What to check when you experience service issues with your satellite downlink
Hereby to explain what you should check
and measure at the Satellite downlink when you experience service/satellite
reception issues.
Always keep a spectrum analyser 365/24/7
permanently running in live+max+min hold, like we always do, on the carrier(s)
you are receiving. This is so that you can check for any possible local
reception problems with the carrier(s).
Here is an example of our spectrum
analyser when an airplane flew through our downlink beam (26 Feb 2016).
If you experience this then go to www.flightradar24.com and check the air traffic near the
downlink in the direction of the satellites to see if this could be the reason
for your reception issue.
If you are near an airport with many air
movements, then you can expect similar issues.
Email the plot to us here in EVC via email
evc@eurovision.net or send it via Telegram chat https://t.me/EurovisionEVC so we can check with our downlink.
We have multiple downlinks from all our
teleports so we can see if the problem is your downlink or
satellite/transmission related.
Check the Novelsat Demod for frame errors.
This needs to be zero at all time. Please
clear these prior to any transmission and check whenever you have (video/audio)
issues if the counter increased.
Email the snapshot to us here in EVC via
email evc@eurovision.net or send it via Telegram chat https://t.me/EurovisionEVC so we can check with our downlink.
Check the Novelsat Demod for events in the
event log.
This needs to be empty at all time. Please
clear these prior to any transmission and check whenever you have (video/audio)
issues if there are any events listed.
Email the snapshot to us here in EVC via
email evc@eurovision.net or send it via Telegram chat https://t.me/EurovisionEVC so we can check.
Make sure that the date and time is
correctly synced to GMT.
If you don’t have a C band filter (or one
that doesn’t suppress it enough) then it will be a similar outage time. just a
different response on your spectrum analyser (see below).
You can see here 9 negative spikes which
means 9 radar pulses in 1 spectrum analyser sweep (1 x 100 ms) causing multiple
disturbances.
If the issue is the airplanes (weather)
Doppler radar then it will only happen more often (stronger) as they are amplified
(bundled) by your antenna when they fly towards you and are nearby. Since the
airplanes are continuously moving (direction, altitude, airplane type and size,
radar setting and direction), this changes the situation each time due to these
variations.
https://www.youtube.com/watch?v=4sOcskanw3I
Radar in the nose of an airplane
Manufacturers do not add a band pass
filter in the LNAs/LNBs because these are expensive. Since the LNB
manufacturers need to make sure their equipment works fine in a wide
temperature range (usually -20 C to up to +50 C) and the only way to make this
work is to open up in the input range. Usually this means that you can add
750-1000 MHz extra (manufacturer dependant) both below and above the specified
input range to make this work.
Airplane Radar uses frequency in between
4200 and 4400 MHz. Since this power is above the official input specs from the
LNA/LNB means the in band range will be suppressed (like shown on the spectrum
analyser plot above) resulting in a downlink outage. So the only way to avoid
this is by using a proper CBF (with enough suppression = more is better).
See here a simulation with an explanation
of how the air plane Doppler radar works in the nose of each airplane.
If your downlink station is near any open
water (sea/lake/pond) then it can be affected by humidity. This is the most
likely reason for fluctuations (and loss of demod lock) is scintillation (aka
de-polarisation).
This effect is due to humidity (ea. rising
sea water, fog, high humidity) depolarising your downlink signal. When this
happens you will see the signal ‘dance’ up and down or act like a wave on your
spectrum analyser. See attached video of our Singapore
office downlink to show you what this looks like on the spectrum analyser.
There is a document on https://www.slideshare.net/thandaiah/link-power-budget-calculation-and-propagation-factors-for-satellite-communication that describes this.
Because temperatures can easily be above
50+C in the sun, your outside equipment like LNB/LNA can be affected causing
microscopic signal breakups. You can only see this with a spectrum analyser
running quicker then 1ms with 100 kHz RBW or better. This is because the
temperature range usually is in between -20 and +50 C for the equipment. You
should either provide electronic equipment with a heatshield or cold air flow
to cool it and keep it below +50C (better to be closer to +40 C).
If the presence of motorised vehicles are
nearby your downlink, your problems might even be cause by dodgy ignitions. See
attached two videos what you should see on your spectrum analyser if that is
the case.
If your reception issues are also the air
conditioners you have then the RFI will only happen when they switch on and off
when the aerial attenuation is low (for example low humidity or less/no
obstacles in between antenna and airco unit). I see changes in RFI (caused by
our own and other roof top air conditioners) SNR locally at our Washington
office due to these changing weather related circumstances.
See here a plot to show you what this
looks like on the spectrum analyser.
As you can see is that we catch left and
right of the carrier the aircon RFI at different levels. Because I can’t drop
the carrier but based on our demod frame errors and event logs, we know with
this that there is also still RFI underneath the carrier. So this only means
that it is just not visible on the spectrum analyser (because it is below the
top of the carrier).
Here below is a plot from summer 2016 when
the air conditioners were running more frequently.
The yellow box is to show you were there
is officially no satellite transponder any more (IS34 start at 3700 MHz) so
this is local.
Our confidence return at our teleports is
clean all the time so we know this is not a satellite/transmission related
problem.
Hope this helps. Let us know here in EVC
via https://www.t.me/EurovisionEVC Telephone
+41
22 717 2790 or email evc@eurovision.net
where we can assist with any questions you
might have.
When you contact EBU Eurovision EVC to
report any service issues, please have all off the following:
Max+min+live hold spectrum analyser trace.
(Mention when the last time it was reset).
Downlink setup (C band pass filter,
antenna size, unused ports open or terminated, cable length with brand and
model, etc) Pictures are always welcome to understand the installation (the
more the better).
Novelsat Event log snapshot. (Mention when
the last time it was reset). Make sure the Novelsat has Date and time in GMT.
Snapshot of the Novelsat monitoring page
with the margin, SNR and frame errors (Mention when the last time it was
reset).
Date and time in GMT of the start – stop
times when the issue(s) happened.
www.Flightradar24.com
snapshot (there is a history that allows
you to go back in time so you can see the air traffic at the exact time of the
issue).
It is vital that proper monitoring is done
at your downlink, like we do, if you want to find the reason for the issue(s).
All the info can be sent via Telegram to
us on https://www.Telegram.me/EurovisionEVC
or via email to evc@eurovision.net
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