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FM APRS function
Posted: Mon Oct 25, 2021 6:57 pm
by Uken
Hi!
Is it possible to add fm aprs function to opengd77 software?
Thanks!
Re: FM APRS function
Posted: Mon Oct 25, 2021 8:52 pm
by VK3KYY
Please explain n more detail exactly what you mean, including use cases and modulatin standard etc
AKIF, The hardware is not cspabile of transmitting or receiving high speed the based data eg like FM packet radio
Re: FM APRS function
Posted: Tue Oct 26, 2021 6:44 pm
by Uken
It's about a function like in yaesu VX-8, you know gd-77 does not have GPS, so APRS frames would have to be sent with the location entered manually.
Re: FM APRS function
Posted: Tue Oct 26, 2021 8:12 pm
by VK3KYY
OK.
I looked up the underlying data transfer modulation and protocol for APRS, and its 1200 baud FSK
The hardware does not specifically pport this transmission or reception modulation protocol.
The RF chip can transmit FM DTMF tones, but I have no idea whether it could transmit a different tone every 1/1200 of a second.
Its not designed to do this
I won't be wasting my time finding out whether it can ...
Re: FM APRS function
Posted: Wed Nov 03, 2021 12:50 am
by VK3KYY
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.
However, there is another thread about sending APRS data via the DMR TA, and I think this may be possible.
Albeit again, the location would be whatever the operator entered into their radio.
Re: FM APRS function
Posted: Sun Oct 23, 2022 6:50 am
by VK3KYY
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.
APRS uses standard 1200 baud packet radio standard, which is based on the Bell 202 modem standard (from over 40+ years ago), which has 2 tones, and modulated as AFSK. Typically most FM 2-way radios can work with this, and thus there are many external modems via hardware or software (or "mic-encoders) for this mode. The OP can certainly use an external solution, but of course he would want an internal solution.
There needs to be some circuitry that can do this modulation and feed into the audio input of the radio, typically a small microcontroller that can be programmed to have this protocol, nothing fancy, but if it doesn't exist in the GD-77, then it can't be used (or if exists, but can't be re-programmed to do such).
I can think of a GPSr equipped "speaker mic" with a built in micro-controller, can probably be used for APRS transmitting. There have been products built in the past to do this.
Do you have a link to the modulation standard for this ?
e.g. what tone frequences are used to define logic 1 and 0 ?
Re: FM APRS function
Posted: Sun Oct 23, 2022 9:54 am
by ok1pt
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 ?
Hello,
I think it't there (Bell 202 modulation):
https://en.wikipedia.org/wiki/Packet_ra ... io_channel
With regards / 73
Pavel OK1PT
Re: FM APRS function
Posted: Sun Oct 23, 2022 11:22 am
by VK3KYY
Thanks.
I already found this but its not a detailed technical specification
Re: FM APRS function
Posted: Mon Oct 24, 2022 5:19 am
by ok1pt
VK3KYY wrote: ↑Sun Oct 23, 2022 11:22 am
Thanks.
I already found this but its not a detailed technical specification
Hi Roger,
so possibly this one is better ?
http://www.softelectro.ru/bell202_en.html
73, OK1PT
Re: FM APRS function
Posted: Tue Oct 25, 2022 12:35 pm
by newbie01
Also interested in this, especially now that I see the MD-UV380 is supported.
@VK3KYY Do you happen to own a hackrf(+portapack)? I've been poking around the mayhem firmware and learning a bit about APRS... you're likely (okay definitely) way ahead of me on what it would take to implement on a radio, but
this might help.