About road noise immunity radioslave
In the 90-ies of the last century in the UK often happened that the owner the car was not able to use it as a door lock did not respond to the radio signals transmitted by the FOB key. The reason for the block was radio interference, sources which the media were quick to call the parasitic radiation Amateur radio stations operating in the range of 70 cm (440 430... MHz).
Indeed, some dedicated to radioslave frequency (418 and 433.92 MHz) lie near and even within this range, but the true cause of accidents - not low quality Amateur transmitters, and poor selectivity and extremely poor noise immunity of receivers radioslave. Many of them, especially those which are engaged in various service centers - elementary sverigekartan with a bandwidth of several megahertz. They are sensitive even to interference with frequencies far beyond Amateur range.
The interference-prone and more expensive superheterodyne receivers radioslave the factory setting. Many of them, having an intermediate frequency of 500 kHz, provided by any filters for image rejection receive channel. And he lies in the immediate vicinity of the working frequency band transmitters British Amateur repeaters (433,0...433, 375 MHz).
In some vehicles (such as Vauxhall Vectra) the door is locked radiozamok can still access the normal key while you will hear the alarm is triggered. Once the key is inserted in the ignition and turned, the alarm will turn off, and the immobilizer will allow to start the engine. Special difficulties do not arise here if the driver knows what to do.
But sometimes (for example, on the car seat, locked the castle creates the driver is much more problematic. To start the vehicle, it is necessary not only remember the secret code, but also to know quite a complex way of its input. Some immobilizers aftermarket installation is impossible to disable, if radiosonic blocked by the obstacle.
In 1996 in the UK established the RAKE, which included representatives of all stakeholders, including ham radio. It the long-term objective is to achieve the allocation for radioslave new frequencies in ranges that are free from interference. Mid-term goal of the announced improvement castles, operating at a frequency of 433.92 MHz. A brochure with the recommended the characteristics of their receivers.
Requirements that need to be performed to ensure reliable operation near Amateur radio stations (resistance to interference with a field strength of not more than 1 mV/m in the band 433,921 MHz and 100 mV/m beyond), was not too hard, and already in 1997, it was stated that the problem is solved.
It was rather difficult to deal with interference from professional systems, which the primary basis of the assigned frequencies lying close to those that have been selected for radioslave. Known case of mass locking with an operating frequency of 418 MHz in the Parking lot at the supermarket, near which establishes a base station system digital trunk connection with TETRA transmitters operating in the band 420...425 MHz.
Antenna earth stations, and Amateur repeaters in the UK often mounted on the same mast, and the first suspicion always falls on ham radio. Need for collaboration with professional radio systems selectivity automobile manufacturers radioslave promised to achieve by 2000
In summer and autumn 1998 British motorists and hams tested on the immunity of radioslave with an operating frequency of 433.92 MHz. Interference created the transmitter 32 mW, the antenna which is disposed at a distance of 3 m from the driver's window. In accordance with the British standard signal transmitter was simulated amplitude (depth 80 %) of a sinusoidal signal at a frequency of 1 kHz. The fact that the lock has been committed, if the lock could not be opened, even bringing keychain-key close to the window.
It was found that radiosai only eight of the 19 tested different cars model release: 1997 - 1998 satisfy the requirements RAKE 1997, the remaining 11 may be locked working nearby Amateur radio range of 70 cm.
Results beyond requirements RAKE 2000, showed only radiosai Nissan QX and Volvo V70. At the receiver the first one is the most narrow of proven bandwidth, and the second to transfer the code applied frequency, not amplitude keying of the carrier.