Cambium epmp 300-25 getting low signal in winter

Hello there,
Can anyone facing this kinda issue?
cambium Force 300-25
while day time device is performing very well but after evening getting signal very low.
How to get rid of getting very low signal issue at night time in winter.
there is 22KM distance between access point and station point.
Access point tower height 80feet
Station point tower height 80feet.

I would be really very helpful to have your answer.
Thanks in advance.

What is the signal during the day vs night ?
What are the MCS rates during day vs night ?

Does the AP have other customers on it ? Are they also getting lower signal ?

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Thanks for replies…

Downlink RSSI -67 dBm
Downlink SNR 20 dB
Uplink MCS 6
Downlink MCS 5


Downlink RSSI -85 dBm and above
Downlink SNR 8 dB
Uplink MCS 1
Downlink MCS 1
and got signal lost for hours.

Radio Configuration
Cambium Force 300-25
Device set as ePTP Master slab
Channel Bandwidth 80Mhz
Frequency Carrier 5100Mhz
Distance about 22KM

Wow! So… are there huge temperature changes between day and night? Does any part of this link cross a body of water or perhaps a cemetery?


There is around 28-33 degree at day and 21-26 degree at night.

According to ISP Design
sight view between access point and station point.
device height

"…or perhaps a cemetery? LOL

My first thought is that a 22 km link for a 300-25 with a 16 inch dish AND an a 80 mhz channel is asking a lot. Using F300 CSMs with a high gain dish would be a better solution if you are on a budget.

Is this actually a back haul or just a point to point for a customer? What you are describing sound like classic temperature inversion issues, which can be seriously worse if crossing water, i.e. the English channel, lakes, large ponds river bottoms, etc which is why Eric asked that question.


Sounds like thermal ducting, temperature inversion, or maybe fog coming out of the trees if it gets cool enough.


I’m very curious about this question…


it is a point to point connectivity.No, there is no lake, but link passes by some river and green land

I’m sure @Eric_Ozrelic was referring to this:

Ghosts occur when transmissions bounce off a mountain or other large object, while also arriving at the antenna by a shorter, direct route, with the receiver picking up two signals separated by a delay.



Is there a possibility of torsional movement of the tower due to temperature changes day and night.
The atmosphere has slight changes in the expansion of the metal. During the day, the sun directly hits the metal, which is several degrees warmer.
The disturbance is more pronounced if the tower is not symmetrically loaded and if it does not have a sufficient number of torsion stiffeners.
The antenna is mounted during the day and adjusted to maximum.
Maybe the night moves it left or right.


So temperature related problems like ducting, inversion, expansion and contraction of the mounting/alignment materials have been covered. Multipath and Ghosts also covered.

All I can add is maybe birds are roosting on/in the dishes ?


Let me add my 2cents here also. Thermal ducting does occur at 5 GHz, but is unusual. The ducts form on North to South links most predominantly. The duct can form at 2-4 AM, with the most tropospheric scatter happing right at dawn. As the sun rises, the ducting dissipates, and by 1 hour after sunrise, the duct is gone. There is a website that predicts tropospheric ducting activity… Tropospheric Ducting Forecast for VHF & UHF Radio & TV ( In past life with Wi-max @ 2GHz, I did an extensive study of ducting to a system in Richmond, IN. Watch TV had a 700 ft tower in Lima, OH broadcasting on 28 channels in the 2.5 GHz band. During the spring (May/June was the worst), around 2 AM, the noise floor on the WiMAX started to rise. At around 5 AM, the systems in Richmond behaved as though we had LOS between the TV tower at Lima, OH and the WiMAX tower receivers in Richmond. Based on the probability from this website, I could predict the timing, and depth of the ducting. Ducting did not occur every night, and after July 15th, and before April 15, ducting was rare. I had a tower crew climb 2 of my WiMAX towers at 1 AM on 2 very high probability days, using an Anristu spectrum analyzer, with pre-amp, we watched the noise floor rise, and after the noise was higher than -90 dBm, we could make out the video, audio carrier, and color burst of each video channel in the analyzer.
So, with ducting, the RSSI does not change, but the SNR does, as the noise floor increases from the interfering site. With strong ducting, the SNR can actually be negative, meaning the noise is higher than the signal. I would say that ducting is not a candidate for this reduction of signal strength, especially if the RSSI reduction happens on both ends of the link.


I think this is a tower problem. What kind of tower is it? What height? Is there any tie (sorry, don’t know the right english word)?
Looks like some element changing with temperature and modify the radio orientation.

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I noticed you used ISP designer, have you modeled this in LinkPlanner? if not please do so just to confirm as I have had issues with ISP designer not being accurate in some locations.

I do think that you are seeing some sort of thermal ducting that is going away at night, this could also be an alignment issue that you aligned into a strong sidelobe with a reflection and the thermal duct now prevents the reflection at night.

22km on an f300-25 link? I know it is doable, but damn!

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