What is a wireless repeater?

In short a wireless repeater is a device that extends the range between a wireless transmitter and the receiver, (detector to control panel).

On some occasions, it may be necessary to install a detector   in a location where it is just too far away to trigger the alarm system reliably.  Repeaters can effectively double the range of a transmitter.

Some wireless alarm systems offer repeaters, but usually no more than one in the entire system.  The reason is that having more than one requires the repeater to operate with some level of intelligence.  If the system had more than one, you could end up with a transmission loop in which the repeaters kept talking to each other with the same message over and over.

Visonic have overcome this problem by using intelligent repeaters.  Visonic repeaters only listening to repeaters with a higher number, up to 16 repeaters can be used in the one system giving the control panel a theoretical range of 8klm.  Starting at ‘0’ for the panel, ‘1’ for the first repeater, ‘2’ for the second and so on.  They don’t need to be in a straight line, just as long as they can reach any lower numbered repeater or the panel.  It’s unlikely that any installation would require such a straight line range, but in some commercial applications where buildings are separated by lane ways and roads, repeaters can be very useful. 

It must also be remembered that each repeater, although having a small backup battery installed, must also be connected to mains power.

Repeaters are a useful tool in the installers bag, and are generally used to overcome range problems associated with the building construction, such as multiple concrete walls and floors, or remote buildings.

What is Spatial Diversity?

In brief, Spatial Diversity refers to the way a receiver is configured.  In terms of a standard wireless receiver, a Spatial Diversity receiver has two receivers and two aerial, whereas a standard receiver has one receiver and one aerial.

Two of the biggest issues facing a receiver are “Phase Nulls” and “Dead Spots”

By way of explanation, imagine dropping a stone into a pool of still water and watching how the ripples radiate out in an even expansion.  This is the transmitter.  Now select any point on the pond and place a stick there and note how even and ordered the rings are when they pass that point.  This is the receiver.  But drop the stone in the same pond but close to a wall for example, and something different happens.  As the rings radiate out from the source they can go either directly to the receiver and/or, they can bounce off the wall and then hit the stick (receiver).  As the rings (waves) from the original source and the “reflected” source meet they can cancel each other out, creating a still area, a “Phase Null”.  The only way to overcome this problem in the case of a wireless alarm system is to move either the transmitter (wireless PIR or whatever), or to move the receiver, until the phase null disappears.   The easiest and quickest way is to move the PIR.

Unfortunately this may only be a temporary fix!  Radio Frequencies (RF) can be reflected and interfere with the direct signal by any number of objects.  Steel doors, ventilation ducts, central heating ducts, fridges, ovens, metal fans, a fry pan and even sizaltion inside the walls.  If any of the objects move even the slightest amount, the receiver may end up being in a phase null from any of the detectors.

Phew!

However, there is a solution.

Spatial Diversity receivers have two aerials (separated in space) connected to two independent receivers.

It is therefore physically impossible for the receiver to be in a phase null from any transmitter at both aerials at the same time.

Now let’s look at dead spots. 

Let’s go back to the pond again.  Now place a large object in the pool like a cardboard box.  The box can have the effect of “shielding” the receiver from the transmitter, however random this might be.  It is a real problem with RF but there is a solution.  You guessed it, Spatial Diversity.  Two heads are better than one, and dead spots rarely occur with a wireless alarm system that has Spatial Diversity, unlike with standard wireless receivers.

Of course ALL Visonic wireless alarm systems have Spatial Diversity, making the installation a breeze.

So there you have it.  It might seem complicated but it’s not. 

Especially when it comes to making the installation easier and more reliable.

Next time we’ll look at wireless repeaters.

Bye for now.

Dual Technology Detectors Versus PIR Detectors

What are they and how do they work?

PIR detectors (Passive Infrared Receiver) have been around for over 25 years now, and during that time have been developed to the point where they are reliable and consistent in there operation, with negligible false alarms. Mirror optic PIR detectors are among the best.

So why would manufacturers have ventured down the “Dual Technology detector path, and how do they work?  As with many things in this world, there is a misconception that cheaper is better.  Maybe with some things, but not motion sensors for alarm systems!  Consequently PIR detectors got cheaper and false alarms increased.  Naturally, the PIR detector was to blame.  Not rteally, but the cheap ones were. 

A Dual Technology Detector combines two different technologies into the one package.

