On Thu, Oct 24, 2013 at 3:50 PM, Derek dlahouss@mtu.edu wrote:
luke.leighton <luke.leighton <at> gmail.com> writes:
it's because they use a $0.15 part <at> 433mhz with a wide-band reception instead of a $1 part with proper narrow-band filtering. i assume that this is also the reason why, if you are locked out of your car, you can ask someone with a GSM mobile phone to press a duplicate door-opener AT THEIR END of the conversation...
Luke, you said this with too straight a face. Maybe you're just taking the piss,
i'm not - it was however an apocryphal story. good one, too :)
but GSM uses a voice codec with between 3k and 12k of bandwidth. If it's not an audible part of speech, the codec should drop it to the floor.
my guess is that what's going on is that R.F.-level interference between the transmitters is resulting in a transmission that the broad-band car receiver ICs are capable of picking up, and that yes, the modulation rate is within the bandwidth of GSM codecs. if ever you've stood next to a stereo with a GSM phone and got "b-bp, b-bp, bzzzzz" when someone speaks, you'll have a ... ok you get the idea
anyway back to it... :)
l.