lørdag den 27. oktober 2018

The Bluetooth radio in BBC micro:bit

The BBC Micro:bit has caught my attention. Last month, I described a morse trainer with the micro:bit. Since then I've played with the integrated radio (a micro:bit term), which is a
Bluetooth Low Energy (BLE) transceiver. It can connect two or more micro:bits via Bluetooth. You can connect a micro:bit to a smartphone if the right app is installed. You can even create software on the smartphone and download it into the micro:bit via Bluetooth!


The BBC micro:bit (component side). 
Picture credit: microbit.org

The following project shows a morse transceiver. It can send dots and dashes to one or several micro:bits. Each micro:bit runs the same software.

Here is the coding in the Blocks Editor:

Function of button A and button B.

The radio channel is set to 10 when the program starts. If the user clicks the A button, 0 is transmitted and will sound as a dot on the receiving micro:bit. If button B is pressed, a 1 is sent and it sounds as a dash in the receiving end.

Function of the receiver.
When the micro:bit receives a number, it is decoded in the "on radio received" block. If a 0 was received, a dot will sound using "play tone for 200 ms". If  a 1 was received, a dash will sound using "play tone for 600 ms".

The morse transceiver is demonstrated in this video (Danish language):

73 from OZ1BXM Lars Petersen
Homepage: oz1bxm.dk

søndag den 30. september 2018

Morsetrainer with BBC micro:bit

My grandchild Noah showed me his new BBC micro:bit. It is a tiny microcomputer which is being distributed free to school children aged 10-11 years. The purpose is to introduce the pupils to coding. The micro:bit computer is small, about half size of a credit card.

The tiny micro:bit computer (rear view).
I decided to create "something" for pupils in relation to ham radio. I ended up with a morsetrainer. It shows characters (letters, numbers) on the microbit display and plays them loud in morse code, one letter at a time. The pupil decides the pace of new letters coming via button pressure. Another button press repeats the letter.

Micro:bit displays "A" (front view).
The morsetrainer's circuit diagram is shown below. The speakerboard is an accessory. A pair of computer speakers can do the same. The different units are connected using short cables with crocodile-clips.
Circuit diagram of the morsetrainer.
Sending morse code requires a morse key. My idea was to build one, rather than buying one. Building a morse key can be exciting for pupils. They produce something useful with their own hands! The key shown below is made from wood, a plastic ruler, a knob, and some screws, bolts, and wires.

Homemade morse key.
If you want to download the Python source code and the hexfile, download this ZIP-file.
If you want to view a video (in Danish), click this link.
If you want to download a PDF description (in Danish), go to this page.

73 from OZ1BXM Lars Petersen
http://oz1bxm.dk

lørdag den 18. august 2018

DSLWP-B satellite signals received today

😊 I've finally received JT4G signals from the Moon-orbiting satellite Longjiang-2 alias DSLWP-B alias LO-94. I am so happy for this event! 😊

When is the signal available?
BG2BHC announces date and time for the DSLWP-B transmissions. He does it via his Twitter account as you can see in the screen-dump below.

Tweet from BG2BHC.
Frequencies. There are two different frequencies used by DSLWP-B: 435.400 MHz and 436.400 MHz. To receive on 435.400 MHz, I set my Yaesu FT-847 dial to 435.401.500 MHz. The lowest JT4G tone was 600 Hz when I used this dial setting.

Antenna and preamp
I decided to deploy my 18 element 70 cm LFA yagi antenna. The boom length is 4.30 meter, and the claimed gain is 18.0 dBi. My preamp is Extra-70 from HA8ET. The premap went into oscillation earlier. However, the preamp performed normally when I fitted a different type of balun!

18 element LFA yagi for 70  cm.
The antenna follows the Moon as it traverses the sky. Antenna elevation is performed by a Kenpro KR-550 rotator. There is automatic antenna control by PstRotator.

Azimuth and elevation
The timeslot for reception of DSLWP-B this Saturday was 2 hours. The slot is from 18:30 to 20:30 local time. There were other timeslots mentioned by BG2BHC in his tweet, but the Moon was below the horizon in Denmark during these times. The antenna direction is shown in the table below. AOS = Acquisition of Signal. LOS = Loss of Signal. AZ = azimuth (horizontal direction). EL = elevation (vertical direction).
AOS and LOS for DSLWP-B as seen from Denmark (Aug 18, 2018)
JT4G decoding

The WSJT 10 waterfall.
The DSLWR-B downlink contains telemetry sent with GMSK. Every 10 minutes there is an JT4G transmission to identify the spacecraft by its callsign BJ1SN. The JT4G protocol has 4 tones spaced 315 Hz. All tones are clearly visible in the WSJT 10.0 waterfall (see screen above).


The call BJ1SN decoded by WSJT 10.
I decoded the callsign BJ1SN 7 times. The signal strength was -12 dB maximum, and -16 dB minimum.

73 from OZ1BXM Lars

søndag den 29. juli 2018

Several attempts receiving DSLWP satellite signals

The Chinese satellite LongJiang2 (also called DSLWP-B) orbits the Moon since May 25, 2018. The satellite's weight is 47 kg. The 2 watt signal from the satellite is transmitted in the 70 cm amateur radio band (435.400 MHz or 436.400 MHz). I've decided to listen for the new sat.
DSLWP Lunar Satellite.
Several receiving attempts and why they failed
My first receiving attempt was 4 weeks ago. My yagi antenna and preamp was ready for reception. Power to the preamp was fed via the coax cable. However, the preamp oscillated, and S9 noise was generated. No JT4G signals received.

