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Messages - greator

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The RF Workbench / Re: Arduschreiber HF-Beacon mkII
« on: July 19, 2020, 0636 UTC »
I accidentally overheated the circuit when it got stuck in transmission for a longer period of time(a wire short probably) whilst enclosed in a small airtight box, i think a couple of the components overheated. Since i didnt get the stability i wanted to be able to run slow hell i have started looking around after a better design of the PA-stage.

The RF Workbench / Re: Arduschreiber HF-Beacon mkII
« on: July 18, 2020, 0559 UTC »
I havent seen my tx on any of the web-SDR, so i tried to switch over to slow-hell but discovered that the PA has a bit of an issue with frequency drift when transmitting longer than the short pulse of field-hell. The signal starts our at one frequency, but then drifts about 250Hz higher during that "dot".

This is a problem with fldigi, since the filter is very narrow. When using the shorter field-hell "dots" this isnt seen, but it wouldnt bee an issue either since the fldigi filter is a lot wider.

The TX didnt have any other issues, so i will take if off the air and start building its enclosure and work a bit more on the code.

The RF Workbench / Re: Arduschreiber HF-Beacon mkII
« on: July 17, 2020, 1516 UTC »
Testing "CQ TEST" at 7001,6kHz, fieldhell, at 5W once every second minute from southern part of scandinavia. I will have a look at the web-sdr to get a picture of the range. The antenna is a longwire with a reasonable ground plane.

The RF Workbench / Re: Arduschreiber HF-Beacon mkII
« on: July 17, 2020, 1428 UTC »
This circuit gives a bit more than i expected, driven with 13v i get 5W out, with 55% efficiency! It also works surprisingly low in voltage. In standby mode the TX only uses 4mA. The frequency can be adjusted with about 2kHz, using the 22pf variable capacitor on the oscillator.

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.

The beacon has worked nicely since i put it up for testing, it even seams to be watertight enough to withstand the climate. The only thing i will need to fix is that when the voltage drops(sunset) the beacon starts to transmit, sends a short beep, and then the voltage drops and the Arduino restarts on low voltage, and sends another beep etc... I will add a voltage check that needs to pass before transmission starts.

I am testing out a beacon using Arduschreiber, using a 20W solarpanel. I got it running in the QRP spectrum of 40m, so i am going with 175mW of output to not cause any interference. There is no battery backup, so it will probably be running between 06.00 to 21.00 each day.

The beacon sends a short bit of text with some information, and the temperature, i am messuring it with a 1N4148, the forward voltage is about 0,6 volts depentent on temperature, about -2mV per degree celcius. With the internal adc refence of an arduino on 1,1v it works pretty well.

The transmitter is built into a watertight box, and all connections are sealed with melting glue.

Frequency: 7028.33kHz
Interval: 3 minutes
Mode: Slow-hell
Power: 175mW
Antenna: Simple longwire antenna, 5m with a couple of meters of ground wire.

Here is a short descreption of how i wired the Arduino to the keyer, and the temperature temperature sensor(diode).

Arduschreiber v1.2 is out!  ;D The code is now updated with the complete GL character set.


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.

The arduino Nano is glued to the under side of the circuitboard :) I used hotglue to attach it, and it worked really well. I will post a couple of pictures soon!

Thanx for the comments! I will try to make a better description of the transmitter/arduino package and how to build it. The code is available in .txt format on the link below :)

I have named the program Arduschreiber, and this is version 1.1 updates were done on a few points:
  • What pin to key transmitter is now set globaly
  • Speed setting available in code to switch between feld-hell and slow-hell


Next step will probably bee to add the special characters(-,/+- etc) to the code, now its only alphabet, space and numbers. The program takes up 22% of flash and 36% of SRAM on the arudino nano(Atmega 328p), to more characters is not a problem. The key to solve this is to store letter efficiently, before i solved this i could only fit about 10 letters. Now each 1/0 is a bit, before it was a whole byte  :-*

The code function in the forum doesnt seem to work, it looked nice in preview but when i posted it just unfolded. Perhaps the code is simply too long for a post..

I did some test with slow hell, at 1/8 of the speed of feld hell, it worked nicely. I had to re-make some of the code but it was done quickly, the longest microsecond delay is something like 16000us and you need about 32ms in on/off time in slow mode. There is now a comment describing what time to youse, in the code.

It would be interesting to see if there is any program that can recieve even slowe Hell than the oridnary 1/8-speed of Feld.


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 / Re: HF Beacon, design questions
« on: June 21, 2020, 0826 UTC »
Somehow the oscillator will not work with certain frequencies, it just doesnt oscillate(tested with the oscillator only). I will have to spend a little more time on the circuit this summer, and order a few more crystals.

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