The AM Forum

A good read mentioning hams & SWL's:

http://www.radioworld.com/article/johnston-laments-fm-noise/23733

73DG

Thanks for posting this. That's a very nice summary of what many hams now experience, especially if they live in an area with little separation between homes. Direct radiation from unfiltered switching devices and the propagation of the RF noise they emit along the power distribution lines is very difficult to escape if you don't have a "back 40" to plant your antennas in. The statement below certainly hits the target rather painfully.

"The fact that these manufacturing abuses can happen indicates to me that the regulatory agencies involved may have lost control of the situation."

What I find more troubling is this thought:  Do these regulatory agencies even care?

Rob W1AEX

Good read

When I was in business, some of what I did was to trace interferences to TV reception.  Over the 45+ years of this work I found everything from soup to nuts causing interference of all sorts.

No all was noise, a lot of RF type problems.

I found that about half of the noise problems were from power lines and the same amount from problems inside buildings.

Tracing noise from power lines had its own set of problems.  If you call the power company, they would check for noise at the location of the complaint.  Very often the noise source was nowhere near that address.  It could be a half a mile or more from the complaining customer.

I had my own method for locating power line noise and never failed to correctly locate it.  Even when the power company disagreed.

Noise that would have shown up in an analog TV picture doesn't bother a DTV picture.  Although, I'm sure if the noise was close enough and strong enough it could interfer with DTV reception.

Fred

What was your method?  I have several powerline related noise issues here, I could use a sure-fire technique.

I don't know about Fred, but what I do is start out covering the neighborhood in my car with the AM rx on 1710.  this is a start but only helps if the source is really nearby and you drive by a pole where the noise is really raw.  But if I get a few suspects I go back on foot with a HF rx and a VHF airband AM rx.   sometimes I can get it down to a pole that way.   If I'm really lucky I can actually hear the arc noise standing near the pole. 

What stinks is the prob. can suddenly vanish with a change in wx; or it crops up when it is dark and cold out and walking around at night when it is 15 degrees is no fun;   Or it turns out to be a street light, which is a different kind of problem.   Every year we go through relatively warm moist wx in summer and I kind of forget about this.  Then the first fall night it cools down and the humidy drops there's line noise all over poping up like spring dandelions. 

I've done the car thing, I have a quarter mile of line that is radiating raw ac hash. It may be more than one pole in this line but it will completely wipe out the strong local BC station, and makes operations somewhat tough on HF.  I have a scanner that will monitor the Aviation bands which are 2-meter am so I gotta make up a battery pack for it and a two meter yagi to pick out the noise sources.

man the neighbors will really love THAT look around the 'hood! 

One thing to keep in mind when chasing the RFI source; it (source) could be coupled to the support cable used to hold up the telephone/TV cable lines.

This issue kept me scratching my head for a while till I found a place where power distribution lines and telephone/cable services separated. Then it dawned on me the support cable was acting like a long wire antenna which carried the hash all over the neighborhood.

As mentioned before in another thread, spoke with the neighbor where the source is located. No dice/happyness there. Filed a complaint in June 2010. The FCC agent from Vancouver, WA was here for about 10 minutes last April 2011, but the source wasn't on at the time. Agent left and hasn't been back.

Gud luck in getting anything done about RFI.

Craig,

Noise that would show up on an analog tv picture does not show up on a digital tv picture but it most certainly can and does lower SNR. This is one of the problems with some DTV stations going back to VHF.

Like clockwork. Just about the time the summer static has finally faded away and the bands become usable again, the power lines start acting up.

<<<man the neighbors will really love THAT look around the 'hood! >>>

Been there.  Walking around lugging a yagi, HT, headphones at night...cop car drives by sloooooowly ...I'm trying to be obvious in not pointing the yagi at houses.....



yep, and then, when everyone is having a ball working each other, you're blowing operating time chasing a power line noise.  I got fed up with that and decided to focus on working out antenna nulling methods.  receive antennas that are shielded or oriented so I can get a halfway decent S/N ratio.  I'd be tickled pink with a S5 noise level.  I work enough guys who strap above that I could just pot down the RF gain to get rid of the noise.   We're just not going to win this under the circumstances by running around trying to snuff out noise sources, not when all these wall warts are coming in with no filtering at all.  Like that guy in the article said, 4 out of 5 switching supply engineers he talked to said their companies don't care about filtering.  The things we can control are receiving methods and strapping power. 

