Radio Intererance Whilst Phone Charging - A Theory

[BargeeSpud]

Hiya,

 

Some time ago I put up this article about the above problem I was experiencing at the time but none of the suggestions turned out to be helpful with this particular issue, sadly, but not the fault of those who contributed them.

 

Well, I've now cured it.

 

What I have finally done is to replace my bog standard car aerial for a fibreglass, 8' marine FM aerial mounted on a collapsible mount with the cable going directly to the radio through the roof without being "earthed" to the steel. OK, the antenna & mount is a bit expensive, but radio reception is now phenominal due to the height of the antenna. A massive improvement in reception plus no interferance whilst charging phones is VFM for me.

 

Now for the "theory" aspect.

 

Because my boat is geared up for 240V with the system being earthed to the hull, I have a theory that there might be some sort of cross "contamination" (for wont of an accurate description!) possibly with the negative side of the 12V system. This could have meant that the original car aerial was double earthed, both with the steel and the radio chassis and when I bypassed the steel fitting the new antenna, this insulated the aerial from the theoretical cross "contamination".

 

Now if my theory is accurate, with the benfit of hindsight, I could possibly have solved the problem a lot cheaper than I have done with a different type of car aerial where the cable does not need to be erthed to the steel.

 

Does this theory sound a bit Betty Swallox or am I on the right track?

 

Over to all you techies out there!

 

Edited September 26, 2016 by BargeeSpud

[Tony Brooks]

Car aerial instructions are usually are adamant that you must clean to bright steel under the panel you are fitting them to and they tend to have teeth to dig into the metal. Although on modern cars the radio is often carried in a plastic moulding slightly older ones fitted into metal that was part of the body, plus they have a negative connection that also is connected to the body.

 

This being the case I can not see much difference between your boat and a car so I suspect you are not on the right track.

 

I suspect it has more to do with a weak signal from the aerial getting swamped by local interference from the charger. Why the signal should be weak I have no idea but you might have had a build up of water in the cable & connections or even in the aerial mounting moulding.

[WotEver]

I'm with Tony. Weak signal before with original aerial, good signal now. Lots of possible causes for the original weak signal not limited to poor 'earth' connection (which you shouldn't have on a boat anyway).

[Paul C]

There's definitely some merit in the OP's theory, which I believe is a "ground loop" or similar phenomenon - however I'm fairly confident the receiver would filter this kind of thing out.

 

So I agree with the Tony's, in that the charger is acting as a radio transmitter too, emitting loads of harmonics of whatever fundamental frequency it operates at, right up into the radio (and all sorts of other) range too. So its making for a poor/noisy environment for radio reception. The new aerial is simply better at picking up its own desired range of frequency, so it gives the receiver a much stronger signal, a much better chance of filtering out the undesired frequencies, resulting in much better radio reception.

[Tony Brooks]

What I have not addressed is how the interference was getting into the radio, mainly because it a bit like prop sizing to me, a black art.

 

It could be on the 12V supply or coming through the air. In the latter case it could be using the 12V leads as an aerial, somehow getting into the aerial or getting through the cooling holes and into the radio.

 

Not that it matters, the new aerial has solved it for now.

[BargeeSpud]

Thanks for the replies chasps.

 

It all makes sense & I was never certain that my theory would be accurate, but in the crazy world of electronics, it might have been.

 

Tony's suggestion about water contamination at the point of entry through the steelwork would've explained it perfectly. Except that I'd smothered everything in that red gel you smear on battery terminals when I fitted the original aerial to bright steel at fitting & it was pristine when I took the aerial out.

[WotEver]

At least you've now removed one point of potential stray current corrosion.

[cuthound]

Phone chargers use switch mode power supplies. These regulate the output by switching the mains on and off, typically at 20kHz. This results in high frequency currents leaking to earth (harmonics), and can also be radiated, both of which can be picked up by a car aeriel.

[BargeeSpud]

Phone chargers use switch mode power supplies. These regulate the output by switching the mains on and off, typically at 20kHz. This results in high frequency currents leaking to earth (harmonics), and can also be radiated, both of which can be picked up by a car aeriel.

Except the charger in question that caused the interference before I changed the aerial was a 12V car version, not a mains one.

[Top cat]

In that case it's switching the 12V on and off to drop it to 5V.

