MW Transmission (NEC)

8/3/2019 MW Transmission (NEC)

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Prepared by Engr. Jawad KhanBSS/TXN Support Engineer

EPTSC-Cll


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What is MW transmission? Microwave transmission refers to the technology of

transmitting information or power by the use of radiowaves whose wavelengths are conveniently measuredin small numbers of centimeters; these are calledmicrowaves. This part of the radio spectrum rangesacross frequencies of roughly 1.0 gigahertz (GHz) to30 GHz. These correspond to wavelengths from30 centimeters down to 1.0 cm.


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Advantages of MW. High frequencysmall size of antenna

High frequency narrow beam width

Narrow beam width no interference and highbandwidth

Easy in relocation

No bad effects on humans.


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Link planningThe design and construction of a microwave radio link

network is based on a number of factors. These include: Distance between microwave radio terminals Terrain properties, eg bodies of water, cliffs, forests, snow

Frequency of operation, often governed by licensing costs,frequency availability, planned distances and evensuspectibility to rain fading.

Fading, dispersion and multipath distortion. Size of antennas, feedline properties, need for towers etc. Council and community development permissions

governing visual intrusions. Cost of equipment and cost benefit analysis including

equipment maintenance.


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WHY NEC??? High efficiency/Quality and reliability.

low power consumption

Temperature resistable. User friendly

Easy software/HW installation.

Software is simple and easily understandable.

Different modulation schemes avaialable.

High system gain/high spectrum effieciency.

Can use freq from 6 GHz upto 52 GHz.


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Common MW link Setup.The b/m basic Equipment is required for a MW link.

An indoor unit (IDU)

A Parabolic MW dish AntennaAn outdoor unit (ODU) connected to Antenna.

An IF (intermediate frequency) cable to connect IDUwith ODU using standard straight and L connectors.

A negative 48V DC voltage from standard rectifiers.


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IF cable. IF cable is an intermediate frequency cable i.e. its just

a simple coaxial cable but its called IF because it carryinformation signals in intermediate frequency rangei.e. 140MHz (Rx) and 340MHz (Tx).

Coaxial cable has the common property that the itshows more attenuation/losses to high frequency

signals. Short Test is made for IF cable to check cable and

connectors.


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Protected and unprotected links.

Protected links have main and standby paths availableand one is used at a time. They are represented by (1+1)

Unprotected links have only one path and if that pathgets down, all transmission breaks. They are donated

by (1+0).


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Different types of common links

configuration Unprotected 1+0

Hotstandby 1+1

Unprotected Twinpath Space diversity

Frequency diversity

XPIC (cross polarization interference cancellor).


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Details of link configurations. Unprotected 1+0 link has one 1+0 IDU, one IF cable,

One ODU and one Dish.

HotStandby 1+1 link has one 1+1 IDU, two IF cables,two ODUs and one Dish.

Twin path is the same as Hot standby but it hasdifferent traffic on both of its paths at the same time so

both paths are unprotected.


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Space Diversity link. SD link has two Dishes (one called main and other

called standby) at each side, 1+1 IDU, two IF cables,two ODUs.

Two IDUs and 4 ODUs can be used to make it moreprotected.

Both frequency and Polarization are the same for both

dishes. There are three paths made in this configuration i.e.

one from Main to Main and two from Main to standbydishes.


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Frequency diversity links. Frequency diversity is the same as space diversity but

the main difference is that frequency of both dishes isdifferent and polarity is the same .


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XPIC PASOLINK NEO can improve its transmission capacity

up to dual STM-1 in 28 MHz bandwidth by using XPICtechnology. In case of this capacity upgrading fromone STM-1 system, the additional parts are dualpolarize antenna, one more ODU/ IDU set, some XPIC

cable kit and additional firmware. The upgrading canbe realized with existing STM-1 equipment.


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Dish size and frequency

consideration. The higher the frequency is, the narrow will be its

beam width and vice versa.

The longer the link distance is, the lower frequencysignals are used to get wide beamwidth and better RSLcan be achieved.

High freq signals travel less distance then low freq and

high freq signals are more attenuated then low freq. High freq needs small size dish antennas then low freq

so the longer the link distance is, the smaller freq willbe used and dish antennas of large size will be used.


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Line of Sight.LOS should be clear because MW transmission is point

to point transmission and if the dishes are not alignedto each other then better RSL will not be achieved andmore closer RSL near threshold RSL, the higher will bethe risk of link f luctuation.


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Commonly used NEC MW links.The b/m NEC MW links are commonly used in Mobilink

Pakistan.

Pasolink V3 Pasolink V4

Pasolink Mx

Pasolink NEO

Pasolink NEO CPV


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E1 capacity.the b/m E1 capacity Equipment is commonly used here.

4 E1

16 E1 48 E1

63 E1 (STM-1)

2 x STM-1 capacity can be obtained using XPIC

technology.

C-Node is used to add/drop media in SDH like 63 E1Pasolink NEO as the media is totally synchronous.


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SoftwaresThe b/m softwares are used.

PNMT (for pasolink)

PNMTj (for pasolink NEO) java version.

Software installation will be taught directly duringtraining.


