rf fundamentals pcom

7/30/2019 RF Fundamentals Pcom

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EI071097-1 Product Training

PRESENTATONon

RF, Environment & PathCalc

forP-Com

AirLinks

toTULIP SOFTWARE (P) LTD

NEW DELHI


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AGENDA

RF SIGNAL PATH FUNDAMENTALS

ENVIRONMENTAL CONSIDERATIONS

PATH PLANNING AND CALCULATIONS

Q & A, DISCUSSION


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RF Signal Path Fundamentals


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What is a Path ?

Antenna to Antenna.

Line of sight and appropriate distance.

Free Space.

No path obstructions


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Earth Bulge

Earth curvature.

Antenna height


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Fresnel Zones

I st Fresnel Zone

Mid-Path


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Fresnel Zones

Radio signals spread to occupy a broad cross-sectional

area of space as they travel. It can be visualised as a fat

cigar or zeppelin-shapedregion that extends from one

antenna to the other. This region is known as the FirstFresnel Zone (FFZ), and is always thickest at the mid-

point in the path between the two antennas.

The FFZ thickness or girth is a function of path length;the longer the path, the broader the Fresnel Zone.



Fresnel Zones & Earth Bulge

The practical ramification of the Fresnel zone is that a

path greater than 11 km that appears to be LOS path

may not be adequate for radio signals because the

earth bulge may obstruct too much of the signal.

To avoid this obstruction, the antennas must be high

enough to allow the FFZ to clear the earth bulge. In

practice, it has been found that if only 60% of theFresnel zone is clear of obstructions, it is essentially

equivalent to a clear Fresnel zone.



Fresnel Zone and Earth Bulge (Contd)

The criteria used to calculate FFZ is as follows :-

H = 43.3 x (D/4F)

D = Path distance in miles

F = Freq in GHz H = Height in feet.



Fresnel Zone and Earth Bulge

H = D/8 + 43.3(D/4F)

43.3*(D/4F) 1/2

60% First Fresenel

D 2 /8

Earth Bulge

D = Distance Betwen Antennas

H



Minimum Antenna Height

H = (D/8) + 43.3 (D/4F)

H = Antenna Height in feet

D = Path Distance in miles

F = Freq in GHz



OPTIMUM ANTENNAHEIGHTS vs. DISTANCE ( at 2.45 GHz)

These antenna heights are minimum for free space loss for 2.45 GHz, smooth earth

curvature. And grazing 60% of the first Fresnel zone. If there are trees, hills,

or large building in the path, then a more a detailed analysis of the path must be

calculated, or the path must be measured with two RF modems.

Free Space Loss

130 dB

Free Space Loss

128 dB

Free Space Loss

124 dB

Free Space Loss

118 dB

Free Space Loss

104 dB

ONE MILE

FIVE MILE

TEN MILE

FIFTEEN MILE

TWENTY MILE

* Height is in Feet

112 82 56 34 14

14 34 56 82 112



OPTIMUM ANTENNAHEIGHTS vs. DISTANCE ( at 5.75 GHz)

These antenna heights are minimum for free space loss for 5.75 GHz, smooth earth

curvature. And grazing 60% of the first Fresnel zone. If there are trees, hills,

or large building in the path, then a more a detailed analysis of the path must be

calculated, or the path must be measured with two RF modems.

Free Space Loss

130 dB

Free Space Loss

128 dB

Free Space Loss

124 dB

Free d Bs

118 dB

Free Space Loss

104 dB

ONE MILE

FIVE MILE

TEN MILE

FIFTEEN MILE

TWENTY MILE

* Height is in Feet

91 63 41 24 10 10 24 41 63 91



RF Signal Propogation

Reflection

Refraction

Diffraction

Absorption



Interference

In-band interference

Out-of-band interference



Dealing with Interference

Use Spectrum Analyser

External, supplemental bandpass filters - for out-of-band

interference.

Correct antenna choice - High gain directional antennas

to enhance desired signals.

Cross-polarised antennas



Antennas

Directional Antennas

Yagi

Sold Parabolic

Semi Parabolic

Omni-directional antennas



Antennas

Axis of Best Omni Performance

Omnidirectional Antenna

Side View

Signal coming into Omni Off axis

because remote site antenna is

too close or to too low with respest

to the positioning of the omni.

