I have this old Panasonic DR-28/RF-2800 back from the 80’s, in my bedroom that I do not want to give for recycling. As a matter of fact, I am very sentimentally attached to it. It was my first analog radio receiver with a digital display along with a tuning dial, a BFO for SSB and CW (morse code) reception, an RF gain to cope with strong signals, a true analog (needle type) signal strength meter, long-medium-short wave (HF) coverage, FM band, portable battery operation plus mains, a retractable antenna, and it is still working!
This type of radios, by today’s standards, have poor selectivity, sensitivity, and noise figure, all of which can be improved by analog upcycling, using better filters and low-noise preamps. But even after doing so, they cannot easily compete with modern digital Software Defined Radios (SDRs) that have Digital Signal Processing (DSP), software-built selectivity filters and the like. Adding all these extras can increase the budget significantly.
SDRs on the other hand, require some sort of audio signal processing which can be carried out through a computer or a micro controller integrated to the SDR, as well as some kind of synthesized Variable Frequency Control (VFC) to move over to the required frequency spectrum (e.g. 150 KHz to 30 MHz) where analog broadcasting activity still exists, and Radio Amateur (Ham) operations take place 24/7. The purchase of such type of good SDRs with built-in sound processing can be quite expensive.
An alternative solution to an SDR is using a DVB-T USB dongle (costing a few Dollars on eBay), which can be turned into a degraded quality SDR (http://www.rtl-sdr.com/about-rtl-sdr/) by using appropriate software like the HDSDR (http://www.hdsdr.de/). However, even though their frequency coverage goes as high as 4 GHz, they are limited usually to around 22 to 26 MHz on the lower side of their tuning range due to component limitations. Therefore, if we wanted to tune lower we would need to use/build a frequency converter. As the unit requires Bandpass Filters (BPF) at the front of the converter, it is less practical to implement. Recall, that the majority of Shortwave stations and Ham radio activity takes place between 1.8-30 MHz.
The next alternative is WEB SDR servers that essentially provide a remote web service on top of a well-calibrated radio station connected to a high-quality antenna “listening” all year round. There are three important features for WEB SDR:
It is not required to have expensive receiving equipment or antennas to listen to broadcasts worldwide. Many times a short retractable 1.5-meter antenna is not adequate. On the other hand, in the case of WEB SDRs the only thing necessary, is access to the web.
We can avoid suffering from the contamination of the HF spectrum with noise often created by switching power supplies and modern electric street lights in our neighborhood, preventing the reception of low-power distant Ham transmissions or low-power commercial broadcasts. For that reason, a WEB SDR can be your solution for “easy” listening.
Some WEB SDR servers offer full coverage of the High Frequency (HF) spectrum, i.e.150 KHz-30 MHz.
Last December while staying at our son in Holland, I had no Ham Radio with me. By using my tablet or mobile phone I accessed such a WEB SDR, i.e., a remote SDR station set up in some other part of the world. I could remotely tune and listen to Ham and Shortwave stations without a dedicated radio receiver and the required antenna for capturing weak stations. In fact, there are many excellent WEB SDRs around the world that can be accessed with zero cost for extra equipment or software.
This scenario gave me food for thought, and my experience with microcontroller-based Direct Digital Synthesis (DDS) and Variable Frequency Controllers (VFC) made me think that I could build something to access a WEB SDR using some of my home-built radios. I was living with that idea for some time. The announcement of “Upcycle it Design Challenge”, gave me the idea to try integrating this concept in my Panasonic analog receiver, so that I can improve my Radio bedtime listening and Ham station monitoring. I am a keen Radio Amateur myself and I enjoy monitoring the Ham Bands.
A particularly good WEB SDR server that offers such coverage is hosted at the amateur radio club ETGD at the University of Twente (Wide-band WebSDR; http://websdr.ewi.utwente.nl:8901/).
In contrast to other web-controlled receivers, the WEB SDR at UTwente can be tuned by multiple users simultaneously. The system is composed of a "Mini-Whip" antenna, a homebuilt SDR board which samples the entire shortwave spectrum, connected via gigabit ethernet link to a PC, and further processed with custom software before streaming to users. The active receiving element is about 5 by 10 cm large. Such an antenna only works well with a good grounding; theirs is on top of a 20m high building, the upper part of which is all metal. It would be nice to have such a good antenna at home, but this is not always possible, especially if you live in a flat. So it makes sense to try and use their setup.
If we enter the URL http://websdr.ewi.utwente.nl:8901/?tune=198am in a browser, we are automatically tuned in to BBC Radio 4 broadcast on 198 KHz Long Wave! Well, you have just entered the Radio Listening business through WEB SDR. There are still many analog transmissions, but now we are able to “listen” to them digitally.
When using a WEB SDR server to listen to broadcastings we must also have two more things in mind: the reception conditions obviously apply for the location where the WEB SDR server resides rather than at our current location. Also, there is a small delay in the reception, similar to any other streaming application; that does not change the fact that we can directly scan the HF spectrum for any kind of broadcasts.
My “Upcycle it” task is to embed a client for a Software Defined Radio Web Server (WEB SDR) into my old radio receiver using the Edison Subsystem. Ιn that way I will extend its reception beyond analog signals that are being directly received via its retractable antenna, by remotely connecting to the WEB SDR at UTwente via WiFi. Consequently, my receiver gets an uplift, which was impossible to be thought of at the time of its original production back in the eighties.
