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Topics - greator

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The RF Workbench / Arduschreiber HF-Beacon mkII
« on: July 15, 2020, 1619 UTC »
After having test run the mkI version in my garden with good results I have done a new construction of the transmitter, the basic design is the same but the source of the schematics is different(came with Chinese QRP TX from Ebay), some of the values are a bit different, and the source of the 74HC240 is other. I 3d printed a holder for the Arduino Nano, witch turned out nicely.

Now im just waiting for a few more components for the lowpass filter, according to the designer, the PA-stage will put out about 10W at 13.8v. Im expecting more lika 2-3W.

Does anyone know what this signal is? Found it at 4280kHz, sounds a bit like RTTY, but i cant decode it like one of the ordinary RTTY modes. It transmitts for 3-4s, then pauses with only a carrier wave for 3-4s and then starts over.

I thought i would share a small side-project, sending Hellschreiber from a small HF-beacon using a arduino. I took some effort to write the code in such a manner that it would fit in memory of a Nano, but it worked in the end! The code is simple tu use, just enter a string and it will send it.

Hell has a few good low-power alternatives, as slow hell. It should just be a question of setting the "speed" right(the number of micro seconds each dot take). But i have only gotten it to work with the normal field hell so fat.

Download link to arduinocode(Arduschreiber): https://gofile.io/d/FHAUjF

Edit: Moved code to txt-file in link to make thread more readable

The RF Workbench / HF Beacon, design questions
« on: June 01, 2020, 1500 UTC »
Hello Everyone!

I have started to build an HF beacon, and thought someone here might be able to help me with parts of the design. The beacon will have a simple 10W transmitter, and be controlled by a arduino and have a few sensors, the antenna will be a less than perfect longwire with a counterpoise. Placement will be on tree. There will probably be a 10-20W solarpanel and a 12v led-acid battery with 5-10Ah. Frequency will be in the range 2-8MHz.

Communication protocoll:
The beacon will have a name, that will be transmitted in CW. Lower speed will make it easier to read on fldigi/DM780 etc.. The values for voltage, temperature and lightlevel on the other hand, might be better to send in dits(0-10 dits = 8-15volts etc...) A timed pulse would also be usefull, but consume more power. What is the normal transmittion interval of a HF beacon these days?

Power management: I live in a Scandinavian country, in the winter its only about 5-6hours of daylight. A lower limit on transmittion will prevent deep discharge of the battery, but perhaps transmittion intervals should be proportional to the voltage? 11-14v = transmition each 5 to 1 minute? At the lower frequencys, its perhaps better to save battery power for the night, when there is better propagation.

Solarpanel: To prevent overcharging(havent got a power regulator), it might work to simply disconect the solar panel when voltage is above 14volts.

Protection: I am thinking about using some kind of epoxy to protect the transmitter and control circuit from water. Does any epoxy work?

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