YAGI Antenna at Remote Air Link Site

Side View


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Antenna Lobes

Side lLobe

Main Lobe

OMNI TOP VIEWSIDE VIEW

Side Lobe

Main Lobe

Side View YAGI DIRECTIONAL

Top View

Main Lobe

Side Lobe


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Antennas Used with AirLink Modems

S-Band

Omni-directional, 0dBi Gain, 360deg 3dB Beam Width

Omni-directional, 7dBi Gain, 360deg 3dB Beam Width

Directional-Semi Parabolic, 24dBi Gain, 8 deg 3db Beam Width

C-Band

Directional-Solid Parabolic 2, 28 dBi Gain, 6deg 3dB Beam Width Directional-Solid Parabolic 4, 34 dBi Gain, 3deg 3dB Beam Width


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Antenna Frequency & Bandwidth

Antennas are tuned to operate within a band of

frequencies.

The band of frequencies determines the antennas

bandwidth.

A t Ali t


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Antenna Alignment

The goal of antenna alignment is to ensure that the

main radiation lobe of each antenna is accurately

pointed at the other.

The basic approach is to move each antennas direction

of aim until a peak reading is obtained on the AirLinks

RSSI or RSQ indicator. This procedure should beperformed for both antennas of the link.

On shorter links, the RSSI/RSQ indication may

saturate, making the peak indication difficult to discern.Saturation can be avoided, and a sharper peak

obtained, by temporarily decreasing the tranmit power

of the units.


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RF Bands/Channels/Bandwidths

AirLinks are currently available in two bands:

S-Band (2.4000 to 2.4835 GHz)

C-Band (5.7250 to 5.8500 GHz)

S-Band is divided into Channels, C-Band is one

Channel

The number of available channels in a given banddepends on the links occupied bandwidth, which-in

turn-depends on the data rate.


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RF Bands/Channels/Bandwidths

Model Tx Bandwidth

AL 64 5.1 MHz

AL 128 10.2 MHz

AL 256 20.5 MHz

AL 384 30.7 MHzAL 512 41.0 MHz

E1 120.0 MHz


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S-Band RF Bands/Channels/Bandwidth64 and 128 kbps

Available 64 kbps Modem

Available 128 kbps Modem

2400 2483.5

2400 2483.5

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

1 2 3 4 5 6 7


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S-Band RF Bands/Channels/Bandwidth256, 384, and 512 Kbps

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

1 2 3 4 5 6 7 8 9 10 11 12 14 15 16

256 Kbps

384 Kbps

512 Kbps


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Bandwidth vs Beamwidth

Bandwidth and Beamwidth are two entirely different

concepts.

Bandwidth refers to the operating frequency range of the antenna

(or radio)

Beamwidth refers to the size and shape of the radiation lobe of

the antenna.


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Horizontal and VerticalPolarization

Vertical Polarization Horizontal Polarization


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Horizontal and Vertical Polarization

Polarization is the orientation of the signal as it travels

through space. Typically, this orientation is either

horizontal or vertical.

Signal polarization is the same as the orientation of the

antennas radiating element (often called the driverelement). Eg. If the elements of a Yagi antenna are

oriented horizontally, the signal is polarized horizontally.

For any given link between two units, it is imperativethat both antennas have same polarization. If they are

not, additional unwanted signal loss will result.


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Horizontal and Vertical Polarization(Contd)

Two antennas are said to be Cross-Polarized when theyare oriented at right angles to each other. In this case,

very little (if any) signal energy that is transmitted by

one antenna will be received by the other.

Cross-Polarization can be used to great advantage

when the two antennas belong to different links (such as

at a hub), and you want to minimize any potential

interference that one link might cause to the other.Signal polarization is solely a function of antenna

orientation, and consequently, of antenna mounting.


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Burst mode - Full Duplex

Burst Mode or Ping-Pong is a technique of band-width

conservation also called Time Division Duplex (TDD)

Advantages:

Simpler RF Circuitry: Does not require expensive duplexers

Enables burst synchronisation eliminating near-end interference

concerns

How it works 4 msec Tx, 4 msec Rx, 4 msec Tx, 4 msec Rx, ...


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Environmental CONSIDERATIONS


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Planning

InstallAirLinkunits in weather-protected locations

Observe operating environment specifications

Install for a minimum cable run betweenAirLinkand

antenna

AirLinkshould be accessible for maintainance checks


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Lightning

Lightning risk analysis

Geographical location

Site exposure

Mission critical link

What is Lightning ?

