26 June 2014
BUILD IT YOURSELF
By Robert Reed
rjr@ncweb.com
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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.
At the very bottom of the heap is the general-purpose generator
which may run from $200 upward. These are basically intended for