Rain Fade (Link Drops in Heavy Rain/Down Pour)

User submitted question: There was heavy down pour for about one hour today and all our links on 11Ghz and some on 23Ghz frequency band went off which cause an embarrassing situation to us. I will like to know if this is normal.

Rain fade is going to be a natural occurrence with any frequency other than 6 GHz, with higher frequencies like 23 GHz being impacted quite a bit more.

There are a few things you can do to improve performance:

1. Make sure the alignment is exactly on the projected value. Any deviation greater than 3 dB from the alignment will result in substantially worse rain fade than specified in the path calc. See:
   Antenna Alignment Guide : Trango Support
   Receive Signal Level (RSL or RSSI) is Too Low : Trango Support
2. Ensure ACM is enabled to provide ~20 dB improvement in rain fade from QAM256 to QPSK. (May need to license/coordinate this change.)
3. On newer radios with newer firmware, enable ATPC + ACM with increased tx power (Adaptive Power Control) at the lower modulations. This will provide an additional ~6 dB of transmit power when the modulation shifts in very heavy rain. (May need to license/coordinate this change.)
   See: ATPC with ACM - Adaptive Power Control : Trango Support
4. With AP1 radios, possibly consider purchasing the extra power key for increased transmit power. (May need to license/coordinate this change.)

If all of the above options have been exhausted, return to the path calc and examine the figures used for rain rate and the the link availability (the annual rain (%-sec) line. Based on historical data and with the assumption that all other data on the form is correct (most notably the RX signal), this will give you an expected average % of time that the link will be available and the number of seconds over the year that the link will not be able to run at the selected modulation. For example, if the Annual rain (%-sec) line shows: 99.99710 - 913.26, this link on average should experience an uptime of 99.99% and will be unlocked 0.01% of the time because of rain - or 913 seconds on average per year. This is 15 minutes per year and could be all at once during one torrential rain-pour, spread out across two, three or more storms, or possibly even not occur in one year and be down for 30 minutes the next year.

Beyond those suggestions and analysis, if it is determined that rain fade is impacting the link beyond the tolerable amount, one would have to consider increasing the size of the antennas, switching to a lower frequency or switching to a model that would allow higher transmit power.