FM APRS function

VK3KYY
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Re: FM APRS function

Post by VK3KYY » Fri Nov 18, 2022 4:02 am

ve7mdt wrote:
Fri Nov 18, 2022 3:09 am
VK3KYY wrote:
Sun Oct 23, 2022 6:50 am

Do you have a link to the modulation standard for this ?
e.g. what tone frequences are used to define logic 1 and 0 ?
Sorry, Roger, I haven't been back to this forum lately and missed your post.

I haven't looked at any implementation of the Bell 202 modem or 1200 AFSK packet radio, but I know it's been implemented in many small microcontrollers, even PIC, like the TinyTrak product (which version 1 was released on QST for its code and schematics many years ago), which is an encoder.

It's basically 2 audible tones modulated on to the FM audio. 9600 packet is entirely different as that's GMSK iirc.
I've been working on DMR APRS and its now in the latest release.

I don't have time to investigate whether the hardware would be capable of sening 1200 tones per second, but I think its not very likely, as the hardware is only designed to send slow speed DTMF tones.

kt4lh
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Re: FM APRS function

Post by kt4lh » Sun Nov 20, 2022 2:33 pm

VK3KYY wrote:
Fri Nov 18, 2022 4:02 am
I've been working on DMR APRS and its now in the latest release.

I don't have time to investigate whether the hardware would be capable of sening 1200 tones per second, but I think its not very likely, as the hardware is only designed to send slow speed DTMF tones.
I totally missed that this is what function you had added, woah. Would hotspot pass SMS from other radios now? I'll have to dig out the Pi I had set up for hotspot with a GD77 and give this a try.

Tested some, doesn't seem to. Very well may be user error. Set Brandmeister to Motorola, in-call enabled, Anytone 878 was already set to M-SMS, hooked up GD77 with latest FW to my Pi Star, I do see it receiving the SMS, callsign 8267646 TG 39, but don't see it making it out to aprs.fi or such. At least I think the DMR APRS beacon generated this, not sure, also tried to send a SMS and it didn't fail, but I didn't see it go anywhere either.

If I try the same on my mmdvm hotspot I see "DMR DATA" show up in the Local RF Activity, haven't seen this on the GD77 Hotspot. Maybe it's not expected to work, just figured I'd try it. It'd be awesome if this were possible though :)

VK3KYY
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Location: Melbourne, Australia

Re: FM APRS function

Post by VK3KYY » Sun Nov 20, 2022 7:53 pm

kt4lh wrote:
Sun Nov 20, 2022 2:33 pm
VK3KYY wrote:
Fri Nov 18, 2022 4:02 am
I've been working on DMR APRS and its now in the latest release.

I don't have time to investigate whether the hardware would be capable of sening 1200 tones per second, but I think its not very likely, as the hardware is only designed to send slow speed DTMF tones.
I totally missed that this is what function you had added, woah. Would hotspot pass SMS from other radios now? I'll have to dig out the Pi I had set up for hotspot with a GD77 and give this a try.

Tested some, doesn't seem to. Very well may be user error. Set Brandmeister to Motorola, in-call enabled, Anytone 878 was already set to M-SMS, hooked up GD77 with latest FW to my Pi Star, I do see it receiving the SMS, callsign 8267646 TG 39, but don't see it making it out to aprs.fi or such. At least I think the DMR APRS beacon generated this, not sure, also tried to send a SMS and it didn't fail, but I didn't see it go anywhere either.

If I try the same on my mmdvm hotspot I see "DMR DATA" show up in the Local RF Activity, haven't seen this on the GD77 Hotspot. Maybe it's not expected to work, just figured I'd try it. It'd be awesome if this were possible though :)
The DMR APRS, is "In Call GPS" , where the location is sent as part of the Talker Alias data.
This is defined in the ETSI specification.

The firmware does not support SMS messages at all, hence can't support SMS based APRS that other radios use

AFIK. The only commerical radios which support "In Call GPS" are Motorola and possibly Hytera, AFIK Anytone use SMS APRS, as does the official firmware on some of the TYT radios.


Currently the OpenGD77 Hotspot does not seem to be passing the In Call GPS data, I think this is simply because it needs to pass one additional packet of data.

I have some other urgent bugs to fix, but I will then be looking at why the OpenGD77 hotspot is not passing this data.

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DU2XXR
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Re: FM APRS function

Post by DU2XXR » Tue Nov 22, 2022 4:48 am

VK3KYY wrote:
Wed Nov 03, 2021 12:50 am
ve7mdt wrote:
Mon Nov 01, 2021 10:42 pm
I guess the OP wants something like on the Anytone AT-D878UV, which can transmit APRS packets, or the AT-D878UV-II, which can transmit and receive (decode) APRS packets. I own the former, but I have no idea how the circuitry got this to work in the radio.
Interestingly I see FM APRS is one of the key selling / differentiation points with the Anytone radios.

Since the GD77 etc doesn't have GPS, even if some way could be found to transmit APRS, which I think is unlikely, the location would only be updated if the operator manually entered and changed it in the radio.

So it would be of very limited use, and not worthy of the amount of time and effort that would be needed to investigate if pehaps there was some way to trick the hardware into sending and receiving this data.
APRS messaging is one such use case, and is not dependent on location. IMHO and IIRC, positioning is just one aspect of AFSK APRS, with messaging being a big part of the use case.

VK3KYY
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Re: FM APRS function

Post by VK3KYY » Tue Nov 22, 2022 5:27 am

4I1RAC wrote:
Tue Nov 22, 2022 4:48 am
VK3KYY wrote:
Wed Nov 03, 2021 12:50 am
ve7mdt wrote:
Mon Nov 01, 2021 10:42 pm
I guess the OP wants something like on the Anytone AT-D878UV, which can transmit APRS packets, or the AT-D878UV-II, which can transmit and receive (decode) APRS packets. I own the former, but I have no idea how the circuitry got this to work in the radio.
Interestingly I see FM APRS is one of the key selling / differentiation points with the Anytone radios.

Since the GD77 etc doesn't have GPS, even if some way could be found to transmit APRS, which I think is unlikely, the location would only be updated if the operator manually entered and changed it in the radio.

So it would be of very limited use, and not worthy of the amount of time and effort that would be needed to investigate if pehaps there was some way to trick the hardware into sending and receiving this data.
APRS messaging is one such use case, and is not dependent on location. IMHO and IIRC, positioning is just one aspect of AFSK APRS, with messaging being a big part of the use case.
This is a bit achedemic, as the radio is probably incapable of sending 1200 baud data on FM, and almost certainly is not capable of receiving it

OH1E
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Re: FM APRS function

Post by OH1E » Tue Jan 10, 2023 6:42 am

Have this older 80’s radio with z80 cpu and even that is able to send fm aprs. Its coded in assembly, the ram etc its way smaller than opengd77 software. fm aprs is way better as it not keep repeater open all the time.

n6io
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Re: FM APRS function

Post by n6io » Wed Jan 11, 2023 12:35 am

I have the Anytone 878UV plus and recently upgraded it to receive APRS by installing a new Bluetooth board that includes hardware to decode the APRS data. Sending APRS is trivial and requires very little processing power. But decoding the tones requires a lot more processing which is why AnyTone offloaded that work to this separate board. Even with the decoder board APRS performance is poor, requiring a signal about 10db above full quieting.

It shouldn't be difficult to have OpenGD77 send APRS but without a GPS it's not very useful.

Craig - N6IO

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