Foundations of Amateur Radio
When you start life you learn early on the difference between being told about an experience and the actual experience. There's a saying that comes to mind, I use it regularly in my day job: In theory there is no difference between theory and practice, while in practice there is.
I thought I'd do the quote justice to see where it came from, not from Einstein, who was three years old at the time it was coined and neither Yogi Berra or Richard Feynman had been born. Quote Investigator puts it in the Yale Literary Magazine of February 1882 and attributes it to Benjamin Brewster, but I digress.
A little while ago the regulator in Australia altered the rules of engagement in relation to amateur radio for people holding the license that I do. All Australian amateurs are now permitted to transmit digital modes. Not that this should have been any impediment to the exploration of the receive side, but I had a few other things on my plate to try. Still do.
Over the weekend I sat in my driveway with my radio and had the urge to see if I could actually do some PSK31, a digital mode that had a low entry barrier, since there were defined frequencies, and I could use a decoder on my phone.
So, I set about doing just that. I had already programmed in the various frequencies into my radio the week before. I hadn't actually heard any signals, but that didn't deter me. I set about getting myself set-up for what I'm calling a driveway hack.
Picture this. A folding table with my radio. A stool next to it with me on it. The radio connected to an antenna, a vertical that was attached to a neighbour's roof with a magnetic mount and my phone running DroidPSK. I was tuned to the 10m PSK frequency, had the volume turned up, holding my phone next to the speaker, watching the waterfall.
Nothing.
I called up a mate who had this all working and we set about trouble shooting my set up.
He made some transmissions; nothing.
I listened to the 10m beacon, loud and clear.
He made some more transmissions, still nothing.
Then we realised while I was switching back and forth between the beacon and the PSK frequency that his radio was set up for a different standard PSK frequency. Gotta love standards, there's one for every occasion. Changed my frequency and for the first time I could actually see stuff in the waterfall display on my phone.
If you've never seen a waterfall display, it's a tool that helps visualise the signal strength of a chunk of spectrum over time. It's pretty nifty and a waterfall displays a lot of information.
Starting with colour, the idea is that a colour represents a particular signal strength. Red for full signal, yellow for half, blue for the lowest detected signal and black for no signal. Fill in the gaps with the colours of the rainbow.
If you represent a line made of dots with the start of the line at say 0 Hz and the end of the line at say 3 kHz, you could split the line into 300 dots, and each dot could be coloured to represent the average signal strength for a little 10 Hz slice of spectrum.
If you wait a second, move the line you drew down and then measure again, you'd end up with two lines. The line from now at the top, the line from a second ago below it. If you do this every second, you'll end up with lines flowing off the bottom of the screen, the oldest lines at the bottom and the newest ones at the top.
That is a waterfall display. Over time you'll start to recognise what a particular signal looks like on the waterfall and there are even modes where you can draw on the waterfall, but I'll leave that for another day.
As I said, I could now finally see signals on my waterfall display.
I'm not going to dig too deep here, because there's much confusion in the language surrounding all this and I intend to get the names straight in my mind before I express them here, but after figuring out that you have to tell DroidPSK which signal you want to decode, I finally managed to decode the transmission from my friend.
After putting on some headphones and realising that the clicks I was hearing from my phone were actually artefacts from the speaker, I also managed to transmit a CQ signal which my friend decoded. He then acknowledged my callsign in his next transmission.
So, I now have two screen shots, his and mine, showing that we both saw each other using 10m PSK31. There wasn't a signal strength exchange, mainly because I have yet to figure out how to determine that and where it's visible, but for all the things that matter, I managed a contact with PSK31 thanks to Randall VK6WR, very exciting!
Since then I've started experimenting with decoding WebSDR, that's HF signals coming in via the internet and being decoded on my computer from the web audio. I'm still working on that, but there is so much to learn and play with and a transmitter isn't yet needed to have fun. I should mention that you can also decode satellite signals like this.
Digital modes, just when you thought that the rabbit hole couldn't get any deeper.
I'm Onno VK6FLAB
