[amsat-bb] Day/Night SNR above 1GHz??

[Dani EA4GPZ]

El 07/11/16 a las 06:43, Scott escribió:
> Hello everyone!
> 
> With talk of some of the future amateur satellites using higher and
> higher frequencies, I can assure you that I for one am going to have
> a lot of questions about the world above 1GHz.
> 
> Since I have been taking baby steps by monitoring L-Band with some
> success, a pattern has become so regular that I wonder if it will be
> applicable if/when I am ever equipped to work next generation AmSats
> in the GHz range.
> 
> I have noticed (quite reliably) that the quality of my received
> signal easily doubles at night.  One example would be the Outernet
> data stream from Inmarsat 4-F3.  The SNR value reported by the
> Outernet software might be in the area of –6- during the day, but
> often jumps to –11- or –12- (or even higher) at night.
> 
> Is this normal?  Should I generally expect to have significantly
> better performance above 1GHz at night (at least in the case of
> ground-to-space contacts)?
> 
> If so, of course that would be nice to know before trying to work
> nextgen satellites on those higher frequencies.

Hi Scott,

I wouldn't expect that day/night plays any significant role on microwave
propagation.

In fact, propagation effects that do play some role in terrestrial
microwave propagation are much harder to notice for satellite
communications, just because the propagation path through the lower
atmosphere is shorter. For instance, rainscatter is really a thing for
terrestrial microwave, but for satellite it takes a huge storm for one
to notice anything. I managed to obtain some good results on 12GHz
during a big hailstorm:

http://destevez.net/2016/05/hailstorm-in-12ghz/

Have you considered that the difference is not in signal strength but in
background noise level. Maybe you have local QRM from devices that only
run during the day.

The sun is also quite noisy, but you need to point a high gain antenna
towards the sun to notice. Some parts of the Milky Way are also noisy,
but not so much at 1.5GHz.

I would take measurements of both the noise floor and several 1.5GHz
signals during day and night and compare. SDR recordings would be ideal
for this. Take some SDR recordings at day and night during different
days, then do all measurements on the recordings and compare.

73,

Dani.