Eb/No seasonal variations?

Hello Chris,

This can happen because of a few reasons, some reasons comes into my mind:
1. The dish is not pointed exactly to the center of box of the satellite, so your EbNo varies.

2. At night your LNB performs better because of lower temperature.

3. You have some humidity in your feed system which drains into water at night, which improve your performance.

4. Less likely, but especially at lower elevation and at special places around the globe, at certain seasons, you might be affected from scintillation. Try to take a look at this link for example.

https://www.ips.gov.au/Satellite/1/1

HI Chris,

As far as I know, scintillation will not affect Ku band, but maybe Im wrong.

What is your dish size and what satellite are you pointed at?

I would recommend you to check for condensation in the feedhorn window during the day as well.

Kind regards,
Nimrod

Pointing errors, with fixed dish, allow variations of signal level over the day to occur due to satellite movement.

Ideally you should peak up the dish pointing when the satellite is at the centre of the stationkeeping box.  This is  often not reliably practical as it may occur only once every few weeks or daily, depending on the east-west position which drifts slowly over many days. Contact the satellite operations center for advice.

The satellite movement in this case is an ellipse, gradually changing size and drifting sideways. If north-south station-keeping is ceased, the daily movements gradually become an elongated north-south pattern, as the inclination increases at the rate of 0.8 deg per annum, to form a classic figure of eight pattern.  Little fuel is needed to maintain east-west stationkeeping, but it is quite normal to allow satellites to use a full daily range of +/- 0.1 or +/-0.15 deg in all directions.

Typically a satellite might be launched with 'negative' 0.5 deg inclination, this being allowed to decrease to zero during the first few months, and, towards end of life, after say 15 years, the inclination will be allowed to increase above 0.15 deg, to say 3.2 deg over a further 4 years of 'inclined orbit' operation.  

Tropospheric scintillation occurs particularly at low elevation angles.

This example is Ku band tropospheric scintillation at 5.4 deg elevation, due to boundries between layers of moist and dry air in the lower atmosphere.  To minimise rain attenuation, rain noise and tropospheric scintillation effects, avoid C band operation below 5 deg, and Ku band operation below 10 deg elevation.

Ionospheric scintillation is noticed in the tropics and at low frequencies like L band and C band.  It is associated with sun-spot activity and peaks every 11 years.

Best regards, Eric.