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.