GE MDS DS-EL806-24 2.4 GHz TransNet User Manual xxxxA TNET2 4 OEM Body

GE MDS LLC 2.4 GHz TransNet xxxxA TNET2 4 OEM Body

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Contents

Users Manual Part 3

18 TransNET OEM 2.4 Integration Guide MDS 05-xxxxA01, Rev. 01

4.0 EVALUATION BOARD DOCUMENTATION

This section contains an assembly drawing and parts list for the OEM

Evaluation Board. In addition, a separate foldout schematic of the Board is

included at the back of this manual. Board documentation is provided to assist

integrators who need to create compatible interface circuitry between the

OEM transceiver and host equipment.

NOTE: The foldout schematic may also be accessed from the TransNET Support

Package CD, or from our website at: www.microwavedata.com.

4.1 Assembly Drawing

Invisible place holder

Figure 14. Evaluation Board Assembly Diagram

4.2 Parts List

Table 6 lists the electronic components used on the Evaluation Board.

Table 6. OEM Evaluation Board Parts List

Ref. Desig. Part Description

CR1 DIODE, SOT23 SMALL SIG 914 5D

CR4 CR5 CR6 RECTIFIER, 30V B13

CR2 CR3 DIODE, SCHOTTKY POWER, SMT, SNGL, UPS840

Q1 Q2 TRANSISTOR, SOT23 NPN 6429 M1LR

C8

R10

R3

C26

R9

C9

C4

C1

C20

C18

C19

R5

TXD

GND

R11

NA

A

C

CR1

R7

C23

C24

C10

C7

+

C30

R4

R8

CTS

REG_PWR

C13

ALARM

C29

C11

C2

C5

C3

o

28

U1

C31 C6

16

J4

CR2

C16

1

5U4

51U5

R6

R12

RTS K2

<

CR4

<

CR5

R15

C21

C17

R13

C14

+

C12

DIAG_RXD

DIAG_TXD

GND

SLEEP

CR3

FH1

B

E

C

Q1

B

EQ2

C

R14

C15

C22 C25

RXD

UNREG_PWR

K3

K1

SHUTDN

DCD

LED

<

CR6

o

U3

o

1

U2

16 15

21

J2

21

J1

9

51

6

J5

L1

1

J3

MDS 05-xxxxA01, Rev. 01 TransNET OEM 2.4 Integration Guide 19

U4 U5 IC, LINEAR SC70-5 COMPARATOR SNGLE LMV33

U1 IC, IN'FACE SSOP28 RS-232 TXVR SP3238E

U3 IC, IN'FCE 20PIN TSSOP DRIVER SP3222

U2 IC, SWITCHING REG'R ADJ.4.5A LT1374HVIR

K1 K2 K3 RELAY, DPDT

R10 RESISTOR, CHIP 0603 1/16W 5% 2.2K

R4 R5 R13 R14 RESISTOR, CHIP 0603 1/10W 1% 10K

R12 RESISTOR, CHIP O603 1/10W 1% 100K

R7 R9 RESISTOR, CHIP 0603 1/10W 1% 1.5K

R11 RESISTOR, CHIP O603 1/10W 1% 1.82K

R3 RESISTOR, CHIP 0603 1/10W 1% 22.6K

R15 RESISTOR, CHIP O603 1/10W 1% 31.6K

R8 RESISTOR, CHIP 0603 1/10W 1% 470 OHM

R6 RESISTOR, CHIP O603 1/10W 1% 6.81K

C12 CAP, TANT 7343 20% 10V 100uf

C6 C7 C9 C10

C11 C29 C31 CAP, CHIP 0603 50V NPO 5% 100pf

C1 C2 C3 C4 C5

C17 C18 C19

C20 C21 C22

C23 C24 C25

C26 C8

CAP, CHIP 0603 X7R 10% 0.1uF

C13 CAP, CHIP 0603 X7R 10% 470 pf

C14 CAP, CHIP 0603 X7R 10% 4700pF

C15 Capacitor, Low ESR Chip Ceramic, 1210 22uF

C16 Capacitor, Low ESR Chip Ceramic, 1210 4.7

L1 INDUCTOR, SWITCHING, 20%, 10uH

J1 CONN, HEADER, .100 DUAL STR 4-PIN

P/O J1 1-2, P/O

J1 3-4

CONN, JUMPER

FH1 FUSE HOLDER, PCB SMT W/2A SLO-BLO FUSE

Table 6. OEM Evaluation Board Parts List (Continued)

20 TransNET OEM 2.4 Integration Guide MDS 05-xxxxA01, Rev. 01

4.3 Evaluation Board Fuse Replacement

The Evaluation Board is protected by a 2 ampere fuse. The fuse can be blown

by an over-current condition caused by an internal failure or over-voltage.

