This is why EM interference can be an issue....

[rude man]

We have kind of the reverse problem. Since we don't watch very much TV we've shunned the expensive cable company and stuck with over-the-air TV for years. The number of channels is limited but it's worked okay... until the last few years. The number of channels we can get, even with excessive adjustment and moving of the indoor antenna, which we have replaced twice, has been steadily decreasing. Some channels are now completely gone; others are just too noisy. Some would probably have been watchable as degraded analog channels but a digital channel just falls apart when enough is missing.

We are perplexed as to why. Sometimes a channel looks good and then, without any rhyme or reason, we have to struggle to watch it at all. Streaming isn't that expensive. And we have access to free movies. But what's going on?

The conspiracy theory part of my human brain thinks that the cable company is somehow responsible. But it's probably some other source of modern interference. I just have no clue what. Our neighbors WIFI? Cell phones in cars driving by? Something from the nearby transit hub? I don't have, nor am I likely to think it affordable, to buy whatever hardware is necessary to track it down. I don't mind being in the rain. Is there some not-too-expensive way to debug this? Audacity??

You should probably get an outdoor yagi antenna unless you're very close to the stations. They may have reduced power for some reason.

 

[rude man]

I assume those channels are analog TV, not digital TV. Analog channels are turned off as digital TV becomes available. Get an old digital TV, or a set top box.

The rise in the number of switching power supplies and home computers explains why AM radio and analog TV signals are deteriorating.

Analog tv signals are practically gone.

 

[Baluncore]

Analog tv signals are practically gone.

The number of channels is limited but it's worked okay... until the last few years.

This was over years, just like some of the channels were analogue.

But there is little point in discussing systems that use indoor antennas, they are designed for looks, not performance.

Often the VHF / UHF band changed with the A-D transition.
And a room is frequency sensitive, a cavity backed slot.

 

[berkeman]

But there is little point in discussing systems that use indoor antennas, they are designed for looks, not performance.

Sort of. The Fractal Antenna Reflector post that I linked above was in an apartment. You are not allowed to drill holes in the walls to make coax feedthroughs when you live in an apartment. I did have attic access (very tiny), so I did briefly consider trying to route something through the attic, but not for long.

 

[Baluncore]

The Fractal Antenna Reflector post that I linked above was in an apartment.

Where was that link ?

 

[skystare]

Very creative. And I am not above "hillbilly" tactics.

But I'm more interested in what is affecting the previously acceptable signals. Some have degraded over time and others are degraded for shorter periods at what seems like random times. We have twice replaced the antenna, even trying one with an amplifier. Sometimes it doesn't matter where you stand holding it.

Something is interfering. I'd love to know what but have no idea how to figure it out.

Have you tried another TV? Not the easiest diagnostic, I know, but circuitry can decay, often via failing capacitors.
Another source of trouble can be trees growing up into your line-of-sight, causing variable signal absorption affected by rain and wind. Or new buildings. I once upon a time used a 5 cent 1/4 wave antenna made of a stick and zipcord, but new construction between us and the transmitter farm (6 stations in a 2 degree arc) drove me to a quad bow tie on a real mount.

 

[Tom.G]

I have an acquintance that is in a basement apartment. The TV antenna farm is on a mountain about 50 miles away.

Rabbit ears would get 3 to 6 stations, if moved around appropriately, most of the time.

He went to Walmart and bought a US $40 amplified antenna and now gets 60 to 100 stations depending on conditions. The TV reports 112 stations but that's counting all the intermittent ones.

Cheers,
Tom

 

[JT Smith]

Have you tried another TV? Not the easiest diagnostic, I know, but circuitry can decay, often via failing capacitors.
Another source of trouble can be trees growing up into your line-of-sight, causing variable signal absorption affected by rain and wind. Or new buildings. I once upon a time used a 5 cent 1/4 wave antenna made of a stick and zipcord, but new construction between us and the transmitter farm (6 stations in a 2 degree arc) drove me to a quad bow tie on a real mount.

Thanks for the suggestion. I've thought about the TV being the problem. Some of the stations that used to come in perfectly are now essentially unwatchable which could explained by the TV. But other stations are always perfect. And others are fine most of the time but get disrupted for some period of time before returning to normal again.

In any case, I don't have a second TV to experiment with. Maybe I could buy a tuner inexpensively?

Trees or new buildings aren't an issue here.

 

[berkeman]

Where was that link ?

In the quote. Just click the little up-arrow next to "berkeman said", and that will take you to the post. That's true of any quote box with the username and the little arrow in it.

 

[skystare]

Thanks for the suggestion. I've thought about the TV being the problem. Some of the stations that used to come in perfectly are now essentially unwatchable which could explained by the TV. But other stations are always perfect. And others are fine most of the time but get disrupted for some period of time before returning to normal again.

In any case, I don't have a second TV to experiment with. Maybe I could buy a tuner inexpensively?

Trees or new buildings aren't an issue here.

There's a website, http://www.tvfool.com which gives coverage and signal analysis data for almost everywhere in North America . . . might be useful.

 

[JT Smith]

There's a website, http://www.tvfool.com which gives coverage and signal analysis data for almost everywhere in North America . . . might be useful.