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New link

installation/commissioning.When a new link is installed first check whether

installation has been done according to standard ornot. And check safty measures have been taken or not

like grounding of IDU/ODU/Surge arrestors/MW racketc.

Check power using multimeter.

Power on link IDU.

Make sure that you have all required data to configurethe new equipment according to link budget.

(All NEC IDUs commissioning will betaught at site visits.)


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Common troubleshooting steps. First of all if you receive TTs of several down sites then

check your sites connectivity for any possible commonlinks between the down sites.

If you find the down sites common link then contactsite guard (both ends) directly to find out whetherthere is a power failure or not. If not then moveimmediately to one of the end.

Make sure that you have all the required cables andsoftwares in working conditions in your laptop andmust take a rigger tech with you along with full toolkit.


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Common troubleshooting steps. If the IDU is powered off then check the front fuses of

IDU using multimeter and if they are faulty thenreplaced them.

If they are ok then check fuse panel. The fuses in fusepanel and power input/output of fuse panel.

If fuse panel is not receiving input then check

connections at rectifier. If fuse panel fuse is faulty then replace it.

If every thing with power is ok then replace IDU.


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Common troubleshooting steps. Please note down that always visit both ends of the

link before making any decission because mostly issuecan not be judged from visiting one end of the link.

If IDU is powered on then connect to it using yourPNMT/PNMTj .

Check for the current alarms and check event logs.

Check RSL value and if RSL value is less than -45 dbm(i.e. towards -50 -60 -70 dbm) then improve the RSLvalue by making fine tunning in allignment.

RSL should be between -32 -38 dbm approx.


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Common troubleshooting steps. BER : bit error rate/ratio

High BER/Low BER means that there is too muchnoise and attenuation, it can be often due to somewater penetration into the straight connectors. Checkyour connectors and make short test for IF cable.

If your IDU/ODU alarm on the IDU is blinking and

there is a IDU/ODU link alarm in software then thereis something wrong with the connection between IDUand ODU. Check your IF cable, L connector, straightconnector etc.


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Common troubleshooting steps. If there are MOD and DEM alarms then either of your

ODU or IDU needs to be replaced. You have totroubleshoot by changing them one by one, thats the

best way to troubleshoot.

Please note that there are always two types of ODUs.one is high and one is low. Thats why one end is calledhigh and other end is called low. Care must be takenbefore replacing ODU to make sure that high bandODU is not mixed up with low band ODU.


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Common troubleshooting steps. IF the link is PASOLINK NEO then it has more clear

cut alarms then the older versions. E.g.

For short IF cable, there will be an alarm of IF cableshort.

Similarly for OPEN IF cable, there is alarm of IF cableOPEN.

In Pasolink neo, you can change the cards and no needof replacing whole IDU e.g there is a modem card, aninterface card, a control card.


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IF cable Short Test. Open the L and straight connectors from IDU and

ODU and short one end of it.

Take multimeter to the other end and select the shorttest option on multimeter.

Now put the two probs of MM on the inner and outerconnection of the connector.

The MM should beep when the other end is short.


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IF cable Short Test. Now remove the short from the other end. Now mm

should not beep and cable path should be open. If itstill beeps then either of your connectors are short and

needs to be remade. Make this test for atleast 5 to 10 times to get more

confirm results.

If the behaviour of IF cable is sometime open and

some time short even the other end is open and allconnectors have been made fresh then check your IFcable it may have water penetrated inside it. in thatcase IF cable needs to be replaced.


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Interference Test. Send one team to one end and other team to far end.

Both should have laptops and softwares in it inworking conditions.

Now one team will turn off the IDU and the team at itsfar end will check RSL which should be -100 dbm. Takesnap shot of RSL after a few seconds.

Similarly second team will turn off IDU and first team

will take check RSL. If RSL is not -100 then share the snap shots with your

Regional Transmission support Engineer along withdish sizes, dish heights, etc. for both ends.


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RSL improvement/Link alignment. Send your Rigger technician with multimeter to climb

the tower along with serial number of ODU. If the siteis a major hub site then tell him to trace the IF cable

too to avoid outage of another link. He must matchserial number of ODU too before doing any thing.

When he find the right dish then he will get himselfadjusted by fastening his safty belt.

Open multimeter and select 20VDC option.


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RSL improvement/Link alignment. Connect black wire to the tower by using neto tape.

Connect red wire to the back of ODU (optionavailable) now monitor the voltage values at MM.

If alignment is almost out then voltages will be 0.5 to1.30 if RSL is improved to -30s then voltages will be3.40 + - .

For RSL improvement activity on operational Links,

never loose up and down as there can be chance thatdish may get down and big sizes dishes are not easy tocontrol then. Always check left right first to get maxRSL, if no use then do fine tuning on up and down.


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Safety measures and standard. Grounding should be done properly.

IDU should be tight and balanced

There should be enough space between two IDUs min

equal to 1U. All cables and tributaries should be tight and laid properly.

Weather proofing should be done properly.

Dishes should be locked properly after activities.

Correct labeling should be done on everything from IDU todish.

Two meter IF cable should be looped on tower behindantenna .


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Thanks & The end.

Software installations, software using, and HW detailswill be taught during training and site visits.

Documents

MW Transmission (NEC)