Follow the procedure below to remove and replace the fuse:

1. Disconnect the primary power cable and all other connections to the

Evaluation Board.

2. Locate the fuse holder assembly, FH1, behind the green power connector,

J3.

3. Loosen the fuse from the holder using a very small screwdriver, then use

a small pair of needle-nose pliers to pull the fuse straight up and out of

the holder.

4. Use an ohmmeter or other continuity tester to verify that the fuse is open.

5. Install a new fuse in the holder. Replacement fuse information: Littelfuse

#0454002; 452 Series, 2 Amp SMF Slo-Blo fuse (MDS Part No.

29-1784A03).

J2 CONN, HEADER, PC MOUNT .078, DUAL, 16 PIN

Samtec TW Series, Part No: ASP 103812-01

(Mates with J3 on the OEM radio transceiver)

J3 CONN, TERM STRIP, 5MM PCB

J4 CONN, TELE JACK 6POS 6CON RT A SMT W/F

J5 CONN, D-SUB, PCB RCPT 90 DEGREE, 9 PIN

Table 6. OEM Evaluation Board Parts List (Continued)

MDS 05-xxxxA01, Rev. 01 TransNET OEM 2.4 Integration Guide 21

5.0 TRANSCEIVER MOUNTING

This section provides information for mounting the OEM transceiver in a host

device. The module need only be protected from direct exposure to the

weather. No additional RF shielding is required.

5.1 Mounting Dimensions

Figure 15 shows the dimensions of the transceiver board and its mounting

holes. If possible, choose a mounting location that provides an unobstructed

view of the radio’s LED status indicators when viewing the board from

outside the host device.

Mount the transceiver module to a stable surface using the four mounting

holes at the corners of the PC board. Standoff spacers should be used to

maintain adequate clearance between the bottom of the circuit board and the

mounting surface. (Fasteners/anchors are not normally supplied.)

Figure 15. Transceiver Mounting Dimensions

5.2 Antennas & Feedlines

A number of omnidirectional and directional antennas are available for use

with the radio. Contact your factory representative for specific

recommendations on antenna types and hardware sources. In general, an

omnidirectional antenna (Figure 16) is used at master station sites in order to

provide equal coverage to all of the remote units.

3.11”

(7.9 cm)

1.49˝

(3.8 cm)

0.63”

(16 mm)

1.81˝

(46 mm)

3.45”

(87.5 mm)

Top View

Side View

22 TransNET OEM 2.4 Integration Guide MDS 05-xxxxA01, Rev. 01

At remote sites and in many point-to-point systems, a directional Yagi

antenna (Figure 17) is generally recommended to minimize interference to

and from other users and to maximize range.

For systems operating in a very short range environment, small, flexible whip

antennas may also be supplied. Such antennas are available for direct

connection to the transceiver module, or for exterior mounting with various

lengths of feedline.

Invisible place holder

Figure 17. Typical Yagi Antenna (shown mounted to mast)

Feedlines

The feedline supplied with the antenna was carefully selected to minimize RF

loss and ensure regulatory compliance with the antenna being used. Do not

make substitutions or change the lengths of the antenna system feedline. If

you require a different length of feedline for your installation, contact your

factory representative for assistance.

NOTE: Strong fields near the antenna can interfere with the operation of the low level

RTU circuits and change the reported values of the data being monitored. If in-

terference is experienced, it may be necessary to re-orient the antenna with re-

spect to the radio, RTU, sensors or other components of the system.

Figure 16.

Omnidirectional Antenna

(shown mounted to mast)

MDS 05-xxxxA01, Rev. 01 TransNET OEM 2.4 Integration Guide 23

6.0 EIRP Compliance Check

IMPORTANT: To comply with FCC and Industry Canada rules, the effective

isotropic radiated power (EIRP) of an OEM transceiver installation must not

exceed 36 dBm.

