my receiver will not receive and decode the packet. I’ve experimented with values for Prewave Time with different values and between 80-600 ms it seems to be working.

TigerTrak TM-1Stefan Helander
Stefan Helander

TigerTronics TigerTrak TM-1 configuration under Windows 10

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This little APRS-tracker from the late 90’s or early 00’s is a neat little device, however pretty old. It uses an external GPS receiver (via RS232) and connects to a radio, like a HT for example.

According to the manual, the configuration utility runs under Windows 95 or 98 (yes, indeed old stuff). I have a TM-1 lying in a box collecting dust so I figured that I should fire it up and see if I could use it for something fun (today APRS is gaining some attention again since many new radios has analog APRS rx and tx build in, like the Anytones).

It turned out that it worked fine under Windows 10. I used an USB to RS232 adapter. In the device manager, find the COMx-port adapter, under Properties -> Port -> Advanced, I had to select COM1 to COM4 since the old software just supports these ports.

I installed it and right clicked on the program file for the TigerTrak configuration utility and selected Compatibility -> Win 95 (not shure if this is needed but I did it anyway).

To connect the TM-1 to the configuration utility, first start the utility. With the TM-1 connected to the serial port (straight cable), power it on while holding PWR and MODE simultaneusly. The software should indicate CONNECTED and the LOCK led on the TM-1 should go green.

As special path 1 i used WIDE1-1 and special path 2 WIDE2-2. This will cause packets received by a WIDE digitpeater to repeated two hops. If that is overkill (like in an urban area with many digipeaters) you could use WIDE2-1 to limit it to one WIDE hop instead.

Nowadays there is a specific TOCALL for TigerTrak units: APTIGR