RFI radiating from our local hospital

 

FYI to any others in the Frenchs Forest area (or near a large hospital) as I am seeing interference across 6metres and beyond being emitted from the Northern Beaches Hospital  

This is something I noticed over 12months ago, it was not always there  but became more prevalent 6 months ago, I presumed it was someone's rogue solar panel inverter as it only seemed to appear during the day, but then I started noticing it at night, which led me to do more sniffing, so I used the spectrum display on my ic756 to see that it was blobs of noise about 25khz wide, spaced approximately 100khz apart, spreading from about 45 MHz to 60MHz, and it has some drift in it. It could be radiating across a wider range than 45-60MHz, that just happened to be the limit of my radio's receiver.  I could NOT detect the RFI below 30MHz, and could NOT detect the RFI at 144MHz and above.

I decided to go mobile in the local area, to find that the strongest signal strength is coming from the new hospital, then doing sweeps driving around the hospital, the strongest signal was found to be from the western side (60/9) and weakest point is on the eastern side (s1). It not like a data signal, it just blobs of noise.

I think it probably some sort of medical equipment up on the upper floors on the western  side radiating RFI. It seems to start up around 9am in the morning and may stop  as late as 10-11pm

I was discussing this with Mike VK2EK, he said he seen similiar type of signal out at Windsor, then noted he can see the hospital out there. He is going to go mobile to further investigate his RFI source. 

At this point in time it is probably a common piece of equipment used in hospitals, and I know it won't be a Diathermy machine, this RFI is from something else that radiates nicely on VHF Low band.

Next step is try to take something portable to the hospital to do some sniffing internally without getting arrested. Then once I am satisfied of where it is located in the building I can report it to ACMA.

RFI/EMI from Inverter type Air Conditioners

 We replaced our 20 yr old Daiken R/C A/C for a new 18kW Daiken 'Inverter' type R/C A/C a year ago, I discovered this new A/C is very noisy on HF bands, particularly across 7 MHz and 18 MHz, the new Inverter type A/C are more efficient at heating and cooling,  however, the tradeoff is that the external compressor  unit is radiating RFI (Radio Frequency Interference) and EMI from either the Inverter Power supply or the DC fans.   It's bad enough dealing with RFI from damned solar panel Inverters, but at least dealing with  a RFI source in my own place is easier than solar panel Inverters on someone else's roof.

The main times we use this A/C is in middle of winter and summer. At first I did not suspect the RFI was coming from the A/C, as if I switched it on or off, I would not see any change to the RFI at the HF receiver, as I discovered after many attempts, that there was a delay of a few minutes, i.e you switch on, the compressor unit  it does not come on instantly and when you switch off, the compressor does not stop instantly. It took a while to catch on that it was indeed the A/C unit. Then I did various tests to determine from which end of the system, the internal blower unit or the external compressor unit was creating the RFI, it  was pretty easy to determine it was coming from the external compressor unit. I remembered the A/C installer saying these are all Inverter type systems. That triggered my memory about friends working in commercial radio comms saying they use these Inverter A/C systems out on remote comms sites to cool  the equipment in the comms sheds and that they create RFI. Now, I at least knew that the external compressor unit looks like the place where the Inverter Supply is located, or whatever is generating RFI hash is in the external unit.

I did a search on Google to see if anyone else discussing this type of issue and to see if anyone had some good ideas to fix it. For myself, I presuming I need to make use of some ferrite cores in the right place to knock down the interference. Found someone discussing his issue with his Fujitsu Inverter A/C system, so definitely a common issue. Plus some videos and a white paper on the topic. The Mitigation video gives the detailed technical understanding the issue and solutions.

Fujitsu inverter air conditioner radio interference - Fixya

Application_guide_aspects_of_electromagnetic_compatibility.pdf (abb.com)

Ruud Air Conditioner (HVAC) Radio Interference - YouTube

Mitigating Residential Heating, Ventilation and Air Conditioning (HVAC) RFI - YouTube