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mrradiohead

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Reply with quote  #1 
I am not sure if there is a thread anywhere that addresses this issue. I have a 6' dish permanently parked on 103W and have a Manhattan RS-1933 receiver. The signal on the Ion mux is 90 and the quality is around 75.

The question is - what would be causing the signal to very briefly (1-2 seconds) take a dip where it interrupts the picture (pixel breakup and a hiccup in the audio)? This happens about once every 10 seconds or so. Perhaps there is something in my dish setup that needs attention.

*I posted this in Feed Hunting techniques because I couldn't see any other category that made sense.

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Jim Thomas
Springfield, Missouri

WS1870 1.8m w/2 C lnbf's @ 103w & 97w; Fortec Star 90cm ku lnbf @ 97w; 70cm ku w/3 lnb's @ 87w/91w/95w; 70cm ku @ 103w; 70cm ku @ 103w, all routed through x1 8x1 switch, fed to Manhattan 1933 receiver.
majortom

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Reply with quote  #2 
which ion mux? there are two of them.
And is the manhattan the only receiver you have?

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Perfect 10 7.5' mesh Chapparal C/Ku Co-Rotor feed, Norsat 8115 CBAND, Norsat 4106A Ku Thomson Saginaw Actuator, Vbox positioner,
Home Brew Polarotor683 Servo circuit. Openbox S9, Prof7500, v4l-updatelee linux drivers installed.
TheSatBible

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Reply with quote  #3 
Quote:
Originally Posted by mrradiohead
I have a 6' dish permanently parked on 103W and have a Manhattan RS-1933 receiver. The signal on the Ion mux is 90 and the quality is around 75.

The question is - what would be causing the signal to very briefly (1-2 seconds) take a dip where it interrupts the picture (pixel breakup and a hiccup in the audio)? This happens about once every 10 seconds or so. Perhaps there is something in my dish setup that needs attention.


Likely military or "homeland security" related activity.

I know one day I had that issue on c-band (digital signal, picture played fine but blipped out with blocks every 10 seconds on the money).  Every c-band dish exhibited that problem that day.  No problems on Ku-band so I figured it was radar testing/activity from the nearby AFB occuring in the c-band spectrum.    I haven't had the problem creep up often since that day so I am confident it's not one of my top notch PLL LNBs crapping out.



farva

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Reply with quote  #4 
A 6ft dish may not be adequate to keep signal consistently above the noise floor... S/Q levels displayed by your receiver can be deceiving.
capsmvp

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Reply with quote  #5 
I've had this problem before, too. I know it's military or homeland security and have wondered if a c band lnb that starts at 3700 instead of 3400 would fix this issue. I just don't want to downgrade the quality of my norsat lnb for a periodic problem.
jdcpa

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Reply with quote  #6 
My 1933 for several years has had access to 3 C and 1 Ku LNB. 2 C are from 12' mesh, other C and Ku are from 10' mesh. In the installation TP list menu I often see frequent downward spikes in signal on weaker transponders, typically on Ku band, and worse the lower strength and quality are showing. Right now on 103W 4040H signal quality is averaging about 75%, as steady as I ever see it, only ±2% on the 10', and picture quality seems flawless. 4091V is the same.
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mrradiohead

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Reply with quote  #7 
It doesn't matter which transponder its on, it happens on all of them, even the PBS feed on 103W.

Mentioning "military", could it possibly be a NWS radar sweep causing this? I am directly north of the Springfield MO NWS facility (adjacent to the Springfield-Branson National Airport), roughly two miles. The dish looks to the south, directly over the airport and the NWS facility.

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Jim Thomas
Springfield, Missouri

WS1870 1.8m w/2 C lnbf's @ 103w & 97w; Fortec Star 90cm ku lnbf @ 97w; 70cm ku w/3 lnb's @ 87w/91w/95w; 70cm ku @ 103w; 70cm ku @ 103w, all routed through x1 8x1 switch, fed to Manhattan 1933 receiver.
boblop

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Reply with quote  #8 
Any airport of a size to have more than grass for a runway will most likely be using radar equipment.

When a radar "sweeps" it means the antenna which both transmitters and receivers rf energy is moving so it can see all of the air space around the air port. It does not sweep all of the freqs which your receive can see.

I have an air port here about 10-12 miles south that can land 474s. I "never" have any problems with their radar because I use a proper size sat dish for the sat signals I wish to receive.

About 3/4 miles to the south west I have an air port with a grass runway. Even when those little airplanes fly above my dish farm I have no signal problems.

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wejones

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Reply with quote  #9 
Quote:
Originally Posted by boblop
.....
When a radar "sweeps" it means the antenna which both transmitters and receivers rf energy is moving so it can see all of the air space around the air port. It does not sweep all of the freqs which your receive can see.
......


