Considerations for a 25km Microwave PTP link


I’m modeling a link that is approximately 25km, and 99% of which is over a body of water.

I have recently had the pleasure of adding various PTP820c’s (in a few different bands, all licensed) to my network, and they have been very reliable and stable thus far, but the longest link I currently have is 16km.
This newest link I’m looking at would be approximately 25km…and as mentioned above, it’s almost entirely over a body of water.

My concerns here are firstly feasibility, then reliability and capacity.
Ideally I would be looking for a very high reliability (99.99xx%), and close to gigabit capacity. From what I’ve modeled so far in Link Planner, this seems to be a tall order…

So, real talk… is this too far for a reliable and high capacity Microwave link? It no, which band and radio is best? Also, aside from curvature of the earth, what other considerations would you give to a link like this? Is thermal layering an issue for Microwave links?

Any advice would be appreciated!

I don’t think the distance is a problem. You should model this using a PTP850C in xpic 2x 80MHz channels and probably using 3’ dishes with the 11GHz band. This will give you around 1.3gbps FDX. What I’m more worried about is the water and as you mentioned thermal layering and multipath reflection, etc. Unfortunately, I don’t have much advice for you other then try to get up as high above the water as possible. I’m even wondering if a smaller wavelength like 18GHz and it’s smaller fresnel zone might work better. Again, I don’t have a ton of experience shooting over water, so hopefully some other forum members can chime in here.

For links over water you should definitely consider using spatial diversity. If you are not familiar with planning diverse links, please take a look at the section in the LINKPlanner User Guide, Setting Diversity — Cambium LINKPlanner Online Help (5.6.7) for more guidance. The reflection editor in the LINKPlanner path profile will help you to get the correct separations.

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