PDA

View Full Version : OT - RF help needed



rockrat
09-03-2010, 09:36 AM
Not on topic but I know there is a good spread of what people study around here so I know I'll get some thoughts on this topic.

I am a big radio listener. I always have the radio on around the house and in the shop. I enjoy a bit of everything including the baseball games broadcast on an am station south of us.

I have had a few reception issues now and then on am but all of them were my doing and un-doing. Lately it has been a different story.

About 3 months ago there was a lightning strike close to the house. It knocked the power out for about 10 of us and the electric company came out to fix the issue quickly. But since then I get intermittent RF that will kill any am broadcast that is more than 25 miles away. There is so much static that I cant stand to wait (30 seconds to 3 minuets) for it to go away.

I had first thought it was something in my house but have since ruled that out with turning off circuit breakers and then finally using a battery powered am radio with my main turned off to verify that it was not in my house.

I have a 440v 3phase run at the rear of my property that has been there for about 10 years now. After the battery powered am radio trial I thought that the pump station which is supplied by the 440v was causing the interference. Maybe lightening had damaged a contact and now it was creating an issue. But after talking to the fellow that services the pump station I have 95% ruled that out.

I called the electric company who sent a nice fellow out. He walked the area with an am radio but there was no interference that day. He noted that unless the interference is constant, it cant be them. He also noted that it could be a bad switch in someones home back feeding rf into the system and they dont have the resources to handle that. I dont think I believe him on that but thats where I am right now.

So my question is, I can localize the signal by walking the area with an am radio but the area will be large. Is there any way that I can try to pinpoint the signal easily? If not, I'm thinking of calling the FCC and see if they can send a truck out to find the issue. My only other thought is to get a power recorder that can monitor for dirty power, get readings and go back to the power company and start complaining with more evidence.

Thoughts?
rock~

DFMiller
09-03-2010, 10:21 AM
Have you correlated the noise to time of day and to weather conditions? Then I might see if you can find a local Ham who might be able to help you out. I believe the ARRL publishes a rather good RFI book that might give you some pointers on finding it. Narrowing down the area will help. Have you found that the signal varied if you hold the AM radio in front of you and spin around? You body should affect the signal strength. Doing that several locations might help you Zero into the location.

Dave

MaxHeadRoom
09-03-2010, 10:26 AM
If you have an older AM radio that has a fairly long internal ferrite rod antenna it is possible to at least get the direction it is comming from by swinging the radio through 180, at maximum strength the direction will be perpendicular to the antenna rod.
Of course it could be in either direction from there, but at least you have an axis to work from.
Max.

fredf
09-03-2010, 11:34 AM
typical the nulls (lowest level) are sharper and may be easier to get a direction from

Evan
09-03-2010, 11:52 AM
Make a loop antenna for better directionality. Cross two sticks with deep notches in the ends and wrap a couple of hundred feet of wire around the outside to make a diamond (square). Fasten the radio in the centre and bring one end to the radio and put a dozen wraps on the radio. Connect the other end to a standard 365 mfd transistor tuning cap in series with the lead wrapped around the radio. You now have a tank circuit that can be tuned for AM band frequencies. It is directional off the edges of the loop and can be tuned to either increase or reject a frequency.

Take a direction reading on the interference, note the compass bearing and then move half a mile and do it again. You should have a pair of lines that converge in one direction and diverge in the opposite. Move perpendicular to the convergence lines and take some more readings. This will give you an area of probability that lies near the intersections of the lines.

Willy
09-03-2010, 12:52 PM
I had exactly the same issue as you have a number of years ago.
The intensity of the interference would vary from totally intolerable to almost undetectable.

I, like DFMiller mentioned, found a pattern that pointed to decresed interference when the humidity was high, almost non-existent during a hard steady rain. I isolated the source to be at it's strongest to a couple of nearby power poles.

