# AM radio interference in my house **URL:** \ **Category:** Factual Questions\ **Created:** [January 28, 2016, 4:48am UTC](https://boards.straightdope.com/t/am-radio-interference-in-my-house/744466 "2016-01-28T04:48:12Z")\ **Posts on this page:** 7\ **Page:** 3
**Author:** ![HeyHomie](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/heyhomie/32/207_2.png) [@HeyHomie](https://boards.straightdope.com/u/HeyHomie)\ **Post date:** [April 28, 2016, 1:09am UTC](https://boards.straightdope.com/t/am-radio-interference-in-my-house/744466/43 "2016-04-28T01:09:17Z")
> [@Askance](#): > > If it was really caused by something downstairs, I can’t understand why it apparently moved around … Because a hydroponic grow box is roughly similar in shape to a tall wall safe. You could easily move them around, probably even without a dolly. ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [April 28, 2016, 1:53am UTC](https://boards.straightdope.com/t/am-radio-interference-in-my-house/744466/44 "2016-04-28T01:53:32Z")
> [@HeyHomie](#): > > Because a hydroponic grow box is roughly similar in shape to a tall wall safe. You could easily move them around, probably even without a dolly. I don’t think the guy downstairs was growing weed, I think he was a spy that moved the shortwave radio that he used to receive instructions from his Commie Masters around. ---
**Author:** ![joema](https://avatars.discourse-cdn.com/v4/letter/j/a9adbd/32.png) [@joema](https://boards.straightdope.com/u/joema)\ **Post date:** [April 28, 2016, 3:43pm UTC](https://boards.straightdope.com/t/am-radio-interference-in-my-house/744466/45 "2016-04-28T15:43:11Z")
> [@Askance](#): > > Two or so weeks ago we evicted the tenant downstairs unit within our house and started renovating, which included replacing just about everything electrical like halogen lights, range hood, bathroom fan and so on. > > A week ago I turned on my shower radio for the first time in a couple of months … no interference at all! Still none today, which is by far the longest period without it since it started. > > If it was really caused by something downstairs, I can’t understand why it apparently moved around … It sounds like your problem is resolved, but here is some more info. These situations are unfortunately very common. With the increasing use of electronic devices such as light dimmers, plasma TVs, electrical motors with variable speed controls, etc. the nearby environment can be showered with Radio Frequency Interference (RFI). Some of the emitting devices may be improperly manufactured or certified; in other cases the receiving device is improperly shielded. In yet other cases both devices are within certified limits, but the regulatory specifications simply allow a certain RF emission which causes interference if in very close proximity. As already stated, often the best initial approach is cut all power to your dwelling and see if the RFI goes away as heard on your portable radio. If it does not the source is outside your house. If it does go away when power is cut, the source is inside your house and after restoring power you can sequentially turn off circuit breakers to find the approximate location. If outside your house and the portable radio indicates rough proximity, you can sometimes walk around and get a rough idea where it’s coming from. Common causes are a malfunctioning power line transformer or debris on a power line insulator. The utility company will usually then help if you can point to the approximate area. If none of those methods are helpful you ideally would want someone experienced and knowledgeable in tracking down RFI problems. Some ham radio operators are experienced at this. Some of the instruments used to track this down are not extremely expensive but unless you do this frequently they aren’t worth buying: MFJ-856 Directional Noise Finder: [http://www.mfjenterprises.com/Product.php?productid=mfj-856](http://www.mfjenterprises.com/Product.php?productid=mfj-856) RFI direction finder gun: [TYPE HFDF VECTOR](http://www.nationalrf.com/type_hfdf_vector.htm) Given two directional fixes, here is an iOS app which triangulates the position of the emitter: [https://itunes.apple.com/us/app/foxhunt-pro/id556391384?mt=8](https://itunes.apple.com/us/app/foxhunt-pro/id556391384?mt=8) There are now available relatively inexpensive (in historical terms) high-resolution RF spectrum analyzers which can examine RFI in great detail. This can help characterize it and when used portably can aid determining the location. Here is one example of two different types of RFI in the 3.5Mhz range. The pulse-type signal was tracked to a malfunctioning Asus WiFi router. [![](https://photos.smugmug.com/photos/i-vwNHPzr/0/X2/i-vwNHPzr-X2.jpg) ](https://photos.smugmug.com/photos/i-vwNHPzr/0/X2/i-vwNHPzr-X2.jpg) ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [April 28, 2016, 4:51pm UTC](https://boards.straightdope.com/t/am-radio-interference-in-my-house/744466/46 "2016-04-28T16:51:43Z")