Transceiver modules are shipped from the factory with an RF output setting

of +27 dBm. This setting is password-controlled and may not be changed by

unauthorized persons. This power level provides EIRP compliance when the

module is used with many types of antennas, however, each installation must

be carefully evaluated to ensure compliance. The formula for determining

EIRP is as follows:

Transmitter RF output power (dBm) + Antenna gain (dBi) – Feedline loss (dB)

Table 7 shows three types of antennas and their associated gains. Note that for

a 10 dBi gain antenna, the system must include at least 1 dB of feedline loss

to achieve EIRP compliance. Higher gain antennas would require additional

feedline loss in order to limit the EIRP to a maximum of 36 dBm.

If no feedline is used (directly connected antenna), with an antenna gain

exceeding 9 dBi, it will be necessary to reduce the transmitter output power

to less than +27 dBm. Contact MDS for further information. In no case shall

the station’s EIRP exceed 36 dBm.

7.0 OPTIMIZING PERFORMANCE

After the basic operation of the radio has been checked, you may wish to

optimize its performance using some of the suggestions given here. The

effectiveness of these techniques will vary with the design of your system and

the format of the data being sent.

Complete instructions for using the commands referenced in this manual are

provided in “PROGRAMMING REFERENCE” on Page 34.

Table 7. Antenna System Gain vs. EIRP

Antenna Type

(Model No.) Gain

(dBi)

Transmitter

Power Setting

(dBm)

EIRP

(dBm)

1/2 Wave Whip Dipole

(MHWS2400MSMA) 2 +27 29

Omni-directional Base Station

(MFB24010) 10* +27 37*

Yagi Directional (MYP24010PT) 10* +27 37*

* These antenna systems must include a feedline loss of at least 1 dB to maintain

compliance with the EIRP limit of 36 dBm.

24 TransNET OEM 2.4 Integration Guide MDS 05-xxxxA01, Rev. 01

7.1 Antenna Aiming

For optimum performance of directional antennas (yagis), they must be

accurately aimed in the direction of desired transmission. The easiest way to

do this is to point the antenna in the approximate direction, then use the

remote radio’s RSSI command (Received Signal Strength Indicator) to further

refine the heading for maximum received signal strength.

In an MAS system, RSSI readings are only meaningful when initiated from a

remote station. This is because the master station typically receives signals

from several remote sites, and the RSSI would be continually changing as the

master receives from each remote in turn.

7.2 Antenna SWR Check

It is necessary to briefly key the transmitter for this check by placing the radio

in the SETUP mode (Page 49) and using the KEY command. (To unkey the

radio, enter DKEY; to disable the SETUP mode and return the radio to normal

operation, enter Q or QUIT.)

The SWR of the antenna system should be checked before the radio is put into

regular service. For accurate readings, a wattmeter suited for 2.4 GHz is

required. One unit meeting this criteria is the Bird Model 43 directional

wattmeter with an appropriate element installed.

The reflected power should be less than 10% of the forward power (≈2:1

SWR). Higher readings usually indicate problems with the antenna, feedline

or coaxial connectors.

7.3 Data Buffer Setting

The default setting for the data buffer is OFF. This allows the radio to operate

with the lowest possible latency and improves channel efficiency. MODBUS

and its derivatives are the only protocols that should require the buffer to be

turned on. See “BUFF [ON, OFF]” on Page 42 for details.

7.4 Hoptime Setting

The default hop-time setting is 7 (7 ms). An alternate setting of 28 is used to

increase throughput, but at the cost of increased latency. A detailed

explanation of the HOPTIME command can be found on Page 44.

7.5 Operation at 115200 bps

Burst throughput at 115200 bps is supported at all settings. The radio will

always buffer at least 500 characters. Sustained throughput at 115200bps is

only possible when the data path is nearly error free and the operating settings

have been properly selected. For sustained operation at 115200 bps, use the

following settings: SAF OFF, FEC OFF, REPEAT 0, RETRY 0, HOPTIME 28.

MDS 05-xxxxA01, Rev. 01 TransNET OEM 2.4 Integration Guide 25

7.6 Baud Rate Setting

The default baud rate setting is 19200 bps to accommodate most systems. If

your system will use a different data rate, you should change the radio’s data

interface speed using the BAUD xxxxx abc command (Page 42). It should be

set to the highest speed that can be sent by the data equipment in the system.

(The transceiver supports 1200 to 115200 bps.)

7.7 Radio Interference Checks

The radio operates in eight frequency zones. If interference is found in one or

more of these zones, the SKIP command (Page 49) can be used to omit them

from the hop pattern. You should also review 8.0 DEALING WITH

INTERFERENCE, when interference problems are encountered.

