I keep on reading about “Digital APRS” vs “Analog APRS”. Youtube and social media are full of these words. This is utterly wrong. Whenever I hear “Analog APRS” I’m going mental: “Analog APRS” simply does not exist. Let’s explain….
Where do the words “Digital APRS” and “Analog APRS” come from?
The term “Digital APRS” and “Analog APRS” came from chinese manufacturers (yes Anytone I’m looking at you) when they started building DMR radios which are capable of sending position information along speech when doing DMR (which is actually part of the DMR standard) and combine them with a 1200bps “AX25” APRS tracker all in one radio.
So basically what they call “Digital APRS” describes the position data embedded in the DMR stream and “Analog APRS” is the 1200bps APRS operated on 144.39 in the US and 144.8 in Europe. Maybe this is used as a marketing trick to state that the radio can do both, I do not know.
Over time the word “Digital APRS” has propagated to DStar users.
What is wrong about saying “Analog APRS”?
Because APRS as used on VHF or HF is digital.
On VHF, APRS relies on 1200bps AX25 for the air interface. It barely consists of two tones which are sent over the air. One tone for 0, one tone for 1. Those tones are called a sub-carrier because the digital information is not conveyed directly by the actual RF carrier but by these two tones which, in turn, modulate the RF carrier in frequency. This modulation scheme is named AFSK : Audio Frequency Shift Keying.
According to ITU designation of emission 1200bps AX25 is classified as F2D. It can be decomposed as :
- F : Frequency Modulation
- 2 : One channel containing digital information, using sub-carrier (our two tones)
- D : Data transmission
As a side note, 9600bps AX25 is F1D.
APRS capable radios sold by Kenwood and other manufacturers clearly mention these designations of emission. F1D (9600bps APRS), F2D (1200bps APRS) and F3E (Analog FM voice)
What is it about the APRS data in DMR ?
DMR originated as a standard for land mobile radio for commercial radios. The position was included as a way for commercial users to be able to track their assets. It is worlds away from APRS. The position data embedded into the data stream in no way directly usable by the APRS-IS network. Conversion to APRS position frames data happens at the network level e.g. for Brandmeister in the master server and is then injected into APRS-IS network.
Add to that, the fact that this is only a truncated version of APRS. APRS is way more than positions on a website, but that’s not the point here.
BTW, DMR is classified F7W as per ITU.
How about D-PRS in DStar ?
DPRS as used in DStar is closer to APRS than DMR. In Icom radios (Kenwood did not stick to this) the position data is embedded as a TNC2 formatted string which can be directly passed as this by the repeater or hotspot into the APRS-IS network. The latest Icom radios can decode more than positions and support objects and WX APRS frames. However, no one is using it as of today.
Now stop sounding like a mogul and stop saying “Digital APRS” and “Analog APRS”. I suggest the chinese manufacturer go back to engineering school and get their basics straight #sarcasm