> [@Leaffan](#): > > Also, AM stations are required to cut their broadcast power after sunset until after sunrise. Does this come into play in the house? > [@Askance](#): > > In Australia? First I’ve heard of that. Why would that be? > > But no, we haven’t noticed a day/night factor here. just to answer this, long-wave and medium-wave AM radio broadcasts carry a lot farther at night due to skywave propogation. in the US the FCC has granted certain AM broadcasters “clear channel” status, which means they can transmit at full power day and night. Other stations transmitting on the same carrier frequency are required to reduce their broadcast power at night to reduce interference with the clear channel transmission. > **[Skywave](https://en.wikipedia.org/wiki/Skywave)** > > In radio communication, skywave or skip refers to the propagation of radio waves reflected or refracted back toward Earth from the ionosphere, an electrically charged layer of the upper atmosphere. Since it is not limited by the curvature of the Earth, skywave propagation can be used to communicate beyond the horizon, at intercontinental distances. It is mostly used in the shortwave frequency bands. > As a result of skywave propagation, a signal from a distant AM broadcasting station, a shortwa... > **[Clear-channel station](https://en.wikipedia.org/wiki/Clear-channel_station)** > > A clear-channel station is a North American AM radio station that has the highest level of protection from interference from other stations, particularly from nighttime skywave signals. This classification exists to ensure the viability of cross-country or cross-continent radio service enforced through a series of treaties and statutory laws. Known as Class A stations since the 1983 adoption of the Regional Agreement for the Medium Frequency Broadcasting Service in Region 2 (Rio Agreement), they ... ---
**Author:** ![Askance](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/askance/32/8281_2.png) [@Askance](https://boards.straightdope.com/u/Askance)\ **Post date:** [April 29, 2016, 3:02am UTC](https://boards.straightdope.com/t/am-radio-interference-in-my-house/744466/47 "2016-04-29T03:02:25Z")
> [@joema](#): > > As already stated, often the best initial approach is cut all power to your dwelling and see if the RFI goes away as heard on your portable radio. If it does not the source is outside your house. If it does go away when power is cut, the source is inside your house and after restoring power you can sequentially turn off circuit breakers to find the approximate location. See post #32 - we tried that. The power was out to the entire house, including the unit downstairs that we just cleared out. Made no difference to the interference at all. Unless there’s a transformer or something that keeps charge and still emits for minutes or longer after being unplugged? I’m starting to think it is next door, and the fact it went away a week or two ago is just coincidence, maybe they’ve done something different. ---
**Author:** ![Askance](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/askance/32/8281_2.png) [@Askance](https://boards.straightdope.com/u/Askance)\ **Post date:** [May 23, 2016, 1:38am UTC](https://boards.straightdope.com/t/am-radio-interference-in-my-house/744466/48 "2016-05-23T01:38:16Z")
Annnnnnnnnnnnnnd as of about 2 weeks ago, it’s back and if anything worse than ever. Damnation! ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [May 23, 2016, 1:40am UTC](https://boards.straightdope.com/t/am-radio-interference-in-my-house/744466/49 "2016-05-23T01:40:19Z")
Time to walk around the neighborhood with your radio. It doesn’t have to be local though. Also, check the skies at night. You know, just in case. [Previous page](https://boards.straightdope.com/t/am-radio-interference-in-my-house/744466.md?page=2)