HFU HF Underground
Loggings => HF Beacons => Topic started by: Dag on June 27, 2015, 2321 UTC
-
I've constructed a sawtooth hifer beacon on a dial frequency of USB 13554.40 KHz running a few milliwatts into a homebrew multiband ladderline-fed-MFJ-tuner tuned zig-zaggin' attic dipole up about 15 feet/3 meters. The signal should show somewhere between 725 Hz and 750 Hz on the spectrum display at the aforementioned dial frequency: the drift is due to ambient air temperature changes.
The circuit is an NE555 in astable mode and an EPSON SG 8002 oscillator and some old junk box parts on a prototype breadboard with a lot of alligator clips.
The calculated time constant of the NE555 with resistor/capacitor that I'm using show a completed cycle each 343.78 seconds or 5 min 43 seconds, but I suspect the capacitors/resistors I have are not of tight tolerance. Hence the time it takes to complete one cycle may be off a little, but it looks pretty much in agreement on my spectrum display.
The frequency shift of the sawtooth is about 3 Hertz and with the narrow frequency shift and slow oscillation of the sawtooth, it takes a slow waterfall to see it.
It runs 24 hours/day using a 7 volt wall wart.
I would appreciate some reports and screen shots to test the consistency of copy before I rebuild it Manhattan-style on copper clad pc board in an insulated enclosure to minimize drift.
Should I move the frequency? Are there other ISM signals on the same frequency that may interfere? Codar?
I intend to construct a new dipole or vertical for this signal, and possibly get it solar powered with a night-time battery voltage source if it proves relatively copyable.
This beacon looks nearly like a straight line on a spectrum display of 3 seconds/dot and 10 seconds/dot. It clearly shows it's sawtooth character at 30 seconds/dot and 60 seconds/dot.
Thank you.
Dag