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Interference every day at the same hour

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mmurtas
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May 31st, 2012 at 11:20am  
Goodmorning,


Everyday, from approx 09:45 to 10:45 UTC and approx 21:45 to 22:45 UTC an interference rise the noise floor of the FWD carrier then the Downstream C/N of the satmodems decrease.
The behaviour is very similar to the sunoutage, but in my area no sunoutages have been programmed in may for the satellite E10A (C band).

There is an another sun phenomena that may affect the service?

Thanks,
Best Regards
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« Last Edit: May 31st, 2012 at 1:03pm by N/A »  
 
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Eric Johnston
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Reply #1 - May 31st, 2012 at 8:16pm  
Some ideas:

A reduction of the transmit power of the forward downstream carrier from the teleport hub into the satellite.
 - Is the BUC getting very hot when the sun shines on it sideways in morning and evening ?
 - Is the hub dish very large and fixed pointing and is the satellite moving out of the beam centre ?
 - is your hub electrical mains power supply voltage stable ?

Interference on the uplink to the satellite on the same frequency as the forward downstream carrier.
- Look on a spectum analyser and see if you can observe an interferer.  Does the spectrum of the interferer correspond to the cross pol spectrum ?
- does the interferer come and go instantaneously or does it gradually increase and decrease.

Satellite beam movement
- Is your hub site at the extreme edge of the uplink satellite beam where daily satellite beam pointing errors may be noticiable.

Sun or moon noise effects should only last a few minutes.

Best regards, Eric.
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mmurtas
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Reply #2 - Jun 20th, 2012 at 8:24am  
Dear Eric,

we can exclude a BUC issue because with the same antenna we deploy another service, free of that.

we can exclude the interference on the uplink to the satellite because this behaviour is different according to the satmodem

we can confirm that our hub site is not at extreme edge of the uplink satellite beam

There is also another useful info... since few days we have observed the same phenomena with some satmodems that worked on another satellite. The window time is the same (from 09:45 to 10:45 UTC and approx 21:45 to 22:45 UTC).

Best Regards,
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Eric Johnston
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Reply #3 - Jun 21st, 2012 at 10:19am  
If the rise in the noise floor of the FWD carrier and decrease in Downstream C/N applies to all remote sites on one satellite, and simultaneously to some remote sites on another satellite, then I would look at the spectrum of the interferer and try to find the source. Is it cross-pol on one of the satellites or high level carrier on very close satellite. What are the polarisations involved ?

Examine the interferer.  Is it a typical digital carrier ? What is its bandwidth ?  What is its centre frequency ?  Is it continuous or TDMA ?  If it is not a regular digital carrier what does it look like ?  Is it a drifting CW, jagged spikes, pulsed etc. Do look over the full span of the transponder in case your 'noise floor increase' symptom is just a side effect of some giant new carrier appearing several MHz away, for example.

It would help to plot the spectrum with and without the interferer at sites with small and very large dish and also the cross pol spectrums.  Communicate with the satellite NOC once you have full documented the problem. What do the spectrums of nearby adjacent satellites look like ?

Does the interferer come and go instantaneously or does it gradually appear and disappear?

If your hub BUC is transmitting more than one carrier then please plot a spectrum of your transmitted BUC output. You may be causing the interference yourself due to intermodulation.  Do your hub uplink carriers or BUC power supplies change in any way ?

Does anything physical occur simultaneous to the interference at or near your hub site e.g. someone visits carrying switched on radio/mobile phone, someone using kitchen equipment, taxi parked outside, ferry in nearly harbour with radar on etc.

Best regards, Eric.
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« Last Edit: Jun 21st, 2012 at 2:14pm by Eric Johnston »  
 
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mmurtas
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Reply #4 - Jun 23rd, 2012 at 11:17am  
Dear Eric,

The issue for E10A (C band frequency, circular pol) is finished on June, 6th 2012. We have registered the new issue on another satellite (20 degree away).  At the moment we detect the issue only on satellite E36B (Ku band, linear pol, Forward carrier with ACM, BW=1300 Mbps).

We suppose that the issue depends also by the installation. Since the issue is not detected by all the satmodems we think that the issue is not caused by our forward carrier.

Please find below the plot (typical behaviour for the outages)
...


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Eric Johnston
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Reply #5 - Jun 23rd, 2012 at 3:28pm  
Well done making the plot of C/N. The gradual nature of the change rules out several possible causes of interference.

I am still uncertain.

This is consistent with a mispointed remote site antenna, such that the small daily movement of the satellite causes the satellite to move noticably down the side of the antenna beam.  Try peaking up the pointing.

This problem is normally associated with larger, fixed pointing, antennas and near end of life satellites with increasing inclination.  Eutelsat 37E (W7 2009-65A) was launched in 2009 and its stationkeeping will be +/-0.15 deg or better.

You have done well to detect this relatively small (-1.4dB) anomaly.  If this causes an outage then your clear sky link margin is too small.  Even light rain at Ku band will cause an outage.  A 3 dB link margin would accommodate your -1.4 dB uneventfully.

Many systems suffer drops of 1.5 dB and no one worries about it.  

There is another older satellite 36A (W4 2000-28A) at the 36E location and I would not rule out some periodic interference ( co-pol or cross-pol ? ) effect.