I think that depends upon the kind of radar in question, and it's purpose.
I used to work at, and live near a military base on the Chesapeake bay.  I used to use the 2M and 70CM ham bands, and occasionally I would get a very strange interference on the 440MHz band.  I'd be listening on a freq, with no problem, then the reception would be wiped out by an unknown carrier, then after a period of time, the interferrence would go away.  After some period of time, the interference would come back. I can't remember how long it took to go away, or how long it took for the interference to repeat. 
   On one occasion, when the interference started, I moved my transceiver up to a slightly higher freq, which was initially clear, but shortly later the interference began there too.  So when it ended there, I turned the freq up a bit more, and the interference began there too.  I was able to follow the interference over 10s of MHz.  This interference had a very strange sound to it, ie it wasn't just a dead carrier, although I can't remember what it sounded like.  But at the time I was on a few radio/satellite mailing list forums, so I described what I was hearing, and asked for suggestions re what it could be.
A couple responses came back asking whether I lived near a military base near the water.  The response suggested that at that time it was a regular occurrence for Soviet ships to steam up the Chesapeake, while using a UHF radar and various snooping equipment.  I have no idea if the info was accurate, but I was told that the Soviet radar swept a wide range of freqs in the range I was observing.
   Anyway, I have no idea of what this RADAR, if it was in fact radar, was doing, but I observed it on numerous occasions.  I think you're right about normal aircraft and/or weather radar, but apparently there are some special use military radars that aren't the same.



 

boblop

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Reply with quote  #10 
When the Russians came up river "steaming" it may not mean they were burning coal and had a water boiler.

At one time many ships were powered in that way. There is the song about Radar Love, I have no clue there. We all have a cooking box called a radar oven. Aircraft and big ships use radar to see or look out over a large area for weather or other airplanes or ships or even to "map" out the ground surface below as with or from an airplane in the sky. And then there is the speed cop with the radar gun now often replaced with the lazar gun.

If one wishes to understand just what might be the cause of rf interference on their receiver then having a spectrum alanyzer which can cover a wide frerq range is a great way to go. My spectrum analyzers are more designed for the L band range but the 37XP can go down much lower also. About 1 MHz up to over 4 ghz.

One could just be rf jamming but you have to look at the signal to know. Using a single freq at a time receiver does not give one a very good picture of what is really out there. Thus per a sat dish they ofter just sum it up as TI as in the unwanted which is getting through. In the analog days we got sparkllies on the video and in the digital stuff we get a mess.

I prefer Radar from the tv series were folks wore green clothes and told jokes and war stories.

My personal experience with radar was working on the rf section of Doppler Radar used in commercial aircraft. Of course with different software these can be also used at local tv stations for weather reporting. I think of most radar as a transmitted signal with a "listening" period when the signal is reflected back and info is extracted from that.


https://en.wikipedia.org/wiki/Radar_signal_characteristics

Note wiki's words about clutter.

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wejones

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Reply with quote  #11 
Quote:
Originally Posted by boblop
.... I think of most radar as a transmitted signal with a "listening" period when the signal is reflected back and info is extracted from that.


Trying to imagine what the Soviet ships might have been doing, perhaps they were scanning freqs hoping to find an echo from a transponder not a reflection off an object. Just a wild guess. Or it could have been US transmissions checking out the soviet ships.
  Where I live now, I often listen to aircraft bands, and occasionally I hear those big AWACs type planes.  One time I was getting some satellite interferrence on the same day I was hearing the planes.  No telling what those AWACs might have on them.

mrradiohead

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Reply with quote  #12 

Alright, who told you guys you could hijack my thread about 103W interference with stories of Russian ships and radar??? You're all giving me visions of "The Hunt for Red October" and Sean Connery! [eek]

Actually, has anyone been able to figure out the interference my satellite dish is getting on 103W, with the every 10 second hiccup (picture pix-elates and audio drops out for 1-2 seconds)???? [confused]

I should also mention that next door to the Springfield NWS facility is the Missouri Air National Guard facility, the second largest one in the state. They are a regular training facility. They have weekly training with old freight B-52s, that fly endlessly around in circles in the sky during mid-week. They also get a monthly visit from Air Force fighter jets that fly in, in formation and make quite a racket. Could the Missouri ANG be using military radar?


