funny issue- new pc fuzzes TV in Excel

[progman1010]

Here's one for you- we just got a new computer (HP M8330F) for the living room. We have our TV hooked up to a high-gain analog antenna on our roof. Channel 4 (ABC) comes in slightly fuzzy to begin with, but no audio interference unless we turn on a fan in the bedroom.

Here's the kicker- the computer doesn't cause any problems at all UNTIL Excel (2007) is active. Either maximized or smaller window, as long as Excel is open and not minimized, it causes interference! We tried all the other programs on the PC, including Word and Outlook.

It's the oddest thing. Any thoughts?

 

[LawnBoy]

I'd bet it's your monitor causing the interference. Are you sure it's properly grounded?


--
The stagehand's axiom: "Never lift what you can drag, never drag what you can roll, never roll what you can leave.

 

[progman1010]

That's what I initially thought too- but then i turned off the monitor, keeping Excel in the foreground and nothing changed.

 

[LawnBoy]

Now that's weird...
Can you tell if the pc has variable speed fans in it? Could the noise be related to fan speed?

Maybe Excel is causing the processor fan to speed up. Or Excel is causing your video card to emit the interference.

Have you tried changing screen resolution, or refresh rate?


--
The stagehand's axiom: "Never lift what you can drag, never drag what you can roll, never roll what you can leave.

 

[lopes1211]

Maybe it's something like speedstep technology. i.e. 3GHz processor only runs at 1.5GHz until it needs the extra horsepower (like for spreadsheets) then speeds up to the full 3GHz. This higher processor frequency then matches or shares frequency harmonics with the fuzzy channel in question.

-CL

 

[Nelviticus]

Whatever it is it shouldn't be emitting anything strong enough to interfere with a TV signal. There are regulations in place in Europe, the US, Canada and many other jurisdictions to prevent this - that's what all those logos mean on every power supply you get these days.

So I reckon it's a fault, but you might have a hard job convincing HP of that

Nelviticus

 

[progman1010]

a quick lookup of the frequencies shows channel 4 as 67.25MHz, but lopes1211 you may be onto something.

This issue also happens when i run a box fan in the other room, but the outlet is on the same circuit. Maybe Excel, requiring more juice than other programs is pulling more through the wall.

I have always had a hunch that the house has poor or inadequate grounding from flickers during thunderstorms. Oh, and when I first turn on the microwave (1500-watt), the TV volume suddenly drops and then fades back into normal volume.

Ok, so I think the conclusion is that Excel is somehow drawing more power and thus causing the interference. Still kinda funny, though. Thanks all!

 

[LawnBoy]

Nelviticus,
Interesting that you should bring that up. In the US electronics have to meet guidelines for noise emmissions as you say. The funny thing is that PCs are rated for commercial or industrial environments, not residential (like every other electronic device I own). I don't know how or why PCs can be sold for residential use when they are rated for commercial, but they are.



--
The stagehand's axiom: "Never lift what you can drag, never drag what you can roll, never roll what you can leave.

 

[BadBigBen]

The funny thing is that PCs are rated for commercial or industrial environments, not residential (like every other electronic device I own).

Not correct! PC/Computers like calculators are regulated under 47 CFR §15 CLASS B...

The definitions describe some of the terms used in Part 15. A sampling follows:

*Digital device: "An unintentional radiator...that generates and uses timing signals or pulses with a frequency > 9 kHz, and uses digital techniques." This applies to personal computers, peripherals, and other equipment using clocks and logic circuitry.

*Class A digital device: "A digital device marketed for use in a commercial, industrial, or business environment and not intended for use by the general public or in the home."

*Class B digital device: "A digital device marketed for use in the home, although it could be used elsewhere." Examples include calculators and personal computers.

Source: Inside FCC Part 15 and Canada's Corresponding Standards


Ben

"If it works don't fix it! If it doesn't use a sledgehammer..."

 

[LawnBoy]

Looks like you caught me with old info, Ben. Dell is now claiming that "Most Dell computers are classified for Class B environments". HP says you've got to look at the label, if it has an FCC logo then it's class B.

Apparently the situation is improving.


--
The stagehand's axiom: "Never lift what you can drag, never drag what you can roll, never roll what you can leave.

 

[BadBigBen]

Lawnboy, no problem, we are here to learn from each other...

btw. my old and venerable Amiga 500 (1987) was classified as CLASS B, that is why it rang a bell... ;-)

Ben

"If it works don't fix it! If it doesn't use a sledgehammer..."