EMI and TV interference.

oldbloke · Guru

EMI and TV interference.

Whenarewethere · Guru

I have interference on the car's AM radio from our Waeco fridge. In the city not an issue, more so the more remote we are trying to get weak signals.

I tried a few of these from Jaycar on the fridge. Didn't help.

I have shielded the fridge which provided a modest reduction in noise in the outback.

In the home a few Osram LED downlights are more noisy than other Philips LED downlights we have, been with AM radio.

I think the best option is a capacitor, but this is a bit beyond my level or narrow skills.

Mike Harding · Guru

Hi Oldbloke

Oh that's easy, I can give you a definitive answer to that question:

They may or they may not.

EMI/EMC issues are very hard to pin down and resolve. There are some
basic EMC rules for design but, essentially, we "suck it and see" and
if it fails testing we try something else.

Given that digital TV is at 250MHz+ I'm surprised the fan and LEDs
are causing a problem but you probably have a high gain masthead
amplifier on your antenna which is the real culprit.

The ferrite cores may well solve the issue; go for the solid core
rather than split (clamp on) if possible; mount it as close to the
fan/LED as sensible and stuff as many turns of the supply wire into
it as you can.

Other than that... turn off the fan and LED when you're watching TV :)

oldbloke · Guru

Mike Harding wrote:
Hi Oldbloke

Oh that's easy, I can give you a definitive answer to that question:

They may or they may not.

EMI/EMC issues are very hard to pin down and resolve. There are some
basic EMC rules for design but, essentially, we "suck it and see" and
if it fails testing we try something else.

Given that digital TV is at 250MHz+ I'm surprised the fan and LEDs
are causing a problem but you probably have a high gain masthead
amplifier on your antenna which is the real culprit.

The ferrite cores may well solve the issue; go for the solid core
rather than split (clamp on) if possible; mount it as close to the
fan/LED as sensible and stuff as many turns of the supply wire into
it as you can.

Other than that... turn off the fan and LED when you're watching TV :)

We have the common Wineguard with booster/amplifier. Yes seems mostly when signal is week.

oldbloke · Guru

So I have always known that aluminium is good at reflecting various radio and microwave signals such as mobile signal. All being a type of electromagnetic energy. So today I did a little Googling and researching and I found that it can reflect emi so I've decided to have a bit of a play in the van next time I get a chance and I'll see if I can reduce this emi I to the TV by using aluminium foil.

youtu.be/s-oJnvCZrt4

Whenarewethere · Guru

Towards the bottom of this page are some photos of modifications to my fridge. Used foil tape & aluminium flyscreen.

With AM radios at home it worked fairly well. The car not so good in the outback, but we are trying to pick up signals from very distant transmitters.

https://thegreynomads.activeboard.com/t65059593/extra-fridge-insulation-wattage-test/

Mike Harding · Guru

oldbloke wrote:
So I have always known that aluminium is good at reflecting various radio and microwave signals such as mobile signal. All being a type of electromagnetic energy. So today I did a little Googling and researching and I found that it can reflect emi so I've decided to have a bit of a play in the van next time I get a chance and I'll see if I can reduce this emi I to the TV by using aluminium foil.

It's worth a go but it is likely the RF energy which is being generated by the switching electronics of the LED/fans is largely being radiated by the 12V wiring which supplies these devices. If that is the case then shielding will do little to nothing and the better solutions will cone from filtering this wiring. In other words the 12V wiring is acting as a transmit antenna.

Aus-Kiwi · Guru

Is the wire feed to unit direct from the battery ? Keep the wires close to chassis and away from from
other wires . If you run a shield wire ! Make sure you ONLY earth it at ONE end or the shield becomes a conduit !!

oldbloke · Guru

Yeh,
Starting to go in the too hard basket. No idea where the wiring is.

Not to worry. I will tinker next time I get to the van. In lock down currently.

valiant81 · Guru

Hi all; Chasing EMI can be a real pain to track down and fix the problem. Ferrite beads can help, but not in all cases. All of your 12 Volt equipment is running of your house battery and all loads are connected to your battery. The interference can be radiated along the 12 volt wiring from the fridge to radio and television, this type of interference and sometimes can also get through to the antenna cable for the television as the interference can and does radiate through the air.
Some time replacing the coax cable with a better quality cable ( RG6 Quad cable ) would help.
I have had some digital channels in homes that when digital first started up were losing some channels and re scanning did not help. Installing the correct antenna and rewiring the whole house in RG6 Quad cable and connection, splitters etc bought back the missing channels.
So have a go at replacing the coax in your caravan, but this also opens up another issue and that is getting access to how the cable is run, some caravans are just about impossible to rewire.

