Interference caused by ducting phenomena

[alaa92]

Hi all,
I am working on studying ducting effect on cellular systems in EGSM and how to reduce the interference caused by ducting
can anyone helps me with useful links or informations about the height above the sea level where ducting occurs or any other details
thanks in advance

 

[VEBill]

Tropospheric ducting occurs over a range of altitudes from ground level up to higher than most mountains. I'm not aware of any counter-measures.

 

[alaa92]

thank you
but i want to know if i will design Base station in area which suffers interference from ducting what is the best height for this BS to reduce this interference ?

and i read that ducting begin from 10-15 meters above the Mediterranean but i'm not sure from this info. so do you know if this is right or not

thanks in advance

 

[VEBill]

The tropospheric ducting that I've experienced in amateur radio is in the 2m band (~146 MHz). In those cases the distant signals bath the entire region, detectable in both directions by everyone, including those in valleys and those on hilltops.

If you have a theory that the ducting can be avoided by having a tower of a certain optimal height, then (as far as I know) that theory is not correct (except perhaps in some limited cases).

On the other hand: If your base station is adjacent to the Mediterranean, the ducting interference is arriving from the sea, and your primary customers are on shore, then aim an antenna system null towards the sea. Easy.

 

[alaa92]

my project is to reduce ducting interference from Mediterranean i will design antenna with no radiation above the zero vertical in VBW but to design this antenna i think the height of the tower is main factor ?
i don't know what's your opinion ?

 

[alaa92]

and as i know to reduce ducting effect ,Downtilting of cellular antennas and to short the tower is good solutions

 

[VEBill]

If tropospheric ducting didn't reach the ground at both ends, then it wouldn't be very interesting.

Obviously a shorter tower is going to be 'disadvantaged' for *all* distant signals, including ducting. Also, the resultant cell size (service area) would be smaller (you'll need more towers), and thus the clients would have to be closer, and thus their signals would perhaps tend to be stronger, and thus they would tend to out-gun the distant signal carried by ducting. Carried to extreme, if you bury your base station in the basement, it would be highly resistant to interference from ducted signals. It's not an interesting relationship, but it may be useful.

 

[controlsdude]

I remember from radar operation in my time (long time ago) was that temperature, barametic pressure, and dewpoint effected ducting. By taking these into account you could put some variables into the computer to calculate a fudge factor.