whats the fuss about FM?

In article snipped-for-privacy@davenoise.co.uk>, Dave Plowman (News) snipped-for-privacy@davenoise.co.uk> 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?...

In article <sjk5k5$f0a$ snipped-for-privacy@dont-email.me, Harry Bloomfield <?.?@harrym1byt.plus.com> scribeth thus

Dunno! Did it ever work?...

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 ...

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.

tony sayer wrote on 06/10/2021 :

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

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.

From the GPS !!

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

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.

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

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

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...

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

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

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

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

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

Quite the opposite:

John

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

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

John