I know that many will object or remind me that there is Radio Garden out there (http://radio.garden/live/), indeed a very clever application, or that I can access a WEB SDR from my tablet or mobile phone, as I had done in Holland last year; I would agree with those people.
But my approach is different. I am going to build an add-on device for Upcycling of old radios that have the required space to have it integrated.
A number of fellow Hams that I have spoken with about my idea are already waiting to duplicate my device for Upcycling their own vintage Radios.
The Hardware
I am visualizing the implementation of an Edison-controlled WEB SDR client, operated from the front of the radio with a Rotary Encoder and push buttons, as follows:
In the front of the radio, we will add a small monochrome Nokia 5110-style graphics LCD screen with a viewing area of approximately 24x34mm.
The LCD is connected to the Intel Edison through the SPI bus; it displays the information as shown in the picture.
Close to the display, there is a Rotary Encoder with a push button and two or four extra push buttons, also connected to the Edison (see description below). There is also an inexpensive USB audio card connected to it so that the audio stream from the WEB SDR can be monitored.
The block diagram for my idea follows:
One half of a DPST (double pole single throw) switch mounted on the radio’s front is used to power the Edison subsystem with the display, while the other half is used to change the audio input on the radio’s original volume control from the analog radio detector to the headphone/speaker output of the USB sound card. In that way, we select either the Analog or WEB SDR mode. Edison’s WiFi interface is used to connect to the Internet.
The Rotary Encoder is used to increase or decrease the desired frequency according to the resolution (Step) that is being selected from the Rotary Encoder’s push button.
The Steps are 10 Hz, 100 Hz, 1 KHz, 5 KHz, 9 KHz, 10 KHz, 100 KHz, 1 MHz, and operate in a cyclic mode; we set the default to 9 KHz (for wideband AM reception in Long and Medium wave bands). Optionally, there are also two buttons, up (f++) / down (f--), that are connected to change the frequency, instead of using the Rotary Encoder. We can wire up both the Rotary Encoder and the two buttons, or either of the two.
There is another push button responsible for the selection of Mode. Mode is the type of demodulation that is being used for reception. Available Modes are AM (Amplitude Modulation), CW (Carrier Wave), LSB (Lower Sideband), and USB (Upper Sideband). The operation is again cyclic and the default Mode, which again can be changed from the software, is AM.
The last push button is Bandand through it, you cyclically select one of the predefined bands that you can store in the sketch. Initially, 11 bands have been set, but we can predefine others too. Upon selecting a Band, it is displayed on the LCD in wavelength, as Shortwave bands are many times referred to in that way (e.g., 14MHz is referred to as the 20 meter Ham band).
All functions and start up values are predefined and can be customized to one's personal preferences.
A theoretical implementation of the schematic is shown in the picture. As Edison bus is on the 1.8 Volts signal level instead of the usual 5 or 3.3 Volts, there has to be some sort of level shifting in the final version of the project with a standalone Edison Computer module or via the Edison breakout board. That is not needed in the Intel Edison board for Arduino displayed below.
One more digital line is used to control the Backlight of the LCD through PWM.
As I did not have an Edison system available, I decided to initially breadboard and test this idea with an available Arduino Pro Mini, the Nokia LCD, the input control buttons and the Rotary Encoder. The diagram for this prototyping which is operating on my workbench throughout is given hereunder.
The Panasonic Radio
The schematic and the service manual of the DR-28/RF-2800 can be found and downloaded from the Internet. The two different models are the European and the American version of the same product. I have actually found the data for RF-2900 (https://www.manualslib.com/download/1107260/Panasonic-Rf-2900.html) which has very small differences from the previous models, but they are just fine for my task. As a matter of fact, even without a schematic the modification can be done easily, as what is actually needed is to break the signal path from the radio detector to the audio preamplifier/amplifier chain of the radio.
Having the schematic to verify that, makes the modification much easier.
This is the inside of the radio. I think the most important issue is that there is reasonable space at the speaker area for adding the new hardware. I will simply call the new sub-assembly “WEB SDR Client” from now on.
I selected the monochrome Nokia LCD because of its footprint/size and because I think has a reasonable size to be integrated on the front panel. If necessary the signals from the LCD can be carried to the Edison board with a flat ribbon cable. Those displays are very inexpensive and easy to source.
This is my actual radio. As you can see, it was already Upcycled many years ago on the analog domain, so the switches and the LED are already there, so they are waiting to facilitate the new Upcycling!
The real challenge for me will be to end with a WEB-SDR Client module that will have the smallest possible footprint, so that it can be used with other vintage radios as well.
The rest of the Hardware
These are the remaining components that I intend to use for the project.
The perforated board with the rotary encoder and the push buttons was taken from another project, so its final layout version will depend on their placement on the free space area on the speaker grill.
As I am thinking on using the Edison breadboard, I have included a small Adafruit board with voltage level translators for the project.
One last useful piece of information for all the Challengers. While I was preparing my test code for Arduino, I needed a library for the Nokia 5110 clone LCD. While searching I ran to the well documented library of Oliver Kraus (https://github.com/olikraus/u8glib/), which supports a multitude of colour and monochrome graphic LCDs. It has helped me making my code work right from the start on my Arduino.
Having laid out my initial project plan, on the next post I will discuss about the software of the project which I have partially tested with an Arduino Pro Mini for its usefulness and how it is going to be implemented on the Edison platform.
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