My wireless speedo stopped working

General cycling advice ( NOT technical ! )
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geomannie
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My wireless speedo stopped working

Postby geomannie » 14 Jun 2019, 9:08pm

I don't know Cumbria and the north Lakes very well, but on a ride out today we passed the perimeter of an area with massive radio masts. I now know this is the Skelton Transmitting Station. https://en.m.wikipedia.org/wiki/Skelton ... ng_Station

Just after we came up to it my wireless Cateye speedo stopped working. Bother I thought, needs new batteries. Cycled past the radio masts and the speedo kicked back into life and worked perfectly thereafter.

So what was going on? What powerful radiation was affecting my speedo? Radio waves, magnetic field or what? All very rum.
geomannie

MikeF
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Re: My wireless speedo stopped working

Postby MikeF » 14 Jun 2019, 9:24pm

Radio waves. Nothing unusual in that with such a simple devices as wireless speedo.
"It takes a genius to spot the obvious" - my old physics master

simonhill
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Re: My wireless speedo stopped working

Postby simonhill » 14 Jun 2019, 10:27pm

I've experienced it a few times when cycling past (foreign) military establishments. I wondered if it was some form of 'cloak' to stop prying ears.

I've also had my Speedo clock amazing speeds in excess of 100 when near some forms of telecoms or electronic equipment. This often happened in China where their telecom equipment seemed to be very poorly shielded.

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Redvee
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Re: My wireless speedo stopped working

Postby Redvee » 15 Jun 2019, 12:56am

I had similar false readings with a Lidl/Aldi cheapo bike computer when passing through one particular set of traffic lights in Bristol and also from the security barriers at the entrance to shops. With the traffic lights the speedo would register 100.4 mph and the electronic security barriers would read 47.4 mph.

ChrisF
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Re: My wireless speedo stopped working

Postby ChrisF » 15 Jun 2019, 10:22am

Electronic devices will have a CE mark which means they will have ben tested to be protected from interfernce from oother equipment. But it's pretty impossible to protect against interference from a radio mast a few metres away, even if it's transmitting at a slightly different frequency.
In the early days of wireless bike computers, they weren't even protected from each other so if you rode alongside soneone else with the same make, you'd get double the speed.
Chris F, Cornwall

Mike Sales
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Re: My wireless speedo stopped working

Postby Mike Sales » 15 Jun 2019, 10:33am

ChrisF wrote:. But it's pretty impossible to protect against interference from a radio mast a few metres away, even if it's transmitting at a slightly different frequency.


I built a 3W amplifier from a kit. When playing with it I found that if I put my finger in the right place I picked up Radio Bristol. This was in Bristol, but not particularly close to the transmitter.
I supposed my finger to the circuit point interface made a diode which demodulated the signal.
I was told of radio signals being picked up on a tooth filling.

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Mick F
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Re: My wireless speedo stopped working

Postby Mick F » 15 Jun 2019, 10:47am

Mike Sales wrote:I supposed my finger to the circuit point interface made a diode which demodulated the signal.
The capacitive effect of your finger - maybe a sort of tuned circuit - as well as the diode effect.
Just a diode, would detect all the stronger signals, not just one.

Many years ago, I put a diode across the TV aerial (VHF in those days) and a headset with croc clips across it. I could hear three or four - maybe more - MW stations.

As for the OP problem, it's obvious really. Any strong signal would swamp the puny Cateye transmission and reception and it doesn't need to be anywhere near the Cateye frequency. No doubt a strong magnetic field would do it too.
Mick F. Cornwall

Mike Sales
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Re: My wireless speedo stopped working

Postby Mike Sales » 15 Jun 2019, 11:21am

Mick F wrote:
Mike Sales wrote:I supposed my finger to the circuit point interface made a diode which demodulated the signal.
The capacitive effect of your finger - maybe a sort of tuned circuit - as well as the diode effect.
Just a diode, would detect all the stronger signals, not just one.

Many years ago, I put a diode across the TV aerial (VHF in those days) and a headset with croc clips across it. I could hear three or four - maybe more - MW stations.

As for the OP problem, it's obvious really. Any strong signal would swamp the puny Cateye transmission and reception and it doesn't need to be anywhere near the Cateye frequency. No doubt a strong magnetic field would do it too.


Thanks for the technical explanation. Did you not pick up TV sound off the aerial!

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Mick F
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Re: My wireless speedo stopped working

Postby Mick F » 15 Jun 2019, 11:33am

It was a complete garble.

Another techy bit:
VHF and UHF telly signals were two-channel transmissions. Sound and vision (obviously!)
Sound was FM and vision was AM.
Therefore, my experiment wouldn't detect frequency modulated transmissions, just amplitude modulations. ie just the vision which sounds like a buzz, but not the sound at all.

A radio frequency AMDSB signal - Amplitude Modulated Double Side Band - is a combination of the carrier wave and the audio wave. Putting a diode across cuts off all the positive-going waves (or negative, depending on which way round the diode is connected) and what is left can be heard. The carrier wave is too high a frequency to be heard.