Thanks for that. I tried it. It's a few years out of date but says that all the channels I used to get I should still get. Oddly the local ABC station is missing from the list. That channel usually comes in perfectly (except when it doesn't for a little while for unknown reasons). I checked the location of the store where I bought the most recent antenna. It's just a few miles from here and their numbers are nearly identical. The store had a TV with cheap indoor antenna and the guy working there said that they got all of the stations no problem.

So again, local interference or maybe it's the TV.

 

[Baluncore]

So again, local interference or maybe it's the TV.

Do you have a UV reflective film on your windows?

 

[JT Smith]

Do you have a UV reflective film on your windows?

No, it's a large single pane window, just glass. I think it's the original from about 90 years ago. Anyway, it's the same window as before when reception was better.

 

[Quarkman1]

A CRT requires a line scan frequerency which is at about 16 kHz (625 system) and is delivered to the scan coils at around 25 Watts. Before the days when interfence from computers and broadband became so severe, line scan interference was very bad. It creates harmonics every 16 kHz right up the spectrum to VHF.
Further than this, the the scan coils vibrated to the frequency and created sound. This 16 kHz whistle was very audible to a teenager and nearly drove me nuts, whilst my parents could not hear it.

If the TV is that old it would certainly use a CRT, but it would scan at 525 lines/sec not 625. I find it odd one old TV could knock an entire village out, certainly one would suspect that it must be producing a large, unsuppressed EM field.

I am a Ham operator too, so I have to be cognizant of interference and have to make sure that all my antennas and equipment and in correct operating condition. Since they are all brand new (or barely used) the equipment functions within the specs, unless I attempt to modify it, which can lead to all sorts of issues with interference.

Hams are generally "blamed" for any interference on nearby equipment but a lot of the new stuff is digital now, so it tends to be less of an issue than trying to get OTA reception. Bad grounding could also be a factor. Interesting article. Wales is a nice country (or nice part of the UK, I guess I should say).

 

[Tom.G]

I once knew a Ham that had a large beam antenna put up on his roof. He, being retired, and having a tile roof, hired an installer. The antenna went up fine. The experienced installer did not run any coax cable though.

It turned out there was a good reason for this lack. Within days, there were neighbor complaints of interference. After the complaints died down (about two weeks), the installer returned and completed the installation.

(I'm trying to think of a catchy wisecrack to close with, unsuccessfully. )

Cheers,
Tom

 

[Baluncore]

Working at the Operations end of the equivalent of OFCOM is interesting because there are more than enough challenges out there to investigate. That goes as much for the EMI as it does for the internal bureaucracy, and external politics.

The big disadvantage is that all officers involved are prohibited by an Official Secrets Act, on pain of imprisonment, from telling some excellent stories. If such stories were told, they wouldn't be believed anyhow, because they would be too close to the truth. The story teller would be accused of being a conspiracy theorist, and the listeners would immediately demand proof.

 

[Keith_McClary]

That is because the news media assume members of the general public would not understand.

You are assuming that the news media understand.

 

[sophiecentaur]

A CRT requires a line scan frequerency which is at about 16 kHz (625 system) and is delivered to the scan coils at around 25 Watts. Before the days when interfence from computers and broadband became so severe, line scan interference was very bad. It creates harmonics every 16 kHz right up the spectrum to VHF.

This has to be the answer. The modulation system that delivered the programs to the TV would have to be Digital - but not relevant.

The power needed for a large screen colour TV scan could be huge (I think 25W could be a conservative estimate for a big screen) and "the whole village" was more likely a few surrounding houses and they could all have been using the same Internet Provider with the same model of router (and they're all pretty shoddy). A recipe for disaster, imo.

You could imagine the old couple had a prized, top-of-the-range CRT colour receiver. Switch-over from Analog to Digital was completed by 2012 and the receiver could have been sold to them cheap, near that date. Presumably they never considered up-grading so they went for a set top box. Time passed . . . . . .

 

[Baluncore]

Aberhosan, Powys, Wales is a lovely little village. It is spread along 180 metres of the lane.
The houses all have small offset-fed dishes on the southern walls.
Google Earth 52°33'41"N, 3°45'16"W
How is “broadband” distributed in that part of Wales?

 

[tech99]

Aberhosan, Powys, Wales is a lovely little village. It is spread along 180 metres of the lane.
The houses all have small offset-fed dishes on the southern walls.
Google Earth 52°33'41"N, 3°45'16"W
How is “broadband” distributed in that part of Wales?

I assume that an optical fibre is provided from a distant exchange to a street cabinet in the village, and then broadband is delivered over ordinary overhead copper telephone pairs to the houses, using either ADSL or VDSL. The copper wires provide an easy route for timebase interference to propagate between houses, especially if the offending TV receiver has a broadband connection.

 

[StandardsGuy]

We have kind of the reverse problem. Since we don't watch very much TV we've shunned the expensive cable company and stuck with over-the-air TV for years. The number of channels is limited but it's worked okay... until the last few years. The number of channels we can get, even with excessive adjustment and moving of the indoor antenna, which we have replaced twice, has been steadily decreasing.

I'm still using OTA TV, but the channels have been rising fast due to digital TV. They are moving to UHF, so maybe you need a new antenna (outside on the roof or a pole).