Old news to most - might help newbies
 

We are all constantly trying to root out the source of
"noisemakers" when listening. The most obvious ones, like fluorescent
lights, etc. are well-known. Well, you can buy in any hardware store or
home center a device that screws directly into the socket base of any
metal-bodied lamp, thereby turning it into a "touch" lamp. Very
convienient. But I discovered today that they are a nasty noisemaker in
AM or SW listening.
In this particular case, the lamp was about 14' from the antenna (in the
room I noticed it), and I don't know over what range that effect would
be noted, but probably anywhere in the house. As the subject line says,
probably old news to most readers here, but may be helpful to newer
listeners still trying to track down noise sources.

Rheostats are also notorious noisemakers, and the principal behind
the two devices is basically the same. For what it may be worth to newbies.

Tony

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In article , Tony Meloche
wrote:

We are all constantly trying to root out the source of "noisemakers"
when listening. The most obvious ones, like fluorescent lights, etc.
are well-known. Well, you can buy in any hardware store or home
center a device that screws directly into the socket base of any
metal-bodied lamp, thereby turning it into a "touch" lamp. Very
convienient. But I discovered today that they are a nasty noisemaker
in AM or SW listening. In this particular case, the lamp was about
14' from the antenna (in the room I noticed it), and I don't know
over what range that effect would be noted, but probably anywhere in
the house. As the subject line says, probably old news to most
readers here, but may be helpful to newer listeners still trying to
track down noise sources.

Rheostats are also notorious noisemakers, and the principal behind
the two devices is basically the same. For what it may be worth to
newbies.

I have not found the old style ballast with florescent lights to be
noise makers unless they are right up near the radio. The ballast type
can be a noise generator if the starter or bulb needs to be replaced.
The newer high frequency switching type can be a noise problem even if
the bulb is OK.

The touch lamps employ the same semiconductor technology as light
dimmers, which is either a SCR or triac type of switching device. These
components switch the AC power to the bulb. In order for them to work
efficiently they have to switch fast or they will dissipate more heat
in the small space they must occupy. This fast switching is a direct
cause of broadband radio noise. Other passive components in the devices
are used to suppress the fast switching transients but don't eliminate
them. It would be expensive and require more space than a light switch
box in the wall to suppress the generated radio noise to the point that
you could not hear it on a sensitive SW radio.

If used to switch a light on or off a semiconductor is no different
than a mechanical switch or relay. The act of turning the light on or
off will generate one pulse to be heard on the radio. The problem with
dimmers is the range between off and on where the device is switching
on and off every 60 Hz AC cycle. The act of dimming causes this every
cycle switching. You can test this yourself by tuning your radio to a
low unused frequency. With the switch off or full on you will not hear
much noise but have it anywhere in between you sure will. You will be
able to change the character of the noise by controlling the brightness
of the light. The light brightness is determined by the amount of time
during a cycle the device is on.

--
Telamon
Ventura, California