8.0 OPERATING PRINCIPLES & SPECIAL

CONFIGURATIONS

8.1 How Remotes Acquire Synchronization

Remotes acquire synchronization and configuration information via SYNC

messages sent from the Master (the MODE M unit) or from any valid

Extension (MODE X unit).

The Master will always transmit SYNC messages. An Extension will only

start sending SYNC messages after synchronization is achieved with its

Master.

The ability to synchronize to a given radio is further qualified by the sender’s

Extended Address (XADDR) and by receiver’s Synchronization Qualifiers

(XMAP, XPRI, and XRSSI).

When a primary is specified (XPRI is 0...31), a radio will always attempt to

find the primary first. If 30 seconds elapses and the primary is not found, then

the radio will attempt to synchronize with any non-primary radio in the XMAP

list.

Once every 30 minutes, if a primary is defined, the radio will check its

synchronization source. If the radio is synchronized to a unit other than the

primary, then the current RSSI value is compared to the XRSSI value. If RSSI

is less than XRSSI (or if XRSSI is NONE) the radio will force a

loss-of-synchronization, and hunt for the primary again (as described in the

previous paragraph).

By default, Extensions (and the Master) begin with XADDR 0.

Synchronization qualifiers are set to XMAP 0, XPRI 0, and XRSSI NONE,

respectively. This default configuration allows any radio to hear the Master.

When an Extension is added, the extended address of the Extension must be

set to a unique value. All remotes that need to hear that extension can specify

this either by designating the extension as the primary (XPRI), or by including

it in their list of valid synchronization sources (XMAP).

26 TransNET OEM 2.4 Integration Guide MDS 05-xxxxA01, Rev. 01

8.2 Establishing a Tail-End Link

A tail-end link can be used to bring an outlying remote site into the rest of an

MAS network. Figure 5 on Page 5 shows a diagram of this type of system.

A tail-end link is established by connecting an OEM transceiver

“back-to-back” with another unit such as a licensed MDS x710 Series

transceiver. The wiring connections between the two radios must be made as

shown in Figure 18. In addition, the DEVICE CTS KEY command must be

asserted at the OEM radio.

Figure 18. Data Crossover Cable for Tail-End Links

8.3 Store & Forward (SAF) Operation with Extension

Radios

The Store-and-Forward (SAF) capability allows individual radios to act as

data repeaters. SAF operates by dividing a network into a vertical hierarchy

of two or more sub-networks. (See Figure 6 on Page 6.) Adjacent

sub-networks are connected via Extension radios operating in “MODE X”

which move data from one sub-network to the next one.

The Store-and-Forward implementation adheres to the general polling

principles used in most multiple-address systems (MAS). Polls originate from

the Master station, broadcast to all radios within the network, and travel

hierarchically downward. All Remotes will hear the same message, but only

one Remote will respond. Messages within a hierarchy only travel in one

direction at a time.

Using SAF will cut the overall data throughput in half, however, multiple

networks can be inter-connected with no additional loss in network

throughput.

If required.

RXD

TXD

GND

RTS

3

2

7

4

DCE

DB-25

MDS x710 Series

Remote Transceiver

(or device requiring keyline)

TXD

RXD

GND

CTS

10

14

5

DCE

16-pin header (J3)

TransNET OEM

Remote Transceiver

(DEVICE CTS KEY)

16

MDS 05-xxxxA01, Rev. 01 TransNET OEM 2.4 Integration Guide 27

Simple Extended SAF Network

Figure 19 depicts a two-level network utilizing a single Master (M) and an

Extension (X) radio. In this network, messages directed to Remotes in the

“K” sub-network, will be relayed through Extension radio Xj,k to the

K-Remotes. Any response from a Remote in sub-network “K” will pass back

through Extension radio Xj,k to the Master Mj. Radios in sub-network “J”

operate on the same set of frequencies and sub-network “K” but with a

different radio-frequency hopping pattern.

Invisible place holder

Figure 19. Simple Extended SAF Network

Networks: J and K

In the SAF operation, the Extension radios are set to MODE X

(Details page 45) and operate with a “dual personality”—50% of the time

they serve as a Remote station and 50% of the time as a Master for

sub-network Remotes.

