Short range unlicensed radio links, with typical ranges of 1 to 100 meters, are becoming more and more popular. Millions of these radios are used today in such applications as automotive keyless entry, tire pressure monitoring, gate openers, wireless security systems, data links, remote meter reading and too many other applications to enumerate. With the number of short range devices (SRD’s) increasing daily, the potential for interference by competing nearby SRD’s or other wireless services has increased dramatically over the last few years. It is becoming more and more important for SRD’s to be capable of reusing the same spectrum shared by other SRD’s. To share the same spectrum, radio receivers must ignore co-channel interfering signals that are weaker than the desired signal. Such a receiver exhibits what is commonly referred to as the “capture effect”. The term “capture effect” is commonly associated with FM or FSK receivers and not with OOK/ASK by the industry in general. The industry also believes that FSK receivers are more sensitive than OOK receivers. This paper will show that, when properly implemented, OOK can actually outperform FSK in both the areas of sensitivity and co-channel interference tolerance.
Super regeneration is based on an oscillator in on / off operating mode. When it is switched on, the oscillation phase is preceded by a short period of very high sensitivity. The time required for oscillation to begin is then a function of the external energy input to the oscillator (detection of an incident carrier). When it is in amplifier mode, super regeneration does not permit a class A consumption, it switches to class C as soon as the oscillations start. A high amplification of its current image therefore reproduces the variations of the incident wave constituting modulation.
Very economical structure: a single HF stage + an AOP
Very low consumption possible.
315MHz is primarily used for remote key less entry (RKE) systems and garage door openers. As a result, this frequency is somewhat crowded, increasing the chances for interference. The FCC allowed power is lower than 418MHz or 433MHz and the selection and efficiency of antennas is limited.
* 315MHz is also widely used in Asia countries, such as China.
418MHz is a good frequency to use in the US as it is not very crowded. This gives the least likely chance for interference and therefore the best performance.
* 418MHz has once been widely used in the European countries, but now more and more new products adapt a 433.92MHz frequency.
It’s a way of preventing unauthorised access to a digital code which might be transmitted via a short-range radio link to do something: open a garage door, lock or unlock a car and perhaps turn its own security system on and off – and much more.
But before we look at these terms, though, let’s go back in time to the days before code hopping and rolling code.
Short-range radio-operated control devices have been around for a couple of decades or so (at least, in any volume). The earliest ones that I remember simply used a burst of RF, at a particular frequency, with an appropriate receiver.
It’s not hard to see the shortcomings of such devices. Simply sweeping the likely band(s) with an RF generator attached to an antenna would more often than not achieve the desired result (desired for the intruder, that is).
Transmitting power: The higher power will result in a further remote distance, but also prone to cause interference with other RF devices.
Receiver sensitivity: The higher receiver sensitivity will result in a further remote distance, but also prone to cause malfunction due to interference with other RF devices.
Antenna using: For example, a stretched antenna will increase the remote distance.
Obstacles: The labeled remote distance is normally measured in open-air, line of sight distance without any interference, but often we will have obstacles such as walls, floors to greatly absorb the radio wave signals, so the remote distance will be much nearer.
Common RF remote control switch / RF relay board can be chosen from either of 3 working modes: Momentary, Latched or Toggle. These 3 working modes are either by using different 2272 decoder ICs (2272-M4 for Momentary, 2272-L4 for Latched, 2272-T4 for Toggle) or using our programmable smart RF relay board (using Jumpers and MCUs).
Short Description of Momentary/Latched/Toggle Working Modes
Single Relay Operating Modes
Momentary: Press->On; Release->Off (For single relay)
Toggle: Press->On; Press again->Off (For single relay)
Latched: Press Button A->On; Press Button B->Off (For single relay)
Relay Group Operating Modes