Modern Radio Receiver Architecture: From Regenerative To Direct Conversion

Modern radio receivers have a distinct advantage over the common early designs which I covered in my previous article. Most of the receivers you will have worked with over the past couple decades are designs by Edwin Armstrong; regenerative, superregenerative, or most commonly superheterodyne. These are distinguished by a few fascinating key traits that bring both benefits and drawbacks.

Today let’s dive into Mr. Armstrong’s receivers. I’ll also talk about DC receivers which, despite the name, are not made to listen to batteries. These are receivers you are much more likely to encounter in modern equipment.

Regenerative and Superregenerative

The regenerative receiver is all about doing more with less. You still see some of these in simple applications like RF remote controls. The idea derives from how an oscillator works. In a simple way of thinking, an oscillator is an amplifier with enough positive feedback that any tiny signal at the right frequency will amplify and then, through feedback, continue to output over and over. If everything were perfect, then, an oscillator would have infinite gain at a given frequency.

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Wireless Weather Station

High schooler [Vlad] spent about a year building up his battery-operated, wireless weather station. Along the way, not only has he learnt a lot and picked up useful skills, but also managed to blog his progress.

The station measures temperature, humidity, pressure and battery voltage, and he plans to add sensors for wind speed, wind direction and rainfall soon. It is powered via a solar panel and can run on a charged battery for a full month. The sensor module transmits data to a remote receiver connected to a computer from where it is published to the internet. Barometric pressure is measured using the BMP180 and the DHT22 provides temperature and humidity values. The link between the transmit and receive sections uses a 433MHz Superhetrodyne RF Kit which gives [Vlad] a range of 50m. There’s an ATMega328 on the transmitter and receiver side. He’s taking measurements once every 12 minutes, and putting the micro controller in low power mode using the Rocket Scream Low Power Library. A 5W, 12V solar panel charges the 6V Lead Acid battery via a LM317 based charge circuit. This ensures the battery gets charged even when the solar panel is not receiving optimal radiation. One hour of sunlight provides enough charge to keep it going for 2 days. And a fully charged battery will keep it running for a full month even when there’s no sunlight.

The server software consists of two parts. The first pushes serial data to a mySQL database. This is written in Visual Studio C# using help from Oracle mySQL connector. The second part publishes the entries in the mySQL database to the web server. This is written in php, and uses  Libchart for graphing. He’s got the code, schematics, parts list and a lot of other information available for download on his blog. There’s a couple of items pending on his to-do list, so if you have any tips to offer post your comments below.