Aus-Kiwi · Guru

A re wire ? Even if temp in the first place is not hard !! Just disconnect original.

Mike Harding · Guru

It is most unlikely changing the type of co-ax will have much/any effect upon interference.

>Installing the correct antenna and rewiring the whole house in RG6 Quad cable and connection, splitters etc bought back the missing channels.

Doing the above *totally* changes the entire system, the change of co-ax type, I have no doubt, is incidental.

Aus-Kiwi · Guru

My reference was to where its powered from . It can be where its picking it up in the first place ? At fuse or junction box . Stereo equipment is best direct ! Where no interference is inline ! Had these issues wiring ECUs .

VK2FJW · Veteran Member

Could one of those pirate CB operators running a dirty 1000 watt after burner through an out of tune yagi antenna. confuse

Mike Harding · Guru

Does anyone still use HF CB?

Mike Harding · Guru

oldbloke wrote:
We have the common Wineguard with booster/amplifier. Yes seems mostly when signal is week.

I'm currently camped in a forest with a marginal TV signal on ABC/SBS and a bit better signal on the commercials.

Under normal conditions ABC is useable but if I turn on my generator or inverter - even at light loads - the small amount of EMI being produced by those items completely stuffs ABC reception although commercials still work. These TVs are not designed for weak signal reception.

oldbloke · Guru

Mike Harding wrote:
oldbloke wrote:
We have the common Wineguard with booster/amplifier. Yes seems mostly when signal is week.
I'm currently camped in a forest with a marginal TV signal on ABC/SBS and a bit better signal on the commercials.
Under normal conditions ABC is useable but if I turn on my generator or inverter - even at light loads - the small amount of EMI being produced by those items completely stuffs ABC reception although commercials still work. These TVs are not designed for weak signal reception.

More to the point I think van Ariel's are not particularly good.

Anyway, I put a mall ferrite bead on the led light wires and tried it out. The ABC signal was weak at the time. (Pixels at the time) and still got a decent pic, light did not effect the pic. Sooo, here's hoping its improved it at least.. will know better in a few weeks when we next take a trip we have planned.

valiant81 · Guru

oldbloke wrote:
Mike Harding wrote:
oldbloke wrote:
We have the common Wineguard with booster/amplifier. Yes seems mostly when signal is week.
I'm currently camped in a forest with a marginal TV signal on ABC/SBS and a bit better signal on the commercials.
Under normal conditions ABC is useable but if I turn on my generator or inverter - even at light loads - the small amount of EMI being produced by those items completely stuffs ABC reception although commercials still work. These TVs are not designed for weak signal reception.
More to the point I think van Ariel's are not particularly good.
Hi guy's : This is the exact thing that happens with a weak signal and a poor BIR ( Bit Error Rate and in analog days it was called signal to noise ratio ). Not enough signal from the antenna and with a poor BIR and this type of problem rears its ugly head.
But what to do, that is the $64,000 question !! A better antenna, maybe !, better coax cable, even if you run the new cable through a window or door to prove one way or the other and see if you are on the right track, certainly worth a try, remove or replace the amplifier, sometimes not possible. Move to a different location and a better signal.
You could go down the satellite parth, but the cost of the equipment and setting up a dish is a bit of a learning curve and with the trees, can be a problem!!
For my 2 cents worth and working in the television repair industry, i have had satellite television for around 10 years and 95 % of the time i can get reception of all the channels.
That or you could also read a book !!

Tailor · Veteran Member

I installed a small inverter next to the TV, so run that on 240V. Stopped the pixelating on the TV.

Having just traced every circuit in the van for another reason, am tempted to install another small battery to just feed the problem light circuit, but guess that open a whole new can of worms.

Mike Harding · Guru

Tailor wrote:
am tempted to install another small battery to just feed the problem light circuit, but guess that open a whole new can of worms.

Install some ferrites and/or small value capacitors on the wiring for the problem light first - you will likely be able to suppress the emissions given time and effort. Ensure the ground supply to the light is good and as short as possible. Try wiring multiple grounds and in-line chokes too.

PeterD · Guru

Tailor wrote:
I installed a small inverter next to the TV, so run that on 240V. Stopped the pixelating on the TV.

