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I am curious to know if it is possible to do packet radio on VHF/UHF using the UV-5R... I have seen some invasive hardware hacks, but without modifying the radio itself (firmware, hardware) it's my understanding that you can only toggle send/receive using the 2.5mm/3.5mm TRS ports.

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    $\begingroup$ Apart from those mentioned below by rclocher3, there are many digi-mode that interface with transceiver with mic, speaker and PTT tx lines. Use PC build in sound. No extra cost. Just get software, most free. Happy trying them out. $\endgroup$ – EEd Aug 15 '16 at 18:10
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You sure can. It's been done before with a Baofeng HT, a Raspberry Pi, a USB sound card, and some custom cables and some open-source sound card modem software. This article explains a step-by-step approach.

This article shows how to create a custom cable for interfacing a Baofeng HT with an Android phone (but should be sufficient for figuring out the wiring for the USB sound card so you can interface with your Raspberry Pi - specifically, you'll probably need to separate the right/left audio from the mic and PTT for the sound card's separate mic/audio jacks). Of course you could use the custom cable and an Android phone or tablet running the APRSdroid software mentioned in that article. There are also ready-made cables like the BTECH APRS-K2 TRRS / APRS Cable.

In the first case, the Raspberry Pi is acting as the TNC; in the latter, the Android and APRSdroid are serving that function.

The point of this cable is to connect the input and output audio cables of your computing device (smart phone, raspberry pi or whatever) to the radio. By setting the VOX and squelch settings just right (e.g. "VOX at ~2, Squelch at ~1"). Then the computer takes the role of the modem and does modulation (for transmitting, triggered by the VOX setting) and demodulation (for receiving, triggered by the squelch setting).

I hope this helps.

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  • $\begingroup$ Looks good. I'll take apart my extra headset and start gathering the bits I need to build it. Thanks. $\endgroup$ – user400344 Aug 16 '16 at 11:51
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In the end I used 'amodem' ( see https://github.com/romanz/amodem ). After a few calibration steps, I could get decent I/O rates - considering the nature of the medium.

Compression of archives is necessary, and may be considered unethical. But the compression algorithms (e.g. 7zip, xz) are public, and anyone paying attention can read the data.

Rates of >=19200 baud (~2.4kB/s) are easily accomplished internationally, while IIRC 57600 baud (~7.2kB/s) are realistic domestic.

Hope others can use this as an intro to PR.

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  • $\begingroup$ I used and ran PBBS for a long time, and the rules clearly state that licensees are not to even attempt to hide the nature of their communications. That does not cover downloading ZIP files on a PBBS. The intention is quite clear. And anyone running a pirate-style fixed station in ham frequencies will be found and the FCC will do what they do best to them. Compression of clearly-named, appropriate compressed files clearly is ethical. It is a responsible way to conserve channel utilization and is to be encouraged. $\endgroup$ – SDsolar May 2 '17 at 6:10
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    $\begingroup$ So clearly-named zip-files is the way to go. Thanks. What kind of throughput did you get with PBBS, frequency/antenna info is welcomed as well. $\endgroup$ – user400344 May 22 '17 at 22:44
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    $\begingroup$ I was based at the Alaska National Guard building on Fort Richardson and we had a half-wave vertical hanging off the same tower used by the state troopers. Out transmitter was 100 Watts. I am searching my memory for actual speeds, but I can tell you that it was sufficiently fast that I don't recall any discussion about it. Back then, though, I am sure we used a TAPR-2 TNC. That would mean 1200 bps. 9600 Pactor was just coming around but we needed to ensure maximum compatibility with anyone who could set up. It operated on 145.010 and had very good coverage due to the location. $\endgroup$ – SDsolar May 23 '17 at 4:08
  • $\begingroup$ btw, we used ZIP files only for programs. Most of our traffic was plain text. During disaster scenarios the system got busy in both directions. $\endgroup$ – SDsolar May 23 '17 at 4:12
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The easiest way now is to get the Btech APRS-K2 Cable: it allows you to receive and send audio to the radio with a single cable. You can use it with the aprs.fi app or with a variety of software from a computer.

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  • $\begingroup$ I've got a data cable which gives me a serial port. It can be used to program channels etc. The TRRS jack on this cable could be good for transmitting audio with VOX enabled. Upvoted. $\endgroup$ – user400344 Jan 17 '17 at 16:10
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    $\begingroup$ Yep, originally, I bought the usb data cable, but this APRS-K2 cable is what I was really wanting. With this, in theory, all you should need is software modem software to transmit digital data. $\endgroup$ – caleb Jan 17 '17 at 16:56
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I recommend against using the modern inexpensive HT radios for packet, especially if you are buying the equipment on purpose for that application. You'd be much better off with 30 year old used ham radio mobile gear, with more power, more selective receiver, more predictable operation, easier UI, and less RF into your digital equipment, easier connections, easier power hookup, and nearly the same cost.

A serious consideration with modern HTs is that the designers are interesting in optimizing voice quality and battery life with no consideration for how this impacts packet radio use. Sacrifices can easily be made which increase usability for voice, but which make packet radio work worse and be more difficult to align.

Audio level consistency. A packet radio receiver modem wants to see an audio level that is both consistent across a packet, but also nearly the same for multiple tone frequencies on a packet. FM voice radios don't need to behave in this way. Indeed, voice compression, bad for packet, actually sounds great on voice.

