Explanation why SNR goes up and down daily


#1

I noticed my SNR goes from abut 6.8 to 11.8, with 11.8 dB occurring at night. The solar flux at L-band is essentially nothing, so what causes it to go up and down cylically? Is it the thermal noise going up and down in the on-antenna LNA? Just curious.
Thanks.


#2

from about 3 to 6pm PST mine will drop to 4ish from 12.


#3

Hi, I’ve also asked myself the same … will it be something related to the rotating movement of the earth? with my DC and the active antenna the SNR stay between 8 and 10 db improving when the sun goes down (11-12 db), and with my helical home building antenna and RPI3 + RTL-SDRV3 the SNR stays between 11 and 12 db improving at night (13-14db) Americas 98 W from Paraguay - South America


#4

What radio signal doesn’t improve at night? If i find a decent article that explains this i will post a link.

OK i cant be bothered to look through countless articles trying to find what i want. In short there is less interference and less traffic at night.


#5

Notice a cycle as well… some times sits around 5, sometimes around 2.5. Have not been able to nail down the time of day around it, but been meaning to put a fan on the board to see if it helps stabilize some of the summer heat impact here.


#6

Anything from 60M to 10M gets WORSE at night. Have you ever operated on HF?


#7

No i havent operated on HF, but i would like to know the science behind your statement. I cant find anything to support that actually.


#8

Discussion of what frequencies and when took under one second in google. Here ya go:
http://www.radio-electronics.com/info/propagation/ionospheric/hf-propagation-basics.php


#9

I dont know, maybe i am just an idiot, but from what i just read HF should work better at night.


#10

Negative. It doesn’t work that way. Certain portions of the ionosphere are optimized during certain periods. Lower frequencies earlier and thus also much later. You should get your ham radio license and try it out!


#11

Yes Higher frequencies work better during the day, and lower at night. 20m seems to be the approximate dividing line. However this is only true for signals being refracted off the ionosphere. I have been wanting to get my ham license for years however the closest exam location that does testing on the weekend is about 80 miles away, and the test is at 9am. I would have a hard time getting out of bed at 7am just to take a test. :grin:


#12

Well there ya go. The good news is you only have to do it once if you study all three levels.
(at least in America). Many have done all three tests at once (ya gotta).


#13

It will be the best get out of bed thing you ever did. I did mine and it has opened up a whole new world and now with all the satellite stuff. I am now into the next frontier SPACE.


#14

The answer is really interesting: The Inmarsat satellites are not in a geostationary orbit, but only in a geosynchronous orbit. They don’t orbit the earth along the equator, but on a slight tilt. So what happens is that the elevation changes slightly - up and down during the day. That pattern is actually a figure eight that is very narrow called an analemma. Geostarionary satellites are a special case of geosynchronous satellites. Their orbit is aligned exactly with the equator. They appear at one spot.

You can see the orbital position of the satellite carrying Outernet over the Americas here.
Inmarsat 4-F3

Notice it’s higher up in the sky at night and then lower during the day.

–Konrad, WA4OSH


#15

Only on what hams call the “low bands”, from 7 MHz and lower in frequency. The radio waves tend to follow the follow the surface of the Earth at night and not absorbed as much resulting in quieter background noise. This is all part of a much larger picture called RF Propagation, a very difficult science to predict. Remember the Sun is major contributor to all this, even at L Band.