 This topic has 113 replies, 1 voice, and was last updated 3 months ago by Akbar Ali.

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YunusaGuest
Hi All,
I am an electrical engineer working with a telecommunication outfit in Lagos, Nigeria.
Could anyone help me on the the following questions please?:
What factors determine the choice of the size of microwave dish in a transmission link.
What are “Space and Frequency diversity” in microwave transmission.
regards,
Yunusa.
AnjungGuestHi Yunusa,
If we want receive signal level better than we need bigger dish. Usually for distance (d) :
d < 1 km the dish is 0.3m 1 km < d < 20 km the dish is 0.6m 20 km < d < 30 km the dish is 1.2 or 1.8 d > 30 the dish is 2.4m
But it is depend on planningSpace Diversity (SD): one hop (system) with two antennas at different height. By using to antennas, we can select one antenna which receive better and then the other at standby mode.
Frequency Diversity (FD) means one system using two frequency f1 and f2 then we select which receive better as ‘working frequency’ and the other as standby mode.
In SD and FD, the selection mode can be made automatically
that’s simple explanation, i hope help youvijayarajGuesthai yunusa,
generally for 0.3mtr dish gain is around 32dBi.For 0.6mtr dish it is around 37dBi.For 1.2dish gain is around 42dbi.when the high gain dish antenna’s used the receiving level will be increased and the link will be stable.
In maintenance view it is difficult to install and maintain 1.2 or 1.8mtr dishes.so its better to go for 0.6mtr dish for short hops.
ArindamGuestDear Yunusa,
The selection of antenna size depends on the antenna gain you need. The required gain is arrived at by calculating the link budget. The following formula gives u the gain for any parabolicdish antenna.Gain(dBi)=20 Log (7.4 f d )
f=frequency of operation in GHz
d=antenna diameter in meters.PriyaGuestCan any body pls tell me wht type of antenna r used in both CDMA and GSM technology for transmission and reception
ShaguniGuestHi
In Microwave what is Hop length? Is it the distance between two point to point antenna?
ArindamGuestHi Shaguni/Priya,
Yes , the hop length is indeed the distance between the two point connected by a microwave link.For CDMA and GSM, typically array of dipoles are used. Visit the site http://www.alandick.com and check cellular antenna section. You will get their radiation pattern and other details.
Regards
Arindam
ShaguniGuestHi,
Thanks Arindam. I want to know the formula for link budget calculation for MW and the factor to be considered for TX Power and RX power in MW transmission. Thanks in advance.Any way, can you please refer any good book or site where I can learn the mw staffs
ArindamGuestHi,
The most simple formula for calculating the MW link budget is
Path Loss(PL)=92.4+20log f+20Log d
where PL is in dB
f=frequency in GHz,d=distance in km.Now the power budget equation is
Rx Sensitivity=Tx Power+Tx Antenna Gain+Rx Antenna GainFeeder/connector LossesPath LossFade Margin.
Fade Margin takes care of rain attenuation or ducting(typically 40dB).Please note that this is very crude formula and does not take into account earth bulge,atmospheric and seasonal variations, which are very important for long haul links. It is okay for short links within a city.
I would suggest a book named “Telecommunication Transmission Systems by Robert J Winch” McGrawHill Publication. You’ll get very good insight to MW systems.
vijayarajGuestHi,
Pathloss=32.4+20logf+20logD
F=frequency in Mhz.
D=Distance in Kilometers.Is there any free software tool for making microwave mux diagram?
Suresh NarayananGuestHi Priya
CDMA and gsm Both are using log periodic Antenna .
SaikatGuestCan any body pls let me know how the MW Link Budget is normally calculated?
WaqasGuestWould anybody please provide me with pathloss calculation formula for Macro and Micro cells for GSM900/1800 system.
Thanking you in advance
Hi allGuestAnyboby know about costing structure for about 1000 sites for a 1900MHz, a new rollout project.
Best regards,
Phuc
sureshGuesthi what frequency is usein for CDMA technology?

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