whats the fuss about FM?

[tony sayer]

They did swap at some stage, long history that station!

Its now on the local mini DAB MUX:)....

[tony sayer]

In article [e-mail]>, Dave Plowman (News) [e-mail]> scribeth thus

At the rate their shutting down MF stations;!...

Better get a demo MW TX in fact It'd be interesting to hear it on its widest bandwidth setting?...

[tony sayer]

In article <sjk5k5$f0a$ [e-mail], Harry Bloomfield <?.?@harrym1byt.plus.com> scribeth thus

Dunno! Did it ever work?...

[Jethro_uk]

Oh, and with FM you increase the signal power by increasing the carrier power. With AM you need to increase the input power to increase the signal power. I used to know the equations ...

[Ian Jackson]

The similar sort of consideration for an AM analogue (eg PAL-I) TV signal is that the 5MHz bandwidth noise from a 75 ohm resistor (at 20C?) is about minus 58dBmV (1.259 microvolts). I'm not sure how this relates to (say) 200kHz(???) bandwidth and an FM audio signal.

[Harry Bloomfield, Esq.]

tony sayer wrote on 06/10/2021 :

Yep, worked first time, but it would be difficult to tune and tended to drift from memory.

[Harry Bloomfield, Esq.]

Mark Carver brought next idea :

Mine is supposed to do that, getting a speed input from the GPS. I have never noticed any difference when it's turned on, even when configured for maximum.

[Mark Carver]

From the GPS !!

Don't they just use a simple mic in the engine bay ?

[Harry Bloomfield, Esq.]

No mic in the engine bay. It could use it's built in mic, the one it uses when bluetooth connected to my phone, but I read it uses the GPS speed report.

[The Natural Philosopher]

Not even that. Mine will get louder if I open a window

[John Walliker]

Car audio systems often have access to engine speed and road speed data from the CAN bus. They then apply an algorithm to boost the output level according to a combination of those speed measurements. Doing it this way is more consistent than using GPS data (which they could also access equally easily).

John

[The Natural Philosopher]

sort of h-bomb to crack a nut technology.

A cabin microphone is infinitely better. Such as the one used for the integrated bluetooth connected hands free mobile phone...

[John Walliker]

On Thursday, 7 October 2021 at 18:11:37 UTC+1, The Natural Philosopher wrote:

Its not as simple as that. The system that plays music may be made by a different supplier to the hands-free phone system which complicates interfacing. For a microphone to be useful at estimating road and engine noise it must first cancel out the music which is being played. It also needs to have a suitable frequency response. The built-in directional microphones have strong attenuation of the lower road and engine noise frequencies for obvious reasons, but this makes them less suitable for measuring those frequencies. Their outputs are also processed by automatic gain controls, noise suppressors and echo cancellers optimised for telephony. In contrast, the car audio system will already be connected to a CAN bus like almost everything else in the car and often also to a separate "entertainment" bus such as a MOST optical fibre ring. It would of course be possible to send unprocessed audio from the microphone to the audio system over the entertainment bus, but it would still suffer from an unsuitable frequency response. Overall it is much easier to grab information about engine and road speeds than to process audio from a microphone that is intended for other purposes. The boost is unlikely to be more than around 10dB, so lookup tables based on the CAN data are perfectly good enough. Car manufacturers try very hard to reduce the number of point-to-point connections to save weight, cost and complexity.especially when different combinations of optional extras would potentially require different wiring harness configurations. It is much preferable to interconnect everything with a few communication buses rather than lots of individual cables.

John

[Jethro_uk]

I can remember finding a valve car radio in a box in my Dads garage.

[The Natural Philosopher]

Very easy if its a mic in the player itself. Remember it doesnt have to 'cancel out the noise' - it is enough to take a sound envelope of what is being fed to te speakers and compare it with a sound envelope of the noise its hearing. Or sample the noise level during quite pieces of music.

It doesn't have to be massively accurate - it simply wants to improve S/N of te music in quiet periods

It also

Those are also the frequencies that are not necessarily heard as 'noise' by the human ear

Their outputs are also processed by automatic

Their raw inputs however. are not.

Bollocks

It would of course

[The Natural Philosopher]

I remember one in a car a mate had that I fixed.

But IIRC we got a £7 tranny one from Halfords to replace it

[The Natural Philosopher]

Mine certainly uses a noise detector as opening h windows causse the volume to increase

[John Walliker]

Quite the opposite:

"MOST (Media Oriented Systems Transport) is a high-speed multimedia network technology optimized by the automotive industry. ... The serial MOST bus uses a daisy-chain topology or ring topology and synchronous data communication to transport audio, video, voice and data signals via plastic optical fiber (POF) (MOST25, MOST150) or electrical conductor (MOST50, MOST150) physical layers." and "MOST technology is used in almost every car brand worldwide, including Audi, BMW, General Motors, Honda, Hyundai, Jaguar, Lancia, Land Rover, Mercedes-Benz, Porsche, Toyota, Volkswagen, SAAB, SKODA, SEAT and Volvo."

John

[Andy Burns]

I had to disable it, because it overcompensated and became TOO LOUD

[John Walliker]

If its done properly you should hardly be aware that it is happening.

John