mounting the SD antenna

[mohamad]

dear all friends in this forum;
I ask this question a few days later but no one reply to me;
Where I should mount the space diversity antenna on the tower;
I know that it should be lower than main antenna with proper to wavelength;
and my question!
shall I position the space diversity antenna with regard to clearance rule for LOS links?
thanks a lot for your attention
mohamad

[byja]

Mohamad,
there was such discussion at Transmission Planning social group. Join that social group here, and see topic dealing with SD antenna separation.

Furthermore, I haven't heard one good reason why diversity antenna should be lower than main antenna. On the contrary, there are arguments to opposite:
1. diversity antenna is usually smaller, and it's better to keep larger (main) antennas low on the tower due to wind load and weight.
2. if it's an all indoor system higher antenna means longer waveguide, which means more attenuation. Main antenna also does transmission, therefore less output power.
The only reason why people put main antenna higher is probably LOS and clearance.
As for the clearance for diversity antenna, I suggest you read ITU-R P.530-X, it has a suggestion for clearance criteria both for main and diversity.
I use same criteria (100% F1 for k=1.33, 70% F1 for kmin) for diversity and main antenna if it's BB switching SD, and less strict for diversity for IF combining SD.

[mohamad]

hi byja
I reed ITU-R 530-12 recommendation exactly;
as I see this recommend sugggest that we mount the space diversity antenna lower than main antenna because of lower surface multipath fading;
lower antenna means that we violate the clearance criteria and so we have diffraction loss in the link planning calculations;
with refer ro ITU-R 530-12 the advantage of decreasing the occurance of surface multipath fading has to be weighed against the diffraction loss up to 6dB;
another argument! if you use the same criteria for the main and space diversity antenna the pathloss give us the same height;
I use k=1.33 and 60% for kmin for space diversity anenna and then check the diffraction loss and understand that the diffraction loss is below the 6dB;
in the transmission planning social group you said that the Best antenna sepparation is the distance between minimum and maximum receiving level,how can I change the dB to meter? for different variable we have different distance between minimum and maximum receiving level,what variable should I choose?
I hope this argument will be useful for us;
thanks a lot for your attention

[byja]

Will get back with a more detailed explanation as soon as I get some spare time...