For anyone that is interested . . .
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Masters Communications announces the availability of new test
equipment for amateur radio communications - a FM deviation meter.
Several years ago I set out to make an affordable communications
service monitor, but that task as a complete unit never
transpired. Since then, some aspects of a service monitor have
been made available in the way of cheap Asian test equipment.
There are FM signal generators, spectrum analyzers with tracking
generators, VNA's, and other things that easily fit the ham or
hobbyist's budget. While this stuff isn't laboratory grade - it's
better than not having anything. This inexpensive equipment is
great for testing FM receivers, but there is a current lack of
equipment to test FM transmitters. What does a ham do to
quickly,
easily and accurately measure deviation on a FM transmitter,
set up a repeater controller, or make measurements on a link
transmitter or adjust an ASL node? There's got to be a better
way..
Sure, there some inexpensive are ways to do it - but none are easy
to do / use, and may require a computer and complicated software
Plus - you might not have access to a modulating frequency of the
right value to do Bessel Function for your required deviation.
Case in point - VARA FM Wide. VARA FM creates a 1500 Hz tone when
you press the "Tune" button. This frequency results in a first
Bessel null at 3.6kHz deviation. That's pretty far removed from
the optimal value of 2.2 - 2.5kHz deviation for VARA FM Wide. A
real deviation meter can easily read the deviation of a FM
transmitter - even though the tone(s) produced by software doesn't
work well with Bessel nulls. None of this type of testing shows
distortion which is evident when you hit the limiter. There's got
to be a better way...
What about the Heathkit IM-4180, AEA DM-1, and MFJ-224? They are
long gone. I've owned all of these, and they were kludgy. The
Heathkit and MFJ are tuned with a VFO knob, were rather unstable
and difficult (at best) to use. The MFJ only covered 2M. The AEA
was crystal controlled - so it was limited in frequency coverage
and only had a very granular display. None of them were very
sensitive, nothing like a real service monitor. There's got to be
a better way....
Here's a
better way:
The FMDM-150M Deviation Meter is fully explained on our
website. If you are interested - check it out when you have the
time.
Comments and questions welcomed....
Kevin Custer
Masters Communications
Palm Coast FL
USA
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