That being a PIR and a Microwave detector.

The logic behind this move it seems is that because they detect movement in two entirely different ways, and both must be triggered at the same time to activate an alarm, there will be fewer false alarms right? Wrong.

A PIR Detector is looking for a rapid change in thermal energy moving across its field of view.

A Microwave Detector on the other hand is looking for a mass moving towards or away from it.

So in theory, in order to trigger it must see something with a thermal signature and a large mass moving within its field of view.

Sounds great, but in practice dual technology sensors create more problems than they solve.

Let me explain.

A dual technology detector can be easily defeated by moving in an arc across the face of the detector (the microwave detector can not see this), or in a straight line towards the detector (the PIR detector can’t see this). So in order to be detected it must see a mass with a thermal signature moving diagonally across its field of view.

In order for this detector to actually detect, it has to have both technologies set to high sensitivity. This leads to a movement detector that is overly sensitive and can actually generate false alarms, not eliminate them.

A microwave detector has in fact an almost limitless range. If they are incorrectly located (looking towards the outside of a building instead of looking in), the microwaves can detect a large mass moving several hundred meters away, such as tucks and cars. They can also see through plaster walls and wooden floors, and detect movement outside the intended area, including fans, running water in plastic pipes. They are also easily reflected off flat metal surfaces, including building insulation into unwanted areas.

This is probably why Microwave detectors on their own have been rejected as a reliable method of detecting intruders.

On the other hand an overly sensitive PIR is just that…sensitive. This can easily lead to a situation where, on a stormy night for example, the PIR half is constantly dropping in and out of alarm due to colds winds. The microwave is being upset by the tin walls of a shed rattling or it sees something it shouldn’t, and when the two occur at the same time….false alarm.

A quality PIR motion detector will always outperform a dual technology sensor. End statement.

What is a wireless alarm?

Let’s take a closer look at Wireless Security.

So, what is a wireless alarm, and how does it work? To answer that question we to first need look at how a “hard wired” alarm system works.

A standard “hard wired” alarm system uses cables to connect and power the motion detector, it’s as simple as that. Motion detectors are typically powered directly by the control panel, which uses 12 volts DC. When the detector senses motion, the alarm is triggered through these cables. So as long as you can get a cable to the detector, it can be connected to the control panel.

The problem occurs when it’s physically impossible to get cabling to the desired detector location, or is cost prohibitive.

Did you know that over 50% of the cost of a hardwired alarm system is in the cable and the labour of installing the system? In a wireless alarm system it’s around 5%.

A wireless alarm system on the other hand replaces these cables with an “in-built” battery (to run the detector), and a wireless transmitter to get the alarm signal back to the control panel.

Broadly speaking, wireless detector batteries will last from 1 year to 5 years before needing to be replaced. As a guide, 3.6 volt Lithium battery powered detectors last the longest – up to 3 - 5 years, and detectors with 2 or 3 AA batteries the least, around 1 – 3 years. This might seem the wrong way around, but Lithium powered detectors are substantially more efficient with their power usage.

The wireless detector uses a set frequency to transmit a coded signal back to the receiver in the main control panel. Each detector in the system has its own unique 24 bit code which (in the case of a Visonic system), has in excess of 16,000,000 combinations. Once the system has “learnt” each detector's unique code, it will not listen to any other detectors in the vicinity.

Wireless security systems have in fact been around for many years, decades in fact. In the early days they were unreliable, battery hungry and generally only used as a last resort - mostly as an add on to a hard-wired alarm. They often struggled in making it from one room to another, let alone the entire house! For this reason, many security installers avoiding using them, and still do, preferring instead to use a hard wired system, even in the most difficult applications. However, wireless security has come a long way since those early days, with complete top to bottom systems now available. What I mean by this is that ALL components are wireless. Recent innovations in battery development now allow power hungry components such as internal and external wireless sirens to be fully wireless.

Wireless alarm systems now have excellent wireless ranges, in some cases exceeding 500m line-of-sight (LOS). LOS means that the measurement is taken without obstacles between the transmitter and the receiver, in an open field situation. This is a good indicator on how well the system will then perform indoors. In some cases they can comfortably cover expansive multi storey homes and buildings etc..

Wireless alarm systems are not only extremely reliable and afforable, they can offer features and benefits way beyond a hard wired alarm system.