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Jim Thomas
Springfield, Missouri

WS1870 1.8m w/2 C lnbf's @ 103w & 97w; Fortec Star 90cm ku lnbf @ 97w; 70cm ku w/3 lnb's @ 87w/91w/95w; 70cm ku @ 103w; 70cm ku @ 103w, all routed through x1 8x1 switch, fed to Manhattan 1933 receiver.
farva

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Reply with quote  #13 
If we look at the Ion muxes on SES-3, the frequency bands are:
3840 H 26681 SR 3/4 FEC DVB-S QPSK 
so band is 3840 + 36mhz = 3840-3876 mhz

4040 H 30000 SR 2/3 FEC DVB-S2 8PSK
so band is 4040 + ~40mhz = 4040-4080 mhz

Now what could be affecting that band hmmm....
Weather radar operates in C-band but outside those frequencies used for c-band satellite.
Terrestrial radio (TV, cellular, etc) operates in a different band
Who knows what the military is operating on so leave them out for the moment.

But what about harmonics? The strongest harmonic is the first order harmonic at 2x frequency. So divide by 2. Lets look at 1920-1938mhz and 2020-2040 mhz.

In Greene county, 1930-1945mhz is licensed to AT&T for 3G uplink (from the phone to the tower). No licenses turn up in the 2020-2040mhz range. So it's possible that a cell phone near you could be causing interference. The amplitude of this harmonic would be a fraction of the already small (max 2W) tx power of a cellphone.
wejones

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Reply with quote  #14 
To me, I think radar would be the most likely cause, mainly because of the repeating every 10 sec .  Some that military radar is quite powerful.  Plus the interference doesn't have to be at the frequency of the radar itself.  It can mix with other signals and re-radiate at some other completely different frequency.
   There are other possibilities for interferrence, but it's hard to rationalize anything else only affecting one channel and repeating every 10 seconds.   However I have one  receiver that had a firmware bug that caused it to do something like this.  This receiver did it on all signals, but different channels did it at different rates.  Some would break up every 10 secs or so, but others would break up every 2 or 3 minutes.  I think it depended on the bitrate or the symbol rate, I can't remember.  I also seem to remember some specific channels doing something like this because the PCR being messed up or missing or something.  Ie something like the video would go along, trying to sync to the audio, then after a period of time it couldn't sync anymore and there would be a momentary blip in the video.  And I remember one computer sat program that wouldn't play some channels at all, unless you gave it a fictitious PCR PID.  But in any event, it's possible that it's a receiver quirk involving PCR.
  Just a couple ideas, but radar still seems most likely to me, even if the freq of the radar is nowhere near that of the sat signal.  Also, relative to the harmonics mentioned in another response, it's possible that the harmonics might be in your receiver or LNB, not in the actual signal. I think LNBs generate the LO freqs by using harmonics of lower freqs, so it could be that some other harmonics are getting through in addition to the desired one, causing reception of out of band signals.  But again, this wouldn't explain the 10 sec cycle.  I still like RADAR.


majortom

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Reply with quote  #15 
to help rule it in or out, take a spin to the radar site, and count the time between revolutions, possible only if no radome over radar antenna so ya can see it.
Then take a look at the spectrum with a spectrum analyser or cheap SDR type poor man's spectrum analyser, plugged in to your L-Band IF, and see if the noise floor is changing at the same rate of the radar sweep ya saw at the radar site.
They do make terrestrial filters for CBAND TVRO, but I think ya need to know a little bit about the exact signals / mechanism causing it, to determine what if anything will help. And yes, obviously there is no substitute for a properly sized antenna in the first place.


Quote:
Originally Posted by mrradiohead
I I am directly north of the Springfield MO NWS facility (adjacent to the Springfield-Branson National Airport), roughly two miles. The
dish looks to the south, directly over the airport and the NWS facility.

You shouldn't need a LOS to the horizon at that azimuth. Can you move the dish such that there is some obstruction to the south of you?
That or place some large structure in front of the antenna to the south of it.
You need a new garage don't you???[biggrin]


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Perfect 10 7.5' mesh Chapparal C/Ku Co-Rotor feed, Norsat 8115 CBAND, Norsat 4106A Ku Thomson Saginaw Actuator, Vbox positioner,
Home Brew Polarotor683 Servo circuit. Openbox S9, Prof7500, v4l-updatelee linux drivers installed.
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Fellow Members, your posts are welcome here! Do not worry about posting everything perfect. Different receivers and LNB's will give you different Frequencies and Symbol Rates. Some set top boxes, PCI cards and USB receivers, Do Not Require all of the same information that others may need. It is not Required to post everything that others may need to tune in a feed. It is just most important to share the find. We can always adjust the Frequency and Symbol Rates and try the various Modulations and FEC's on our own receivers until we get a lock and then give a polite reply with what works for your receiver, as that information might help others as well. We all appreciate the efforts and energy of the Posters!

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