Re: daily cyclic signal change

David J Taylor GM8ARV 🏴󠁧󠁢󠁳󠁣󠁴󠁿 🇪🇺

On 01/06/2021 17:22, Hendrik Fleming wrote:
After using Eumetcast for a year, I only now got David’s statistics running on my site.... I am very slow... I also watched the daily variation in SNR, also started wondering how to get it stable. Dish is an old motorized dish with a controller stemming from 1997, but was wondering if modifying the whole mount system so that elevation and skew can be changed and controlled with something more modern,  but that is a long-term project for me.
here is my daily variation of HVS-2 over here in Norway. (Only monitoring it for the past few days, and the major dropout on day 2 was because of a heavy cloud-cover)

Delighted to see that the software is of some use. If you have a Web site where you could upload that data I'd like to add it to the Europe-wide charts here:

The daily variation has been discussed quite a lot, and I suspect there is no single cause.

- The satellite output may vary - we do see changes from time to time and they are usually obvious when comparing the results from several stations. I don't believe this is a contributing factor.

- The satellite pointing may vary. For those in the centre of the beam sent from the satellite there is little variation, but towards the edge of the coverage the effect will be greater.

- If the receiver dish is not directly pointed at the satellite, the signal will be towards the edge of the beam polar diagram, i.e. not at the flat part of the response but where the response is less a degree or more from the centre. In this part of the response any movement in the apparent satellite position will result in a change of signal level which is much greater than at the top part - the flat part of the response curve.

- The receiver dish may change alignment through temperature changes during the day and night. Perhaps this effect is greater in the summer?

From your system description, I do wonder how accurately you can point your dish with that motor and controller? Satellite TV often has a greater signal level so that small pointing errors go unnoticed. If possible, I suggest trying a very small manual adjustment of the dish pointing to see whether there is any improvement. You should also check the skew (twist) on the LNB as good rejection of the cross-polarised signal is important.

Having said all that (phew!) 4 dB is /just/ adequate. Oslo looks to be a little further off the main beam than Edinburgh, but past experience suggests that the coverage may not be exactly as the prediction shown here (and attached):

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