Improved tv reception tip.

[Fisherman]

On some trips I noticed that although I would pick up plenty of tv channels the reception was poor. But on our last trip I noticed that keeping the supply cable and the aerial cable as far apart as possible improved the situation considerably. So I decided to screen my supply cable to help prevent electromagnetic interference from the supply cable. Although coaxial cable is screened it can still be compromised when in close proximity to a supply cable.

I removed the supply cable and wrapped several layers of aluminium foil around its full length, including where I had folded it to reduce length. For mainly aesthetic reasons I then shrouded the cable with some black plastic covering. You could use black insulating cable.

Normally when I try to tune in my tv outside my home I am lucky to get 6 obscure channels.
But when I tried with the supply cable screened I got 67 channels including BBC channels but no ITN.
The last time I managed this was with my last van which had a much better directional aerial, but fitting one on my new PVC proved to be problematic. So I am stuck with this omni directional aerial,
which is ok, but inferior to the directional aerial.

We are not totally reliant on the aerial for TV, we also use our 5G modem, which has proven to be money well spent.

 

[merl]

So I decided to screen my supply cable

The supply cable to what exactly? 12v supply or 230v supply?

 

[Fisherman]

The supply cable to what exactly? 12v supply or 230v supply?

Mine is 12v, but AC can be worse.

 

[merl]

Mine is 12v, but AC can be worse.

I know you can get interference from mains cables (EMI) but shielding a 12v DC power cable..... that's really surprising so thanks . No idea what's going on, why would the 12v side contain any radio frequency hash let alone enough to make its way through the braid (screen) of the TV coax....RF is baffling and mysterious, more like a black art than a science.

 

[Fisherman]

I know you can get interference from mains cables (EMI) but shielding a 12v DC power cable..... that's really surprising so thanks . No idea what's going on, why would the 12v side contain any radio frequency hash let alone enough to make its way through the braid (screen) of the TV coax....RF is baffling and mysterious, more like a black art than a science.

Both DC and AC create a magnetic field when the current is in motion. The level of the field corresponds to the size of the current. Insulation makes no difference and offers no protection from the field. You need to create a barrier by using copper, or tin foil. If you can split the cable and cover both polarities individually, then the outer covering this improves protection from the field. I only covered the outer part of the cable. When installing alarm systems we would never use the same cable for power and signalling, and always tried to keep mains and 12v cabling at least 150mm apart. Never put AC and 12v cables in the same trunking either. Coaxial cables carry signalling, and although screened can still suffer interference from electromagnetism.

 

[merl]

Both DC and AC create a magnetic field when the current is in motion.

Yep I know but the field from a DC cable would be a DC field without any RF component, a DC field wouldn't bother a TV radio signal operating at several megahertz. When you have a masthead antenna amplifier it usually gets it's 12V power supplied up the actual coax itself giving the coax a massive DC component and this doesn't block the HF TV signal so I can't see how a microscopic DC field can have an effect. Not only that the DC field within the power cable would be neutralised because the +and the - run side by side, same thing happens with a DC clamp meter when you try and measure current with BOTH +and- together, you get nothing.
Did you connect your tin foil to ground/earth/connect to 0 Volts? If not then surely you've actually created another metal object to collect and/or re-radiate RF, basically an antenna not a ground shield?
As I say, baffling to my head and can't for the life of me understand what's going on but if it works it works eh.

 

[r4dent]

Improved tv reception tip.​

Why would you watch TV at the tip ?

 

[Fisherman]

Yep I know but the field from a DC cable would be a DC field without any RF component, a DC field wouldn't bother a TV radio signal operating at several megahertz. When you have a masthead antenna amplifier it usually gets it's 12V power supplied up the actual coax itself giving the coax a massive DC component and this doesn't block the HF TV signal so I can't see how a microscopic DC field can have an effect. Not only that the DC field within the power cable would be neutralised because the +and the - run side by side, same thing happens with a DC clamp meter when you try and measure current with BOTH +and- together, you get nothing.
Did you connect your tin foil to ground/earth/connect to 0 Volts? If not then surely you've actually created another metal object to collect and/or re-radiate RF, basically an antenna not a ground shield?
As I say, baffling to my head and can't for the life of me understand what's going on but if it works it works eh.

It worked that’s what matters as you say.

