HF APRS/Packet: The First Thing I Did In 2018

2018 is here, and while I don’t make resolutions, I kind of made one last night and I already kept it. I wanted to do something on the radio I hadn’t done and had only been thinking about, so I decided to try and give APRS/Packet over HF a try.

Last night just after the ball dropped, I was sitting in front of my computer like it was any other evening (because seriously…all that happened is the year changed) and I came across a post on Reddit talking about APRS on other bands. Someone mentioned operation on HF and posted some links to some information. It had been a while since I read on the subject, so I sat and read.

This was something I’d been wanting to do ever since I built my sound card interface a couple years ago. In fact, I remember reading into it before but just got overwhelmed with the information. The explanation behind software TNCs was confusing, the explanation behind using the software was confusing; none of this was written for someone who had just started out, and nearly two years later not much had changed. But the links in that Reddit post made the software required a little easier to understand; and those two years did net me the knowledge of having a bit better idea of WTF I’m doing.

So just after midnight, I decided to give it a shot. So let’s look at what I used, how it was set up, and any issues I had (which were many).

UZ7HO Soundmodem

When looking for a software TNC it seemed my main options were DireWolf, UZ7HO’s Soundmodem, and apparently the AGWPacketEngine. I went with UZ7HO’s software TNC since it was late and I wanted something that might be easier to understand, and it was listed as having a GUI.


I wanted to try UI-View but when looking at the “recommendations” of what needed to be done to make this abandoned application work; I said no thanks. Any program that requires me to jump through 4,000 hoops to use is not worth my time. While I usually avoid ham software that costs money; this one didn’t require me to fork over money to get the basic functionality I wanted. It’s also modern, so I didn’t have to spend 3 hours hacking UI-View.


The basic setup and how the programs interconnect is the easy part. You run UZ7HO as the modem/TNC. Your APRS┬áprogram connects to UZ7HO like it would a normal TNC. IT sends commands, UZ7HO sends them out over the radio. This isn’t much different than most digital mode software except it interfaces directly with a sound card setup, where this is using the second piece of software to interface with the radio.

But this wasn’t as easy as it sounds. AGWTracker set-up just fine, that wasn’t the issue. The issues I had were with UZ7HO and getting my VFO set.

For those who don’t know, most APRS (and it seems packet information) happens on a specific set of frequencies in the 30m band (it can happen elsewhere but when I look…30m is the most commonly mentioned). So what that requires is you to know the audio frequencies of the mark/space used by your TNC, then select the appropriate sideband mode and adjust your VFO accordingly.

The problem is when I looked online, there are multiple different ways of setting up your tones and VFO. Some people said to use a specific frequency on LSB, another group said use USB. The documentation for UZ7HO didn’t make any mention of what polarity it sent stuff in…so I pretty much had to guess. I figured I’d try both ways. I knew how to avoid straying over 10150khz..so figured as long as I did that, then firing off a few incorrectly tuned packets wasn’t going to be the end of the world. Afterall…this is ham radio, it’s all experimentation.

While I was able to push some RF out…I didn’t get picked up. Now I wasn’t sure if it was lousy propagation, a lack of power, or a misconfiguration. I wasn’t seeing a lot of packet activity at that hour…making it harder to have something to tune against and check. I see a packet or two not get decoded but was that because I was off frequency, or in the wrong sideband mode and mark/space was reversed?

I did some research to see if anyone talked about specifically setting up UZ7HO with something, and most people wrote about setting it up with VHF. That didn’t seem to help me at first, but it made something click. If people are running this with VHF radios….then it’s very likely going to require me to use USB mode.

Throwing caution to the wind I reconfigured my VFO and UZ7HO once again. This time I was going to park myself 900hz away from the lower tone and set UZ7HO for 900/1100 operation. While I know most people recommend using 1600/1800; I think that’s just to keep with the “convention” of older hardware TNCs. The important part is that my radio transmits it’s tones on the right frequencies. How I accomplish that shouldn’t matter?

No, it doesn’t. No sooner than I set my software and rig up this way, I immediately saw a packet fire from an HF IGate pop up in the modem terminal. I was ecstatic! This told me I was absolutely on the right path to getting it working. Decoding even a single packet told me the modem was tuned properly.

I jumped back to AGWTracker and told it to fire off my location. Within seconds I saw a blue house icon with NQ4T-4 pop-up on APRS. I had been picked up by that same iGate. It worked! I’d just successfully run 300 baud AX.25 on HF.

I did attempt to run an HF iGate after that using the same soundmodem and APRSIS32. I had some success, I was able to push the beacon from the one HFIgate to APRS-IS; but I had some other issues. While I wanted to push data over IS, I didn’t want to beacon over it and would have rather just transmitted beacons over HF. I wound up doing both, which meant my HF beacons never made it into the system as they got dumped for being duplicated with the packet it uploaded directly. I did see my own packet come back over APRS-IS in the client, but it never showed on the IS system as coming in from the internet.

The other problem I had was with UZ7HO’s program. I have a lot of “playback” devices on my computer according to Windows. Three of them are various onboard sound options; headphones, analog out, digital out. 4 of them are “NVidia Output” from my GPU’s DVI/HDMI ports. I also have a USB headset and USB DAC hooked up. For input devices, I have a couple of onboard sound and one from my headset. I used the standard headphone out on the front of my PC. In fact, the only thing I use my onboard sound for is radio; I’m either using the headset or my DAC.

The problem with UZ7HO is it seems to insist on using default output device in Windows. You can change it in the program…but if you do certain things (I never figured out what); then it seems to default back to that. There were several times I heard my radio click to transmit but heard the packet data coming out of my headset! I could manually pick it in the program, yes; but if I did anything like change volume…it would change back. The solution is to set the headphones to default, right?

Except that seems to be a bad solution in my book. With being set as the default device, that means any and all sounds that are just played to the OS will come out over the headphone jack. This sets up the potential to transmit sounds and other things I shouldn’t. Now I don’t use a Signalink or anything else VOX like (Signalink is VOX, it’s just glorified over-complicated VOX even if it’s not using your rig’s VOX), then I won’t do like I *constantly* hear in the FT/JT bands and transmit every single alert my computer plays. But there was still a chance Windows could “ding” while transmitting a packet. This would be bad because not only is this not allowed on 30m, but it would also have me emitting out of band.

I can’t really run a HF IGate 24/7 right now; I only have one antenna. I thought it might be fun to set up and have it running during my idle time when I’m at work; though I’d have to disable beaconing over RF anyway if I’m not home.

I guess I’m going to have to either find another software TNC that doesn’t have the same device limitation as UZ7HO, or contact the author and see if he has any suggestions. Dire Wolf is another popular option I’ve considered trying. I may get around to it.


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