Ku dish size question

[Brct203]

i'm playing a bit with a 6ft Ku offset Channel Master dish and comparing reception to a 90cm Fortec Star offset

The surface of reception being proportional to the square of the diameter, and 3dB being roughly equivalent to doubling the signal strength, one would expect about 6dB more on the SNR for each transponder.

And for the most part it is pretty close, I'd say 5 to 6 dB, with LPB at 9dB compared to 3.5, and some strong transponders getting to 18-19dB (I did hit 20dB in the past when NHK was still on 103W).

Now there's one satellite where I'm seeing a much more modest improvement: 99W. Sure it's better than on the 90cm, but for example the 90 cm gets the PBS mux at 12.6dB and the 6-footer gets it only at about 14.5dB, so barely a 2dB increase

any idea as to why that would be? Could it be that that's about as good as it gets, and maybe the noise floor is caused by other signals (or maybe even the uplink) rather than the noise floor of my dish and electronics? (meaning a large dish gets more signal but also more noise )

Thoughts?

 

[comfortably_numb]

I've heard others say that there is a point of diminishing returns with dish size relative to KU reception, but I don't recall who said that (or when).

 

[cyberham]

How do they compare if looking even further west to the most western satellite you can receive? I wonder if going through a lot more atmosphere has an adverse effect. After all, 99W is haunted according to comfortably_numb.

 

[comfortably_numb]

After all, 99W is haunted according to comfortably_numb.

 

[Brct203]

I've heard others say that there is a point of diminishing returns with dish size relative to KU reception, but I don't recall who said that (or when).

interesting observation... we're having a bit of a thunderstorm right now - light rain but with large raindrops, but thick dark clouds in the line of sight to 99W.

I could see the SNR on the 90cm dish go down faster than on the 6-footer, and the 2dB difference was at some point more than 5dB difference on 12140V. For a while the 6ft signal was rock solid while it was long gone on the 90cm. Eventually even the 6ft lost it as it dropped to 5dB (and still 3dB on the 90cm).

in other words, the larger dish was a lot less affected by the rain fade, up to a certain point - and not just because of the added signal margin

at some poiint the SNR on PBS went from 14dB and 12dB (6ft and 90cm respectively) to 10dB and 5dB