A
archive10
Guest
Just realised how much the atmosphere can influence reception quality (and therefore any test results comparing dish X with Y with same/different LNBs at different installs!)
In another thread, I was bewondered by the difference in strengh and - more significantly - quality (C/N) readings between apparently similar days.
It seems that moisture in the air and probably also inversion layers etc has a significant role to play:
Earlier this evening (around 18:45), I re-aligned my CM180 to 28.2E, focus on 10773H (BBC Mux).
Weather was good, mostly clear skies (no Cu), but some cirrus southwards.
After much careful alignment, I maxed out at around 10.4 dB C/N ratio and 69.8 dBuV strength.
Didn't seem quite up to previous results, but that was what I could coax out of the set-up.
Got similar readings across the other 2E/F transponders.
Left the whole thing rigged up with meter etc, and went for dinner.
Checked 10773H again at 21:30, after sun-set. The evening had taken over. The dew had fallen...
And lo and behold! At slight increase in strength from 69.8 dBuV to 70.6 dBuV, but an increase in C/N ratio from 10.6 dB to 13.5 dB!
That's 3 dB!!
The 3 dB increase in C/N was consistent across several other 2E frequencies (didn't test others).
Now this may be due to sat fluctuations, but I have a strong gut feeling this is due to moisture disappearing, and/or other changes to atmospheric conditions such as temperature inversion layers etc.
This shows just how much dispersion and distortion the microwave signal suffers from passing through water and water vapour in the atmosphere.
And makes you think about signal strength reporting - not only is it influenced by orbital fluctuations, it is quite weather dependent too!
In another thread, I was bewondered by the difference in strengh and - more significantly - quality (C/N) readings between apparently similar days.
A little strange experience over the past few days:
I tested various LNBs on tuesday. Got consistant 12.5 dB C/N readings on 10773H with both Inverto Black Ultra Quattro and Inverto Black Pro + CM feedhorn.
Measured several times having swapped the feed back and forth.
All yesterday, I suddenly got 11 dB on 10773 (and similar drops on other 2E transponders) - without changing anything from the last 12.5 dB measurement.
This evening, I'm down to 10.2 dB, even across a span of several hours. Still not changed anything physical. Weather is splendid - clear skies and not a cloud in sight.
Signal strength has also dropped, but only around 0.8 dBuV.
There could be several reasons:
1) Dish has moved. Very unlikely, the dish has been up 4 years now, and survived several gale-force storms wihtout budging. Difficult to see why it should move in light winds in the summertime.
2) LNB is not fastened properly after experimentation work, and is "un-skewing". Not the case, the LNB is firmly fixed to the LNB holder.
3) Daily fluctuations of sat orientation. But this should be over the period of a day, but with similar readings at same time on different days.
4) General fluctuations in satellite orientation. Not sure if 2E changes regularly that much??
5) Moisture in the air - assuming that moisture absorbs and disperses signal. But the airmass seems to the same, and we're talking up to 2+ dB now.
Dunno - maybe it's a combination of many factors...
Weird thing is that 2G readings on 11023H taken at the same times are roughly the same, with a light reduction in strength (0.5dBuV) and possibly eve a slight increase (0.2 dof C/N.
Does anyone else reckognise this behaviour?
Is this what you guys experience regularly?
Short-period (days) fluctuations of 2+ dB?
It seems that moisture in the air and probably also inversion layers etc has a significant role to play:
Earlier this evening (around 18:45), I re-aligned my CM180 to 28.2E, focus on 10773H (BBC Mux).
Weather was good, mostly clear skies (no Cu), but some cirrus southwards.
After much careful alignment, I maxed out at around 10.4 dB C/N ratio and 69.8 dBuV strength.
Didn't seem quite up to previous results, but that was what I could coax out of the set-up.
Got similar readings across the other 2E/F transponders.
Left the whole thing rigged up with meter etc, and went for dinner.
Checked 10773H again at 21:30, after sun-set. The evening had taken over. The dew had fallen...
And lo and behold! At slight increase in strength from 69.8 dBuV to 70.6 dBuV, but an increase in C/N ratio from 10.6 dB to 13.5 dB!
That's 3 dB!!
The 3 dB increase in C/N was consistent across several other 2E frequencies (didn't test others).
Now this may be due to sat fluctuations, but I have a strong gut feeling this is due to moisture disappearing, and/or other changes to atmospheric conditions such as temperature inversion layers etc.
This shows just how much dispersion and distortion the microwave signal suffers from passing through water and water vapour in the atmosphere.
And makes you think about signal strength reporting - not only is it influenced by orbital fluctuations, it is quite weather dependent too!
) 