Congrats on your purchase, Black Cat Systems has been around for a long time making small hobby projects like this, and various apps for signal logging of stations and other things.
I remember that project from a few years ago, several senior members of Part-15 were working on it and I think each added a separate part to the circuit. I didn't see the results and if anyone got theirs on the air, but Tha Dood built a similar rig and had it on the air.
I've been interested in this band, and when I first was interested in getting a crystal for 13.560 to build a small transmitter, they were expensive. Recently a hobbyist who retired sent me some of the small can 13.56 commodity crystals as used in the Black Cat rig, and I was thinking about making a simple modulated oscillator for the band to see what it could do.
You could even experiment with the beacon by adding an AM modulator to it, transistor or even a diode modulator, since it has extra power output headroom.
I like that it has a 5-pole low pass filter, even for 5 milliwatts, and uses the ATTiny micro controller as a keyer, that's all you need in something simple.
Maybe we should suggest that Black Cat make Part-15 mediumwave gear as well, I don't think they're doing it.
I bought a couple 13.560 mHz 4-pin oscillator chips when everyone was talking about getting on 13.560. They work just fine and you can even modulate them by simply putting an audio source in series with the power lead. Of course the output wave form is a square wave since they were intended to be a TTL clock signal. But, passing that through a 5 pole filter would clean it up. My intent was to build a buffer and final modulated stage to follow the oscillator chip. Some day I'll get around to it. As it was, the signal could be heard maybe 100 feet away using just a short piece of wire for an antenna. The Black Cat beacon should be here today so perhaps tonight or tomorrow I'll have it on air!
MRAM 1500 Charter Member ALPB Previous Chairman ALPB
I think it would be cool to be able to send an AM carrier through it. If you build a dipole antenna for the correct length or build an ATU for it I think you could do some serious distance. I would think you stand a good chance if they ever up the rules to 100 milliwatts down there.
Good real-world experience there, and it seems a few miles is already pretty good for just being a test. I'll have to give it a shot, and probably since I'm pretty close to your QTH as HF goes, it might be best to try to hear it in the middle of the day, like high noon.
Maybe those other signals on 13.56 were Flo's price gun from the insurance commercials, that was my first thought.
I've heard other beacons there, and things that sounded like digital modes, and voice communications, but that was on an analog receiver, so it might have been adjacent to the Part-15 band, I wasn't sure.
I found out about it through Popular Communications magazine, when someone wrote about frequencies hidden away on HF, and you could hear spies and other strange signals, so I started checking them out, and 13.56 was on the list.
Thursday afternoon I listened on a SDR in Southern Pennsylvania, didn't hear MRAM, but zooming in on the display there were 5 or 6 carriers showing as vertical lines clustered around 13560, and an elevated noise level, S5, 10 khz centered on the center frequency, compared to the average noise level of S3 outside of the band. Maybe the noise was all of those RFID systems leaking off microvolt signals from stores and warehouses everywhere.
I heard what I thought was one CW operator, and maybe a second one, but the dots were lengthened to 1-2 seconds, listening in CW mode. I could see it on the display better than actually hearing it.
A friend thought we might be too close together to receive the signal, and maybe he means with our low sunspot numbers? I could check out a propagation predictor to see when it could be possible to have a path between our locations.
It took just a little over an hour to assemble the Black Cat Beacon and tweak the tuning. It's on air now. I was able to (Edited by author on Sat, Feb 8 2020)put it within 500 Hz of 13.560. If you happen to hear it, let me know.
(Edited by author on Sat, Feb 8 2020)
For some expectations about that, below is a table showing the free-space field vs. distance from a 13.56 MHz transmit system producing 15,848 µV/m along a given direction/bearing at a distance of 30 meters from its radiator.