A huge din is created by the alarm system and video surveillance here. I can't exactly rip that out unless I want to go from tactics to battle with the local dope fiends. Had some luck with clamp on ferrites but it's the lousy cheap coax cables supplied with the units.

A huge 14.318 signal comes from my neighbor's house. Not sure what to do there, they are not inclined to care much because it's 'not their fault' what the TV or other electronics do, and they didn't understand what I was explaining anyway. I do not want to make a bad neighbor because from time to time they let me use their driveway to load weighty items meaning I don't have to start and move a 25000 lb diesel truck.

There is an intermittent huge power line noise that blots out most of 80M but I've never been able to locate it to a pole. As a wise poster already said, it could be some distance away.

I am working with CENELEC band power line modems at work but don't start throwing the rotten veggies yet, it's all below 143KHz and no higher in the USA than 500KHz (thanks to the FCC? we allow power line modems above 143KHz?) and each one has a low pass filter built as part of its bandpass unit. I took an HF RX into the lab just to see what was there, no problems with our reference designs.

None of the interference situations are getting any better for hams.

No one cares about noise, only making things cheaper for themselves for convenience or profit. Only complaints to the utility or FCC will get any action.

here at this qth summer noise peaks 9+20 - 40 meters usually has a window in the morning - higher bands when conditions permit actually are quite fun to operate! - cw mostly but hey! - without modulation - there still be conversation
greg

For power line noise you can pinpoint it to the pole using an ultrasonic detector.   Look up a QST article by W1TRC (SK) in the QST archives.

I had the same thing happen to me last Winter. It was about a 1/2 mile away from the house. Very broad hash sound. Then it would stop!. I kept looking and one night it quit while I was driving around. And I noticed that the noise suddenly appeared, and a street lamp caught my eye that suddenly turned on.
So, I parked a little distance to watch the suspect and noticed that well after it re-started, that the terrible hash was back and then the lamp went out and the noise went away. I got on line to Penn Power and got into their automated street lamp outage report and a day later they called me from their truck to say that the entire assembly had to be replaced. 3 days later all was goodness.
Fred

I have had great luck using a 3-element hand held yagi (cut for the aircraft band) and a small radio shack portable scanner listening in the aircraft band.  Of course the receiver operates on AM in the aircraft band, so it hears powerline crapola just fine.  I use a variable attenuator in the coax from the antenna to the reciever, and switch in more and more attenuation as I approach the suspect pole.  Check from several directions to be sure it points to the same pole each time.

I'd say defective lightning arrestors are probably 70% of the problems I've seen, with hardware and insulators making up most of the rest.  In order to lower your "profile" with the police and other nosey folks, purchase and wear a hard hat.  You will look "official" and be under the radar of most of the rest of the curious.

If the FCC would only do the job we the taxpayers are paying them to do. Like someone here on the board said, it's not unusual to open some of this consumer junk and find holes in the circuit board for the filtering circuitry, but the components are missing. Once the unit passed certification, they just started leaving out the filtering components on the production runs. Or you get the FCC people on the scene and they say "yes, the noise exceeds Part 15 limits. Put up a better receiving antenna", or like the case of the noise-generating traffic light, they just walk away and say it's in violation but they aren't going to take any action. Janet Jackson's boob is a far greater menace to the public interest, convenience and necessity than is ubiquitous RF noise pollution.

If the broadcast industry with all its money is having such little success in getting the "proper authorities" to deal with this problem, what hope is there for a few thousand radio amateurs?

Strap softly and turn up the wick.

Wonder how much rf you would have to pump directly into the a.c. power mains to kill a few unfiltered switching power supplies.

" You will look "official" and be under the radar of most of the rest of the curious.  "

Dave, you're right.  What I was trying to say was that analog TV would show even low level noise.  Noise at that level or really any level doesn't show up in the DTV picture as it was seen on an analog picture.  Of course, noise on the signal lowers the SNR and could cause the DTV to not work at all.

