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uk.tech.digital-tv (Digital TV - General) (uk.tech.digital-tv) Discussion of all matters technical in origin related to the reception of digital television transmissions, be they via satellite, terrestrial or cable. Advertising is forbidden, with no exceptions.

Interference



 
 
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  #31  
Old August 31st 15, 04:14 PM posted to uk.tech.digital-tv
Woody[_5_]
external usenet poster
 
Posts: 1,865
Default Interference

I remember back in the 70's when the first electronic ignitions were
around, Cambs police had Volvo's - 144 or something like that - into
which were fitted Vanguards.

Transmit at any time and the car would loose 30mph almost exactly. If
you were doing less than 30 it stopped. One of my colleagues in
'Cambridge Service' found the answer. The electronics were in a large
plastic box (about the size of a modern under-bonnet fusebox) and thus
totally unscreened. He wrapped it in tin foil, wound wire round it
like string around a Christmas present, and earthed it to the battery.

Sorted.


--
Woody

harrogate3 at ntlworld dot com




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  #32  
Old August 31st 15, 04:28 PM posted to uk.tech.digital-tv
_Unknown_Freelancer_
external usenet poster
 
Posts: 75
Default Interference


"Jim GM4DHJ ..." wrote in message
...

"Woody" wrote in message
...

"tim....." wrote in message
...

"Ian Jackson" wrote in message
...
In message , Jim Lesurf
writes
In article , Ian Jackson
wrote:
There was a time when amateur radio 'interference' to domestic TV,
radio
and Hi-Fi was almost a certainty with certain products. The problem
was, of course, that the manufacturers 'forgot' that this equipment
might sometimes be subjected to HF fieldstrengths of several V/m -
and
that it might have many feet of external wiring attached to it
(aerial
drop coax, speaker leads etc) which could - and did - act as fairly
efficient HF receiving aerials.

Often, a satisfactory cure was the addition of a 3 or 4 components
costing a few pence - or even simply a slightly different design
approach which essentially cost nothing in component. Most attempts
to
influence the manufacturers fell on very deaf ears - and probably
still
do.

To be fair, there can be rather more to it than " 3 or 4 components
costing
a few pence each".

It certainly can - especially if you set out to design equipment to be
more-or-less interference 'bomb-proof'.

Some years ago, I worked (as a software engineer) on a product that the
company though that they could save a few pennies on the construction by
not bothering to provide over-charge protection to the battery circuit.

When in use the product lasted 6-9 months before becoming bricked.
(Something which, of course, could never reasonably be tested before
release)

the company went bust


30 years or so ago Vauxhall brought out the Astra GTE with its electronic
and part digital dashboad. No-one had bothered to test it for RF
sensitivity.

The Astra GTE was very popular as a lease car with Gas Board radio
engineers who promptly fitted AM transceivers in them - and quickly found
the problem. Tx, no issue, but speak into the mic and the rev counter and
temp gauge went full scale and the speedo and fuel gauge went to zero.
What is more they stayed there until the ingition was power cycled (the
first power-on-reset?)

The problem was passed back by Vauxhall to Delco who made the instrument
cluster assembly. Aften about four months work they found that the cure
was qty 3 1nF ceramic caps, cost (in quantity) 2p each. They decided it
was too expensive.


Woody

harrogate3 at ntlworld dot com


I could run 100w SSB HF until I replaced the bosch MAF with a cheap chinky
replacement now when I TX the engine stops ......


On a similar note this (+ a bit of history) is why filling stations dont
allow mobile phone use on their forecourts.
i.e. Nowt to do with fire hazzard. Even Myth Busters couldnt prove it!!

'In the 80s'.....when CB radio was popular certain persons used to boost
their EMR by use of 'burners'.... an RF amp.

At some point someone found that if you keyed your mic a few times after
you'd completed filling your car up, the pump forgot how much fuel it had
dispensed, and presented an irrational figure.... either way too high or
low.
So frequently they would be sent on their way without paying, whilst the
forecourt owner had to call in the engineers.

