Author: Alfred But
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AOR AR-3000 Troubleshooting – PLL error
The Problem My AR3000 has been in occasional use for 30+ years. Several months ago it failed to start. Pushing the power button resulted in no sound and the icon “PLL ERR” showed up in the LCD screen. Diagnosis and Repair I had the gut feeling that the problem was due to faulty electrolytic capacitors.…
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Tektronix 494P Spectrum Analyzer Repair – Display blank
Several months ago I fixed the video offset problem of my HP8562A. (See the post: HP8562A Spectrum Analyzer Repair: Fixing Video Offset / Display Issues. ) Last week my Tek 494P refused to work – the display was blank after power on. A quick diagnosis revealed the following: Troubleshooting I remove the instrument cover to…
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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 for frequency synthesis applicartions
Introduction 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 step recovery diodes are expensive and very fragile (easily damaged by ESD). Now they are hard to find. This post shows one low-cost alternative design…
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HP8562A Spectrum Analyzer Repair: Fixing Video Offset / Display Issues
The Problem 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 shown in Fig.1. Trying to display the built-in cal. signal further confirmed the problem. The photo below showed the 300MHz cal. signal,…
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My first radio experiment – Crystal Radio
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 