I relayed this info to the local electric utility provider who promptly sent out someone to check it out, but I was at work at the time and of course the weather was wet so no luck. About a month later while at home I spotted a power line crew in the vicinity doing regular maintenance and relayed my concerns and findings to them. Well I must have got lucky because one of them knew precisely what I was talking about and exactly where to go. Fortunately he already had his spurs on, climbed up the pole gave a grounding connector a healthy smack with a hammer, and it's been quiet ever since.

MaxHeadRoom
09-03-2010, 01:23 PM
typical the nulls (lowest level) are sharper and may be easier to get a direction from

Good idea, the direction will be in line with the ferrite antenna rod if using this method.
Max.

Evan
09-03-2010, 01:52 PM
Next time it is noisy just go for a drive along the road(s) with the feeder to your house. The poles are grounded about every 4th pole so if one is corrupted you should see an increase near that pole instead of a null.

Your Old Dog
09-03-2010, 03:47 PM
The power dude flat out lied to you when he said unless it happens all the time it ain't there fault. I had a TV set blown because loose lines crossed in high wind. I put a peak reading meter on it and was able to show the guy I had a spike of 220V on my receptical. Also, transformers can become leaky and sometimes be seen on damp nights. A simple Am radio in your car is all you should need WHEN the static is acting up. Ride through the neighborhood and it will be loudest when you get close to it. Tune off of any stations so that the AGC becomes more sensitive in seeking a signal to amplify.

I had a problem on an expensive ham radio that I lived with for years. Could never understand it being so random. One day while sitting in my den listening to the radio with my feet up on the desk my wife was setting the table for dinner. After a minute or so I noticed that every time she put a dish on the table I got static in the radio? I went down to the basement and noticed a basement light fixture right under where on of the table legs would be above. The bulb was tight but when I disassembled the fixture one of the plastic wire nuts was loose and the wires were all black. I cleaned up the wires, put the same nut on only tight and the problem was solved. Do you have a similar problem with an outdoor light that might get blown in the wind or vibrated by heavy traffic?

Look for similarities to the problem. High winds, heavy traffic, high humidity, wifes hair dryer, electric range on, day, night,......etcetera !

Unless you are in a large area, the FCC won't be much help. They rely alot on Amateurs Radio Ops who are known to be bright and they volunteer. Power line problems are difficult because the line itself makes a great antenna to radiate the noise great distances. That don't mean you won't find the problem in your hood :D

Pete F
09-03-2010, 03:55 PM
Make a loop antenna for better directionality. Cross two sticks with deep notches in the ends and wrap a couple of hundred feet of wire around the outside to make a diamond (square). Fasten the radio in the centre and bring one end to the radio and put a dozen wraps on the radio. Connect the other end to a standard 365 mfd transistor tuning cap in series with the lead wrapped around the radio. You now have a tank circuit that can be tuned for AM band frequencies. It is directional off the edges of the loop and can be tuned to either increase or reject a frequency.

Take a direction reading on the interference, note the compass bearing and then move half a mile and do it again. You should have a pair of lines that converge in one direction and diverge in the opposite. Move perpendicular to the convergence lines and take some more readings. This will give you an area of probability that lies near the intersections of the lines.

+1. That is exactly how we find Emergency Locator Beacons (from aircraft and boats) in search & rescue.

-Pete

Willy
09-03-2010, 07:11 PM
Rockrat, I realize this is a little off-topic, but as a AM radio junkie for most of my life I know that long distance reception can be unpredictable at times.

Question is have you considered internet radio?
I finally made the switch a couple of years ago and could not be happier. As long as you have either wired or wireless internet available in a room, you will enjoy crystal clear reception to literally thousands of AM and FM radio stations.

Just a thought.

Evan
09-03-2010, 07:57 PM
That is exactly how we find Emergency Locator Beacons (from aircraft and boats) in search & rescue.


