Pathloss 4.0 Frequently ask

9. ) SUBJECT : ANTENNA POLARIZATION RATIO


Question :

On the manual books refered to interference chapter said that " the ratio of horizontal and vertical polarized signals is unknow. And all data are on those links that are analysed.

Answer:

the paragraph that you mention introduce the details of the below calculations.

Effectively the transmit antenna is not perfect and radiates the expected signal on one polar and also some energy on the alternate polarisation; let's say:

Expected signal is V polar; then the alternate radiated signal is H polar of which the power ratio is given by the VH curve

Similarly the receive antenna will also capture some H polar signal to the V port with the HV gain curve

Consequently, it is relevant to calculate the different combinations between interferer and interfered signal from both Transmit and Receive antenna and to select the minimum antenna cross-polar decoupling gain in order to evaluate the interfered received signal

Obviously, this is a worst case calculation because antenna manufacturer indicates antenna mask performance and a particular interferer captured on the corresponding azimuth and site angle will very often be received lower than calculated

But it is the standard method that should be applied to perform interference calculation

10. ) SUBJECT : VIGRANTS BARNETT CLIMATIC FACTOR (cf) & ITU-R RELIABILITY METHOD

Question:

What is the best way to determine the climatic factor (cf) in the Barnett & Vigants reliability formula? Not the C Factor!

Standard values seem to vary from 0.5 to 1 and 2.

How can we determine the exact value depending on the climatic conditions of a specific area?

I am especially looking for many areas in the province of Quebec in Canada.

Where can I find a climatic factor map?



Answer:

Maybe maps for the climatic factor cf do not exist (are not published). Then use instead the C factor with associated maps. The C factor is also by definition equal to cf for average terrain rouhness S = 15.2m



For a more detailed calculation you can use one of the newer ITU-R P.530 reliability methods. These are applicable worldwide

Thanks a lot Lars for your reply and your suggestion about the climatic factor for reliability calculation.



I only began to compare the ITU-530 methods with the Barnett & Vigants method.



Which method is the more reliable after you? 530-6 or 530-7/8 or the newest 530-9 ?



I get similar results when the path inclination is near 0 mr, but I get very different results when the path inclination is about 10 mr. What do you think about this?



Thanks a lot for your collaboration

ITU made a lot of changements over the last years for the recommendation P530. Therefore, if you are sure what kind of parameter set for the Barnett&Vigants is correct for your area you can choose this model.



If you have no idea the P530-9 recommendation gives a detailed model where you only need the data provided by ITU and the GTopo30 DTM from USGS to get the right parameters. You do not have to look anywhere else. This model seems to be proved with hundreds of hops all over the world. Nevertheless there will be a new recommendation P530-10 soon. Let's see what will be new this time.

Rejean, here is my comments to the three ITU-R P.530 reliability methods implemented in PL4.



P.530-6(detailed planning)uses an average grazing angle which for many(most) paths is ambiguous or even meaningless.



P.530-7/8 does away with this average grazing angle. Instead many link classes are introduced, which makes it somewhat cumbersome, especially for coastal links.



P.530-9/10 (detailed link design)uses a terrain database (GTopo30) and the refractivity gradient data are incorporated in PL4. This makes the method convenient in use, but the method itself and/or the PL4 implementation may be unreliable (see the thread in this user forum initiated on Sep.13, 2002 by AK).



At present I regard P.530-7/8 to be the most reliable method.

Thanks a lot Mike for your reply.



I will use both methods (Barnett & Vigants as well as ITU 530-9) and compare them on each link. Then I will probably be able to take a better decision.

Thanks for your comments about each ITU method.



The main point I am wondering about is why the path inclination has such an effect on the reliability result?

ITU 530-6 and 530-7/8 are the only two methods using this parameter.



I get 99.9999% compared to 99.999% if the path inclination is respectively 10 mr instead of about 1 mr. Is it the reality?

In general a high low path is more reliable than a path without any inclination. The reason for this is the less high probability for multipath with a certain inclination.