Telex 38109-977 Modern Day Wireless Intercoms, First beltpack based wireless intercom system

Figure 6.1 The first beltpack based wireless intercom system.

RECEIVER

FOR

WALK

AROUND

1

TRANSMITTER	2	3	4
FOR
WALK
AROUND
1

TRANSMIT ANTENNA	RECEIVER
TO ALL	ANTENNA FROM
WALK AROUND RX’S	WALK AROUND TX’S

		ANTENNA SPLITTER
COMMON TX	RX	RX	RX	RX
FOR ALL
WALK AROUND	FOR	FOR	FOR	FOR
PACKS	WALK	WALK	WALK	WALK
	AROUND	AROUND	AROUND	AROUND
	1	2	3	4

Each user station in the system consisted of two beltpacks, one for transmit and one for receive. Two beltpacks were necessary to combat the phenomenon know as desensing, where a transmitter in close proximity to a receiver causes the receiver to have greatly reduced sensitivity. Desensing is discussed in greater detail in a future section. Each wireless user’s transmitter was on a unique frequency which corresponded to their own receiver in the base station. All of the wireless users’ receivers were tuned to the same frequency which corresponded to the single base transmitter. A single headset with a split feed cable eliminated the need for an external headset interface box. See Figure 6.1. By utilizing this system, each wireless user could communicate to both hardwired and wireless intercom users in a full duplex mode.

This system, at long last, provided engineers with a reliable and functional solution to the wireless communications problem. Future systems would combine the transmit and receive beltpacks and incorporate numerous interfacing and operational advantages. We look at some of these in the next section.

Modern Day Wireless Intercoms

Today’s wireless intercom systems are technological giants compared to their earlier predecessors. They allow users to “cut the cable” of hardwired party-line systems and move about freely within the system’s operational range. Modern wireless intercoms can be either party-line intercom systems or individual beltpack systems that allow users to operate independently from other wireless users. Good quality systems can be seamlessly attached to existing hardwired communications systems commonly used in broadcast and other facilities. As discussed previously, modern, high quality wireless intercoms offer a distinct advantage over traditional, two-way radios in that they offer a more natural full-

C h a p t e r 6 - I n t r o d u c t i o n t o W i r e l e s s I n t e r c o m S y s t e m s 87