Modern electronics and radio interference

[Rod Speed]

Fredxx [e-mail] wrote

<reams of your shit any 3 year old could leave for dead flushed where it belngs>

[Rod Speed]

Brian Gaff [e-mail] wrote

But it makes no sense for everyone to pay more for their electrical appliances just so a microscopic number of people like you who like doing that can continue to do that.

It's more likely that far fewer are doing that anymore given that wifi, bluetooth and Zigbee etc are done so much better now.

We use wifi, bluetooth and Zigbee etc instead now.

Nope, by the need for much better performance than X10 etc could ever do.

You can say the same thing about a copper pair phone line and it works fine as one anyway.

[me9]

I get interference from PLT, but (unlike ADSL) it is filtered out on th e amateur bsnds.

[Brian Gaff]

Yes but only on most of the bands, not in between where a lot of the interesting stuff is. Brian

[Fredxx]

ADSL is becoming obsolete so you should be back to clean wavebands!

[Andy Burns]

Are there any frequencies that ADSL uses which VDSL doesn't?

[The Natural Philosopher]

Both use as many frequencies as they can!

From the top of baseband all the way up to the SW band.

However optical fibres will clean the RF spectrum in the LW,MW and SW bands.

Leaving just wifi and blue tooth...and 2g 3g 4g 5g...and DAB radio, and satnav...

[Peter Able]

Whatever the kit my neighbours' are using, no allowance seems to have been made for the bandwidth of whatever the kit is putting out.

For instance, the bandwidth cut-out for the 80m band drowns out anything above about 3765 kHz.

SNAFU

PA

[Fredxx]

I was thinking about fibre, where the interference will be very local and not from an overhead "aerial".

[me9]

That's about the transition frequency between upstream and downstream for ADSL, one is usually stronger than the other.

[Ian Jackson]

Some time ago, the internet phone line to the building behind my house went (very obviously) 'one-legged', and the transition from down- to up-stream at 3765kHz was VERY apparent. The router would have been transmitting at maximum level.

I did a bit of experimenting, and found that if I transmitted a burst of RF below 3765 I could turn the router off. After a few minutes it would wake up, and go into training test mode

The upstream carriers (spaced every 4kHz) were extremely strong. There were also much weaker (but still troublesome) carriers below 3765, which (I understand) were probably intermodulation products coming out of the router's upstream transmitter. Eventually, the modem usually appeared to establish some degree of two-way (albeit usually intermittent) communication. I did intend to 'have a few words', but fortunately, after a few days, an Openreach van appeared - and soon the interference ceased.

[me9]

Some years ago I had a similar problem on 30m (10MHz) Suimilar bursts of RF changed the "white noise" into carriers at 4kHz spacing leavoing the bits in between clear. After that as long as I transmitterd regularly they stayed clear.

[The Natural Philosopher]

Well not out of it directly. Ever hear of a metal oxide rectifier? Bits of oxidised metal that show non linear response in term of voltage/current relationships.

Just like an RF mixer does.

In RC model aircraft we called it the 'rusty fence effect' . Capable of making the model flap about all over the sky.

But a corroded contact on a DSL line is just perfect for creating all sorts of high strength intermodulation products and radiating them all over the place.

You can even hear it on the line, even a relatively good one, as those products extend into the audio baseband, It comes over as a faint 'hiss' on a silent line that is running broadband carriers on it. Disconnect the router and the hiss goes.

I once had a problem on the production line of some audio kit I had designed. Suddenly all the amplifiers showed out of spec distortion.

I traced it to silver oxide on the connectors beiing used multiple times a day to test the boards. A quick spray with IPA and a wipe with a cotton bud and the problem vanished...

[Ian Jackson]

Why not?

Otherwise the 'rusty bolt effect'.

I doubt if this was just a 'corroded contact'. It was probably a 'clean' open circuit on one of the two wires.

[The Natural Philosopher]

That doesn't do the intermodulation bit however.

You need a semiconductor, not an open circuit

[Ian Jackson]

Don't you think that the router upstream transmitter uses semiconductors?

[Tim Lamb]

In message [e-mail]>, Ian Jackson [e-mail]> writes

Sorry to *butt in* but is there any likelihood of illegal radio transmissions interfering with overhead telephone cabling?

[The Natural Philosopher]

You are like the man in the village pretending to read from an upside down book...You only fool the really stupid.

We are not talking about routers.

We are talking about the difference between an open circuit and a corroded contact in a wire.

[The Natural Philosopher]

Sure. I remember the day I switched on my illegal 5W 27Mhz transmitter in the living room and totally collapses the 605 line TV picture.

Or the time a friend acquired a police radio and used it to break into his neighbours hifi when they played it at 3 a.m.

But unless open reach has a slew of fault reports all on the same overhead, its rather unlikely

[Theo]

I wonder how many people are using PLT kit nowadays? It seemed like, despite manufacturers' promises, it was hard to get above 100Mbps. Which might be fine for VDSL but isn't fine for any faster connection. It seems like that space in the market has been occupied by mesh wifi. I wonder whether PLT will gradually fade out as people upgrade to higher speeds?

For another thing, PLT requires an adapter at each place you want a connection, whereas mesh wifi is accessible from anywhere with just the hardware already in your device. PLT and wifi also have similar degrees of reliability (bandwidth worse and fluctuating, compared with wired ethernet). So hard to see why anyone would install PLT today.

Theo