Just another Amateur Radio Operator

Tag: AX.25

Packet Communications!

First Packet Connection

I’ve played about briefly with AX.25 in the past when tinkering with APRS, but never really had much success with it and with TNCs being both hard to come by and damn expensive for what they are, it has always been out of my reach.┬áRecently I acquired a couple of second hand TNCs and have spent the weekend setting up and connecting.

The first TNC I attempted working on was a Paccom TNC 320. This meant creating a cable to go from the 5 pin DIN connection on the back of the TNC to the 6 pin mini-DIN connection in the back of my ICOM radio. The first attempts at this involved using the mini-DIN tails from old PS/2 Mice or keyboards, testing to see if their wired up pins were going to be any good for the TNC and then just soldering the 5 pin DIN on the other end. I spent an evening with VK7ZMS doing this and after much testing, we got to the point where we had PTT and 1200 baud AF working, but no RX. Even then. the AF out tones were low.

Over the weekend I bit the bullet and visited Jaycar and bought some more mini-DIN, 5 ping DIN and multi-core wire and created my own cabling. This time I was also armed with an MFJ-1270B TNC which was my fallback option if I had no luck with the Paccom.

Plugged everything in, fired up a Putty serial connection, got presented with garbage. Changed the terminal baud settings, still got presented with garbage. Thought at this point it’s probably a good time to read the manual. Interesting thing about the MFJ TNCs is that they use 7 bit words, not 8 bit like many other devices. Updated my settings and bingo, was presented with text that looked like a TNC.

Ran the calibration tests, PTT worked, I could hear tones being sent loud and clear, and most importantly I was receiving packets as well. I was in business. Finished assembling the cable, plugged everything back in and found I had Rx, PTT but no tones out. Back to workshop again and found in the final assembly I had caused a small short across some of the pins. I fixed the issue, liberally applied hot glue to hold it all in place and provide isolation and put it all back together again, and now it works!

As you can see above, I have managed to successfully connect to VK7ZMS. I have also connected to VK7HDM-9 using VK7ZMS as a via.

I already know of a few other amateurs getting interested in packet again, so who knows, we might see a bit of a packet radio revival in southern VK7!

Everything Old….

The last time I was active on air was a brief period in 2011. During this time, I just wasn’t that interested in radio and it took a back seat to other projects and interests.

Fast forward to July 2015. My lovely partner has gone overseas for a few weeks and I decided to spend a couple of evenings at my local radio club which holds amateur TV nights most Wednesday evenings. This wasn’t new to me. What was new however was a couple of work colleagues deciding to come up with me and the discovery that the stuff I couldn’t do before I now could, especially having bought a contemporary new transceiver.

So now I find myself not knowing which way to go first with many of these “old” things (and not so old) that are all new to me again:

  • VK3YT’s endeavours with High Altitude Balloons I find just amazing, and can easily see this becoming science projects in high schools or colleges, promoting amateur radio, electronics and further research.
  • JT65 Weak Signal Modes┬ábeing used for high altitude balloons, HF communications, EME, Meteor Scatter and a whole range of other types of communications that are just not suitable for voice communications
  • Traditional Modes such as BPSK, RTTY and STTV, and more exotic modes like THROB, Feld Hell and Contestia. Previously I did not have the hardware available to do this at home. Now I do. Enough said there really.
  • Packet Radio. AX.25. One of the many projects I am currently running with. I have acquired an old TNC, and it’s just a matter of interfacing it with the radio.
  • Speaking of interfacing, I need to make a suitable new interface for my Icom IC-706MkIIG that includes PTT and audio in.
  • Amateur Satellite communications. It doesn’t seem as hard as it sounds remarkably, and I think that would be great fun.
  • FreeDV – The new digital voice mode on the block. it’s achieving some amazing things like FM quality audio with weak signals, and is definitely a QSO mode I want to try.

This, along with station maintenance and improvements is definitely going to keep me busy in the foreseeable future. I’ll touch more on the station maintenance in a later post.


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