Fred

PS. My wife is complaining again that CH 4 has been off the air early AM.  She is missing her programs.  I'm taking the heat over this.  I told her that I'll pass along the complaint to the proper personnel.

Does he have his trusty A.M. radio with the two designated CD freqs???


http://home.comcast.net/~morrised2006/jpgs/RCA~GT1.jpg

I have one of these and it sounded great!!! My dad would always get angry if I turned it on at home cuz the battery was $50.00........circa 1961. "Never use a battery operated radio in the house" he proclaimed!!!

<<<PS. My wife is complaining again that CH 4 has been off the air early AM.  She is missing her programs.  I'm taking the heat over this.  I told her that I'll pass along the complaint to the proper personnel.>>>

If you are on the edge of a station's outlying coverage area you'll probably notice it disappears in warm wx.  the problems are that the digital signal is much more vulnerable to three things:  ground clutter, "tree sway" and rain.  Ground clutter is obviously buildings; tree sway is foliage moving in the wind.  When leaves get wet from rain it's even worse.  The ground clutter alone may be okay (it's there in winter after all) but it combined with leaves, leaves moving in the wind and finally wet leaves moving in the wind will kill a DTV signal.

Another complete no-go:  indoor antennas.  We have a lot of people out here who used to do fine with attic TV antennas.  With DTV they just don't work.  It's hard to convice these folks that they have to get their antenna out and up higher, and it has to be bigger. 

Hmmm, maybe I can use this to convince the XYL that we really need a 100ft tower in the back yard for the TEEE VEEE reception. 

Rob,

I installed and serviced TV antenna systems for 45+ years.  I'm now retired from that work.

Dave W2VW is the main engineer for CH 4 transmitters in NY.  Major work is being done to the xmtr equipment.  They carry out this work from about 2AM to early morning from what Dave tells me.  Very often they have to shut down the xmtrs to do the work.

Fred

Hi Fred,

FB; didn't know you installed TV antennas.  Now with DTV if the signal drops into the noise a viewer just sees a black screen with "No Signal" so they often assume the station is QRT.   I  pictured your wife getting up early every day and not getting Ch. 4 because of that and thinking they are off the air, but they really are.  Just like 50 years ago when stations went off every night.

Rob

A DTV (8VSB) demodulator starts working with a signal around twelve to thirteen dB above the noise floor. If the signal falls below that you get nothing, if the signal is above that you don’t see any difference in the picture. So the FCC in their wisdom figured that the DTV broadcasters only needed a fraction of the power they were running on analog and adjusted the TPO/ERP numbers down. For the UHF broadcasters that’s no big deal, actually save lots of money. The one television station I work for went from a dual IOT transmitter running 60 kW with an ERP of 2.8 million down to a little solid state transmitter running 4.8 kW with an ERP 192 kW for the same coverage.  UHF stations were use to running high power and the noise floor on UHF is lower but VHF stations were limited to 50 kW ERP on low band and 312 kW on VHF high band so with the reductions to the VHF stations they are way more prone to terrestrial noise and interference. What's worse is many of the old legacy broadcasters on VHF had their DTV channels on UHF and had good coverage with their UHF D channel but after the big turn off they migrated back to their VHF channel and then discovered that no one can pick them up. The interesting thing about this is that in DTV all the channel identifying information is virtual and the actual channel means almost nothing so if they stayed with their UHF channel they can still call themselves whatever channel they want and it makes no difference to the viewer. Don’t think anyone realized that VHF DTV was going to suck so much. Another interesting thing is back in the nineties when I attended the Zenith DTV song and dance school the engineers their used a calibrated 8VSB(DTV) signal generator with a fixed output and had a wide band noise source that was mixed with its output and by varying the noise source up and down were able to demonstrate the relationship between noise floor and signal level so to simulate decreased signal they would mix in more noise and increase the level of the noise floor as opposed to reducing the signal level from the generator and at the time I thought this was the stupidest thing ever but over time have come to think it just the same as reducing signal level. If you're wondering what all this may have to do with AM remember that analog television was AM also.
Ray F

Hi Ray, yep I had heard some of that but not all of it, thanks for the summary--I also heard FCC came up with the ERP and S/N = coverage area based on the idea of a viewer having an antenna 30 feet up but the ground clutter data they had from maps was from the early days of TV and is about 50 to 60 years out of date.  IOW land areas that were open then are all built up now.  

