Air Conditioner RFI
Displaying 1-10 of 10
| Jul 24th 2011, 19:58 | |
KD4LNTotal Topics: 0 Total Posts: 0 |
A new AC/Heating central air unit has just been installed in my house. It is generating spikes approximately every 18 khz and steady noise at a lower level between spikes. The greatest interference is on 17, 15, 12 and 10 meters. The spikes ride upward of 30 dB above ambient noise and the steady noise appears to be at least 10 dB.There is also interference on 40 and 20 to a much lesser degree. The pickup is via close by antennas/transmisssion lines, not through the AC power. The central system fan appears to be the source of the spikes and then when the cooling system activates the steady noise appears. I have found unused wires in the thermostat cable and grounded them at one end - the AC unit. This includes cabling to the outside heat pump. It did nothing. Any thoughts? Help.... Jim, KD4LN |
| Jul 25th 2011, 11:12 | |
w1rfiSuper Moderator Total Topics: 0 Total Posts: 0 |
Let me start by explaining what ARRL knows about these systems and what it doesn't (yet) know. Background With today's concerns about energy efficiency, technology is changing to make better use of energy. Most power supplies today use digital switching technology because it is more efficient than older analog power supplies (and a LOT lighter). Switching supplies typically make noise every "N" kHz, where N can range from 5 kHz to as high as a few hundred kHz. Other switching supplies appear to create a broadband hash that extends across many MHz. Electirc motors can also be noisy. Older motors could use brushes and armatures or commutators, and sparking could cause noise over many MHz. Motor speed could be controlled, but the process to do so was somewhat inefficient. Many newer motors more efficiently control motor speed with pulse-width modulation. These are used in equipment such as pool pump motors and HVAC systems, among others. If the pulses are not well filtered, these motors can make horrible noise, and ARRL does have a few reports of interference from systems in neighboring homes. In most of those cases, the neighbor was not cooperative and those neighbors now have an autograph from Laura Smith of the FCC. The cases are still being resolved. For the most part, PWM motor systems are controlled by the FCC Part 15 rules on conducted and radiated emissions. There are exceptions. If the frequency of the pulse rate is below 9 kHz, the device is not considered to be using RF energy, so it is classified as an incidental emitter, subject only to the rules that require good engineering practice in the design and that require that the operator of the device control harmful interference. The bad news is that there is another exemption to the rules that control emissions: residential appliances.These, too, are subject only to the rules that require that actual intererence be addressed. Your case You are correct that the problem is caused by conducted signals, but when those signals get on to wiring connected to the unit, that wiring radiates the signal. Most Amateur receivers have very well-filtered ac lines, so it is unlikely that the problem is caused by conducted emisisons being conducted into your radio. This can be demonstrated quickly by disconnecting the antenna from your radio. If the noise goes away, it is a radiated phenomenon. The good news is that based on the signal levels you are reporting, it appears that the system does meet the rules and, at the levels reported, it is probable that interference from neighboring homes would be much lower than you are reporting. The 18-kHz spaced signals could be audible, but not loud and more than likely, the broadband noise would not be present if this were being operated in a neighbor's house. This means that your unit does contain more internal filtering than the present FCC rules would require. However, in cases of operation close to the unit, ie it is operating in your own home, additional filtering may be necessary. The noise coming from the unit could be either common-mode or differential mode in nature (see http://www.arrl.org/files/file/Technology/RFI%2520Main%2520Page/Hallas.pdf). More than likely, the noise is being conducted onto the ac mains. It could also be conducted onto other wiring such as the thermostat wiring although this would be unlikely, especially since it didn't change with grounding of the unused pairs, which would probably would have made a difference (for better of for worse) if the noise were on the thermostat wiring. If the noise is common-mode in nature, you may obtain some relief with a common-mode choke. Obtain an FT-240-31 ferrite core (Amidon, Dan's Small Parts, Palomar) and wrap about 10 turns (if possible) of the ac wiring supplying the unit onto the core. You will need to include hot and neutral leads, plus the ground wire. You can also use -43 ferrite mateiral. It will probably be necessary to cut the wirng and install the common-mode choke using wire nuts. This should be done by a qualified electrical contractor or installer. A serious shock hazard exists on the electrical wiring, and incorrectly done, the system could pose a serious safety hazard! Considering the frequencies involved, you may be able to use clamp-on ferrite chokes and obtain some relief. Make sure they are either -31 or -43 ferrite material. You would need five to 10 of the larger clamp on ferrites to provide much effectiveness at upper HF. At lower frequencies, even more would be required. Still, they may be a good troubleshooting tool. However, having said all that, it is more likely that your interference is caused by a differential-mode signal that would not be much impacted by the common-mode chokes. In this case, a differential-mode filter may be required. Corcom makes a series of ac line filters that may be of help, although you will have to carefully match the configuration and current ratings. Now, for the part we don't know -- the ARRL Lab is in the process of testing a number of these filters, to ensure that they will be effective. Especially if your system operates on 240 volts at fairly high current, the filters will be expensive. That's the bad news. The good news is that this case of interference to your own home gives ARRL a unique opportunity to have the ham have better access to the system than would occur in a neighbor's home, so if you are willing to work with our staff by telephone, in consutation with the manufacturer as needed, ARRL will obtain what appears to be a suitable filter and we can get some specific reports on its effectiveness. When all is said and done, we won't ask you to incuor the additional expense of removing the tilter. If you are game, contact Mike Gruber, W1MG@arrl.org and ask him how to proceed. When ARRL completes its testing of the ac-line filters, we'll post the results on the RFI area of the Technology pages on the ARRL web site. That's where we stand today. We'll try to help get this resolved for you, as this will be the easiest PWM case we have to date, because it's yours instead of a neighbor/s. (Hopefully you are a homeowner, not a renter!) 73, Ed Hare, W1RFI ARRL Lab Technology forums moderator |