Best regards, Eric.
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mmurtas
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Reply #6 - Jul 6th, 2012 at 11:16am  
Dear Eric,

The issue is suffered by more satmodem in the network. We have two different test satmodem in the network, with the same type of antenna (120 cm). Only one is affected. As you suggested, I think the the issue may be caused by a mispointing.

Ref: http://s10.postimage.org/vm1via46h/sat1.gif

...

Regarding the old satellite, I wish to reminder you that we registered the same issue, one month ago, on E10A satellite.

Many thanks for you support,
Best Regards
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Reply #7 - Jul 6th, 2012 at 12:21pm  
Sun outages, due to a very high increase in noise floor, are associated with the sun passing through the main beam of the antenna.

Small, normally unnoticed, increases in the noise level will also occur when the sun passes through the antenna sidelobes. I wonder if this is the case.  Sun outage calculators require the antenna size and frequency to be inputted.  Pretend the antenna is much smaller with a very wide beamwidth.

To evaluate this possibility we need to know the lat/long of the affected receiving site, the satellite orbit position and the date/time GMT.

It would be of interest to know the size of the remote antenna and frequency also.

What is the relevent satellite uplink beam coverage map. If the beam extends beyond the edge of the earth the sun noise could enter on the uplink ?

I've copied your pair of S/N graphs to the satsig server as I note that your earlier one on imagehost.it has gone missing and is now a broken link above.

Best regards, Eric.
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mmurtas
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Reply #8 - Jul 6th, 2012 at 7:11pm  
Please find below all the answers:

- All the affected satmodem are located in the Tyrrhenian sea

- Satellite: E36B - 36°E / Ku band. I have not the Uplink coverage map anyway all the satmodems are sited in a good position (G/T = +3 dB/K)

- The time is UTC

I already checked for sunoutage, but them were in March.

Regards
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Reply #9 - Jul 6th, 2012 at 9:21pm  
Regarding the Satmodem 2 above, the center of the event occurs about 08:58   What time zone is this ?  I need it converted to GMT.    What date, if possible ?

Please what are the lat/longs of the Satmodem 1 and 2 sites ?

What is the surface in front of the antenna in the direction towards the satellite ?  Sea or metal deck perhaps?

What struts support the feed ?  Are there any wires in the air obstructing the beam ?  Wires and sub reflector support struts cause sidelobes.

Best regards, Eric.
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« Last Edit: Jul 6th, 2012 at 10:35pm by Admin1 »  
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COTPjohn
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Reply #10 - Jul 7th, 2012 at 3:02pm  
Is there such a thing as MOON OUTAGE?  Do these outages occur at exactly the same time or might it be closer to the moon cycle?
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Eric Johnston
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Reply #11 - Jul 7th, 2012 at 5:11pm  
When the moon is behind the satellite the noise level does increase, but by less than with the very much hotter sun.

Example:
Assume your LNB/antenna has noise temperature of 150K
Assume sun noise temperature is 8000K
Assume moon noise temperature is 220K
Antenna gain = 41 dBi

Normal earth station G/T = 41 - 10log(150) = 19.2 dBK
Sun conjunction earth station G/T = 41 - 10log(8150) = 1.9 dBK
Moon conjunction earth station G/T = 41 - 10log(370) = 15.3 dBK

Earth station G/T is a critical factor in the link budget so your overall C/N will decrease and certainly fail with the sun conjunction.

I'm puzzled why the event occurs every day.  Sun or moon events normally happen daily, for a period of up to a few minutes, for a period of about 7 to 9 days, with negligible and brief effects on the first and last days and most intense and prolonged effects on the central three days.

Best regards, Eric
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« Last Edit: Jul 7th, 2012 at 9:07pm by Admin1 »  
 
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mmurtas
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Reply #12 - Jul 9th, 2012 at 10:17am  
Dear Eric,

Many satmodem suffer this issue, them are located in all the area of the Tyrrhenian sea (CEST: UTC+2). For example one point is 40°N, 11°E. The issue is started one month ago and it is still present.
The antennas are different... some plastic dishes (Andrew 120 cm: http://www.satsig.net/cgi-bin/yabb/YaBB.pl?board=direcway;action=display;num=117...) and other metallic ones.

Best Regards,

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Eric Johnston
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Reply #13 - Jul 9th, 2012 at 11:28am  
Satellite 36 deg east
Site 40N 11 E
Beam pointing Azimuth=144 true, Elevation=37

Time of anomaly 8:58 am UTC+2 =  6:58 GMT

On 9 July, today:
Sun azimuth 144 deg, elevation 70.2 deg, at 10:40 GMT
Moon azimuth 144 deg, elevation 45 deg. at 02:05 GMT

So conclusion is that it is not due to the sun or moon.

There are two satellites at 36E. Maybe as they move some slight interference occurs.

It would be worth plotting the spectrums before and during the anomaly and looking to see what differs.

Do Eutelsat have a monitoring site at Cagliari in Sardinia? They might be willing to help but if they are busy beware that they may regard this as a timewasting investigation into a minor degradation.  Make it clear that the degradation does matters to you. It certainly needs investigating as it might get worse !.

Best regards, Eric.
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