Topics

1

The RF Workbench / Cheap beacon construction examples

« on: July 26, 2023, 0042 UTC »

I made couple similar beacons this summer, and want to share their construction.
Transmitters are primitive, 190-200 mwt output with 3.3V power from LiFePo cell, almost 500mwt with 6.3V from solar panel.
Charge current limited by solar panel, contoller only every 8 sec switch off charging and masure voltage on battery.
Controller - attiny85, voltage not stabilised, but limited with resistor and 4-5V zener diode. This circuit not draw power at night because maximum battery voltage is 3.5v. Attiny work with internal 1.1V reference voltage and internal rc generator, brownout level 1.8V Flashed via arduino as isp, with ATTiny Core for arduino. Actually program ismodified NicoVarg99 cw beacon, because program allow use not hardcoded text strings, so we can measure and send some telemetry. I only add voltages measuring and control charging circuit.
Boards covered with Plastic 71, bottom side of the boxes drilled for drainage and ventilation, because in closed boxes forms condensation.
https://github.com/NicoVarg99/Arduino-CW-beacon

Controller schematic


First beacon, 27.143MHz




Second beacon, 13.56MHz

2

The RF Workbench / Dual (multiple) frequency beacon

« on: July 25, 2023, 1955 UTC »

Because propagation changing from day to night i try to make dual frequency and simple transmitter for qrp beacon. I try diode commutator and it works.
Beacon powered from 5v 350 ma solar panel and 3V 6A/H lifepo accumulator. Because my controller know voltage on solar panel he will switch frequency on twilight and dawn, it even can be done by primitive voltage comparator, without any programming

3

Software / OpenWebRX+

« on: July 20, 2023, 2309 UTC »

Almost year ago i set up this websdr server, and i think he is awesome.
1 Opensource, and fast developing software.
2 Can be installed in ubuntu and debian on aarch64 or amd64 simply, via some commands on terminal, or as Docker container, or have prepared sd card images for raspberry pi
3 Very simple settings via admin webpage, the only thing you should do in linuc CLI is a adding websdr admin.
4 Really awesome: support a lot of sdr receivers: rtl-sdr, hackrf, airspy, sdrplay, HPSDR (hermes), USRP, Bladerf.
5 Can decode online a lot of amateur and professional digimodes, from CW to HFDL, and meteofax. In some modes, like HFDL, AIS or JS8 he can display received coordinates on map.


6 Have a map which can display also other websdr, kiwi or openwebrx websdrs.
7 Average load with single user only 25-30% higher than pa3fwm websdr on same hardware. Simultaneously working 5 rsp1a with 8mhz bandwidth + hackrf with 20mhz bandwidth eat approx 60% resources of my old Xeon E3-1270v3.
8 You can set some receivers which can work simultaneously, or set some "profiles" which set frequency, bandwidth, gain and lot more settings for single receiver, and swith between them (of course this is problem for more than 1 user on server).
9 Have free tuning option, but with some trickery.
So we have software which easy to install on almost any computer (include not raspberry singleboard arm, for example Orange pi and Rockpi), very agile and free to use.
The beauty of this project is that you can easy and cheap (you need only not very powerful computer and external ip) share your sdr with other people. Not need to buy relatively expensive and rare hardware or struggle with several configs for having only 2 megs of bandwidth in case of websdr.

https://github.com/luarvique/ppa
My websdr

link http://hoshinokoe.ru:8073

4

The RF Workbench / Common mode supression

« on: March 18, 2023, 0935 UTC »

My english still very bad, but i should tell here about my experiments.
Common mode noise i measure between PC case and grounding in 9 floor building via 10:1 voltage divider - almost 13 volts.
http://hoshinokoe.ru/files/0ARTICLES/common_mode/interf_pc_case.jpg
My previos schmatic for CM supression. Miniature galvanic isolated 9:1 transformer instead of balun, second miniature 1:1 transformer near receiver
http://hoshinokoe.ru/files/0ARTICLES/common_mode/common_mode_protection.jpg
But in the big building grounding very noisy, almost like a mains power. So intead of classic long wire and grounding much better use a two random wires attached to balun.
Measuring of some variants.
http://hoshinokoe.ru/files/0ARTICLES/common_mode/LW_and_noise.jpg
Then i add a long, 30 cm common mode choke, made like a anode choke, but winded with two paralel wires, to reach maximum reactance.
http://hoshinokoe.ru/files/0ARTICLES/balun_for_SWL/SWL_balun1.jpg
I still not measure this long balun, but it seems t be its better then only miniature transformer.
Today i made a Austin tranformer for HF to measure its reactance for common mode.
http://hoshinokoe.ru/files/0ARTICLES/balun_for_SWL/Austin_trans_isolation.jpg
Certainly reactance depends on design, bit this particular design has 4-5 db better common mode suppression in 50 ohm schematic compared with compact balun from aliexpress.
http://hoshinokoe.ru/files/0ARTICLES/balun_for_SWL/wideband_trans_isolation.jpg
The only problem with austin balun - this is a magnetic transformer, so you can't use random ferrites ripped from vga cable chokes. And it has high leakage inductance, so losses in poorly designed austin transformer can ruin advantages of low winding capacitance.
Now i use "long" balun with my personal sdrs and parallel with web-sdr on my personal webpage.
For example - coastal station Skagen on 1700KHz, distance approx 1200km.
http://hoshinokoe.ru/files/0ARTICLES/balun_for_SWL/skagen_coastam_mf.mp4
Yes, still bad but with classic amateur contruction in my case noise floor would be much higher

