What you’ll learn:
- Radio contact with Voyager 2.
- Setting up office background music with FM radio.
- Building a QRP ham radio.
Radio is our oldest electronic technology. Spark gap got it going, but it was the vacuum tube that really made radio viable and ultimately successful. And while everything today is made with integrated circuits, tubes are still with us in many applications. Radio also remains, although the term has become a bit retro. Wireless is a more common term that we hear more often, especially regarding the world’s most complex two-way radio—the smartphone.
Anyway, here are a few examples of how what you might call “old-time radio” continues to serve us well.
The World’s Longest Communications Distance
Does a 11.7-billion-mile wireless connection sound like a record to you? It does to me. Wow! What’s the dB path loss on that distance? It’s the approximate distance from Earth to the 43-year-old Voyager 2 spacecraft that’s far out in the space boonies. It was launched in 1977 to explore the distant planets Jupiter, Saturn, Uranus, and Neptune. Voyager continues to move even further from Earth and has, as the scientists say, gone beyond our solar system into interstellar space.
NASA lost track of Voyager 2 months ago when the only Earth station capable of talking to it went down for maintenance and repairs—namely, Deep Space Station 43 in Canberra, Australia. It took seven months to repair and upgrade the humongous 70-meter (about 230 feet) diameter dish antenna.
With some new higher-power transmitters and the dish’s awesome gain, DSS43 was able to contact Voyager 2. It took a 34-hour turnaround transmission for the spacecraft to respond with “hello.”
This reminds us that radio’s 186,400-mile-per-second speed is just not as fast as we thought. That’s as fast as it gets. NASA credits the initial simple low-power design of Voyager for its long life. Still a good design goal. Anyway, how about that as a memorable event for an ancient technology like radio?
A Better Source of Music?
My son John recently told me about some of his IT friends at work and how they went about setting up to play background music in the office. They used a smart TV as the receiver and sound output source but, of course, it had to have an internet connection, Wi-Fi, and a subscription to Spotify.
After opening an account and setting up a few playlists, they finally got it working for about $100/month. It delivers random playlists from several of the music genres.
Subsequently, John asked them “What if I told you I could do the same thing with about $20 worth of equipment and otherwise totally free?” One guy said, “no way,” others scoffed.
The answer, of course, is local FM radio on a $20 Sony transistor radio. In some big cities, a half-dozen FM stations play music all day that anyone can access at no cost with minimal equipment. Broadcast radio. Who would have thought? Does the younger generation know about FM radio?
A Simple Retro Radio Receiver
Not too long ago, I made up my mind about wanting to become more active in amateur radio. Yes, I admit being a ham (W5LEF). Having decided that, I realized I had little or no equipment. So, my plan was to start again with a popular ham communications specialty called QRP, meaning low power. The idea is to use minimal power (QRP is generally defined as less than 5 W) to make worldwide contacts on one of the high-frequency bands.
I chose the 40-meter ham band from 7.0 to 7.3 MHz. A good starting point for me was to build a receiver first. After some searching, I discovered the massive interest in a retro radio chip designated the NE/SA602. It was originally developed by Philips Semiconductor (now NXP) sometime in the 1980s. There’s an improved follow-up chip called the SA612.
The 602 IC contains a Gilbert cell mixer and a Colpitts oscillator in an 8-pin DIP. Cheap and easy to work with. The good news is that dozens of articles and other coverage are available about using the device to make a simple direct conversion radio.
Direct-conversion radios mix the incoming signal with a local oscillator signal of the same frequency. With zero IF, the circuit is self-demodulating. The circuit directly recovers the transmitted information signal. Morse code or continuous wave (CW) is the most common mode of operation, but it does a good job on single-sideband (SSB) suppressed-carrier voice.
I dug out as many of these 602 articles I could find and located the IC datasheets online. All of the various receiver circuits were similar. I made my own version using the articles and other info.
I built my radio on a breadboarding socket. The filtered and demodulated output of the mixer was sent to an LM386 IC audio power amp and a 3-in. speaker. I connected my 67-ft. wire antenna and a 9-V battery for power and, voilà, it worked. Both CW and SSB signals came in loud and clear. Tuning is done with a reverse-biased rectifier diode (1N4007) used as a variable capacitor on the Colpitts LO.
The whole thing cost me less than $30. If you have a good junk box you may be able to cut that. The hardest part was figuring out (called design?) all of the input tuned circuits for selectivity and an oscillator-tuned circuit. Finding inexpensive inductors of the right value also was a challenge. I used the molded axial type rather than wind air core coils or make toroids.
I’m happy with the radio. I was totally surprised to have it work so well. I was guessing another gain stage would be needed in there somewhere. I will eventually get around to rebuilding it or a duplicate on perf board or a PCB. I can use this as my main station receiver until acquiring a new commercial radio.
There’s another retro radio for you. The 602 came out in 1980s but it’s still a top-notch IC and product. If you’re looking for a hands-on project, this is a good one. I’ve also run across versions for shortwave listening and as a VHF AM aircraft pilot-to-tower radio in the 108- to 135-MHz range. Almost all commercial ham kit radios use this design. Try it—you’ll be surprised at the effectiveness of retro.
Next project is a transmitter. Just a couple of transistors that will deliver about 3 to 5 W should do it.
5G Radio
So, while many retro radios are holding their own, the big radio questions of the day are:
- Where the heck is 5G?
- And what the devil is 5Ge?
I’ve been asked several times lately what 5Ge really is. It’s AT&T’s rebranded LTE Advanced Pro mobile-phone system that’s in place until AT&T rolls out more real 5G sites. 5Ge is probably just as fast as some initial 5G systems. Kind of makes you wonder if we need 5G. We will get it, of course, but over an extended period. I guess LTE is now regarded as retro. It appears the speed of becoming retro is accelerating.
Tell me your retro radio stories.