I know. I was in Provincial Emergency Search and Rescue program many years ago. :)

squirrel
09-03-2010, 08:15 PM
Not on topic but I know there is a good spread of what people study around here so I know I'll get some thoughts on this topic.

I am a big radio listener. I always have the radio on around the house and in the shop. I enjoy a bit of everything including the baseball games broadcast on an am station south of us.

I have had a few reception issues now and then on am but all of them were my doing and un-doing. Lately it has been a different story.

About 3 months ago there was a lightning strike close to the house. It knocked the power out for about 10 of us and the electric company came out to fix the issue quickly. But since then I get intermittent RF that will kill any am broadcast that is more than 25 miles away. There is so much static that I cant stand to wait (30 seconds to 3 minuets) for it to go away.

I had first thought it was something in my house but have since ruled that out with turning off circuit breakers and then finally using a battery powered am radio with my main turned off to verify that it was not in my house.

I have a 440v 3phase run at the rear of my property that has been there for about 10 years now. After the battery powered am radio trial I thought that the pump station which is supplied by the 440v was causing the interference. Maybe lightening had damaged a contact and now it was creating an issue. But after talking to the fellow that services the pump station I have 95% ruled that out.

I called the electric company who sent a nice fellow out. He walked the area with an am radio but there was no interference that day. He noted that unless the interference is constant, it cant be them. He also noted that it could be a bad switch in someones home back feeding rf into the system and they dont have the resources to handle that. I dont think I believe him on that but thats where I am right now.

So my question is, I can localize the signal by walking the area with an am radio but the area will be large. Is there any way that I can try to pinpoint the signal easily? If not, I'm thinking of calling the FCC and see if they can send a truck out to find the issue. My only other thought is to get a power recorder that can monitor for dirty power, get readings and go back to the power company and start complaining with more evidence.

Thoughts?
rock~
Another freak thing might be a High Voltage insulator has a carbon track that formed in a crack that was caused when the lightening hit. If you have line voltage 14 kv and up close to your location this could be the problem as a result of that lightening strike. If you have the buzz at night look carefully at the insulators with binoculors. Also note the intensity of the street lights those are a big source of noise.

PeteF
09-03-2010, 08:44 PM
Also consider that the lightning strike was merely a coincidence and the interference is actually coming from another source such as an industrial area/welder/etc. nearby. There was a large porcelain factory called Caroma not too far from where friends lived. The factory would fire the kilns at night when power was cheaper and it used to cause all sorts of grief to the adjacent residents. If it's entirely random I'd go with some form of arcing/earthing issue. But of there's any form of pattern then I'd be thinking man-made interference. It's possible somebody has made some change in their equipment that just happened to be at the same time as the strike. They may have even had equipment damaged in the strike and replaced it with something else.

I just mention the above as I've been in similar situations years ago when I was working in this field and found it best to keep as open mind as possible for as long as possible lest you get dragged down a completely wrong path. Good luck, these things can be a bugger to track down.

Pete

J Tiers
09-03-2010, 09:34 PM
yet another potential cause is the lightning arrestors..... When they have been "hit" they may have their stand-off voltage affected. problems of an AC buzz in the radio may be due to the start of breakdown on line peaks.

Radio interference from the power line is usually caused by corona, which changes its frequency range depending on how "heavy" it is. Certain radio bands can be used to detect very faint corona in certain types of insulation test.

However, interference coming from ground wires may be a totally different problem. It may be nothing *directly* to do with the power company, not involving power at all, could still be there if the line is unpowered.

With a number of AM radio and other stations around, an antenna (the long ground wire) with a rectifier (the corroded connection of a ground lug) can cause several stations to "beat", creating primary , secondary, tertiary etc sum and difference signals.

920kHz and 1470kHz can create a fine signal on 550kHz in such a situation, for instance.

lightning can either weld connections, or arc and blacken them to a wonderfully bad connection, it just depends.

Evan
09-03-2010, 10:58 PM
There is so much static that I cant stand to wait (30 seconds to 3 minuets) for it to go away.


