900Mhz fresnel challenge/question

Products PMP
1

Hello everyone,

We are installing our first 900Mhz AP at one of our towers and have a question regarding potential fresnel issues with our first customer.

Our AP sit is visible from the customer premises but there’s a hill about a mile away from the SM. The path is 39 mile, I was wondering if this can present a fresnel issue.
Here’s a pic taken form our customer roof.

http://i293.photobucket.com/albums/mm78 … aylink.jpg


Thanks!

2

Is your tower on top of a hill? Tower & AP height?

At ~39 mi. your number one obstacle is distance from CPE (SM) to AP. While 900Mhz Canopy is spec’d to do up to 40mi. LOS I can’t say I’ve seen any reports of a successful link at that range. We’ve got several 15-20mi. 900MHz LOS links using an M2 17dBi or KPP 17dBi yagi w/ a connectorized SM shooting to a Cyclone 900 w/ MTI H-Pol omni. I’m sure we could reach customers 25mi. out while maintaining adequate link efficiency, but then we’d be exceeding max EIRP levels.

Those hills appear to be in the fresnel zone, so I’d recommend you raise the antenna as high as possible.

3

Agreed. Unless you’re dealing with extremely low noise floor, very high antenna heights and adequate antenna gain, you won’t see 40 miles.

4

you might be able to do 39mi assuming the following:

1. AP antenna is 12dB or better
2. Noise floor is less than -85
3. LOS is perfect
4. CPE antenna is 15dB 900MHz grid.

However it’s unlikely that you will be able to get/maintain a 39 mile link.

5

Thanks for your input.
Looks like we’ll give it a shoot. Since we don’t have any 900 gear we’ll try it with a 5.7 backhaul and high gain antennas.
I’ll let you know how it goes.
F.

6

with 5.7 You’ll probably have a lot better chance than with 900. As your fresnel zones will have a smaller diameter. Also the higher gain directional antenna you use. the smaller the beamwidth and the better chance you’ll be able to shoot through the gaps in those hills.

You might want to run a link calculation to see what you’re going to need for each end.

Also RadioMobile will be able to calculate your loss due to fresnel encroachment even at that distance. And you can use that coupled with the Coordinate locations for each node of the link. And remember to budget enough fade to accomodate for the thermal fade at those locations as well.