[HCARC] Noise

[Kerry Sandstrom]

Steve,

Sorry I haven't had a chance to reply sooner.

I think it is unlikely to be either the coax or the ground.  Either can make 
noise but mainly if there is a big big signal going through it - Nothing 
from a receiving antenna.

Two noise sources I've had trouble with lately is an Ott light.  This is a 
special color balanced light that my wife uses for sewing.  Its problem is 
that it has an electronic circuit to get the correct voltage for the lamp. 
It's like a dimmer circuit and very noisy.

The second noise source was a battery charger for a cordless electric drill. 
Again, it used a dimmer type switching circuit.

A few years ago I had a problem with a computer power supply that was quite 
noisy.  Changing the power supply was the only cure for that problem.

Any kind of an electronic dimmer is also a possible source.  New ones are 
pretty quiet but old ones are a problem.  New ones can be a problem if a 
component has failed in the dimmer.  Many ceiling fans use a dimmer like 
device for fan speed control.

What is near where your antenna runs?  It is more likely to be something 
near your antenna than something a long ways away.

If you have a choice of bandwidths in your receiver, listen for the noise in 
the widest bandwidth possible with the RF gain reduced.  You have a better 
chance of hearing what the noise really sounds like then.  A narrow receiver 
filter stretches the noise and running the RF gain at max overdrives the 
receiver.  Be sure you're not using any audio filters.  Also be sure the 
noise blanker, if you have one, is off.  See if you can tell if the noise is 
60 Hz or 120 Hz.  60 Hz typically is from the AC line while for 120 Hz there 
is a full wave power supply probably involved.  An oscilloscope with line 
sync is a good tool to use, but not one that many people have.  I have a 
couple old receivers with 16 + kHz bandwidths for multi-channel signals that 
are quite useful for looking at noise.  the sound and appearance of noise on 
a wide receiver is dramatically different than in a 2.4 kHz or 500 Hz narrow 
filters.

Does the noise change at all with time of day?

When did it show up?  Was there something that you know changed about the 
time the noise showed up?

What is the frequency range of the noise?

Does your receiver have some kind of a 'calibrator' that you use to check 
frequency?  Is that turned off?

Simply turning stuff off isn't always adequate.  There is a lot of stuff now 
that is always connected as long as its plugged in.  The on - off switch 
doesn't turn much on or off.  Don't go around turning stuff off, unplug it!

Any questions, just ask.

Kerry