Lightning protection

Primary

Secondary


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Lightning Risk Analysis

Geographical locaton. The frequency of lightning activity

varies greatly with geographical region.

Site exposure. An antenna mounted on a 50m tower is

more susceptible to a lightning strike than one mountedfew meters off the roof of a low building.

Mission critical link. If a particular link is mission

critical, then the cost of thorough lightning protectionmight be money well spent.


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What is Lightning ?

Lightning is a cloud-to-cloud, cloud-to-ground, or even ground-to-cloud electrical discharge.

The actual stroke, or discharge to ground, is equivalent to acurrent source of up to a 100,000 Amperes.

The current pulse has a typical rise time of 2 micro sec and adecay time of approx 40 micro sec. This fast rate of rise of thepulse contributes to its destructive power, because just a smallportion of the stroke traveling through a small inductance caninduce large voltage potentials.

Direct hits are rare - the greatest likelihood for damage isthrough near misses and induced surges in power andtelephone lines


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What is Lightning ?

2 uS < 100uS

10-100KA


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Lightning Protection

Primary protection.The goal of Primary protection is tokeep destructive lightning current out of your equipment.

The likely entry points into your system include the

antenna and the AC power line.Secondary protection. The goal of Secondary protection

is to help the lightning current leave the equipment

easily if it does enter.

A good ground must have low resistance and - because

of the lightning strikes fast rise time - must have low

inductance.

Li ht i P t ti (C td)


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Lightning Protection (Contd)

Generally, more than one copper or copper-clad steelground rod (at least 6long) is required to achieve a

good ground. Several shorter rods, interconnected with

bare, buried wire, will have a lower impedance than a

longer rod. Radials - ground rods staked in a star

formation and interconnected with large gauge soild or

stranded wire - can further reduce the impedance in

rocky or sandy soil.


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Lightning Protection (Contd)

Metals should be similar; copper should never touch

steel

Another form of primary protection is gas tubes or spark

gaps

AirLink E1 and Acess units, as well as the AirLink Pro

E1 have built-in secondary protection called Transorbs,

which protect the units against the small surge that getspast the primary protection


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Antenna Grounding

Grounded tower

DC-grounded antenna bonded to tower

Lightning rods

Co-axial impulse suppressor

R i F d W t V


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Rain, Fog and Water VapourAttenuation

AirLinkmodems operate at frequencies ranging

between 2.4000 and 5.8000 GHz. At these frequencies,

attenuation due to rain and fog is not significant factor inthe path calculation

Atmospheric absorption due to oxygen and water

vapour is quite small at frequencies below 11GHz andcan be usually ignored.


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Antenna Wind Loading

Varies by antenna type

Specified by manufacturer

Performance and safety considerations


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Path Planning and Calculations


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Site Survey

Adequate access to the Antenna site

A line-of-sight path

Antenna mounting structure should be adequate to bear

the antenna under all wind and other conditions

Conform to all applicable codes and requirements. Therouting and securing of all cables should conform to all applicable

codes and requirements Future obstructions


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Fade Margin

aaa

Path Loss

( LR)

Connector/Cable

Loss ( LCL)Connector/Cable

Loss ( LCL)

Antenna

Gain (G MT)Antenna

Gain (G MT)

System Gain ( GMC )System Gain ( GMC )

Air-Link Modem Air-Link Modem


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Fade Margin

The Fade Margin is a measure, in decibels (dB), of how

much additional signal attenuation the system can

endure without dropping below the required BER level.

It is the maximum tolerable signal power loss. Fade Margin is the extra signal power added to a given

radio link to ensure that the link will continue working if it

suffers anomalous signal propogation effects (such asfading)

The Fade Margin is the result of the path equation.


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Fade Margin Equation

Fade Margin = GSG + GANT - LCL - LPL

GSG = Total system gain in dB

GANT= Total antenna gain of both antennas in dBi

LCL = Total connector/cable loss of all cables in dB

LPL = Total path loss in dB

A path for anAirLinkmodem typically needs only 20 dB

Fade Margin and in some locations as little as 10-15 dB.


