Author: Alfred But
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Evolution of Radio Receivers – Part 2: The Superheterodyne Architecture Explained
1. Introduction The first commercial radio broadcast began in the 1920s. In the early days, radio receivers were constructed with an antenna feeding a LC tuned circuit which was followed by a simple crystal detector or a vacuum tube amplifying stage and then a diode detector to recover the audio. This is the basic Tuned…
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Evolution of Radio Receivers – Part 1: The 2-Transistor Reflex TRF Receiver
Introduction In the mid 1950s, while almost all table-top radios used vacuum tubes, pocket-size transistor radios started to appear. Most of these radios employed the superheterodyne architecture which needed at least 4 transistors for adequate performance. However transistors at that time were very expensive. For cost saving, a few low-end models used the tuned radio…
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An Easy-to-build Active Small Loop Antenna for Urban Indoor MW/SW Reception
Motivation I am living in a downtown apartment where an outdoor “large” antenna is impractical. My only feasible location for a fixed antenna is at the balcony. Obviously for SWL-ing at frequency below ~15MHz, only electrically small antennas can be used. Moreover man-made noise is very high in my area, rendering a whip antenna unusable.An…
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A low cost comb generator
A comb generator is a simple but useful piece of equipment. Most comb-generators rely on a Step-recovery-diode (SRD) to create very narrow pulses which are rich in harmonics. Unfortunately SRDs are expensive, hard to find and very fragile. The above circuit and figure show one low-cost design that replace the SRD with a PIN diode.…
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HP8562A Spectrum Analyzer Repair: Fixing Video Offset / Display Issues
My HP8562A has been in excellent condition for many years until one day when I powered it up, the displayed trace was weird. The whole spectrum display was shifted up, as in the above photo. Trying to display the built-in cal. signal further confirmed the problem. The photo below showed the 300MHz cal. signal, which…
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My first radio experiment
My first radio project was a crystal radio which was similar to the above picture. As a poor student, the selling price of the kit was too much for me. Fortunately I found a article on building crystal radios from an electronics magazine. I copied the circuit, bought low cost components from the surplus market,…
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Hello Electronics/Radio Hobbyists!
If you are a hobbyist and interested to know the evolution of radio/electronics for the past 50 years, you are in the right place. Don’t worry, I will not bore you with well-known history, which has been detailed in many good books. Instead I will give detailed circuit description to the radio receivers/transceivers I have…
From Hobby to Professional 