Medium Wave Radio Project
I want to build a good quality medium wave radio receiver, something that can receive some of the more distant stations that become receivable in the evening, but also hold up against the very strong local stations that can literally be received with a just germanium diode connected to a crystal earpiece.
Usually when I design and build a radio, I start at the audio amplifier end, because even if nothing else in the radio works, you have an audio amplifier. This time I’m going to start at the antenna and work my way along - for some reason I have a surfeit of audio amplifiers…
I want the radio to use an external antenna, rather than rely on the more common internal ferrite rod antennas used in medium wave radios. So I’ll start with a circuit to connect an antenna of random impedance to the ~50 Ω impedance circuits I’ll use in the rest of the radio.
I’ll also built a bandpass filter for the medium wave band, to keep as much interference from adjacent bands out of the radio.
The rest of the design of the radio will be worked out as I go. I’m thinking generally to go with a two-stage superhet design, using an first IF around 10.7 MHz and a second IF around 455 kHz, possibly using a W7ZOI HyCas IF stage on the second IF.
For the detector, I’m thinking about trying either a synchronous AM detector or trying an Analog Devices power detector IC I have laying around. The audio stage will probably be based around a design from Vasily Ivanenko
If I keep everything pretty generic after the first IF, I can use the radio for any other frequency range too. It should make for a useful test-bed for designs, as well as be a fun thing to design, build and debug. I might even listen to the radio on it from time-to-time.