DC signals (BIAS) on the receive audio are also OK for FM voice, especially with built in speaker equipment, but this also is of questionable value for a packet radio modem.

POP and CLICK removal: It is easy to remove pops and clicks from the audio by replacing annoying wave forms with duplicates of preceding or following wave forms, or by shifting the time of the wave forms. This is a well documented (and no longer patented) scheme used originally in broadcast radio transmission. This makes the receiver sound much better, at low cost, but makes packets less reliable, and this effect is nearly undetectable without an analog equipped logic analyzer. It's very confusing. I have on low authority that this is done in modern 2-way FM radio-on-a-chip devices.

Battery saving by disabling the radio: By having the control processor leave elements of the radio disabled for periods of time the radio can use less battery power while quiescent, but it would also not be awake to notice the start of a packet message. Baofeng radios are replete with this technology.

The Chinese brand-name radios have been known to emit energy at frequencies outside the ham band at levels beyond those permitted by the various government radio authorities (D.O.C. in Canada, F.C.C. in the USA). They have also been known to emit radio waves at near transmission levels through the chassis which can impact the stability of DC wiring in the vicinity of the radio. This is also confusing to somebody new to integrating digital, audio and RF equipment.

Used 2-way or ham radio equipment is particularly applicable to packet radio. A used ham radio which is missing the critical CTCSS PL TONE generator is nearly useless for repeater operation but is very usable for packet radio. Kenwood TM2550, TM7950, TM7800, are perfectly fine packet radios and are 25 watts output or better. Yeasu and Icom have offerings in the same age-class. Because they are not useful to non-packet hams, they show up for low prices, even competitive with brand new Baofeng UV5R radios.

In the commercial 2-way market, the Kenwood TK705d or TK805d is a fine radio for packet. Those are on ebay at under $50 delivered, even as I type. While some commercial 2-way radios need PCs and software to program, the TK705d and TK805d are front panel programmable, or can be made that way by moving or adding a 2-pin jumper.

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Sure it's possible. You'll need some sort of Terminal Node Controller (TNC), either one implemented in hardware or software, plus a set of cables that plug into the 2.5 mm / 3.5 mm TRS ports. If you're using a hardware TNC then you'll need some sort of computer and a serial or USB cable between the computer and the TNC. I've used a different model HT to send and receive APRS packets with a TinyTrak 4 as my TNC and xastir (APRS software for Linux), and it worked fine. APRS is a protocol that sends and receives specially-formatted AX.25 packets. I've heard there are "software TNCs", i.e. computer programs that generate audio tones to be sent to the radio, but I can't vouch for how well they work, having never tried them.

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  • $\begingroup$ What cheap/old TNCs would you recommend I look for on eBay? $\endgroup$ – user400344 Aug 16 '16 at 11:59
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    $\begingroup$ @user400344 TNCs, even used ones, seem to be quite pricey, because they were expensive when they first came out 30 years ago. Given those prices I'd probably experiment with software TNCs. If you want to do packet rather than just broadcast the location of your car via APRS, then I'd advise investing in a good antenna up high, and possibly a 50 W radio, before sinking money in a TNC. You need good signal-to-noise ratios for packet, especially if the other station is another home station rather than a digipeater atop a mountain. $\endgroup$ – rclocher3 Aug 16 '16 at 15:31
  • $\begingroup$ I don't care about my position, I most often know where I am. APRS is cool though, don't get me wrong. I need packet for something as simple as hamchat. I would even go as far as to prostitute myself and write it in python which is never pleasant. $\endgroup$ – user400344 Aug 16 '16 at 16:55
  • $\begingroup$ Well, the good news is that you're not the first person to want this. I'm sure you will find a software solution. As for hardware I think the best way to do this is with a USB sound interface and a cable like this: smile.amazon.com/gp/product/B01LMIBAZW - these little sound interface units work with both PC and my Android tablet with the USB port: ebay.com/itm/… - I can't recommend specific products here; just showing these as examples. $\endgroup$ – SDsolar May 2 '17 at 17:55
  • $\begingroup$ @rclocher3 has a really good point (+1) - a good radio and antenna do need to come first. Make sure you can hear other packet activity from your location. You want to be able to make solid connections to others. Scratchy sound doesn't work well with sound card interfaces or actual TNCs. You want enough power that they can hear you also. That means both transmitter power and a good antenna installation. As for TNCs, the prices have really surprised me. Even the little MFJ-1270 units are now more expensive than they were in the 80s. So starting with a sound card approach makes sense. $\endgroup$ – SDsolar May 2 '17 at 18:05
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I built a homebrew interface that uses a small USB soundcard with mic and ear 1/8" jacks. Each of those drives a 600:600 ohm transformer.

On the radio side, the transformers drive the mic and ear connections via the 2.5 and 3.5mm jacks.

I also used a cheap USB to serial board to run an optoisolator to trigger the radio PTT. The reason for this is that if you use the radio VOX to initiate transmit, the radio will stay in transmit for some time after the data have been sent, and it misses the return data from the packet server. This took me some time to discover!

All that being said, I have found that it is hard to set levels properly, and my connection reliability has been spotty. I have been able to send/receive email using Winlink Express along with soundmodem software, but quite often, the system just keeps trying to connect without success, so I'm not sure that using the Baofeng radios is the best solution.

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