Yes, including transoceanic ones!
Recently, I picked up some TA7642 chips from Amazon on a whim. Originally, I wanted to make a shortwave receiver with an external BFO for a QRP project, but I learned that these chips only worked up to around 3MHz. However, not all hope was lost.
No matter how hard I tried to breadboard the circuit, it just wouldn't work! That led me to discover an important thing about AM radios - they need to use ferrite-cored inductor antennas as these have higher Q ratios than smaller axial inductors. It's not too difficult, and you'll need to experiment with coil winding numbers to find the sweet spot. Generally, this is between 50 and 90 turns of enameled wire on a ferrite rod.Setting this project aside, I pulled out my late 1960s-era Zenith Royal 20 pocket radio I mentioned somewhere on this website. Around 10pm last night, I began to tune the dial in search of weak signals, and boy did I find plenty! I tuned into the following stations:
- WSM-AM 650 in Nashville, TN (home of the Grand Ole Opry!!!)
- KXSP-AM 590 in Omaha, NE (relatively close, but still a ways away!)
- WLW-AM 700 in Cincinnati, OH
- WGN-AM 720 in Chicago, IL
- WBBM-AM 780 in Chicago, IL
- KOA-AM 850 in Denver, CO
- KYW-AM 1060 in Philadelphia, PA
Now, I want you to take in the last one. My QTH is in rural Northwest Missouri, and I was receiving a commercial AM station all the way from urban Pennsylvania!!! I was so surprised, and although the signal was relatively weak (about S1 or S2 if I had to guess with volume up all the way), it just goes to show you that AM radio is just as exciting even if you're not a ham or regular SWL.
So what can we learn from AM radio? First off, it's nowhere near dead, and it's probably a long way from the final station shutdown. Where FM can carry signals with crystal clarity, AM can carry intelligible signals beyond 100 miles and in some cases, beyond tens of thousands of miles if conditions are just right, using less power than FM stations. AM radio is just below the 160m amateur band, and in fact, it behaves the same way. We can use AM as a propagation tool for the bands directly above the broadcast band, including 160 and 80 meters. And remember, this is propagation for AM - SSB and CW, by design and convention, can travel even further due to bandwidth efficiency. Lastly, it's a hobby you can do at the end of the day after shutting off the ham equipment. Before bed, I've often listened to AM stations broadcasting news, sports, talk, and even radio shows and dramas from over 50 years ago! Reruns, of course :) I can receive a station about 40 miles south of me perfectly clear.
Now, about the TA7642...
This is an excellent place to start if you want to build your own DX-grabbing AM radio. This chip can run efficiently off of one AA battery and condenses around 6 or 7 demodulation and amplifier stages into one small TO-92 footprint. Used in conjunction with a few resistors, capacitors, a transistor amplifier stage, and a tuned ferrite inductor-variable capacitor LC circuit, this chip can provide up to 72dB or more of pure AM broadcasts, even from around the globe if you're lucky!
If you remember (or maybe not) in the 1970s the Ferranti ZN414 chip or the more recent MK484 chip, this is the upgrade to both of those chips. Circuits found online appear relatively simple to construct and design. In fact, the TA7642 can work with any regular 8 ohm pair of headphones all the way up to the high-impedance crystal earphones of around 20,000 ohms or more!
I will attempt to reconstruct this exciting circuit and see if I can beat the Zenith's impressive DX power. Stay tuned as I succeed and fail!
How to Listen to DX AM
AM is best listened to once the sun sets. For my area, it's around 8:30pm CDT or 7:30pm CST. You'll need an external antenna of some sort, which is usually a very long piece of wire with a few loops around the radio or the ferrite rod itself and the rest of wire acting as the receiving antenna. About 100 feet of wire is plenty.
Orient the antenna perpendicular to the transmitting station, preferably outdoors. This will minimize or even eliminate any RFI/EMI that AM radios are susceptible to.
Oh, and please, for the love of all things holy, DO NOT USE THIS ANTENNA DURING A THUNDERSTORM! Which brings me to the next topic...
Without an antenna, an AM radio can be used as a lightning detector. Think of it as a thunderstorm "Geiger counter." Every time lightning strikes, the AM radio will pop or crackle, which means that lightning is nearby and you should seek shelter if you haven't already. How loud the cracks are and how often they occur generally indicates how far away the storm is and/or how volatile it is. Of course, any thunderstorm is dangerous and lightning is the number one killer of nature every year.
You'll need to tune into weak stations to hear DX, similar to amateur radio. If you need, use an external amplifier like a cheap LM386 module. This should aid in pulling in weaker stations. It may or may not be possible to pick up transoceanic stations wherever you're located, but if you're coastal, there's a good chance you might be able to! Even if you can't pick up these international stations, I think it's really cool picking up interstate stations. Also, I recommend you keep a log with frequencies, callsigns, and station QTHs.
What are you waiting for??? Go prove that AM radio is far from dead!!!
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