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retiredengineer's Avatar retiredengineer
06:05 PM Liked: 20
post #1 of 4
01-10-2010 | Posts: 557
Joined: Aug 2007
Can anyone explain why, when I turn on my microwave oven, my TV picture hesitates and breaks up. This happens on all VHF and UHF stations. I installed a surge protector with an EMI filter on the power plug but that didn't help. I'm guessing that the signal levels coming from my outdoor antenna is barely above the TV receiver noise floor and that the microwave oven has no or poor internal EMI filters. It must be generating and radiating EM pulses that is very wideband and my antenna is picking that up.

My apologys if this is not the correct forum to post this question.

Thank you for your help.
holl_ands's Avatar holl_ands
09:08 AM Liked: 65
post #2 of 4
01-12-2010 | Posts: 3,733
Joined: Jun 2004
Double check your power strip's total rated wattage (110 volts x amps) to see
if it will handle the microwave's input power. If it is compatible, try your
EMI Power Strip directly on the microwave oven's power cord. This will
reduce interference BEFORE it has a chance to radiate from the house wiring.

You can get EMI Filters that attach directly to the wall:
http://www.parts-express.com/pe/show...number=125-010
http://www.parts-express.com/pe/show...number=125-006
http://www.tripplite.com/en/products...xtModelID=3974
http://www.tripplite.com/en/products...?txtModelID=98

An extra 6-ft of power cord not only radiates somewhat more, but also
reduces the power ratings from 1800 W to an unaccepable 1440 W:
http://www.tripplite.com/en/products...?txtModelID=97
http://www.parts-express.com/pe/show...number=125-030

The above products all provide "40-80 dB" of EMI suppression, which
is considerably more than you'll find in most "Surge Protector Strips".
Tripplite even provides detailed specs to explain the "40-80 dB" hype:
http://www.tripplite.com/shared/tech...ual/931411.pdf
A much larger power filtration system is needed to exceed these numbers.

It is ALSO possible the high electrical load of the microwave is drawing down the
AC voltage as it goes into your TV (check it with a meter). Flip power breaker
switches (or whatever) to determine whether they are on the same electrical circuit.
If they are, temporarily (or permanently?) run an extension cord from the TV (etc)
to an outlet that is NOT on the same circuit as the microwave. If this cures the
problem, you at least know what is needed to "fix" the problem.....perhaps
an UPS (Uninterruptible Power Supply) that is ALWAYS providing power from
the battery....as opposed to those that sit idle waiting for input power to fail....
retiredengineer's Avatar retiredengineer
06:17 PM Liked: 20
post #3 of 4
01-13-2010 | Posts: 557
Joined: Aug 2007
holl_ands, thank you for your detailed response. I'm sure any of those devices you mentioned will solve my problem.

However, I read else where that installing ferrite beads on a coax, audio, or AC cord might help alleviate EMI problems. So I went ahead and installed a snap-on ferrite bead on each of the three wires in the AC cord of the TV.

Now I am a happy camper. The interference is gone except for three stations. On those stations, I occasionly see macroblocking but the picture is still watchable. Apparently my Sony TV inadequately filters the AC power lines.

Again, thank you for taking the time to respond.
DrDon's Avatar DrDon
11:17 AM Liked: 290
post #4 of 4
01-14-2010 | Posts: 12,800
Joined: Mar 2002
Split off from OTA FAQ.

Doc
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