Sporatic broadband interference VHF high band

[videobruce]

Audio samples

I finally got around to record this. Attached are four samples. One had a different frequency of keying (for lack of a better term.
Also, the overall frequency of this has dropped considerably and I have not been able to track the offending frequencies down with my SA either.

https://clyp.it/user/h3hsldiz

Let me know if this works.

 

[RFI-EMI-GUY]

I finally got around to record this. Attached are four samples. One had a different frequency of keying (for lack of a better term.
Also, the overall frequency of this has dropped considerably and I have not been able to track the offending frequencies down with my SA either.

https://clyp.it/user/h3hsldiz

Let me know if this works.

Just yesterday I had a repairman out to finally replace the blower motor inside my Carrier air handler. Thankfully under warranty saving $1200.

While looking into this, I learned that this is a 3 phase DC motor with an electronic controller inside the end cap.

The controller sends high voltage (300VDC) pulses to the windings which are wired in a DELTA configuration and they spin a huge permanent magnet rotor. It is pretty clever design, variable speed, reversable (by programming).

However in looking into it they have some common failure modes, #1 is failure by shorting or leakage to ground of the stator coils. #2 is the failure of a 1 ohm NTC thermistor (inrush current limiting) on the power conditioning board that turns 240 VAC to over 300 VDC. In the case of mine failing, I could hear repetitive clicking like static discharge which could be the stator windings arcing over, or perhaps a piezo electric effect of the NTC Thermistor starting to break down.

With the technician mentioning the W word (warranty), my curiosity about fixing the problem went away. However I did observe that the GENTEQ ECM module lacks any form of RF filtering and there are a dozen power and control wires exiting it.

These types of motors are now common in dishwashers and washing machines.

The last sound clip reminded me very much of my AC fan motor running in slow speed.

 

[videobruce]

Funny you mentioned that. There are two evaporators next door, but when I passed over them with my handheld the interference didn't get any stronger. By that accord, it should of blanketed out the receiver , but it was just as strong around the opposite side of the house. The frequency both of then run their AC's doesn't correspond to when I get the interference.

But, interesting info anyway. I'm not convinced it even is this tenant.

 

[RFI-EMI-GUY]

The air handlers inside the home may have the sort of motor I describe. The outdoor units are likely conventional phase induction motors with a run capacitor. Those should be electrically, very quiet. Depending upon how the thermostat is programmed, the home owner may have the "run or circulate" modes set and therefore the fan inside the air handler will run all the time, or on 15 minute intervals and the operation of the outdoor compressor unit will operate only when heating or cooling is required. If you pick up any signals near the outdoor compressor at all it will be from the brown control wiring from the air handler cabinet if nearby.

Some oil fired furnaces have spark plugs that run constantly.

I am suggesting the air handler because appliances like dishwashers and washing machines run only a few hours a day and therefore less of a nuisance. But I would not rule those appliances out.

The last place I lived, I could tune in a very narrow 150 MHz signal that sounded like alternator noise and would accelerate and decelerate at a random rate. I thought it might be a public bus or something. However I was in a very rural area without much traffic or construction . It was always on the air. I finally concluded it was probably a variable speed motor controller for the community water well a few blocks away.

Wait till it happens again. Move outward from yours and adjacent neighbors houses to see if the signal drops off. If it does, head back and introduce yourself to the neighbors. Ask them if they have appliances on, which ones and ask that they turn them off. Ask about the thermostat as well.

 

[krokus]

It was always on the air. I finally concluded it was probably a variable speed motor controller for the community water well a few blocks away.

That makes me wonder if there is water infrastructure in the area, either potable or waste. A waste water lifting station could account for some variability, like in the samples.

Sent using Tapatalk

 

[RFI-EMI-GUY]

The only way to solve these problems is leg work. Get a sensitive receiver, a 3 element VHF yagi antenna and an attenuator. Start walking and pointing. The OP is as likely to discover something new and unheard of.

I used to do this as a living I really enjoyed it. Unfortunately nobody wants to pay anyone for doing this work. They think the FCC will swoop in and save them. Seldom happens.

 

[Ubbe]

I always managed to find the source of interference by just using the rubber duckie on a handheld scanner.

It will receive the weakest signal when the antenna point at the source. There are always reflections that will disturb the process so note what different directions you get and move to another spot and try to get the weakest signal again and repeat until you have enough readings to draw a conclusion where the source are.

/Ubbe

 

[jim202]

Have you considered the possibility that there is a fish tank with a noisy heater thermostat?

Some of the older homes had power transformers for the door bell. These are hard to find and the only way to really locate or eliminate a house is to kill the main power electrical breaker. Some people are not prone to allow this to happen as it will cause them to go around to all their clocks and have to reset them.

Another cause of problem noise is electric fences. But these are easy to identify and they sound like a clicking or arcing noise that goes on and off in pulse type activity that is the same rate all the time.

You could have bad insulators on the electrical power lines. Finding these can take some effort in driving around the streets with a car radio or portable tuned to an AM channel with no station and looking for the peak of the noise. Banging on the pole might change the arcing noise some, but don't tell the power company you used a sledge hammer on their pole.

Good luck on locating the source of your noise. Pay close attention to the time of day, if it is raining out as to if the noise changes. Locating noise sources is not easy and normally very time consuming.

I have even traced some noise down to a power transformer. Like at my house we had some strange power fluctuations. Called the power company. They came out and looked at the connections on the transformer that feeds my house. The man found that the low voltage connections at the terminals on the transformer had been arcing. He cleaned the connections, powered us back up and have not had a problem since.