If all you did was to put the headset across the terminals without a diode and therefore leaving both audio signals, the audio would be cancelled out so you wouldn't hear anything.

This is a good piccy. The diode would split the signal along it's length.
amdsb.jpg
Mick F. Cornwall

GranvilleThomas
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Re: My wireless speedo stopped working

Postby GranvilleThomas » 15 Jun 2019, 6:06pm

For my sins I am a licensed Radio Ham and this effect is well recognised amongst radio enthusiasts and is a very common problem faced by car owners as well, trying to use the key fob to either access their cars or lock them in areas of high RF signal strength.

This will also be the same problem effecting wireless bike computer in certain circumstances and tends to be caused by the fact that the receivers in these type of devices are built very cheaply for the sake of simplicity, size restraints and of course to maximise profit by using as few components as possible.

Consequently these devices are not very 'selective', in other words they are not very efficient at filtering out transmissions from frequencies other than the one they should be receiving on and any strong local transmission will be received by the device (bike computer for example) even if it is on a different frequency and because it is a very strong RF field will broadcast over the top of the transmission from the wheel transmitter and display erroneous readings.

I probably haven’t explained this very well, but I tried my best honest :D

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Mick F
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Re: My wireless speedo stopped working

Postby Mick F » 15 Jun 2019, 6:28pm

GranvilleThomas wrote:For my sins I am a licensed Radio Ham .........
CQ CQ CQ :D

I spent many a long year in the RN as a radio and communications technician, as well as specialising in radars, displays and weapon engineering plus some years working with cryptography equipment.
Mick F. Cornwall

GranvilleThomas
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Re: My wireless speedo stopped working

Postby GranvilleThomas » 15 Jun 2019, 6:47pm

Mick F wrote:
GranvilleThomas wrote:For my sins I am a licensed Radio Ham .........
CQ CQ CQ :D

I spent many a long year in the RN as a radio and communications technician, as well as specialising in radars, displays and weapon engineering plus some years working with cryptography equipment.


Wow, amazing background and knowledge then, you are the professional and for me it is just a hobby :D

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geomannie
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Re: My wireless speedo stopped working

Postby geomannie » 15 Jun 2019, 9:19pm

Hi Folks

Thanks for responding. I was just bemused as to why my speedo had stopped working & I guessed the radio masts were to blame- somehow. It sort of takes my faith in technology away from me a bit. If they can kill your speedo, what can they do to your GPS?
geomannie

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Mick F
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Re: My wireless speedo stopped working

Postby Mick F » 16 Jun 2019, 9:28am

GranvilleThomas wrote:Wow, amazing background and knowledge then, you are the professional and for me it is just a hobby :D
WAS.
Joined up in 1969 and did a four and a half year apprenticeship.

My latter years in the RN saw me as middle management and without a tool or test equipment. Just a pen, a diary, and a clipboard. :cry: Left in 1996.

Technology moved on and left me behind somewhat, even though I was in charge of a big team of "modern" technicians. I understood all the theory though. My time as a man on the coal-face was enjoyable and stimulating, but so old fashioned nowadays. For instance, the weapons direction computer of mine was a huge affair seven or eight feet long, two feet deep and six feet tall. It could all have been done on a modern laptop! :lol:
Mick F. Cornwall

GranvilleThomas
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Re: My wireless speedo stopped working

Postby GranvilleThomas » 16 Jun 2019, 4:33pm

Mick F wrote:
GranvilleThomas wrote:Wow, amazing background and knowledge then, you are the professional and for me it is just a hobby :D
WAS.
Joined up in 1969 and did a four and a half year apprenticeship.

My latter years in the RN saw me as middle management and without a tool or test equipment. Just a pen, a diary, and a clipboard. :cry: Left in 1996.

Technology moved on and left me behind somewhat, even though I was in charge of a big team of "modern" technicians. I understood all the theory though. My time as a man on the coal-face was enjoyable and stimulating, but so old fashioned nowadays. For instance, the weapons direction computer of mine was a huge affair seven or eight feet long, two feet deep and six feet tall. It could all have been done on a modern laptop! :lol:


Well, technology moves on faster and faster for all of us and there is no end in sight. I was thinking about my first bike computer from the mid 80's I think it was.

I don't know if anyone had one of the the old original Avocet ones, I cant remember how much it cost but this was obviously before the days of the internet and I remember that there were none available in the local bike shops and I had only seen a picture in Bicycling magazine.

The now closed 'Reg Braddick Cycles' in Cardiff agreed to order one for me and I remember thinking how amazing and advanced it was at the time when I fitted it to the handlebars on my Barry Hoban 531.


Avovet_1984.jpg


I had this for a few years until it started letting in rain, but of course looks very dated now compared to modern devices and in fact I bought one of the latest Aldi wireless computers for less than a fiver a couple of weeks back, this would have been 'the stuff of dreams' back then and not very advanced compared to the latest devices available for cyclist, but as has been demonstrated by the op in this thread advanced technology is not by any means infallible.