The second attempt was 2 weeks ago without the preamp, and no antenna elevation. The Moon was high in the sky, about 40 degrees. No signals detected. I have to aim the antenna directly at the Moon!

My third attempt was done this morning. The antenna was controlled in azimuth and elevation, and this time the preamp was fed via an external power supply. But preamp oscillation continued; lots of noise, no signals.

I am not giving up. I will continue listening for the lunar satellite DSLWP. Next time, my antenna will be equipped with azimuth and elevation rotators, and NO preamp!

DSLWP links
Main page in Chinese and English:
http://lilacsat.hit.edu.cn/wp/?page_id=844

Project description with links (AMSAT-UK):
https://amsat-uk.org/2018/05/19/dslwp-satellites-lunar-orbit/ 

Schedule for DSLWR-B activation:
Follow the Twitter account of BG2BHC

Vy 73 de OZ1BXM
Homepage: oz1bxm.dk
Twitter: @oz1bxm

fredag den 1. juni 2018

Lima SDR: Windows 10 USB interface

I am currently building the Lima SDR kit which is an all-band all-mode SDR transceiver with 1 W output. I am following the instructions in "HW/SW Handbuch 2.1, 2014, by DL9WB". Yes, it is in German!

This photo shows the programable synthesizer SI570 (square 2) connected to the USB chip (square 1).

The unfinished RX board (Lima SDR).

The concept is shown below. A test application on the PC controls SI570 via an USB interface.
SI570 controlled by a test application via USB.
However, I had problems installing the USB driver on the PC. I followed the instructions in "HW/SW Handbuch" but it did not work. Here is how I solved the driver problem:
  • Install the certificate (it is on the CD-ROM: AmateurRadioRootCertificate.crt)
  • Download and run PE0FKO-USB-Driver-Installer
Link to the Driver Installer: http://pe0fko.nl/SR-V9-Si570/PE0FKO-USB-Driver-Installer.exe

Installation of driver is complete.

The installed driver is from 11/10/2012 and the version is 1.2.6.0. Now the USB connection works, and the SI570 output frequency can be set. Hooray!

USB_Synth.exe controls the output frequency of SI570.
Vy 73 from OZ1BXM Lars

lørdag den 26. maj 2018

Kenwood TS-440 error: dots-in-display

Kenwood TS-440 can develop an error where only dots are shown in the frequncy part of the display. When the microprocessor in TS-440 detects a PLL unlock condition, it blanks the display and shows a row of dots. See the picture below.

Kenwood TS-440 with dots in the display caused by PLL unlock.

There are 5 PLL's in the TS-440 and any of them can cause the "dots".

There are 2 PLL's where glue was added at the factory to protect the circuit against vibration. Over time the glue can become conductive because it absorbs moisture from the air. Conductive glue is poison to a VCO, which is highly sensitive to voltage changes.

VCO5 (PLL-unit) is used on all bands. It will affect all frequencies if VCO5 goes into the unlocked state.

VCO1 (RF-unit) consists of 4 separate oscillators. Together they cover the entire operating range of the radio. If one of the oscillators is unlocked, it will affect the range covered by that device.

What is the solution to the dots-in-display problem?

My solution is radical and labor intensive: I remove all components from VCO1 and VCO5 and clean the PCB thoroughly to remove all glue. Then I fit brand new components and adjust the VCO. The PCB is then reinstalled into the transceiver and a final alignment of the VCO's is performed.

The method above has shown good results, and I have done it twice. You can read more by visiting http://oz1bxm.dk/TS440/ts440-repair.htm

Vy 73, OZ1BXM Lars Petersen
Web-page: oz1bxm.dk

lørdag den 21. april 2018

Microwave meeting in EDR Horsens

Today I attended a microwave meeting in Horsens, Denmark. The radio club EDR Horsens  hosted the meeting. The aim was to introduce the participants to microwaves: 10 GHz, 24 GHz, and 47 GHz. Most participants came from Denmark, but there was also one person from Norway and two from Germany.

During the first part of the meeting, there were lectures on different subjects:
  • Microwave measuring techniques (by OZ2OE)
  • How I started on 10 GHz (by OZ7Z)
  • How OZ5TG  transformed an obsolete radar system into a big EME station
The afternoon was dedicated microwave communication in the field. Most participants drove to a nearby "mountain" called Ejer Bavnehoj (JO45VX). This location is 170 meters above sea level and the third-highest natural point in Denmark. Most stations operated from the brick tower situated on top of the "mountain". All stations used battery power.

The brick tower of Ejer Bavnehoj, Denmark.

LB2S and his 10 GHz station (Ejer Bavnehoj, Denmark)

OZ2OE and his 24 GHz station (Ejer Bavnehoj, Denmark).
The microwave meeting in EDR Horsens was a great succes. Good food, nice people, quality lectures, and successful microwaving in the field - what more can you want?

OZ1BXM (me) in QSO on 47 GHz (Ejer Bavnehoj, Denmark)
Vy 73 from OZ1BXM Lars
Homepage: oz1bxm.dk