How many of you use a Faraday shield bag for your key fobs?
12-05-2018, 11:35 AM
#111
Permanent S Mode Member
Receivers are complex devices, they are not passive. They include a bunch of powered active electronic components whose job it is to filter out the unwanted signals and amplify the narrow band where the the FOB signal is expected to be found. So yes, more money can possibly buy you a better receiver. Someone said in a previous post that you can easily build a 100x better receiver than the one in your car but take that with a grain of salt. Improving reception is not easy and not cheap so good luck building a cheap one 100 times better but don't think that because your car cuts off at 3 feet that this distance cannot be improved upon.
Last edited by MH62; 12-05-2018 at 11:42 AM.
12-05-2018, 12:03 PM
#112
AudiWorld Super User
Actually, if you put your keys on a belt clip, or in a hip pocket, and turn so that your whole body is directly in between the key fob and the Audi? The car may insist that there is no fob here, and refuse to open. This is sometimes called "body shadow" and is a larger problem that even effects handheld radios worn on the belt. (Which is one reason that police/fire radios often have an antenna up on the shoulder mic, in clearer space.)
Considering how long it takes a human being to move three feet, and how many times a radio can say "Hello?" in that time period, three feet is plenty generous. When GM's Chevrolet division put the first keyless entry system on Corvettes around 1990, they had a range or around twenty feet. Get that close to the car and it automatically unlocked for you. People complained. Automatic unlock went off the market.
With cars having 360-degree "backup" cameras now, how long will it take for one to have smartphone facial recognition, so the car only unlocks when the owner's FACE can be found? Iris recognition?
Fobs are just so...Your father's Oldsmobile?
Considering how long it takes a human being to move three feet, and how many times a radio can say "Hello?" in that time period, three feet is plenty generous. When GM's Chevrolet division put the first keyless entry system on Corvettes around 1990, they had a range or around twenty feet. Get that close to the car and it automatically unlocked for you. People complained. Automatic unlock went off the market.
With cars having 360-degree "backup" cameras now, how long will it take for one to have smartphone facial recognition, so the car only unlocks when the owner's FACE can be found? Iris recognition?
Fobs are just so...Your father's Oldsmobile?
12-05-2018, 12:55 PM
#113
Permanent S Mode Member
Yes, and based on that feedback, today's engineers most likely go out of their way to "detune" the car's receiver to make sure it doesn't work over 3 feet. So again, the 3-foot limit we currently observe between car and FOB is not the maximum distance doable.
12-05-2018, 01:09 PM
#114
AudiWorld Super User
Receivers are complex devices, they are not passive. They include a bunch of powered active electronic components whose job it is to filter out the unwanted signals and amplify the narrow band where the the FOB signal is expected to be found. So yes, more money can possibly buy you a better receiver. Someone said in a previous post that you can easily build a 100x better receiver than the one in your car but take that with a grain of salt. Improving reception is not easy and not cheap so good luck building a cheap one 100 times better but don't think that because your car cuts off at 3 feet that this distance cannot be improved upon.
12-05-2018, 01:55 PM
#115
AudiWorld Super User
Receivers are complex devices, they are not passive. They include a bunch of powered active electronic components whose job it is to filter out the unwanted signals and amplify the narrow band where the the FOB signal is expected to be found. So yes, more money can possibly buy you a better receiver. Someone said in a previous post that you can easily build a 100x better receiver than the one in your car but take that with a grain of salt. Improving reception is not easy and not cheap so good luck building a cheap one 100 times better but don't think that because your car cuts off at 3 feet that this distance cannot be improved upon.
12-05-2018, 02:52 PM
#116
Permanent S Mode Member
when you say powered active device, do you mean active as in the impedance of a RC filter. Or do you mean active as in transmitting power? Which a reciver does not do. True, receivers can have better frequency filter networks, but it still cannot amplify a signal that is not there. A bigger antenna would increase the receivers sensivity to pick up a weak signal, but I think most thieves do not walk around with a big antenna in one hand and a transceiver in the other hand.
"Active components include amplifying components such as transistors, triode vacuum tubes (valves), and tunnel diodes.Passive components can't introduce net energy into the circuit. ... Passive components include two-terminalcomponents such as resistors, capacitors, inductors, and transformers."
It's actually quite hard to determine if a signal is there or not as it just doesn't stop but attenuates over distance. So for one receiver, the signal may be so low that it becomes just noise but another more capable receiver may be able to extract it.
12-05-2018, 04:46 PM
#117
AudiWorld Super User
As defined by wiki :
"Active components include amplifying components such as transistors, triode vacuum tubes (valves), and tunnel diodes.Passive components can't introduce net energy into the circuit. ... Passive components include two-terminalcomponents such as resistors, capacitors, inductors, and transformers."
It's actually quite hard to determine if a signal is there or not as it just doesn't stop but attenuates over distance. So for one receiver, the signal may be so low that it becomes just noise but another more capable receiver may be able to extract it.
"Active components include amplifying components such as transistors, triode vacuum tubes (valves), and tunnel diodes.Passive components can't introduce net energy into the circuit. ... Passive components include two-terminalcomponents such as resistors, capacitors, inductors, and transformers."
It's actually quite hard to determine if a signal is there or not as it just doesn't stop but attenuates over distance. So for one receiver, the signal may be so low that it becomes just noise but another more capable receiver may be able to extract it.
12-05-2018, 07:48 PM
#118
Plus, even if the relay can extend the signal inside the car to start it, that would be much riskier for the thieves, since starting the car would alert the owner while the one with the remote box is running back.
12-05-2018, 10:16 PM
#119
AudiWorld Senior Member
Thread Starter
In practice, it's usually too late by then. Cars have been stolen this way.
12-05-2018, 10:17 PM
#120
AudiWorld Senior Member
Thread Starter
Receivers can definitely be built to pick up weak signals. No doubt there. It comes at a cost and bulk. Large antennas and such for example. If somebody really wants to get your car they can. Nothing is ever a 100% secure. It's generally a cost/reward equation. At some point it's not worth the cost anymore.