Temperature and 450 900 MHz


Over the past month I have noticed what seems to be an apparent correlation between Signal Level, SNR and Temperature.

As this being summer here in the States the temperatures for the most parts have been in the mid 80's to high 90's

As the temperatures decreased I noticed that the receive signal level would increase a dBm or so and would in turn increase the aggregate throughput.

This past Monday the morning temperature was in the mid 60's.

I accessed the web interface for the 450 900 Mhz to check the link status and this is what I discovered.

Receive Power         -75 (-78 B / -78 A)

SNR                         19 B / 17 A

Session Status             18  8X/4X MIMO-B

                                136  8X/4X MIMO-B

Downlink               26.91 Mbps

Uplink                    9.01 Mbps

Aggregate               35.92 Mbps 

Current link status with the temperature is in the low 80's

Receive Power         -82.5 dBm ( -86.0 dBm B / -85.0 dBm A )

SNR                         10 B / 9 A dB

Session Status             18  8X/2X MIMO-B

                                136  8X/2X MIMO-B

Downlink               13.35 Mbps

Uplink                    4.50 Mbps

Aggregate               17.85 Mbps 

Is this normal to see such fluctuation in performance due to temperature?

Is there something wrong with the radio or antenna?

What have others seen with regards to temperature?

Look forward to the input.  Stay safe everyone.

What's the humidity like during these swings? What kind of trees are you shooting through?

Q: What's the humidity like during these swings?

A: humidity is fairly constant

Q: What kind of trees are you shooting through?

A: pine trees

We test all products through the entire stated operating range (from -40 to +60 C) to validate consistent performance across this whole range.  What you are experiencing seems environmentally dependent, and could be due to some kind of rf ducting phenomenon.

We certainly do not see similar performance variation over temperature normally.

Hi Matt

Thanks for the reply.

I do not have the understanding or depth of knowledge that you and others have on this form so I am unable to question the possible cause being RF Ducting.  I will read up on it and try to digest it.  Maybe a little fasting would help.

That being said how can I rule out equipment malfunction? ( Radio or Yagi )

With a link distance of 3 miles over dry land does RF Ducting have that much affect?

Does this suggest that during the colder months that the performance of the link will increase?

Am I the only one experiencing this?

Thanks again.

Regarding humidity, I wanted to know what the humidity level was like in your region. High humidity through trees can have an effect on 900MHz non-LOS links.

I've seen my 900MHz PtP link have some pretty big swings, but it's typically during heavy rainfall, when the trees are saturated with moisture. I've also noticed when it gets really hot that the link might lose a few dB, and I attribute this to the trees sucking down more water and thus there's more foliage, but that's just a theory.

Hi Eric

Rain does not seem to have a negative impact on the link as a matter of fact it seems to improve the performance a bit.