OT:Radio Interferance

[G&M]

headquarters

What sort of engine management does a black cab have ?

[G&M]

immobiliser

Dolphin went bust. Qualcomm bought the remains in the hope of launching a CDMA mobile phone based service on this band but were told in no uncertain terms to FO.

[G&M]

Agreed. And it usually is. The lack of in-car use means no Doppler shift so the filters can be really tight at such low cost that I would be surprised if there are any units being sold now that have this problem.

[Bob Eager]

I think it was the immobiliser that was affected - not the EMS.

[Brian Reay]

Not sure that is true anymore. Pressure is moving to above 1GHZ- I can see bits of spectrum around 440>490MHz going begging before too long.

[Brian Reay]

Diesels may not have ignition circuits but they do have engine management and may have immobilisers.

[Brian Reay]

How much Doppler would you expect due to a car's velocity with at the frequencies in question?

(Try:

You may like to compare your answer with a useable bandwidth for the application.)

[tony sayer]

In article , Brian Reay writes

And tracts of Band 1, and 153 odd, and a lot of low band PMR and bits of Band 3....

[tony sayer]

In article , G&M writes

Can't be the drivers right foot now can it?;)

[G&M]

Are you kidding ? The WI-MAX people had their eye on some of these frequencies (and even the current TV ones scheduled to be turned off in

2012) in the hope of getting them for unlicenced WMAN use (75Mbps over 30 miles was mentioned) and have been told to come back with a serious amount of money. Spectrum is valuable. Specturm without point of sight restrictions is incredibly valuable !!

However the US may give them a frequency somewhere below 900 MHz so expect to see their illegal use overhere in due course.

[G&M]

Modern diesels with engine management and 'black cab' diesels are two different beasts with about a hundred years of evolution between them. However somebody has since pointed out it's the immobilisers working on 4xx MHz which are the problem.

[G&M]

About 100Hz or so. More than enough to keep the Viterbi co-efficient calculator busy in a GSM mobile and enough to make a DECT receiver lose frame sync completely.

[Mark]

Modern black cabs use modern Ford Dura Torq DI with electronic controlled injectors and all the resulting crap necessary to make a diesel go bang.

[Brian Reay]

More like 200Hz at legal speeds, but 100Hz is close enough for the discussion.

Of course, the problem isn't so much the absolute maximum shift but how it changes that keeps the decoding system 'busy'- once it settles down to a given shift it should track. Cars don't change speed that quickly. Think about what happens if the phone changes cell- or are all cell tranmitters withing 100Hz of where they should be? ( That is a question- GSM isn't my field.)

-- Brian Reay

FP#898

[Peter Crosland]

Hello Ian. Perhaps we should keep radio discussions here instead of uk.radio.amateur since it is DIY in a broad sense and this NG is much more civilised!

[G&M]

No - but the multipaths do, often in opposite directions.

Yes. All locked to an atomic clock. It is difficult enough for phone receivers to do the gymnastics of looking for better basestations without them being miles out in frequency.

[Brian Reay]

Do multipaths like this impart white Gausian noise? (I'm not saying they don't, again it is a question.) Just I thought Viterbi convolutional techniques were most suited to such noise OR is this another use of Viterbi?

Fair enough, although I didn't think 100Hz was miles out ;-)

(Doubt it explains why my Sony phone has just died!).

[G&M]

co-efficient

The convolution algorithm extracts data from noise. And if the data is full of reflections and echoes it will train to these (on the known preamble sequence) and extract the following data.

As a proportion of 900 MHz no. But once converted to baseband that's a hell of a lot of offset.

Keypad (again) ??