MadSci Network: Computer Science
Query:

Re: Do computer monitors interfere with pagers?

Date: Sat Sep 27 17:35:27 2003
Posted By: Dwayne Rosenburgh, Senior Electronic Engineer
Area of science: Computer Science
ID: 1063477842.Cs
Message:

It may be possible that your computer monitor is interfering with your 
pager, however, I believe this to be unlikely.  Your problem is 
exasperated by the intermittent nature of the interference.  In general, 
frequencies that are harmonics are the most likely to cause interference 
problems.  For example, if you pager is operating at 400 MHz, then a close 
by device that has a frequency of 800 MHz, or 1200 MHz, etc. may cause a 
problem.  Alternatively, your pager may be operating at a harmonic of some 
other device's frequency (i.e., another device that is operating at 200 
MHz).  Either of these situations can cause interference.  A second cause 
of interference is due to close-by, or adjacent frequencies.  Sometimes, 
devices that have a frequency that is close to another device's frequency 
will cause interference.  For example, a pager may operate over, say, the 
frequency range of 400 MHz - 410 MHz.  Another electronic device may be 
operating from, say, 390 MHz - 399 MHz, or from 410 - MHz to 415 MHz.  
Either of these two devices may cause interference; especially, if they 
have a stronger signal.

Sources of interference are usually hard to identify.  When the 
interference is intermittent, finding the source is much harder.  I would 
expect your computer to be a better candidate as the source of 
interference than your monitor.  I do not know what frequency your pager 
receives on, but I would guess that it is somewhere between 300 MHz and 
800 MHz (it could be higher than 800 MHz, but not likely to be less than 
300 MHz).  Therefore, your computer's CPU may be operating near your 
pager's frequency, or at a harmonic.

If you find the source of interference, there may not be a practical 
solution to eliminate it.  If both devices (i.e., the interfering device 
and your pager) are operating within their specifications, then the only 
solutions are to shield one or both devices, or increase the distance 
between the devices, or do both.


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