[Robert Sumption] a.k.a [W9RAS] takes on the daunting challenge of building a WWII spy radio called the Paraset as the topic of this week’s Retrotechtacular. It was originally a tube based CW (Morse code) transmitter/receiver used by the French underground to communicate with the Allies. Many of these radios were dropped behind enemy lines and could run on European AC or 6 V DC with the added advantage of being able to use most anything for an antenna, including fence wire. These small, low power and highly mobile radios tuned in the 3 to 8 MHz range were instrumental in the resistance. But they still make for a really fun scratch-built radio project.
Many of us tried the old “Two tin cans connected by a string” experiment as kids. [Michael Rainey, AA1TJ] never quite forgot it. Back in 2009, he built “El Silbo”, a ham radio transmitter powered entirely by his voice. El Silbo is a Double Side Band (DSB) transmitter for 75 meters. While voice is used to excite the transmitter, it doesn’t actually transmit voice. El Silbo is a CW affair, so you should bone up on your Morse Code a bit before building one. Like many QRP transmitters El Silbo’s circuit is rather simple. A junk box loudspeaker is installed at the bottom of the can to convert voice power to electrical power. The signal is passed through a step up transformer, and used to excite a 75m crystal. Two NPN transistors (in this case MPS6521) pass the signal on through a second transformer. The signal is then routed through an LC network to the antenna.
Back in 2009, [Michael] brought El Silbo to the Maine coast in an attempt to make a transatlantic contact. This isn’t as far-fetched as it sounds – [Michael] has “crossed the pond” on less power. While the attempt wasn’t successful, [Michael] has made connections as far as 1486km, or 923 miles. That’s quite a distance for simply yelling into a tin can! One of [Michael's] favorite El Silbo stories is a 109KM conversation (QSO) he had with W1PID. [Michael] found that the signal was so good, he didn’t have to yell at all. He reduced power by dropping to his normal speaking voice for the “dits and dahs”. The two were able to converse for 17 minutes with [Michael] only using his speaking voice for power. We think this is an amazing achievement, and once more proof that you don’t need a multi-thousand dollar shack to make contacts as a ham.
A few weeks ago in Finland [Oona] discovered a radio data stream centered around 76KHz in a FM broadcast and she recently managed to decode it. This 16,000bps stream uses level-controlled minimum-shift keying (L-MSK) which detection can be quite tricky to implement. She therefore decoded the stream by treating the received signal as non-coherent binary FSK, which as a side effect increased the bit error probability. [Oona] then understood that the stream she was getting was the data broadcast by Helsinky buses to the nearby bus stop timetable displays. She even got lucky when she observed a display stuck in the middle of its bootup sequence, displaying a version string. This revealed that the system is called IBus and made by the Swedish company Axentia. However their website didn’t provide the specs for their proprietary protocol. After many hours of sniffing and coding, [Oona] successfully implemented the five layer protocol stack in Perl and can now read the arrival times of the nearby buses from her apartment.
The biggest Internet provider in Portugal needed a system to turn FM broadcast stations in Angola, Cabo Verde, and Mozambique into a web stream. Like every good project, the people in charge of the engineering turned to Hackaday staples – Raspberry Pis, Arduinos, and TP-Link routers, all stuffed into an awesome modular rackmount cabinet
Each module in this gigantic rackmount system includes an Arduino, a Raspberry Pi, a Silicon Labs Si4705 FM receiver chip, and a TI USB audio capture chip that allows the Pi to turn the audio out from the radio receiver into an audio stream. All the Pis are connected to a 24 port Ethernet switch and to a separate master Raspi that converts data received from each module into an icecast stream.
The engineering behind each module is pretty impressive – they’re all hot swappable, have remote shutdown capability, and have voltage divider on the backplane to detect where in the rack it’s placed. It’s a very cool piece of engineering and a very cool example of using off-the-shelf hardware to do something that could be much, much harder.
