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IMD Testing of Amplifiers
Today's Amateur Radio receivers routinely achieve performance untouched by earlier generations of ham gear. Can our already excellent equipment be improved still further? The fact that many presentations have dealt with receiver capabilities and improvements over the years might seem to imply that all receiving problems have been solved and that the technology is mature. On the other hand, a look at the components actually used in the front ends of current receivers by different manufacturers indicates that just the opposite is true. While improvements have been made in mixers, amplifiers and synthesizers-and from a systems point of view there have been some subtle implementations of individual circuits-there is still work to be done! How else can one explain that different receiver designs-with similar block diagrams, and brought to market with the best of intentions-sound different on the air? Modern ham equipment seeks to achieve high dynamic range in relatively standard, seemingly well-established ways.
A complete discussion of receiver sensitivity, intermoduation distortion, and gain compression, and what they mean in terms of performance. When it came to receivers, the earliest amateur operators were concerned primarily with sensitivity and experimented almost endlessly with different types of crystals, trying to find the one that was the most sensitive. Then came DeForest's Audion, and Armstrong's regenerative detector, and amateurs who could afford the tubes found they had all the sensitivity they could use.
An accurate digital multimeter with a high-voltage probe for safe measurement of voltages above V. For more sophisticated station adjustment SSB audio, modulation envelope, tones in digital modes etc. A good-quality frequency counter with a minimum frequency range of MHz, preferably with a 1 GHz C-channel. Radio amateurs who are interested in aligning and repairing their own or their friends' radio gear may wish to go a few steps further:. A tracking generator for use with the spectrum analyser, or alternatively a vector network analyser VNA.