Microwave link capacity

Bryan Fields Bryan at bryanfields.net
Thu Apr 7 12:28:33 UTC 2016

On 4/5/16 11:45 AM, Robert Glover wrote:
> How well does Siklu handle rain at closer to 1mi. range?

This is not dependent on the radio, it's dependent on the frequency and rain
zone. http://www.softwright.com/faq/support/Rain%20Rate%20Estimates589.gif

If you're in E, it's going to be much more severe fading due to thunder storms
vs. in the D or F region.  There are calculations you can do to figure out
your fading due to rain and how much link availability you need.

The newer radios support adaptive modulation, and will downshift from 2048
>1024 >512 >128 > 64 >16 QAM > and some even go down to BPSK.  Of course you
lose bandwidth for each down shift, so if you need 800 Mbit 99.999% of the
time, you need to evaluate it at the lowest modulation that will give that.

Horizontal Polarity will be slightly more effected by this, so on any links
you're running both polarities, you need to evaluate horizontal.

The real problem is a radio from x vendor at a given modulation is about as
good as any other vendor.  (give or take 3db)  Most vendors use a COTS
chip-set for the modulation, and about the only difference is the packaging.

A 2048 QAM radio will need -63 or better signal just to hit that modulation
and in a 40 MHz channel at 18GHz you don't have much distance with out larger
dishes or higher power.  You in Crane rain zone E?  Shit, better add in 35 dB
for rain fade.   You need a -28 or -30 signal!  That's 2k (1.6 Mi) for that
path.  And you have to rent tower space, pay for engineering, pay for install,
and pay for the gear.

While it's still cheaper than fiber, and deploys faster, a mile of fiber is
not that expensive depending on the area.

Microwave has it's place, but the 20 mile, >1gb links are marketing more than
Bryan Fields

727-409-1194 - Voice
727-214-2508 - Fax

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