Frequently Ask Pathloss 4.0

2. ) SUBJECT : EQUIPMENT SIGNATURE / DISPERSIVE FADE MARGIN


Question :

Dear all

1-I wonder if can any one help me to know more about the radio Equipment signature and its impact on the dispersive fade margin.

2-Also I want to know if there is any consideration in determining the path profiles that the MW signal should take rather than the reflection phenomenon.

Answer :

Hi,

MW radio dispersive fade margin can be calculated based on the signature of the equipment.

Most modern microwave radios have excellent signature curves and therefore high dispersive fade margins of over 50 dB.Insufficient DFM was an issue in early MW radios but not today with the state-of-the-art technology.

If you don't feel like reading the ITU standards, book "Microwave Transmission Networks - Planning, Design and Deployment," McGraw-Hill, ISBN 0-07-143249-3,2004, provides sufficient information on this topic.

Harvey

www.HLTelecomConsulting.com

The dispersive fade margin (DFM)is the replacement for the former signature of analog radios. DFM is usually > 50 dB. You should take this value to calculate the Composite Fade Margin (digital links) or Fade Margin (analog links). You should also considerer the Termal Fade Margin, External Interference Fade Margin and the Adjacent-channel Interference Fade Margin. I recomend you to check the Telecommunications System Bulletin of the TIA.



Regards,

Benjamin Millan

Telecommunication Engineering Consultancy



3. ) SUBJECT : 90 Km LINK OVER THE WATER

Question :

I have been asked to look at a path over ~90Km sea in SE Asia between islands.

Capacity will be about 8M, choosen band is 1800MHz. Can any give me a couple of points I need to look out for? I seem to remember there was some discussion on this forum, but my searching has come to naught.

TIA

Matthew

Answer :

hope you have designed and installed that hope since the question was posted. :-)

Let's quickly summarize the issues; your main concern is and will be reflections from the water (multipath). For the lenght of the hop, space diversity will absolutely be required although it may not be sufficient. You may have to use frequency diversity as well (if allowed).

You have to perform very detailed analysis of the antenna placement on the tower for the space diversity improvement to be optimal.

Use vertical polarization since it may offer additional protection against reflections.

Some ducting issues may also appear but since there is not sufficient information about the link and its location, I am not going to address that issue.

www.HLTelecomConsulting.com