Extended SAF Network

Below is an example of a multilevel network utilizing two repeaters—XJ,K

and XK,L. The example demonstrates the extensibility of the network. In this

case, messages directed to Remotes in the sub-network L will be relayed

through Extension radios XJ,K and XK,L. As in the previous example, the

Extension radios will split their operating time equally between their Master

and Remote personalities. This multi-layered network can be extended

indefinitely without degrading system throughput beyond that initially

incurred by placing the network in the SAF mode.

MJ

RJ

RJXJ,K

RJ

RKRRKK

Sub-Network J

Sub-Network K

28 TransNET OEM 2.4 Integration Guide MDS 05-xxxxA01, Rev. 01

Invisible place holder

Figure 20. Extended SAF Network

Networks: J, K, L

Retransmission and ARQ operation

Functionally, the sub-network side of an Extension behaves like a

corresponding connection between a master and a remote.

When an Extension is using its “master personality” it sends

acknowledgments and performs unconditional retransmissions based on its

REPEAT count.

When an Extension is using its “Remote personality”, acknowledgments are

processed and retransmissions occur as needed, up to the number of times

specified by the RETRY count value.

If new data arrives—from a new source—prior to completion of

retransmissions, then this is considered a violation of the polling model

protocol. The new data takes precedence over the old data and the old data is

lost. In such a situation, new data is likely to be corrupt as it will have some

old data mixed in with it.

Synchronization in SAF Networks

The Master controls the synchronization for a given network for all modes.

Setting the Master to “SAF ON” broadcasts a command from the Master to all

radio units in the associated network either directly or through an Extension

radio. This command puts all radios in the entire system in a special

time-division duplexing mode that alternates between two timeslots. One

time slot for data communications upstream and another for downstream

communications.

XK,L

RL

RL

MJ

RJ

RJXJ,K

RJ

RKRK

RL

Sub-Network J

Sub-Network K

Sub-Network L

MDS 05-xxxxA01, Rev. 01 TransNET OEM 2.4 Integration Guide 29

The Extensions are single radios which serve as bridges between adjacent

sub-network levels. Extensions will undertake a “remote” personality in one

timeslot, and a “master” personality in the alternate timeslot and provide

communications with associated Remotes downstream. Extensions behave

like two radios with their data ports tied together, first synchronizing with

their upstream Master during their Remote personality period, and then

providing synchronization signals to dependent Remotes downstream during

its Master personality period.

All Remotes synchronize to a corresponding Master. This can be the “real

master” (the MODE M unit), or it can be a repeater “Extension” that derives

synchronization from the “real master.”

Payload polls/packets broadcast from the network Master will be repeated to

all levels of the network, either directly to Remotes, or through network

repeaters—the Extensions station. The targeted Remote will respond to the

poll following the same path back to the Master.

Configuration Parameters for Store-and Forward Services

The installation and configuration of a network with an Extension using SAF

is straight-forward with only a few unique parameters that need to be

considered and set at each unit.

In every network there can be only one Master station. It will serve as the sole

gateway to the outside world. The following three tables detail the parameters

that will need to be set on each type of radio in the network.

• Network Master Radio—Table 8 on Page 29

• Extension Radio(s)—Table 9 on Page 30

• Remote Radio(s)—Table 10 on Page 31

Table 8. Configuration Parameters for SAF Services

Network Master Radio

Parameter Command Description

Operating Mode MODE M

Details page 45 Set the radio to serve as a

Master

Network Address ADDR

Details page 40 A number between 1 and

65,000 that will serve as a

common network ad-

dress.

All radios in the network

use the same number.

30 TransNET OEM 2.4 Integration Guide MDS 05-xxxxA01, Rev. 01

Extended Address XADDR

Details page 51 A number between 0 and

31 that will serve as a

common address for radi-

os that synchronize di-

rectly to this master.

Typically, the Master is

set to zero (0).

Store and Forward

Mode SAF ON

Details page 49 Enables store and for-

ward capability in the net-

work.

Table 9. Configuration Parameters for SAF Services

Extension Radio(s)

Parameter Command Description

Operating Mode MODE X

Details page 45 Set the radio to serve as an

Extension

Network Address ADDR

Details page 40 A number between 1 and

65,000 that will serve as a

common network address.

All radios in the network use

the same number.

Extended Ad-

dress XADDR

Details page 51 A number between 0 and 31

that will serve as a common

address for radios that syn-

chronize directly to this Ex-

tension radio serving as

master for associated

sub-network units.

We recommend using zero

(0) for the Master station.

