Howto:Using external antennas to obtain sync in difficult spots

Summary

In an IP1200 system, all radios must be synced and thus form a sync chain. In certain scenarios, it is difficult to provide a reliable sync source though. In such cases, external antennas attached to repeaters may help.

Applies To

This information applies to

• IP 1200

More Information

Problem Details

In order for an IP1200 system to work properly, all radios must be synchronized. This is done by providing a reliable sync source for all but one radio (for details, see Rules for successful IP1200 deployment).

To find a good sync source, there must be another radio “in-sight” that can provide reliable sync through the air. Although a lower signal strength is required to obtain sync from a signal than what is required to actually provide a bearer channel for a voice call, it can be difficult in times to find a reliable sync source.

Consider the following example:

Let us assume that Base B is the sync master. Let us assume further that the opening in the wall between A and B actually is a sliding door which is closed at times. In this scenario, providing proper sync to R (and thus A) is difficult, as when the door closes or is covered by objects moving through the door, B’s signal seen at R will be poor.

To work around, you may attach an external antenna to R and install it on the other side of the wall as shown below. R can now obtain its synchronization from B in a reliable fashion and A may sync to R (and thus B) as well.

Another difficult situation arises when sync or coverage is required that is far away from the next available radio. Consider the following scenario where area B needs coverage:

Area B is entirely out of base A’s coverage area. On the other hand, even if a repeater R1 is placed at the farmost edge of A's coverage area, area B is still out of reach. It can thus not be covered by simply installing a repeater. Instead, 2 repeaters and 2 external antennas are used. R1 picks up the signal from A. The 2 external antennas attached to R1 and R2 will provide the signal to R2 and R2’s standard (built-in) antenna will provide coverage to area B. This works because external antennas are directed. Be sure to always mount the antennas so that they face its peer!

The allowable distance between R1 and R2 (more precisely, between their external antennas) largely depends on the environmental conditions. However, a few hundred meters may easily be achieved. Make sure you do a proper deployment for such scenarios too and take into account that the received signal strength in an outdoor situation depends - amongst other things - on the weather conditions. Heavy rain for example will degrade the signal.

Also, keep in mind that external antennas are not meant for coverage. This is because coverage should be provided by 2 antennas with 90° polarisation for antenna diversity. Such pair is built-in to any repeater or base. Antenna diversity provides for improved reliability when handsets are moved within the coverage area.

When an external antenna is attached to a repeater, all three antennas (the 2 built-in plus the external) are in operation. This is why R1 can pick up the signal from base A and R2 can provide coverage to area B while picking up the remote signal from R1 in the above example.

Please note that in this scenario, there is no handover from B to A as the handset will likely loose signal when walking from area B to A's coverage area anyway. Because of this, you may also consider installing just a single IP1200 to cover area B. Ths IP1200 would then have no sync to A (in fact, no sync at all). However, as handover from area B to A is anyway not feasible, this is not a real problem. This IP1200 would still use the same IP-master though to deliver calls into the same PBX.

Order Information

External antennas are available only on new full-slot repeaters. Full slot repeaters shipped previously cannot work with an external antenna. Make sure there is the original Kirk/Polycom part number 0244 1600 or 0244 1601 on the repeater if you intend to connect an external antenna. The external antenna itself has to be ordered separately, innovaphone order code 50-00999-018.