Nuts and Volts - June 2014

26 June 2014

BUILD IT YOURSELF

By Robert Reed

rjr@ncweb.com Post comments on this article and find any associated files and/or downloads at www.nutsvolts.com / index.php?/magazine/ article/june2014_Reed.

Once our interest in electronics is piqued, our inventory starts to grow — first in knowledge gained by books and select articles, followed by a small inventory of parts, and a few pieces of basic test equipment. We usually start with a simple DMM and some sort of power source. As time goes by, we accumulate a fair amount of basic equipment. However, no test bench is complete until it has an RF signal source of some type.

What I will present here is a sweet little general-purpose RF signal generator that won't take up much bench space, will fill that missing gap, and can be built fairly cheaply.

A 150 MHz RF SIGNAL GENERATOR FOR YOUR

TEST BENCH

Let me start with a brief overview of what’s out there. Signal generators come in a wide variety of flavors. Starting at the very top end would be a generator that oscillates at only one frequency that is extremely accurate, such as might be used by NIST (National Institute of Standards). These are primary frequency standards and time bases by which all other frequencies are referenced to. They have incredible accuracy and can cost upwards of $100,000. Next in line would be very high-end generators with super specs of accuracy and stability, along with any type of modulation that’s available. Today, these mods can be quite complex. Then, we drop down to mid-range generators that — although they still have excellent specifications — will be more application-specific (limited frequency bands, etc.) rather than “all purpose.” Many of these are slow in use due to programming and a myriad of pushbuttons. Once you pick your chosen frequency, they perform excellently, but they can cost anywhere from $1000s to $10,000s.

One corporation I worked for involved using a very complex microwave generator which had excellent specs in a myriad of features and — although you could perform just about any frequency related test with it — it was also slow to get to each specific point of interest. The user manual was a full 3” thick and it would probably take a year to become totally proficient at using this generator. One other thing was that it reportedly came with a $38,000 price tag.