Same effect

T C

[BargeeSpud]

OK, I can understand that there is little difference between the 2 types of charger when they reduce the voltage, it makes sense. However, at the time the phone charger was causing the interference, my laptop's car charger didn't cause any at all.

[Top cat]

I suspect that your laptop charger was putting out closer to 12V and may operate differently.

 

T C

[WotEver]

Or it's better suppressed

[cuthound]

Or it's better suppressed

This ^^.

[Tony Brooks]

 

Tony's suggestion about water contamination at the point of entry through the steelwork would've explained it perfectly. Except that I'd smothered everything in that red gel you smear on battery terminals when I fitted the original aerial to bright steel at fitting & it was pristine when I took the aerial out.

 

Actually I was suggesting that water had got into the moulded plastic base rather than between the base and the roof. Possibly where the aerial rod exits the base.

[BargeeSpud]

Actually I was suggesting that water had got into the moulded plastic base rather than between the base and the roof. Possibly where the aerial rod exits the base.

Ah.

 

Well, the original aerial wasn't great quality so I guess that's the real lesson here,quality counts, you buy cheap you buy twice etc., etc.

[Top cat]

Could you please post a link to where you got your aerial?

 

Thanks

 

Top Cat

[BargeeSpud]

OK, but the aerial & mount I bought stands 2.5m high & cost in the region of £80 at sale prices. The company is Shakespeare & I ordered direct from them as it was cheaper.

 

I'm about to get on the road for the rest of the day so if you're still interested, then post again or pm me.

 

Cheers,

Ade

[Top cat]

Thanks Ade I can track it down from that info

 

T C

[johnmck]

Without spending big bucks, can anyone recommend a good roof mounted aerial, to mate with our Sony car style radio? The current one is carp.

[Tony Brooks]

Not enough info.

 

FM, FM & AM, and/or DAB.

 

Amplified or non-amplified.

 

Are you willing to drill the roof.

 

Where do you intend to mount it. e.g. Glass, through roof, on cratch board etc.

[WotEver]

My advice - get a magmount. I bought a cheap 'n cheerful one off eBay for around a tenner. Cable entered the boat via a hopper window near the radio. Reception was great.

[johnmck]

Not enough info.

 

FM, FM & AM, and/or DAB.

 

Amplified or non-amplified.

 

Are you willing to drill the roof.

 

Where do you intend to mount it. e.g. Glass, through roof, on cratch board etc.[/quote

 

Hi.

 

It is a standard Sony car radio with integral iPod tray. This is fm mw + lw and non digital. As far as I am aware, it is none amplified. The existing aerial is on the steel roof, so a hole already exists, but this could be enlarged slightly.

The dome behind the aerial is one of these.

http://www.3grouterstore.co.uk/3G/Fullband-FB4GDOME.html

I had to enlarge an existing hole to fit it, so the existing hole for the aerial is somewhat close!

Edited September 29, 2016 by johnmck

[Tony Brooks]

No wonder its not working. That aerial says its for mobile phone frequencies, not broadcast frequencies.

 

The aerial in that is probably coiled up a bit but the length of the actual aerial is important for optimum performance and is directly related to the frequencies you are trying to receive.

 

I would suggest that any car aerial sold for FM/AM will do the job but avoid the cheapest. As its to be roof mounted try to get one where the mast unscrews to avoid damage on low bridges etc.

 

Actually the aerial needs to be a different length for FM and AM but usually one will do. However if you are in a weak signal area buying an amplified one that is supplied with 12V when you turn the radio on may be a good idea. The amplifier makes up for the non-optimum aerial length (often for AM).

 

Edited to add:-

 

The link for the dome was confusing unless you are trying to use it for FM/AM. The broadcast band aerial looks like the rod aerial behind it.

 

 

Its hard to tell but it looks long enough to be an FM/AM aerial but apart from length it looks very like the DAB magmount one I use. DAB will not do a good job for AM/FM.

 

Unless you are in a low signal area and as long a sit is an FM/AM aerial I would expect it to work BUT we may be back to a poor contact between the aerial and underside of the roof or water in the mount/cable. If it is an FM aerial the AM reception may be compromised.

Edited September 29, 2016 by Tony Brooks

[WotEver]

... we may be back to a poor contact between the aerial and underside of the roof...

And if we're not, we're back to stray current corrosion territory again.