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System Gain

System Gain is the total gain of the radio system,

without considering the antennas or cables. It is simplythe arithmatic difference between the transmitters

output power and the receivers sensitivity threshold. To

calculate the System Gain: (Tx Power) - (Receiver Sensitivity) = (System Gain)

Eg.An AirLink E1 operating at max power (+20 dBm)

with normal receiver sensitivity (-80 dBm), the system

gain is 100 dB:

(+20 dBm) - (-80 dBm) = 100 dB

R i S i i i


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Receiver Sensitivity

Receiver Sensitivity is an indication of the ability of the

microwave receiver to detect the proper signal. It istypically expressed as a negative dBm value for a

particular BER

Eg. For each doubling of data rate (bandwidth), thesensitivity decreases by 3 dB

AirLink 512 K -86 dBm @ BER 10(-6)

AirLink 384 K -87 dBm





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Antenna Gain

Antenna Gain is the measure of the antennas ability tofocus the RF energy into the preferred direction.

Antenna gain is measeured in dBi - the ratio between

the power radiated by the antenna in a specific direction

over the power radiated to that directon by the isotropicantenna fed by the same transmitter. An isotropic

antenna radiates a signal evenly in all directions.

Some antennas are specified in dBd. This number canbe converted to dBi by adding 2 to the dBd value. Eg,

18 dBd = 20 dBi.


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Cable and Connector Loss

Cable loss depends on the length and type of cable

used. Any 50 ohms co-axial cable whose loss in dB per

hundred feet is low enough (3-15 dB) so as not to

contribute significantly to the total link loss.A higher frequency signal will experience more loss

than a lower frequency signal

The thicker the cable, the lower the loss.

Lost energy is wasted as heat, but is insignificant for

AirLinkModems


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50-OHM CABLE IMPEDANCE

Coaxial cables, antennas, and the antenna connector

on radios all share what is called characteristic

impedance, or just impedance. Impedance is measured

in ohms. The standard impedance for all radio communication

equipment is 50 ohms. All AirLink units are specified as

using 50 ohms antennas, and must be connected tothem using 50 ohms cable. Do not use any cable that

does not meet the 50 ohm impedance specification.


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SWR and VSWR

Standing Wave Ratio (SWR)

Voltage Standing Wave Ratio (VSWR)


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SWR and VSWR (Contd)

SWR is essentially a measure of the degree of

mismatch between radio, the antenna, and the coaxial

cable connecting them. It can be measured by inserting

a device in line with the coaxial cable that connects tothe antenna. The device can be reflectometer (which

gives a direct readout of SWR) or a RF power meter

that can measure both forward and reflected power.

For practical purposes, SWR and VSWR can be used

interchangeably.


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SWR and VSWR (contd)

If the coaxial cable, radio, and antenna are all matched

to one another (all 50 ohms) at a new installation,

measuring SWR is not necessary unless the link does

not work and other corrective actions have failed.SWR is always measured as a ratio relative to 1. Eg.,

1:1, 2:1, 1.1:1, 2.4:1, etc. The ratio is usually shortened

to the first number : 1,2,1.2,2.4, etcSWR of 1 is considered a perfect match. In practice, an

SWR of 2 or less is usually acceptable.


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Path Loss vs Free Space Path Loss

Path Loss is the total signal energy lost in traversing the

complete path, including obstructions such as trees or

buildings. This is difficult to calculate.

Free Space Path Loss is the signal energy lost intraversing a path in free space only, with no other

obstructions.

Sometimes people use the term Path Lossto meanFree Space Path Loss.


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Calculating Free Space Path Loss

Free Space Path Loss (FSPL) can be easily calculated

by determining the distance between the AirLink

modems:-

FSPL in dB = 92.4 + 20 log D (km) + 20 log F (GHz)

F S P th L (K )


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Free Space Path Loss (Km)

Distance Path Loss Path Loss

(Km) at 2.4 GHz at 5.7 GHz 5 114 dB 121 dB

10 120 dB 128 dB

15 124 dB 131 dB

20 126 dB 134 dB

25 128 dB 135 dB

30 130 dB 137 dB

35 131 dB 138 dB 40 132 dB 140 dB

50 134 dB 141 dB


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0

20

40

60

80

100

120

140

160

1 3 5 7 9 15 25 35 50

S Band

C Band

Distance in Km

Path Loss

in dB

Free Space Path Loss (Km)