Having just traced every circuit in the van for another reason, am tempted to install another small battery to just feed the problem light circuit, but guess that open a whole new can of worms.

That tells me that the interference is coming in through the 12 V power input and not through the antenna lead. Ferrite suppressors on the lead from the light, close to the light and more on the TV power lead will probably fix your problem. That will probably easier and cheaper in the long run.

When wiring the ferrites in the circuit, pass as many turns of wire as will fit through the suppressor. For the first try only wire the positive lead through the suppressor. If that does not work then do the same with the negative lead.

-- Edited by PeterD on Wednesday 14th of July 2021 11:15:36 AM

PeterD · Guru

Mike Harding wrote:
I'm currently camped in a forest with a marginal TV signal on ABC/SBS and a bit better signal on the commercials.
Under normal conditions ABC is useable but if I turn on my generator or inverter - even at light loads - the small amount of EMI being produced by those items completely stuffs ABC reception although commercials still work. These TVs are not designed for weak signal reception.

Where are you or were you camped? Sounds like that may be a case of ABC on band 3 (VHF) and the others on band 5 (UHF.) As suggested above, RFI from switched-mode sources often does not get to the higher frequency channels.

Dick0 · Guru

PeterD wrote:
Mike Harding wrote:
I'm currently camped in a forest with a marginal TV signal on ABC/SBS and a bit better signal on the commercials.
Under normal conditions ABC is useable but if I turn on my generator or inverter - even at light loads - the small amount of EMI being produced by those items completely stuffs ABC reception although commercials still work. These TVs are not designed for weak signal reception.
Where are you or were you camped? Sounds like that may be a case of ABC on band 3 (VHF) and the others on band 5 (UHF.) As suggested above, RFI from switched-mode sources often does not get to the higher frequency channels.

And then it may depend upon transmission polarity of horizontal or vertical or both. Longreach, Qld, I believe, transmits ABC & SBS and Commercial on separate polarities. Go figure.

confuse confuse confuse

Mike Harding · Guru

PeterD wrote:
Where are you or were you camped? Sounds like that may be a case of ABC on band 3 (VHF) and the others on band 5 (UHF.) As suggested above, RFI from switched-mode sources often does not get to the higher frequency channels.

Could well be Peter, harmonic energy reduces as the frequency from the fundamental increases. I watch so little TV (< 1h per week?) it's not worth worrying about.

Dick0: My Wineguard antenna is supposed to receive H&V equally - which it probably does. Close proximity transmitters regularly use opposite polarities in order to reduce interaction at the receiver.

PeterD · Guru

Dick0 wrote:
And then it may depend upon transmission polarity of horizontal or vertical or both. Longreach, Qld, I believe, transmits ABC & SBS and Commercial on separate polarities. Go figure.

To be able to figure requires a knowledge of history and frequency assignment constraints.

On the historical side, if TV in Australia in Oz was a simple case of all the frequencies being available when the installation of each areas stations was taking place and all the stations commenced at the same time things would have been much easier. That did not happen. For those of you under 60 years of age, you possibly would not remember TV sets without UHF tuners in them.

TV commenced in Oz prior to the 1956 Olympic Games. The cost of erecting and operating TV stations was enormous. There were very few microwave links for distributing TV programmes between capital cities for the next 20 years. That meant that each transmitter needed a studio located next to it, fully staffed whilst the station was on the air (the ABC was the exception.) That meant that that in areas out of the capital cities TV was slow at being established. There were only two commercial channels in each capital city and one in each country city for the next 30 or so years. At that time all TV was transmitted on VHF until the SBS was established and transmitted on UHF in 1980.

In the late 60s the PMG foresaw the need to introduce UHF to ease the problem of channel crowding in the future. The big problem was that the Country Party was in coalition with the Liberals and Black Jack McEwan refused to support the Libs if UHF TV was used in the new stations in the country (in those days the very high power transmitters were not available and VHF travelled further.) So to pack the extra VHF channels in the bush vertical polarisation was introduced to maintain signal separation. Vertically polarised channels can be reassigned closer horizontal channels than the same polarised channels.

