August 30, 2011 1 Comment
So far I’ve used three digital modes on the HF bands: PSK (mostly PSK31), WSPR, and JT65A. PSK is fun, in that you see signal phenomena in real time, and you see them both visually and in the ability or inability to decode the signal. If the signal fades, you see it fade; if two stations transmit on the same frequency, you can see that too. It allows you to chat with other stations and write whatever you want. But because PSK31 does not have any error correction or automatic acknowledgements, you sometimes receive only part of a transmission. To me, this feels low-tech. I expect digital transmissions to be almost perfect when communication is possible. PSK31 is not.
WSPR and JT65A incorporate strong error correcting codes, so transmissions are usually error free (not always, but almost). But neither of these is good at actually sending information. In WSPR the only information transmitted is station identification and location; you can’t say anything other than who and where you are. JT65A allows you to send a bit of free text, but it’s cumbersome; mostly, it’s also just for establishing the ability to communicate, not for actually communicating information.
Yesterday I finally succeeded in using another digital mode called WINMOR, which really feels like high-tech on HF. WINMOR is part of Winlink 2000, a system that is mostly designed to send and receive regular internet email through HF, VHF, and UHF radios. It is used by radio amateurs, emergency organizations, and NGOs to communicate by email from places that do not have internet connections (like yachts, jungles, etc.). Winlink initially used an HF digital mode called PACTOR, which is very adaptive and efficient. PACTOR requires a dedicated hardware modem; the protocol is proprietary and the modems are expensive. A couple years ago Rick Muething designed WINMOR, an HF sound-card protocol for Winlink 2000 (on VHF and UHF Winlink uses AX25). I downloaded the software a while back but didn’t manage to connect to an HF radio gateway, and forgot about it.
Yesterday I decided to give it another try. The software uses a propagation prediction program and a list of active gateways to suggest gateways that are likely reachable. I tried to connect to the one that was supposed to be best, in southern Russia (on 14MHz). I heard the gateway respond and got a message that I was connected, but when the software tried to deliver an email message I sent, the gateway failed to respond and the connection was broken. I tried a few times and gave up. I also tried gateways in the Netherlands and Germany, but they did not even respond to me. In the afternoon conditions on 14MHz seemed to have improved, so I tried again. It worked! I received the mail I sent myself via HF! I replied and connected again to the radio gateway, and the response was delivered to me over the radio. Very cool.
I was later able to also connect to the radio gateway in the Netherlands, and to upload position reports to Winlink 2000, not just email. The Winlink web site shows the position of all the stations that uploaded position reports recently, and you can also view all the recent positions of particular stations. It’s quite interesting; many stations upload position reports from the middle of the ocean, as you can see here.
Winlink and WINMOR are really interesting. They deliver a useful service. Most of the time, sending email via WiFi, cellular, or wired networks makes much more sense than sending email over HF or VHF radios. But in emergencies and when you’re in the middle of the ocean, Winlink is a really useful service. The protocol is very sophisticated, but you can sort of see some of what it is doing. You hear and see acknowledgements, retransmissions, and other protocol actions. But the biggest difference between WINMOR and many other HF digital modes is that it is an all-or-nothing protocol; it either delivers the data perfectly with no errors, or it fails completely. You don’t get garbled text. This is how modern communication works.
It’s not easy to set up radio gateways; the Winlink 2000 folks want gateways to run continuously (24 hours a day, every day), so setting up a gateway is not something to just experiment with, like I did with WSPR and APRS.
But WINMOR also has a peer-to-peer mode that allows you to communicate outside the Winlink system; perhaps I’ll try that.