5

The RF Workbench / 4096 beacon goes wild soon :)

« on: October 09, 2021, 1242 UTC »

I made my first 4096 beacon
Arduino controlled. He checks voltage on PV, on lead-acid, if one of them higher than usable minimum (pv see the sun or acid battery higher than minimum voltage) he  transmit message with voltages, temperature and EMI (little 2 stages hf amplifier with detector) and if pv voltage higher than battery, and battery not fully charged he turns on charging net. Then going to sleep for some 8sec cyles (maximum hibernation legth with lowpower library)
After every hybernation cycle he disconnect PV and acid battery for checking voltages, then, if PV voltage higher than acid, and acid voltage still not 6.7 v (i use 6v 4.5 a/h and 7.4v 0.5a PV) he turns on charging again.
Tx pixie-style, 0.5w output. 125ma current consumption, approx 1minute length transmission, 10wpm, then 10 minutes pause with dits every 8second. Also i remove power led from arduino pro. So it equals approx. 15ma current consumption.
Now i install beacon on the southern wall and test him with 50ohm load.

6

The RF Workbench / speech synth + Kahn ssb tx on arduino

« on: September 19, 2021, 1654 UTC »

We can made speech synth on Arduino with Talkie library https://www.arduino.cc/reference/en/libraries/talkie/
Also we can produce SSB, (also AM and FM) with arduino and si5351 without filters and phasing nets https://antrak.org.tr/blog/usdx-a-compact-sota-ssb-sdr-transceiver-with-arduino/ with efficency of E class transmitter.
I think should be a way to merge this projects. I mean made a beacon with arduino, si5351 and some transistors, which can speak telemetry in SSB on any frequency in 3.2-50 mhz (minimum, i think frequency range should be much wider). Cheap, simple and power efficient device.
I made both devices, arduino speech synth i use in speaking 27 mhz feral beacon https://www.youtube.com/watch?v=yyRJJnI8Hxg
And i made uSDX transceiver https://www.youtube.com/watch?v=9DjDdcnP0GE
It was not difficult.
 

7

The RF Workbench / Arduino voice telemetry sketch

« on: June 24, 2020, 1845 UTC »

Hi, i compile this sketch from some other sketches and examples for myself, i am bad programmer, but it works.
Arduino measuring temperature on diode, voltage, transmitter output power (rectified output tx voltage and calculates power on 50-ohm load), turns on transmitter and speaks values on english.
More instructions in sketch comments, there are pinout, termometer calibration, available voice synthesyzer vocabularies and other. On my arduino nano 8mhz atmega 168 sketch used 60% of memory.

https://drive.google.com/file/d/1MZXGC5Yg6jr5mtrGw_xZu3xaAU7_T9IB/view?usp=sharing

How it sounds in real radio
https://www.youtube.com/watch?v=yyRJJnI8Hxg

You can also record your own words and phrases with this tool
https://github.com/ptwz/python_wizard
install Python and NumPy
unzip the python_wizard in folder
record a 16 or 8 bit mono .wav file. Better way for it is Audacity, for filtering and compressing sound
run file python_wizard_gui from console (if you add extension .py to its name you can run script by double-clicking on it)
in gui open menu File>open Wav and pick your .wav record
wait until in the big emty field appears hex codes with first string "const unsigned char FILENAME[] PROGMEM =", copy them (ctrl+c) and paste in sketch, in definitions section
in progam loop section write voice.say(FILENAME);
listen your voice from arduino with terrible quality
here the video how it works https://www.youtube.com/watch?v=t3zAZFH2K7E


I think now about using this sketch with simplest SSB transmitters like this single channel filtering ssb http://www.vk6fh.com./vk6fh/7mhzxcvr2.PNG
or simple phasing ssb like this http://www.seekic.com/uploadfile/ic-circuit/20114216472392.jpg
I made once this https://serwis.avt.pl/manuals/AVT2906.pdf simple phasing ssb receiver, and it works not bad.