When it came to TV in the smaller cities and towns, the ABC paved the way. These stations also followed the establishment of microwave bearers so programme distribution became much cheaper. The PMG established and ran the transmitters. These transmitters were located at the microwave link stations close to town and. When the commercial channels followed later the networks chose to locate their transmitters in town often on council water towers. This meant that they could use lower powered transmitters than the ABC transmitters and had cheaper rent. As they were not co-located with the ABC they could use UHF transmitters which by that time were using transistors and were cheaper than the higher power ABC transmitters. They were also co-located with the SBS transmitters which were established by local subscription and hosted by the local councils (as were a lot of the commercial channels.) The location of the TV transmitters still exists in most of those places including Longreach.

You thus can see that piecemeal introduction has resulted in a situation where nicely organised frequency allocation is not possible in a lot of areas. "Go figure." Now you can figure.

-- Edited by PeterD on Wednesday 14th of July 2021 04:35:49 PM

Aaron · Veteran Member

A Faraday Cage is a mesh or metal shield that completely surrounds the object causing the interference or the receiver, and is grounded/earthed to take any stray nasties to ground or earth - a Faraday Cage if properly fitted should eliminate any interference. I wore an aluminium foil helmet as a kid to block aliens sub liminal messages getting through to my brain - and it worked - if only I could do the same with politicians lol

Dick0 · Guru

PeterD wrote:
Dick0 wrote:
And then it may depend upon transmission polarity of horizontal or vertical or both. Longreach, Qld, I believe, transmits ABC & SBS and Commercial on separate polarities. Go figure.
To be able to figure requires a knowledge of history and frequency assignment constraints.
On the historical side, if TV in Australia in Oz was a simple case of all the frequencies being available when the installation of each areas stations was taking place and all the stations commenced at the same time things would have been much easier. That did not happen. For those of you under 60 years of age, you possibly would not remember TV sets without UHF tuners in them.
TV commenced in Oz prior to the 1956 Olympic Games. The cost of erecting and operating TV stations was enormous. There were very few microwave links for distributing TV programmes between capital cities for the next 20 years. That meant that each transmitter needed a studio located next to it, fully staffed whilst the station was on the air (the ABC was the exception.) That meant that that in areas out of the capital cities TV was slow at being established. There were only two commercial channels in each capital city and one in each country city for the next 30 or so years. At that time all TV was transmitted on VHF until the SBS was established and transmitted on UHF in 1980.
In the late 60s the PMG foresaw the need to introduce UHF to ease the problem of channel crowding in the future. The big problem was that the Country Party was in coalition with the Liberals and Black Jack McEwan refused to support the Libs if UHF TV was used in the new stations in the country (in those days the very high power transmitters were not available and VHF travelled further.) So to pack the extra VHF channels in the bush vertical polarisation was introduced to maintain signal separation. Vertically polarised channels can be reassigned closer horizontal channels than the same polarised channels.
When it came to TV in the smaller cities and towns, the ABC paved the way. These stations also followed the establishment of microwave bearers so programme distribution became much cheaper. The PMG established and ran the transmitters. These transmitters were located at the microwave link stations close to town and. When the commercial channels followed later the networks chose to locate their transmitters in town often on council water towers. This meant that they could use lower powered transmitters than the ABC transmitters and had cheaper rent. As they were not co-located with the ABC they could use UHF transmitters which by that time were using transistors and were cheaper than the higher power ABC transmitters. They were also co-located with the SBS transmitters which were established by local subscription and hosted by the local councils (as were a lot of the commercial channels.) The location of the TV transmitters still exists in most of those places including Longreach.
You thus can see that piecemeal introduction has resulted in a situation where nicely organised frequency allocation is not possible in a lot of areas. "Go figure." Now you can figure.

There is no need today to accept such chaotic system transmissions.
Shepparton, Vic. until recently, as other regional areas had dual horizontal and vertical including combination Vhf/Uhf transmissions, and overnight, changed to UHF Horizontal transmission only.
You will still see many residential masts in Shepparton and other Regional areas with a VHF antenna, now unused.
Perhaps QLD is a bit slow updating.

-- Edited by PeterD on Wednesday 14th of July 2021 04:35:49 PM

Whenarewethere · Guru

For the whippersnappers the colour space LAB (lightness & 2 colour channels) so black & white TV could use the colour TV lightness signal is really handy to fix up dodgy images.

The L channel you can sharpen. Better than sharpening in RGB.

If you have JPG compression artefacts, blur the AB channels a few pixels.

So you end up with a sharper image with less offensive compression artefacts.

oldbloke · Guru

Just a flow up. I put one of those ferrite beads on the light wiring. So far so good. Appears to have done the job.

Thx everyone for your help.