When Your Silence Sensor … Doesn’t
Loss of audio
on your FM stereo station fails to trip your silence sensor. What’s going on?
Fig. 1: The 19 kHz
pilot appeared at the receiver’s audio output.
Clear Channel Dayton Senior Broadcast Technician
Paul “Hitchhiker” Lyons encountered this interesting problem. Yet when he unhooked
the tuner audio from the silence sensor input, the device tripped normally.
It turns out that the tuner Paul was using to
feed the sensor was passing the 19 kHz stereo pilot through to the audio
output, seen in Fig 1. This caused the silence sense to remain untripped even
when program audio disappeared.
Paul came up with a simple fix: a 19 kHz
notch filter, paralleled with the audio output. The schematic is shown in Fig.
He chose to build the circuit on a perfboard and
mount it inside the tuner, but the filter could just as easily be placed in line,
external to the tuner.
The schematic shows values for the coil and
capacitor, and is, of course, only one channel. If the silence sensor you use
has a stereo input, you’ll need one for each channel. Paul suggests using a
slugtuned coil for fine-tuning of the circuit.
The oscilloscope shows about a 60 percent
reduction in the level of the pilot signal at the audio output of the tuner.
After installation, the silence sensor worked perfectly. Fig. 4 shows the
reduction in pilot level.
Paul has been involved with broadcasting since
he was a teenager, following in his dad’s footsteps. His father was an
electronic technician and chief engineer.
* * *
You may recall a suggestion from Frank Hertel about
panel labeling in my March 1 column (“Your Panel Lettering Made Easy”).
Fig. 2: A 19 kHz
notch filter schematic.
Amstutz, CBRTE, offers a method that he has found to be simpler, with less
mess, than gluing paper-based labels to equipment.
A couple years ago, Leon ran across a
product from Avery-Dennison Office Products. Avery #6575 is a package of
50 sheets of 8.5-by-11-inch white durable multipurpose labels for laser
printers. These full-page labels can be laid out and printed, as Frank mentioned.
Leon, too, uses the OpenOffice/LibreOffice draw program for best results.
These Avery labels have a peel-away
self-adhesive backing, which eliminates the mess of glue. Another benefit is
that it incorporates “TrueBlock” technology, which appears to be a thin layer
of foil embedded within the label. This helps mask what the label is covering,
so that previous printing or markings on the surface to which the label is
applied will not bleed through.
Fig. 3: Paul
built the circuit on a perfboard and mounted it inside the receiver.
Finally, the label is specially coated to hold
the laser toner well, and resists rubbing off — hence the “durable” aspect of
the product’s name. It is resistant to scuffs, smudges and moisture, so it
doesn’t need to be coated with varnish or clear coat.
Leon has used this on everything from mobile
remote broadcast rack cabinets with the station logo to property ID labels on
tools and parts bins. The labels hold up well, even for areas that are printed
with a solid dark color on the white label surface.
The labels cost about $1 per sheet, but Leon
finds that he can usually combine several jobs on one page, and even use the “waste”
areas to print small wire identification numbers or terminal labels. Avery
also makes this product in pre-cut smaller size labels, if you don’t want to
cut them from a whole sheet of paper.
Fig. 4: With
pilot level greatly reduced, the silence sensor works perfectly.
your office supply vendor for these labels, or visit www.avery.com, keyword 6575.
in love with Avery years ago, when they started making an adhesive file folder
type label that could be used to label audio tape cartridges. What made these
labels so great was the label held secure to the cartridge plastic yet could be
removed easily, putting an end to the gummy paper and glue residue caused by
the typical file folder-type label.)
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