- This topic has 6 replies, 1 voice, and was last updated 15 years, 3 months ago by SPJ.
8th January 2006 at 14:18 #43727AbdelGuest
Are there any solutions for multipath fading caused by microwave links?28th January 2006 at 13:37 #43728SPJGuest
I most cases multipath fading is caused by changes in the atmosphere along your path which can be temperature/humidity related, these changes or layers of different refractive index causes ducts to form which then channels your signal away from its intended path. The way to overcome this is to use freq difersity but will not help in extreme cases. Space difersity will also improve the situation. There is also a combination of space and freq diversity. You can aslo plan shorther links in areas that are heavy affected such as across swamps and bordedring lake or coastel regions. Ultimately in swampy or delta tropical regions you must actually place the divesity antennae on top (above the expected layer formation and the main antennae at the bottom below the expected layer (duct). If you are experiencing the fading seasonaly then these layers typically only accur during certain seasons and not duing your typical day/night transitions. Towers as high as 120 meters over a 30Km link is not uncommon with one antennae at 60 meters and the other at 120 meters.
I also found that hops across beach areas should be avoided, they are aleays affeceted by the tide changes along the path.
Thus first determine if the fading occurs every day or only during certain seasons. It will save you a lot of money.29th January 2006 at 05:21 #43729AbdelGuest
Thank u very much for your answer. If answer you the question; if fading occurs everyday or only during certain seasons, most of our network fades during certain seasons which is the summer season, in our links, we use long range hops 50-70km, and we saw on the pathloss program there is so many multipaths receiving the antenna, and Multipath causes fading, I thought this can be avoided by using top mounted amplifiers to increase the power of the signal as well as to increase the size of the antenna and the gain, May be this is the only solution since our radio modems are designed for 1+0, not for 1+1(space and frequency diversity),
Do you have any idea in such a situation?
what about passive repeaters have you used this before? I want to use a passive repeater because one of our link radio passes over a sea which causes a long terrible outage hours or days, please help me out of this disaster SPJ?
Regards31st January 2006 at 18:13 #43730patrickGuest
what sort of MICROWAVE do you install?
PDH? SDH? frequency?
We have link of 60km or more with SDH, 6Ghz, antenna 2,4meter and we don’t have problem.1st February 2006 at 05:33 #43731AbdelGuest
We use PDH with 7GHZ frequency plus very small dishes the larges one is 0.9 m in diameter1st February 2006 at 06:23 #43732areebaGuest
top mounted amplifiers are not help for multipath fading.
THUS the major method for MP fading mitigation is Diversity (space or freq).
Also you can try another method such as # change the Ant height.
# change the hop path.
FREQ Diversity is good for (freq selective mp fading).
If you have flat fading you have to endouver the other methods.1st February 2006 at 21:43 #43733SPJGuest
I replied to your questions as a new article.
Check it out