Slashdot Mirror
Pirate Radio Station In Florida Jams Automotive Electronics
New submitter titanium93 writes "For months, dozens of people could not use their keyless entry systems to unlock or start their cars when parked in the vicinity of the eight-story Regents bank building in Hollywood, FL. Once the cars were towed to the dealership for repair, the problem went away. The problem resolved itself when police found equipment on the bank's roof that was broadcasting a bootleg radio station. A detective and an FCC agent found the equipment hidden underneath an air conditioning chiller. The man who set up the station has not been found, but he faces felony charges and fines of at least $10,000 if he is caught. The radio station was broadcasting Caribbean music around the clock on 104.7 FM."
If the keyless entry is in the 314mhz (thrid harmonic) range then it could possibly be interference. A poorly controlled oscillator can cause this.
The third harmonic of 104.7 is 314.1 Mhz. Keyless entry systems operate at 314.93 Mhz. The bootleg transmitter/antenna likely didn't have any filtering to reduce spurious emisions or harmonics.
Having been in the industry (broadcast) the issue was not with the FM band transmission. The illegal transmitter was most likely home built, improperly adjusted, and lacking harmonic filters and a narrow band tuned antenna. Most transmitters do not run class A or Class AB amplification like a low distrotion audio amplifier, but in Class C a clipped mode transmission rich in harmonics for high energy effeciency (like a switched mode power supply) and the output is filtered with a resonant tuned tank circuit. If the bootleg transmitter was not tuned, or lacked the tuned tank and tuned resonant antenna, then he was not only broadcasting in the FM band but also providing lots of energy on harmonics of the fundemental.
Fundimental is 104.7
2nd harmonic is 209.4
3rd harmonic is 314.1
My car remote is in the 315 MHZ range and would be impacted by this. The FM signal is not a narrow band frequency as it is Frequency Modulated. It could easily overlap the range used by car remotes. Not getting into the car is only one issue. The second issue is the problem with the chip in the key for anti theft immobolization.
The truth shall set you free!
Corrosion or a Class C power amplifier without an output resonant narrow band antenna or tuned tank. My bet would be home built transmitter with a Class C amplifier and lack of harmonic filtering.
The rusty bolt can give some harmonic power but not nearly as much as an unfilterd power amplifier.
Rusty bolt tends to be problems near a receiver such as a rusty downspout on a builting making a clean transmitter look bad to locals within a building. This is most often seen with Ham radio complaints where the ham is clean, but the TV in the apartment a block away is due to rusty guy wires or downspout on the apartment. IE the harmonic is generated in close proximity of the TV viewer a block away.
http://en.wikipedia.org/wiki/Class_C_amplifier#Class_C
The truth shall set you free!
Negative. Unlocking the car from the inside sets off the alarm. Using your key on any OEM system will disarm the alarm.
There's different kinds of "keyless" systems.
Most "keyless entry" systems are remotes that unlock the doors and disarm any security system the car might have. Otherwise, the car is as normal and has physical keys, physical locks on the doors and requires a mechanical key to operate the ignition.
My Volvo has what Volvo calls "Personal Car Communicator" -- a wireless proximity key that allows the doors to be opened and car started without any button press other than the starter button. The key can stay in your pocket.
Now in the case of my Volvo, the "normal" starting process for non-PCC cars, the same keyfob fits a slot on the dash. There's no mechanical bypass, although I assume starting would work without any battery in the keyfob.
The door locks are all electronic and unless you've read the manual, you might not realize that the keyfob's "key ring" is actually a slim metal key that can be removed from the keyfob and used to mechanically unlock the door.
With a system like this, common to many high end luxury cars, I can see nontechnical people freaking out and saying their car doesn't work, either not letting them in because they don't know the bypass exists or not starting because they don't know the non-wireless starting method (ie, fob in slot or similar).
Or they may just be really high strung people who figure that anything that doesn't work is Mercedes' problem and they need to get the car and give them a loaner.
low-quality transmitters emit more on side-bands, IIUC
"side bands" carry the information in the radio signal. They are created by the modulation of the carrier, and are what make the signal have "bandwidth". While a low quality transmitter may have some noise in the oscillator that appears as side-band information, it is probably not as much "in the side-bands" as a full power FCC licensed FM stereo radio station that has Muzak or other extended signals, also known as "SCA".
It is the poor filtering of the low-quality transmitter that results in the emission of harmonics (third, fifth, etc.) from a non-linearity in the oscillator or the amplifiers. In this case, a third harmonic around 312 MHz, which is a common unlicensed control device frequency.
A number of the Japanese manufacturers use a similar system.
Toyota use a dual NFC (RFID) / "far-field" radio system. The same transponder in the fob is connected to both an NFC antenna, and a battery powered MCU and RF power amp.
With a working battery, a button push on the fob will cause it to transmit an appropriate radio signal to the car. When key-less starting, the battery will provide power to the RFID transponder, and power the RF amplifier to allow a successful authentication whenever the fob is in the interior of the vehicle.
In the event of a discharged or removed fob battery, there is a mechanical key concealed in the fob which can open the vehicle doors. By placing the fob directly on top of the "push-to-start" button, then transponder will be sufficiently energized by the car's antenna (which is concealed in the button) to complete an authentication transaction.