noise on C-band

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tkozloff

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Jun 2, 2005
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I have a C-band dish which works well about half the time, and about half the time it has extensive clicks, pops, pixellation, complete signal drop-out, etc. I have not been able to correlate the noise with anything in particular, except that during warmer weather (!) it is a little worse. It appears randomly at all times of day, in any weather (clear, rainy, windy, hot, cold) and for all satellites (except that the Weather Channel on Sat C-3 never gets knocked out completely). High winds do NOT accentuate the problem. In fact, I have had prolonged perfect reception duing strong winter storms.

I have tried the following fixes, none of which have had ANY effect:

1. Bought a complete new receiver (a General Instruments/Motorola 922)

2. Bought a complete new feedhorn/LNB

3. Had the dish realigned

4. Recentered/retuned each satellite

5. Turned off all electronic equipment in my home. (Occasionally I could correlate pressing the "Enter" key on my computer with a pop in the satellite
audio, but turning off the computer, WiFi network, etc. did not eliminate the problem.)

6. Powered the entire satellite system off a shielded isolation transformer.

NOTHING helps. I can go for days with a beautiful, clear signal, and then suddenly it goes to hell. Usually, if I wait an hour or two, the interference goes away. Buit it comes back, sooner or later.

Any ideas?
 

mkm4

SatelliteGuys Pro
Oct 13, 2003
617
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tkozloff said:
Any ideas?

You seem to have tried everything but replacing cables. Try putting on new barrel conennectors on the cable from the sat to the IRD and/or try new cables from the IRD to your TV.

If that doesn't work it might be interference from radars.
 

drhydro

SatelliteGuys Pro
Oct 19, 2004
1,572
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I have to agree with mkm4 about replacing the cables. Try running a new run of rg6 temporarily from the LNB to the IRD and see it that helps.
 

tkozloff

New Member
Jun 2, 2005
4
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When I replaced the LNB, we replaced all the cable ends/connectors, but not the cables themselves. A spectrum analyzer was applied to the signal coming out of the LNB, and it occasionally showed the noise; we just couldn't determine its source. And if the problem is the cables (or radar), why is the noise sporadic? Usually, if I wait an hour or two, it goes away.

Another curious aspect to the noise is that it begins with a dropped signal (short silences), then after a few minutes rises to silences punctuated by pops and clicks, and then finally to predominately pops, clicks, squeals and other noise with very little actual signal coming through. It would seem very strange if this random timing coupled with a noise creshendo were caused by radar or bad cables.

And why do I get the Weather Channel without interruption? In the worst of the noise, the WC will sometimes show a sparkle or two but no more, while all the rest of the satellites and channels will be badly pixellated, with regularly occurring blank screens.

Again, any ideas would be much appreciated.
 

mkm4

SatelliteGuys Pro
Oct 13, 2003
617
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tkozloff said:
And if the problem is the cables (or radar), why is the noise sporadic? Usually, if I wait an hour or two, it goes away.

Again, any ideas would be much appreciated.

An AWAC or similar radar plane, flying overhead would give sporiadic outages.

Also from this web page:

Terrestrial Interference

If you have a C-band receive system and are having problems with a specific range of frequencies at certain compass headings, you may have a terrestrial interference problem. Those local towers you see everywhere carry lots of information using the same frequency range that you use for reception. Long distance services using local networks are the worst cases. If you live near a military installation or major airport you may also experience periods of interference from their radar and communications equipment.

Some aircraft altimeter radar use these frequencies. If you live directly under a heavily used air traffic route you may also experience problems. This is especially true when receiving digital C-band transmissions. This problem usually manifests itself near major airport flightpaths.

The flight path for the airport may also cause the aircraft to physically intersect your reception path while at low altitude. The interruptions from this problem are usually brief and there is no remedy except praying for a change in wind direction so that the flight paths change.

There are several possible remedies available to help you solve these problems. These include a whole range of tunable notch filters, rejection filters, and screening filters. You may also find that moving your dish to a location that is shielded from the interference source is a viable option. If none of these options are feasible or appeal to you, there is also the possibility that a shielding fence or ring will solve the problem.

If you have access to a spectrum analyzer you can usually see the interference as it occurs. Your satellite installation personnel should be able to perform this frequency inspection if they have an analyzer, but only during an actual case of interference. This may prove difficult as most interference cases are intermittent.

A good indication of terrestrial interference is a problem that repeats in the same frequency range and at the same time of day consistently. The problem may be a long distance service if it occurs between the hours 7:00 PM - 10:00 PM or on weekend afternoons and evenings. These are the peak long distance hours for any given time zone.
 
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