Would you please expand on this comment. Are you saying it lasts for 30 seconds to 3 minutes and then stops? Does it slowly fade away or cut off suddenly? Does the static have any trace of rhythm to it? Does it vary in any discernible pattern while it is present?

Is it much stronger on the low end AM band than the upper end of the band?

The pump still sounds like a very possible culprit. Can you tell when it runs by listening near the pump house? Does the cycle time match the interference in average length? Ask the pump guy if the pump has power factor correction capacitors. If so, one may be damaged and arcing internally.

rockrat
09-03-2010, 11:44 PM
I seem to have quite a list to work through. Thanks everyone.

A few things,

It is not constant. It will start up and stay noisy for 30 sec to 3 min depending then the rf disappears and I get a clear signal again. This is what made me think it was the pump station except, I cant predict it and it varies so much in length. I checked and the pump station runs about 2 min each time it kicks on. It is set to pump at 10 feet of effluence so it will pump at a fairly constant rate for a constant time. I have noted the static and went down to the pumpstation to find it not running. The only thing that I have not done is ask the pump operator to turn it on while I am at the house listening. That may get done this week.

The static comes on nearly instantaneously and turns off the same way. Occasionally it will come on, get a bit fuzzy then better then totally overrun the signal till it goes off.

It is a random static pattern unlike my old washing machine that would create rf that would rise and fall.

There was no problem until after the lightening strike, as an avid listener of the same stations I can honestly say that it was after the strike. There may well have been a new piece of equipment installed that same day but that is a long shot. I noticed it right away and started looking around my house and my grounding thinking that it was something on my end.

The static is present under the power line but not in the yard. As I walk to the power lines, the noise increases and as I walk away it decreases. If I am hearing static under the powerlines it can stop and I will get a clear signal without changing my location.

It really sounds as though there is a load issue or a damaged part somewhere. Maybe even bad grounding. But it does sound as though it is triggered by a piece of equipment that might have been damaged by the storm.

I'm making my check list!
rock~

Arcane
09-04-2010, 01:02 AM
Your Old Dog's post brings to mind an example we had here with RFI. Many many years ago a farmer was experiencing the same problem and nobody could find it, so one day the (old school) supervisor had enough of it and went looking for it. He did manage to track it down...miles from where the problem was noticed. It turned out it was loose line hardware causing it.


I called the electric company who sent a nice fellow out. He walked the area with an am radio but there was no interference that day. He noted that unless the interference is constant, it cant be them. He also noted that it could be a bad switch in someones home back feeding rf into the system and they dont have the resources to handle that. I dont think I believe him on that but thats where I am right now.

As an ex Lineman with 35 years service, 16 of which was as a District Officer, I can guarantee you that guy is incorrect about that.

I did have one instance of RFI where a ham operator was having problems with constant static. We looked and looked and checked everything we could find for blocks around, even checking all the street lights, all the connections in neighbouring pedestals and the transformer that fed his house. Nada! Finally we were going from house to house to inquire if they were having any problems, trying to at least narrow the problem area down. One house I rang the door bell and the interference quit totally! A little trial and error and we determined that the source of the RFI was a little transformer in the basement that ran the doorbells. We unhooked it and the RFI stopped. The owner installed a new transformer to permanently cure the problem.

As you have found, there are so very many things that can cause RFI that it's very difficult to track down, especially intermittent ones. Just a WAG, but I suspect a connection on the primary somewhere is the source caused when the lightning struck. These things can loosen up over the years and the current from lightning can actually melt the metal because of the higher than normal resistance and high voltage. It solidifies again very quickly usually but it becomes a very loose connection when that happens and is basically just making contact by touching. Every now and then it can shift and break loose and arc slightly causing the static. I'm not saying that is the problem but it might be. (I know...lots of help that is!) Good luck!

dp
09-04-2010, 01:11 AM
So I was thinking about cycling power devices and the list here includes:

Furnace, electric blankets, water heater, lawn sprinklers, computer screens going to sleep, trickle charger on my Harley, light sensing porch lights, timer for my outside staircase lights, a bunch of solar powered deck lights, street lights, battery chargers for power tools.