I just realised keeping the cables apart as much as possible helped. So I realised screening the supply cable may help and it did. I will see how we get on next trip and report what happens on this thread I also read on another non motorhome forum someone else had a similar issue, but they used a filter.
But the filter had to be fitted as close to the aerial as possible. That would be very difficult in my case.
Also apparently 12v tvs are more susceptible to this than 230v ac tvs.

 

[trevskoda]

Fit a ferrite ring on power cables, you can also buy snap round ones, very handy.

 

[Tezza33]

The quality of the coax cable also makes a huge difference.

 

[Fisherman]

The quality of the coax cable also makes a huge difference

Absolutely hence why I did not use the one supplied by the tv. I bought this cable from Amazon with gold plated plugs. I think it was only £6 but was the correct length and much better quality.

 

[maingate]

Yep I know but the field from a DC cable would be a DC field without any RF component, a DC field wouldn't bother a TV radio signal operating at several megahertz. When you have a masthead antenna amplifier it usually gets it's 12V power supplied up the actual coax itself giving the coax a massive DC component and this doesn't block the HF TV signal so I can't see how a microscopic DC field can have an effect. Not only that the DC field within the power cable would be neutralised because the +and the - run side by side, same thing happens with a DC clamp meter when you try and measure current with BOTH +and- together, you get nothing.
Did you connect your tin foil to ground/earth/connect to 0 Volts? If not then surely you've actually created another metal object to collect and/or re-radiate RF, basically an antenna not a ground shield?
As I say, baffling to my head and can't for the life of me understand what's going on but if it works it works eh.

It does make a difference.

When I was installing lines of Printing Presses and Coating equipment I had to be very careful of running the cables. I had a mix of high voltage DC, 240 volt AC, 110 volt AC, 24 volt (fixed) DC and 24 volt DC. The most important part was a good earthing system, followed by separating DC and AC as much as possible.

Static electricity could also be a problem to low power systems. I had to go to Italy where a new line had failed electrically. The problem was due to a build up of static. The equipment was well protected but the Factory was made of pre-cast concrete sections (no large steel framework) and basically there was nowhere adequate to earth every line of equipment to. I got round it by getting copper rods sunk into the ground under the concrete floor and attaching the earthing to that. Old machinery could cope but computer controlled equipment was more sensitive.

 

[merl]

It does make a difference.

When I was installing lines of Printing Presses and Coating equipment I had to be very careful of running the cables. I had a mix of high voltage DC, 240 volt AC, 110 volt AC, 24 volt (fixed) DC and 24 volt DC. The most important part was a good earthing system, followed by separating DC and AC as much as possible.

Static electricity could also be a problem to low power systems. I had to go to Italy where a new line had failed electrically. The problem was due to a build up of static. The equipment was well protected but the Factory was made of pre-cast concrete sections (no large steel framework) and basically there was nowhere adequate to earth every line of equipment to. I got round it by getting copper rods sunk into the ground under the concrete floor and attaching the earthing to that. Old machinery could cope but computer controlled equipment was more sensitive.

Yep completely understand the need to shield and separate cables. I work a lot with audio amplifiers and completely understand the way that an audio signal can be polluted by radiated interference from cables, components etc and the importance of sheilding, spacing and positioning. Invariably the problem always lies with a high voltage 'dirty' line interfering with a far more sensitive lower voltage line, so typically mains power cables which not only contain pulses of ,over 320v 50 times a second but also a load of other higher frequency hash typically from local switch mode power supplies, motors etc, the mains power lines actually act as antennas, picking up RF interference and radiating back out into any sensitive (typically low voltage) wire or equipment nearby.
What puzzles me with what Bill has done is that he's screened a LOW Voltage 12v DC power cable and somehow this means he can now pick up many more TV channels?
What was radiating from this little innocent twin 12v power cord that was SO detrimental to the nearby TV coax?
Bill didn't ground his tinfoil cladding (I don't think), so why did that cut down interference?
The more I think about it the dafter it all sounds, I assume that Bill's mod improves the TV reception when he's off grid and the van is on its own private 12v battery supply and not even connected to the dirty mains supply anyway?
To be fair I never asked that question so I suppose there could be hash on the 12v lines from either the battery charger (almost certainly SMPS) when on hookup OR hash generated from equipment being powered by to 12v system, laptops, phone chargers, etc(again all SMPS these days and noisy as hell)...I guess inverters would be terrible for inducing crap into the power lines too so...... Seems like I've talked myself into a solution, welcome to my brain

 

[Boots]

Hi Fisherman,

Thanks for that tip, cheap, easy & cost effective.


Cheers

Boots