I got by before with a small LP on a 20 foot mast.   It almost works in winter.   I'm going to be putting up a big Winegard 14' boom antenna on a 25 foot aluminum tube and feed it with some 75 ohm 1/2 inch hardline I have and hope I get some better signal in summer.  It as 60 or 70 elements and a 10 to 13 dBd depending on what part of the TV band I'm on.   I'm about 40 miles out from Sears and Hancock but I'm also down in a river valley so I won't be surprised if it still stinks, even with a preamp.  I may have to  go higher.  Or quit watching TV  :D  I've quit watching it now anyway.   Who needs TV when you have RADIO!   ;) I'm basically a radio guy.  I love radio.  TV is a waste of time (unless it is giving you a paycheck).

Rob

Tell the little woman you have the problem all fixed for now.

Next time point toward West Orange.

Rob,

FB on trying a big TV antenna.

If your TV stations are only on UHF and high band VHF try using one of Winegard's HB VHF/UHF antennas.  These antennas are easier to install higher as they don't have the larger low band VHF elements.  These antennas work well.  The series is HD-769x, use the largest model.  If you add the preamp, use a Winegard.  They make two U/V models, one having about 20dB gain and the other about 30dB gain.  Don't use the preamps that fit into the plastic box that is affixed to these antennas.  The preamps to use are separate units that you U-bolt to the mast.  Don't cascade multiple amps as this can create more problems that can be hard to detect,  only use one preamp.

Once you add the preamp near the antenna there is no need to use hardline, just use some good RG-6.  You may want to put the preamp lower on the mast to make it easier to reach standing on the roof.  With your problems with reception you should put a rotor on the antenna,  being in a valley you'll need to play with direction.

Fred

More weird DTV fun facts! Sometimes antenna gain is a bad thing, if you have an antenna that’s very directive that may cause more problems than it solves. You can set the antenna for one station but unless the others are where that one is you won't see them. Having the antenna on a rotor can be an issue. The TV has to build a virtual channel table and has to have a good signal acquired from each station in the channel table. You can crank on your antenna but if the channel is not in your table you won't see it unless you directly enter the channel number and also keep in mind that it takes a second or two for the decoder to start working so with a real directive antenna you may pass the peak. Where I live I am lucky being all the local stations are roughly the same heading from my QTH so I have a little UHF corner reflector mounted on top of the tower but being a engineer I did use a spectrum analyzer to peak it. Most demods have a signal level meter incorporated in them that will allow you to peak the antenna. On the subject of demods also beware old first and second generation HDTV equipment. The older HDTV stuff did not have the newer chip sets. First generation chip sets only allowed a limited number of channel configurations and today some broadcasters are doing things like mixed 720/720 as opposed to the older 1080/480 splits and the oldest chipsets will not decode this. Second generation chip sets included an improved fading- ghost algorithm that will allow the decoder to work in multipath where the first two generations before this just stopped decoding when you had a small amount of multipath. The good news is that everything I have seen in the last four or five years has had the latest chip set and none of these issues. The little "welfare" government subsidized decoder has a great chip set and works well also if you ever see any of the "US Digital" decoders that wall mart was selling they will decode anything regardless of PIDs or channel configuration but they do lock occasionally.  Took me a while to buy into the 8VSB way of life but I am a big believer in it today, excellent quality, more channels, smaller easy to work on transmitters and less power required  not to mention will never have to think about differential phase and gain again!, but I do miss old dual 30 kW IOT Comark. The analog transmitters required skill and technique to operate where the digital has one button for on and off.

Okay Fred and Ray thanks, I will try moving the antenna around.  I got the one you recommended Fred, the biggest channel 7 on up Winegard they make, can't remember the model no. but it is the 14 foot long job with around 70 elements that lists for around $179 but I got mine from Summit Source for around $120.