Since the cause was found, they just do not like people using RF kit on
their forecourt, just in case it causes the same probem again.
.....probably because the manufacturers wont accept any losses caused by such
events!

Thing is, they never tell the Police to turn their kit off when they pull
in, as some constantly transmit their location.





  #33  
Old September 1st 15, 06:55 AM posted to uk.tech.digital-tv
Jim GM4DHJ ...
external usenet poster
 
Posts: 50
Default Interference


"Ian Jackson" wrote in message
...
In message , Jim GM4DHJ ...
writes

"Woody" wrote in message
...

"tim....." wrote in message
...

"Ian Jackson" wrote in message
...
In message , Jim Lesurf
writes
In article , Ian Jackson
wrote:
There was a time when amateur radio 'interference' to domestic TV,
radio
and Hi-Fi was almost a certainty with certain products. The problem
was, of course, that the manufacturers 'forgot' that this equipment
might sometimes be subjected to HF fieldstrengths of several V/m -
and
that it might have many feet of external wiring attached to it
(aerial
drop coax, speaker leads etc) which could - and did - act as fairly
efficient HF receiving aerials.

Often, a satisfactory cure was the addition of a 3 or 4 components
costing a few pence - or even simply a slightly different design
approach which essentially cost nothing in component. Most attempts
to
influence the manufacturers fell on very deaf ears - and probably
still
do.

To be fair, there can be rather more to it than " 3 or 4 components
costing
a few pence each".

It certainly can - especially if you set out to design equipment to be
more-or-less interference 'bomb-proof'.

Some years ago, I worked (as a software engineer) on a product that the
company though that they could save a few pennies on the construction
by
not bothering to provide over-charge protection to the battery circuit.

When in use the product lasted 6-9 months before becoming bricked.
(Something which, of course, could never reasonably be tested before
release)

the company went bust


30 years or so ago Vauxhall brought out the Astra GTE with its
electronic
and part digital dashboad. No-one had bothered to test it for RF
sensitivity.

The Astra GTE was very popular as a lease car with Gas Board radio
engineers who promptly fitted AM transceivers in them - and quickly
found
the problem. Tx, no issue, but speak into the mic and the rev counter
and
temp gauge went full scale and the speedo and fuel gauge went to zero.
What is more they stayed there until the ingition was power cycled (the
first power-on-reset?)

The problem was passed back by Vauxhall to Delco who made the instrument
cluster assembly. Aften about four months work they found that the cure
was qty 3 1nF ceramic caps, cost (in quantity) 2p each. They decided it
was too expensive.


Woody

harrogate3 at ntlworld dot com


I could run 100w SSB HF until I replaced the bosch MAF with a cheap chinky
replacement now when I TX the engine stops ......

When indicating left, 40W on 145MHz caused my circa 2000 Focus's left
indicator to flash a lot faster. Indicating right was OK. No other
problems.

According to the owner's handbook, a 2004 New Astra I had was RF specced
at 10W on any frequency.


merc book says 100w maximum on HF but that would only apply with the 150
bosch MAF not the 15 chinky one ..... tee hee


Of course, 434MHz door and ignition keys are known to have problems when
there are nearby amateur transmissions in the 432MHz band. [Why do they
need to use RF? In the 1980s, I found that a Sierra infrared key worked
fine.]


Ian


my ford mustang is unaffected being on 315Mc/s .......


  #34  
Old September 1st 15, 07:07 AM posted to uk.tech.digital-tv
Jim GM4DHJ ...
external usenet poster
 
Posts: 50
Default Interference


Of course, 434MHz door and ignition keys are known to have problems when
there are nearby amateur transmissions in the 432MHz band. [Why do they
need to use RF? In the 1980s, I found that a Sierra infrared key worked
fine.]


Ian


my ford mustang is unaffected being on 315Mc/s .......

so no chance of hammy mens keeping me out of the car by Txing from their
pockets on 432.92 Mc/s


 




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