Using and measuring rf output levels – Contemporary Research QMOD-SDI Integration Guide User Manual
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Contemporary Research
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QMOD-HD Integration
Using and Measuring RF Output Levels
One important fact to understand is that, when combining modulators with other modulators or an
incoming cable feed, the amplitude levels of all the sources must be at least roughly the same.
That means you need to know what those levels are. If the only sources are multiple QMOD units,
just set them all the same level.
When combining with cable, you will want to know the level, measured in dBmV. In most
applications the incoming cable goes into a main amplifier that drives the main RF system. You’ll
want to combine with the incoming feed with the QMOD, then feed the combined RF to the
amplifier.
Very often, the end user may not know the level, or if there are clear channels on the
top of the RF frequencies. To know for sure, the most practical tool is a modern RF
meter. Costing about $1275
can test all sorts of things, including
the signal strength of one or more channels, analog and digital channels,
performance, and other tests. You can find where the cable channels end, and if there
is any noise that you need to filter out.
makes several DisplayMax models as
well, starting at about $800 and up, depending on software options.
Modulators that attempt to auto-adjust output relative RF signal strength don’t work
in commercial applications. Most modulators have 4-5 steps of attenuation, so auto-adjustment is
not precise, anyhow. An RF meter is the only tool that can tell you exactly what the levels are in
the feeds you are combining with the QMOD, the level coming out of the combiner, the level out of
the primary amplifier, and what you’re actually getting at taps and rooms.
You also need the meter before the proposal, so you can test the performance of the customer’s
existing RF system. Like any integration application, you need real tools to measure real
performance in the real world.
See products at
,
skip any analog meters.