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Googling for VHF FM parts, I find the "NiceRF SA818 1W Embedded walkie talkie module":
This Czech ham (and others) has done lot of work on filters, PCB board, and software for it:
Another article agrees: don't transmit with them without filtering:
Here's an under-$60 box using something different? I can't tell. It promotes its weather features more than the APRS.
I think I heard mention of "direwolf" this morning, but I didn't know what it was:
I like the idea of the Ham Radio Of Things (linked from that direwolf page).
A friend co-designed:
The board can be used with a SA818 VHF or UHF. The FL1 next to the SMA connector is where the filter goes. The board can also be used without the SA818 with an external radio. For that you need to use J3.
Also, if you have decided to use an SA818 you probably are going to need this to program it. https://github.com/0x9900/SA818 There is a couple of things the program doesn’t do, but it’s a work in progress.
Another friend writes:
as hardware tnc's go, i'm a fan of rob wx9o's work. his mobilink tnc3 is a terrific TNC. i have several. one is attached to the kenwood in my jeep. APRSdroid speaks to it via Bluetooth and that's how I do my mobile APRS.
rob also supports nucleotnc, which is a roll-your-own edu-variant of the TNC3 for STM32 nucleo and breadboard: [[ http://www.mobilinkd.com/2019/06/24/nucleotnc/ ]].
there is also a $7 nucleotnc pcb if you want to solder things down.
the software is open source. all the mod/demod happens on the STM32 and you speak KISS to it.
the other direction the "soundcard" TNC like direwolf.
you need to get the audio to direwolf. lots of ways to do that. what you are doing for echolink is probably exactly right; it is just the wrong flavor of audio (flat/emphasis/twist).
the NW Digital's DRAWS [[ http://nwdigitalradio.com/what-is-draws/ ]] board is a nice bit of general radio interfacing kit for RPi that includes GPS. It is a bit spendy at ~$150. (PAARA uses a Pi+DRAWS at field day to provide NTP via GPS to the network.)
Yet another friend writes (in 2020):
Twenty+ years ago, I ran APRS using a Kantronics KPC-3+ TNC and software on a laptop.
There were lots of cables in my car.
However, being lazy perhaps, I bought Kenwood radios that have TNC and APRS software built-in.
I originally used Kenwood’s TH-D7GA.
Now I use the TH-D72A HT and TM-D710GA mobile rig.
The only drawback is lack of full keyboard.
It is painfully slow to enter a text message one letter at a time.
Yet I’ve done it many times while camping in the Sierra Nevada while sitting on a peak or under a nice tree with seeming infinite time.
APRS is great for texting (SMS) and sending text emails.
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