Primary Extended

Address XPRI

Details page 51 XADDR number of the pri-

mary or preferred radio with

which this radio will synchro-

nize.

Extension Map XMAP

Details page 51 Functional list of all XADDR

values with which this radio

can synchronize, excluding

the XPRI address

Extension

Received Signal

Strength Indicator

XRSSI

Details page 51 The minimum RSSI level re-

quired to preserve synchro-

nization with a non-primary

radio. (Ineffective when

XPRI is NONE)

Table 8. Configuration Parameters for SAF Services

Network Master Radio (Continued)

Parameter Command Description

MDS 05-xxxxA01, Rev. 01 TransNET OEM 2.4 Integration Guide 31

8.4 Sleep Mode Operation (Remote units only)

In some installations, such as at solar-powered sites, it may be necessary to

keep the transceiver’s power consumption to an absolute minimum. This can

be accomplished using the radio’s Sleep Mode feature. In this mode, power

consumption is reduced to about 8 mA.

Sleep Mode can be enabled under RTU control by asserting a ground (on Pin

6 of J3, the radio’s header connector. The radio stays in Sleep Mode until the

low is removed, and all normal functions are suspended.

The radio can be “awakened” by your RTU every minute or so to verify

synchronization with the master station. When the ground is removed, the

radio will be ready to receive data within 75 milliseconds.

NOTE: The SLEEP function must be set to ON; otherwise a ground on the Sleep Mode

pin will be ignored.

Table 10. Configuration Parameters for SAF Services

Remote Radio(s)

Parameter Command Description

Operating Mode MODE R

Details page 45 Set the radio to serve

as a Remote station

Network Address ADDR

Details page 40 A number between 1

and 65,000 that will

serve as a common

network address or

name.

Same number for all

units in the same net-

work.

Primary Extended

Address XPRI

Details page 51 XADDR number of the

primary or preferred

radio with which this

radio will synchronize.

Extension Map XMAP

Details page 51 A list of all XADDR val-

ues with which this ra-

dio can synchronize,

excluding the XPRI

address

Extension

Received Signal

Strength Indicator

XRSSI

Details page 51 The minimum RSSI

level required to pre-

serve synchronization

with a non-primary ra-

dio. (Ineffective when

XPRI is NONE)

32 TransNET OEM 2.4 Integration Guide MDS 05-xxxxA01, Rev. 01

It is important to note that power consumption will increase somewhat as

communication from the master station degrades. This is because the radio

will spend a greater period of time “awake” looking for synchronization

messages from the master radio.

In order for the radio to be controlled by the Sleep Mode pin, the radio must

be set to SLEEP ON. See “SLEEP [ON, OFF]” on Page 50 for more

information.

Sleep Mode Example

The following example describes Sleep Mode implementation in a typical

system. Using this information, you should be able to configure a system that

meets your own particular needs.

Suppose you need communications to each remote site only once per hour.

Program the RTU to raise an EIA/RS-232 line once each hour (DTR for

example) and wait for a poll and response before lowering it again. Connect

this line to Pin 6 of the radio’s header connector. This will allow each RTU

to be polled once per hour, with a significant savings in power consumption.

9.0 DEALING WITH INTERFERENCE

The transceiver shares the frequency spectrum with other services and other

Part 15 (unlicensed) devices in the USA. As such, near 100% error free

communications may not be achieved in a given location, and some level of

interference should be expected. However, the radio’s flexible design and

hopping techniques should allow adequate performance as long as care is

taken in choosing a suitable location and in configuring the radio’s operating

parameters.

In general, keep the following points in mind when setting up your

communications network:

1. Systems installed in rural areas are least likely to encounter interference;

those in suburban and urban environments are more likely to be affected

by other devices operating in the license-free frequency band and by

adjacent licensed services.

2. If possible, use a directional antenna at remote sites. They conﬁne the

transmission and reception pattern to a narrow lobe, which minimizes

interference to (and from) stations located outside the pattern.

3. If interference is suspected from a nearby licensed system (such as a

paging transmitter), it may be helpful to use horizontal polarization of all

antennas in the network. Because most other services typically use

vertical polarization in this band, an additional 20 dB of attenuation to

interference can be achieved by using the horizontal plane.

4. Multiple spread spectrum systems can co-exist in close proximity to each

other with only minor interference, provided they are each assigned a

unique network address. Each network address has a different hop pattern

associated with it.