In the years before World War II it was theorized that shortwave radio waves could propagate through the ionosphere relatively undisturbed and allow for a signal to be bounced off the moon and returned. [Zoltán Bay] calculated that the return signal would be too faint to be detected above background noise with the radio receiving equipment of the day. To overcome this receiver dilemma he devised a new receiving element consisting of 10 coulometers sharing a common tank of a water solution. Each of the coulometers had a separate electrical connector and when current flowed through the electrode, hydrogen bubbles would form in an attached glass capillary column. By periodically sweeping through all 10 coulometers using a rotating switch attached to the radar receiver, any radar echo as well as random background noise would be readable by the amount of bubbles in the capillary columns. A single radar echo would be indistinguishable from random background noise in the columns of bubbles, but if the sweep is continued for 30 minutes any periodic radar echo would show as an increased accumulation of bubbles in a respective column. By reading these coulometers and knowing the switching period you could determine that you were receiving a true radar echo from the moon.
What an amazing apparatus to amplify a periodic signal above background noise! Nowadays we would call this a long-time integrator or persistence measurement and it’s a relatively simple task. You can download and read [Zoltán Bay’s] paper on “Reflection of Microwaves From the Moon” dated 1946 in PDF form. His integrator apparatus details start on page 17.
It took some years but in 1946 [Zoltán Bay’s] receiving apparatus was tested and did confirm reception from moon bounce. However, U.S. Army Signal Corps with better crystal frequency stabilized equipment was able to perform the same task earlier as seen in the below video without the use of an integrator. Even though the U.S. Army equipment was superior for this task [Zoltán Bay’s] apparatus enjoyed years of service in the field of planetary radar observation where such a high sensitivity scheme was still necessary.
If you dabble in the ham radio hobby we’re sure you’ve heard of GPS position monitoring or tracking using APRS packet data commonly transmitting over the VHF ham band and FM modulated. One of the issues you’ll face using this common method is range limitations of VHF. [Mike Berg] a.k.a [N0QBH ] tipped us off to his latest project to greatly increase the range of a standalone APRS system utilizing the HF bands on single-sideband (SSB).
There are some unique challenges transmitting packet data using SSB over HF bands. High Frequency APRS has been around for decades utilizing FSK AX.25 packet transmissions at 300 baud, but it was quite susceptible to noise and propagation aberrations. More recently PSK-31 at the slower 31 baud speed helped alleviate many of these issues. [Mike] utilized the somewhat updated APRS with PSK-63 and the “APRS Messenger” program to overcome these challenges. [Mike’s] hardware solution consists of a PIC 16F690 micro which is coded to receive data from a GPS receiver, convert it into PSK-63 and then transmit on 30 meters over an attached HF radio. A second receiving station or stations at great distances can pick up and decode the transmission using the “APRS Messenger” program connected to the receiving radio over the computer’s soundcard. The program can then forward the tracking information, if good, to tracking websites like FindU.com and APRS.FI.
You can build your own FreeTrak63 by downloading [Mike’s] parts list, assembly code, HEX file, manual and schematic. The PCB is available on OSH Park if you don’t want to make your own or wire point-to-point. Let’s not forget to mention how hackable this hardware is, being really just an eight bit DAC, micro, serial in and radio out. One could reprogram this hardware to do other modulation schemes like AX.25 packet or MFSK16, the sky’s the limit. If short-distance on VHF with existing Internet linked receiver networks using an Arduino compatible platform is more to your taste, then checkout the Trackuino open source APRS Tracker.
[Bill Meara] has finished up his radio. It both looks and sounds great. It was only a few weeks ago that [Bill] posted a guest rant here on Hackaday. The Radio he mentioned building in the rant is now complete. The transceiver itself is a BITX, a 14MHz Single Sideband (SSB) radio designed by Ashhar Farhan VU2ESE. Ashhar designed the BITX as a cheap to build, and easy to tune up transceiver for radio amateurs in India.
By utilizing parts easily sourced from scrapped TV sets, the BITX can be built for less than 300 Indian Rupee – or about $4.70 USD. In [Bill]’s own words, “Five bucks and some sweat equity gets you a device capable of worldwide communication.” He’s not kidding either. [Bill’s] first QSO was with a ham in the Azores Islands of Portugal.
[Bill] built his radio using the “Manhattan” building style, which we’ve seen before. Manhattan style uses rectangular pads glued down onto a copper ground plane. It makes for a more flexible design than regular old dead bug style building. Looking at all those components may be a bit daunting at first, but plenty of support is available. [Bill] has an 18 part build log on the soldersmoke website. There also is an active yahoo group dedicated to the BITX.