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D

TECHNICAL SPECFICATIONS FOR POINT TO POINT RADIO

CLASSIC AIRLINK SERIES

RADIO TYPICAL CUSTOMER RFQ 64SMP 128S 256S 384S

Output Power Please Specify 28dbm ,650mw 28dbm ,650mw 28dbm ,650mw 28dbm ,650mw

max within28db max within28db max withn28db max within28db

dynamic range dynamic range dynamic range dynamic range

Frequency Range 2.4,5.7 Ghz 2.400 to 2.4835 Ghz 2.30-2.40 Ghz 2.30-2.40 Ghz 2.30-2.40 Ghz

Max Cover Range Please Specify upto 20 to 30 miles upto 20 to 30 miles upto 20 to 30 miles upto 20 to 30 miles

Channel Bandwidth Please Specify 5.1 Mhz 3.84 Mhz 3.84 Mhz 3.84 Mhz

No. of Channel Available Please Specify 15,All nonoverlapping 24 24 24

Modulation Type DQPSK


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AIRPRO SERIES

RADIO TYPICAL CUSTOMER RFQ 19SR 64SR 128SR 256SR

Output Power Please Specify 28dbm ,650mw 28dbm ,650mw 28dbm ,650mw 28dbm ,650mw

Frequency Range 2.4,5.7 Ghz 2400 to 2485.3 Mhz 2400 to 2485.3 Mhz 2400 to 2485.3 Mhz 2400 to 2485.3 Mhz

Max Cover Range Please Specify max 50 km max 50 km max 50 km max 50 km

Channel Bandwidth Please Specify 1.6 Mhz 4.0 MHz 10.75 MHz 21.5MHzNumber of Channel Available Please Specify 50 20 7 4

Modulation Type DQPSK


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Model 100

RADIO TYPICAL CUSTOMER RFQ 2.4 GHz RF Unit 5.7 GHz RF Unit

Output Power Please Specify Std.-0 to +8dbm Adj +10 to +20 dBm

High power option adjustable

+17 to+27 dbm Adj

Frequency Range 2.4,5.7 Ghz 2400.0 to 2486.5 Ghz 5725 to 5850GhzMax Cover Range Please Specify max 75 Km max 75 Km

Channel Bandwidth Please Specify 20 Mhz 20 Mhz

Number of Channel Available Please Specify 4 6

Modulation Type DQPSK10db

At 56kb/s- >17db At 56kb/s- >17db

Carrier Frequency Stability 10 ppm

Clock Sorce internal or Dte Interface Int; Ext (10ppm) Int; Ext (10ppm)Rx loopback Rx loopback

Max Rx Level 0 dbm (No damage) 0 dbm No damage 0 dbm No damage

-30 dbm (No errors)

Rx Sensitivity Threshold Please Specify -91dBm(Thr.1x10 ) -89 dBm(Thr.1x10 )

USER INTERFACE

Interface Type & Connectors V.35,V.35/V.11 34 pin V.35,DSX-1 V.35,DSX-1

Winch(F),RS 232,Rs-422 or G.703 or G.703

EIA 530-db 25(F) specify at order specify at order

DIOGNASTICS

Indicators LED for Power Supply,Sync Power,TX Data Power,TX Data

Error test,TXD &RXD Rx data,demod Lock Rx data,demod Lock

Loop back test LED Summary fault Summary fault

Loopback Option Please Specify yes yes

Monitor/Control Please Specify Local/Rem,Summary Local/Rem,Summary

Fault contact Fault contact

optional NMS optional NMS

POWER

AC Voltage 100-250VAC 90-260VAC 90-260VAC

AC Frequency 45 to 66Hz 50/60 Hz 50/60 Hz

DC Voltage -25 to -60VDC -20 to -56 Vdc -20 to -56 Vdc+12 to +60VDc

Power Consumption Please Specify 55 watts max 55 watts max

ENVIORMENT

Operating Temp Please Specify 0-60 c 0-60 c

Storage Temp Please Specify -40 to +70 c -40 to +70 c

Humidity 0 to 95 c@ 35 Deg c upto 95 c upto 95 c

non condensing non condensing

Altiude Operational Please Specify 4600mts 4600mts

MECHANICAL

Width Please Specify 43cm 43cm

Height Please Specify 4.5cm 4.5cm

Depth Please Specify 33cm 33cm

Weight Please Specify 2.7Kg 2.7Kg

Mounting Choice 19''rack mount or table top Comply Comply


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