- This topic has 113 replies, 1 voice, and was last updated 2 years, 7 months ago by Akbar Ali.
1st June 2004 at 19:11 #38313YunusaGuest
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.
Yunusa.4th June 2004 at 11:12 #38314AnjungGuest
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 planning
Space 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 you12th June 2004 at 08:46 #38315vijayarajGuest
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.28th June 2004 at 08:22 #38316ArindamGuest
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 parabolic-dish antenna.
Gain(dBi)=20 Log (7.4 f d )
f=frequency of operation in GHz
d=antenna diameter in meters.4th July 2004 at 12:10 #38317PriyaGuest
Can any body pls tell me wht type of antenna r used in both CDMA and GSM technology for transmission and reception6th July 2004 at 07:59 #38318ShaguniGuest
In Microwave what is Hop length? Is it the distance between two point to point antenna?6th July 2004 at 11:52 #38319ArindamGuest
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.
Arindam7th July 2004 at 08:56 #38320ShaguniGuest
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 staffs10th July 2004 at 09:54 #38321ArindamGuest
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 Gain-Feeder/connector Losses-Path Loss-Fade 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.14th July 2004 at 23:43 #38322vijayarajGuest
F=frequency in Mhz.
D=Distance in Kilometers.
Is there any free software tool for making microwave mux diagram?29th July 2004 at 13:03 #38323Suresh NarayananGuest
CDMA and gsm Both are using log periodic Antenna .8th August 2004 at 07:57 #38324SaikatGuest
Can any body pls let me know how the MW Link Budget is normally calculated?21st August 2004 at 06:36 #38325WaqasGuest
Would anybody please provide me with path-loss calculation formula for Macro and Micro cells for GSM900/1800 system.
Thanking you in advance24th August 2004 at 03:04 #38326Hi allGuest
Anyboby know about costing structure for about 1000 sites for a 1900MHz, a new rollout project.
Phuc25th August 2004 at 07:25 #38327sureshGuest
hi what frequency is usein for CDMA technology?