Powering PC distrupts FM and ATSC signals - Page 1
Forum section: electronics / beginners

author: kyle
author_rank: Contributor
timestamp: October 19, 2013, 08:12:59 am
content: Hello,I have a PC that whenever I turn it on within 5 seconds my TV loses signal and becomes unwatchable and FM radio picks up lots of static and sounds awful. I don't have a computer case but an overclocked bench setup where motherboard and components sit on my table, could that be a problem? Any ideas? Could a computer fan cause this? PC has a high overclock, i7 2700K is running at 5.2GHz, board's power delivery PWM is set to highest value 500kHz and is using all available 16 phases--Asus P8P67 Deluxe.

author: Stonent
author_rank: Super Contributor
timestamp: October 19, 2013, 08:27:27 am
content: Well FM is 88 to 108 MHz and TV ranges from 400 to 800+ MHz. So something is resonating and emitting energy in those ranges.Without a case to block the signals, it can happen.

author: amyk
author_rank: Super Contributor
timestamp: October 19, 2013, 08:47:57 am
content: CPU core may be at 5.2GHz but the bus clock will be much lower and in the range for creating interference (~100MHz?)

author: geraldjhg
author_rank: Regular Contributor
timestamp: October 19, 2013, 11:57:17 pm
content: maybe you could try and ground as much as possible --mother neg hd poer supply case etc etcshorten cables as much as possiblecheck if power supply has a decent input (really common mode filter) filterplug in different outletsbetter the signal for fm and tvhave fun with oc

author: DL8RI
author_rank: Regular Contributor
timestamp: October 20, 2013, 12:26:04 am
content: QuoteYes. A PC in general radiates as hell, most components are designed quite poor from a EMC-perspective.Your "flying" set-up will distribute even more EMI due to the lack of shielding.

author: ConKbot
author_rank: Super Contributor
timestamp: October 20, 2013, 12:30:32 am
content: If you ever look at a OEM made PC like a dell, you'll notice a lot of stuff related to EMI, finger contacts, ferrites on some cables, etc thats not even paid attention to in custom/modded PCs. I'm quite surprised there hasnt been more instances of interference (either the PC as the source or victim) since modding/custom PCs have gained in popularity. (acrylic cases and the like)

author: kyle
author_rank: Contributor
timestamp: October 20, 2013, 12:50:09 am
content: Thanks for the input guys, looks like I will be getting a case, I avoided using one up to this point because of the water cooling setup and difficulties fitting triple 120mm radiator. Cooler Master HAF 932 should fit my setup. Yesterday I tried unplugging few different components but it did not help, except that signals got a bit better when I unhooked the water pump, swiftech mpc355 18w, but it was hard to tell. I also happen to have an APC UPS with AVR (Automatic Voltage Regulator) functionality that supposedly boosts or trims incoming voltage. I poked around with ohmmeter and checked if there's continuity between motherboards screw holes and ground, and there was, so running a wire from PSU case to mobo's screw hole wouldn't help I guess.I might try holding a grounded side panel from other case that I have or some sort of shielding to see if it helps. I'm using indoor antennas so just moving around disrupts the ATSC signal.

author: johansen
author_rank: Super Contributor
timestamp: October 20, 2013, 01:08:50 am
content: I would recommend leaving the cpu power supply frequency at the recommended value, but reducing it isn't going to stop the interference.try a different power supply.

author: kb3pxr
author_rank: Contributor
timestamp: October 21, 2013, 02:27:30 am
content: It is a case of a lack of a case. I've had trouble with laptops with knocking out FM and Analog TV, the noise of something without EM Shielding is very problematic and you also found out why it is actually illegal (RFI).