I think that about does it. What do you have?

Evan
09-04-2010, 01:30 AM
The first thing to think about to narrow the search is to answer the question: What runs for as little as 30 seconds but never more than three minutes?

I am thinking something with a universal motor that was plugged in at the time of the strike and operating. It may have suffered a nasty arc on the brushes so that now they are sparking like crazy. Universal motors are infamous for generating huge amounts of interference.

The only problem with that idea is that it should generate a whine that depends on RPM.

Random noise. There is a load that turns on and off and is supplied by a dedicated circuit. The circuit has a bad connection which only sputters when the load is running. The bad connection may be on the device so that it is being vibrated when the device is running. It is being transmitted via the power lines rather than via an air wave. Direction finding won't work. However, it must be fairly close OR the load and arcing must be very intense.

dp
09-04-2010, 01:41 AM
One simple test is to prepare the house for a power outage by unplugging all sensitive devices, and when the noise starts, hit the master breakers. That will eliminate everything on his side of the power meter. Have a flashlight handy if needed.

Paul Alciatore
09-04-2010, 06:33 PM
You did not directly answer the question about how it starts and stops. Is it an instant transistion from off to completely on or does it fade in and out? Does it stay at the same level while it is on or does it vary? The answers to these questions would provide a significant clue.

I once had a microwave that generated a lot of interference when it was on. Probably a loose connection or a defective component. I just replaced it. It acted very much like you describe, including the 30 second to three minute durations. Since it was in my house it was easy to pin the blame, but if one of your neighbors has an appliance like this, it may be harder to locate. I think the direction finding antenna is your best bet. You could construct one as Evan describes I would do so. You will need to take directions from at least two locations and find where they cross. A 90 degree crossing angle would be best for the most accurate location so additional readings may be needed. The short duration may make this difficult.

Evan
09-04-2010, 08:03 PM
Bingo. A microwave sure meets the runtime criteria. It is also capable of generating a continous stream of static from arcing in the high voltage supply. Sounds like a good bet to me.

dp
09-04-2010, 08:09 PM
Unless he lives next to a restaurant a microwave oven doesn't sound like it would be a frequent source of noise. Cutting power to the house is still a good first step to determine the search area. If that stops the noise then it is a matter of flipping individual breakers until the problem circuit is found. If the source is outside the power panel then it's time to hop into the family car and cruise the surrounding area with the car radio at the bottom of the dial where no station exists, and follow the noise.

Evan
09-04-2010, 09:22 PM
Cutting power to the house is still a good first step to determine the search area.

He already did that according to the original post.

rockrat
09-04-2010, 09:50 PM
I have cut the power to the house and used a battery powered radio (so that source power to the radio is not tied into the supply) to walk under the power line out back only to find the static.

I thought I had noted in a previous post that the start of the static can be instantaneous but sometimes can start, stop, then fade in and sound worse. It always stops suddenly.

Now the microwave comment has me thinking. I know that the neighbors house has had electrical issues. Also, I know that the wiring over there is not the best. Since we are good neighbors, I will walk over to her house next time the RFI is present and ask if the microwave or other appliance is running.

I did put a clipboard out in the shop to log times and durations of the events in order to maybe see a trend. Sometimes I have to see numbers to see a trend.

Had to bury an aunt today so the hunt is on hold for a few days. Strange how I have stopped attending weddings and started to attend funerals. :(

Thanks!
rock~

dp
09-04-2010, 11:50 PM
He already did that according to the original post.

I thought I remembered he turned off breakers but didn't mention the masters, but it's probably the case he did.

Which rules out his house as the source.