| Aug 4th 2013, 22:37 | |
NZ2ZTotal Topics: 0 Total Posts: 0 |
I just moved into a new home and am contemplating where to put the shack in the basement. On one side is the incoming power, and Internet/cable feed. Very close to that are 3 ac external units. I need to determine a location for the radios as well as the location for a sleeve to feed the antenna wire from the shack to the outside antennas. I can locate the radios anywhere inside, but the antenna wires will in all probability have to come out near the ac ac units. Is there any general guidance on 1) how far from the ac units or electrical power box (outside) to place the radios, and 2) if it is a good idea to have the antenna coax exit the shack near the electric box or the ac pads? Bob - KG2RP |
| Apr 15th 2014, 00:07 | |
KC7ESTotal Topics: 0 Total Posts: 0 |
I have a Goodman heat pump that emits noise every 18kHz-same as yours, primarily from 17-10m. Did you ever come up with a satisfactory solution? 73, Eric KC7ES |
| Apr 15th 2014, 13:07 | |
W1VTSuper Moderator Total Topics: 0 Total Posts: 0 |
Ideally, there should be a line of sight path from your service entrance to your shack's single point ground--that way, if there is lightning strike on the service wiring, there will be a simple and direct path to the station grounding. Typically, lighting will take a path through the home instead of going around a corner to follow a bad ground path. The service entrance ground and the single point ground can be the same, but you will need to work harder remove electrical noise from the single point ground. Ground rods aren't as effective as a good radial system in decoupling noise from grounds. In terms of overall station performance, it may be worthwhile to sacrifice a little bit of transmit signal if you can significantly reduce the noise on receive--typically, we are talking about a fraction of a dB on transmit and many dB on receive, if there is a low SWR on the transmission lines. Zack Lau W1VT ARRL Senior Lab Engineer |
| Jul 2nd 2014, 19:43 | |
WB5RVZTotal Topics: 0 Total Posts: 0 |
This is an old article, but I am wondering if there has been any progress. I have a similar problem:. I have a RUUD Model UARL-060JEC A/C which is throwing up all sorts of spurii. My rig is a Flex 3000 so I am able to see the clear spikes evenly spaced out on the panadaptor display. When I disconnect the antennas, the spikes disappear, suggesting this is not in the line. I also have a battery operated portable. I observed a spike at 14063 MHz on my Flex and tuned the portable to 14063. I then went outside and as I approached the A/C unit, I got a signal at the spike frequency that pegged the S-Meter. When the A/C unit turned off, the signal disappeared. The signal - when the unit was operating was strongest at the unit and dropped several S-units when I brought the antenna of the portable up to the power lines leading to the A/C unit. The shack is in the house in a room about 25 feet from the A/C unit and the antenna is an inverted V on the roof about 35 feet fro0m the A/C unit. I have a feeling (although I have not yet proven it to be the case) that this is not amenable to simply hanging ferrites on the power lines to the A/C unit. I also do not believe the RFI is coming in through the mains, since the Flex, with antennae disconnected, shows a flat noise floor with no spikes. Don't quite know what to do. |
| Jun 21st 2016, 05:07 | |
K4MJGTotal Topics: 0 Total Posts: 0 |
Reviving an old post here, I'm having this exact problem with a neighbor's AC. Antenna is 50' away, coax is 30' away. Every 18Khz centered on 14.300 - MMSN. Has anyone been able to filter this out? |
| Feb 14th 2017, 15:57 | |
K4YCRTotal Topics: 0 Total Posts: 0 |
Has York figured out how to eliminate the 18 KHz interference yet? My unit is still under warranty, the supplier has replaced the controller and the fan motor to no avail. Signals are definitely radiated, not conducted to K-3, which is operated off battery power. K4YCR, Henry |
| Nov 20th 2017, 12:32 | |
W4TJETotal Topics: 0 Total Posts: 0 |
Since replacing my older furnace with a heat pump in September, I too have been plagued by the dreaded 18kc spike, in my case, across 15 meters. Here's the cure for my problem, and likely for everyone else having this problem: My electrical contractor was very eager to investigate, and he spoke to Carrier about this. Carrier suggested replacing the variable speed motor in the air handler indoor unit, also known as an ECM. Today, armed with an older type design, known as a standard multi-speed motor, he swapped out the variable speed unit, and the 18kc spike instantly disappeared completely. He told me to pass along that regardless of brand, the variable speed units are universal, so this is likely to be a problem for anyone installing a new heat pump. He said if you want to rid yourself of the rfi spike, to replace the ECM/variable speed motor with a multi-speed motor. My cost was $150 plus an hour of labor, which I was happy to pay to rid myself of this noise. 73 de Jack W4TJE Fancy Gap, VA |
| Dec 9th 2017, 00:07 | |
OMGlowbugTotal Topics: 0 Total Posts: 0 |
I am now having to replace our central HVAC. My search shows all high SEER units have pulse width motor controls for compressor, condenser fan and air handler fan. I’m planning to work with the installer to connect common mode filters right at AC input to speed controllers. Each one must be designed for load. Earth is on sep. winding. For high current 240vac filter, large FT-240 toroid wound for L1 & L2. Neutral and earth on own toroid. My power line filtering experience has shown better results with earth not wound with hot and neutral. Unsure about this stuff, ask for help! Please don’t get hurt! 73, W5GLO, Marvin |
Displaying 1-10 of 10
