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wejones

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Reply with quote  #16 
My SNR dropped from between 14-15 yesterday to down around 12 today.

Re beacons,I don't know much about sat beacons, but I've seen things with my Icom-7000 in the past that were close to where the beacons were supposed to be, and they would go away if you switched polarity, but I was never sure that what I was seeing were actually the beacons, and not just birdies in my receiver.
   It was always my understanding that beacons were just un-modulated carriers, however I just tuned crazyscan down to the 3700 area, and try to lock in order to see a constellation, and I'm seeing what appears to be QPSK modulation (no lock) on vertical, but not on horizontal.  I'm not set up right now to send the signal to my 7000, so I can't look with it.  I thought it was more normal for them to put beacons at opposite ends of the band if they have H and V beacons, but that isn't 100%.
   Satbeams doesn't have the beacons listed yet, but I don't have a stable enough LNB to tell the difference anyway. The 7000 does have the accuracy.
lost_mesa

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Reply with quote  #17 
I'm not an expert on beacons, but as a long time watcher of them (30+ years) I'll make a few generalizations about them.

They are usually (not always) within 2 MHz of the band edges. For example: 3700 to 3702, 4198 to 4200, 11700 to 11702, 12198 to 12200. DBS birds are usually at their band edges. Satellites with extended C or Ku band frequencies may have the beacons in those frequency ranges. Often there will be one beacon at the bottom edge and one at the top edge of the band and of opposite polarities. Other satellites will have two beacons either at the bottom (Arsat-2) or top edge of the band. Satellites with both C and Ku transponders may have beacons on both bands, or just one.

Most satellite don't have a unique beacon frequency. Many satellites have their beacons exactly 0.5 MHz inside of the band edge.

They may or may not have any modulation (telemetry). The bandwidth is usually under 100 kHz on the ones with modulation, sometimes much less. It just depends on the manufacturer of the satellite. Back in the day I could easily tell a RCA satellite from a Hughes satellite, just by looking at the telemetry modulation, but I haven't kept up with that.

Since the bandwidth is so narrow, they don't show up using programs like crazyscan. A narrow band communications receive that can tune the 950 to 1450 MHz I.F. is a good way to receive them.

I'm not sure about the beamwidth of the beacon antennas. I think they often use a small horn antenna, as I can receive some from satellites that aren't pointed at North America.

Beacons are a very good way to adjust your polarization by rotating the feed for a null on a spectrum analyzer. I mainly use them to track satellites, either looking for a new satellite coming on station, or when a satellite is being moved to a new location. I can get my dish peaked up on a new bird before they start lighting up the transponders. I also use them to tell when an inclined bird is in the beam of my dish.

Here is a list of beacons, not 100% accurate but very good: http://frequencyplansatellites.altervista.org/Beacon-Telemetry_Americas.html

Here is a scan of the beacons from Arsat-2 that I made last night. This was done with a 3 kHz I.F. bandwidth.

Arsat 2 Beacon.jpg 
Probably way more than you wanted to know!


seaveysky

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Reply with quote  #18 
Thanks for your input!  Good info to save for the enthusiast.

Have you been able to audio demod the beacons on Arsat-2?  My old Avcom 37-D didn't come with that feature to test out. 
photoman76

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Reply with quote  #19 
Quote:
Originally Posted by wejones

   Also curious re how Photoman found the SR?  Did the BLSA give that info or was that obtained via the shortwave method?




I found it with the shortwave method.  The BLSA only gives an estimate which can be way off.
lost_mesa

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Reply with quote  #20 
Quote:
Originally Posted by seaveysky

Have you been able to audio demod the beacons on Arsat-2?  My old Avcom 37-D didn't come with that feature to test out. 


I can listed to it with the audio output of my receiver, but have never tried to decode it. I have no idea what the format is.

I've always assumed that the data is probably encrypted anyway, on the grounds that they don't want competitors to know the health of their satellites. I won't expect to see something like Solar Array Output=2056 Watts.

The modulation doesn't look anything like the QPSK signals on the transponders. It looks more like an FM broadcast signal. It doesn't look any different then they did 30 years ago, which I find surprising. Maybe someone who knows more about modulation than I could deduce what they are using.


wejones

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Reply with quote  #21 
Photoman:  Thanks, re SW method.  I wasn't sure if you were still doing that.  Takes me a long time to set up for it.

Lost_Mesa:  Thanks.  That's great info.  I didn't know that some were modulated.  I looked at the list you posted, but didn't see mention of modulation, although I might have missed it. 

I looked at this sat with my SDR receiver, and I see a bunch of signals that  go away when you switch polarity. Some on H and some on V, however only one of them goes away when I move the dish off the satellite, so I guess most of the signals must be birdies in my LNBs (separate H and V LNBs).  With the SDR, I can change the bandwidth and play any audio modulation if it is there.  I tried on both FM and AM, but couldn't hear anything in the audio range.  Seems to be a quieting signal on both AM and FM, although there is a noise that sounds like wind on AM when you tune off freq a bit. Anyway, it doesn't look like there is modulation on this signal.  Also, I'm confused re you seeing more than one beacon.  I'm only seeing the one.
   The signal that looks to me like a possible beacon is on vertical, at ~ 1449.14 MHz {=3700.86), but that could be off a bit due to LNB drift.  I'm using an LNB that's supposed to be+/- 150 KHz drift, but it's usually off more than that. 

Re the images, the 2nd one shows H on top and V on the bottom.  The signal att 1449.0 is a birdie in the receiver.  All the signals except the one at 1449.14 either stayed or got bigger when I moved the dish off the sat, but went away when I changed polarity.

I think I'll try to run the signal to my Icom 7000 now if I can.

EDIT:  Ran that signal to my Icom 7000.  It shows up there at 1449.1071
It still doesn't sound like there is any modulation on the signal.

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lost_mesa

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Reply with quote  #22 
No, the list doesn't mention modulation. I have heard modulation on some beacons, that was gone when I looked again a few weeks later. I've also seen some completely disappear for a time, apparently turned off. But mostly things are pretty stable.

Looking at your first image, there is no modulation on it. If I have time tonight, I'll look at Arsat-2 again to be sure both beacons are up. I'll also try to find a few examples of beacons with modulation.

The two Arsat-2 beacons should be exactly 1 MHz apart, but with opposite polarity. With your separate LNBs, each with its own LO error, that exact spacing won't be apparent, so it's hard to pick them out among the birdies. But if they don't go away after moving the dish a few degrees, they aren't beacons.

I use the beacons to calibrate the LO errors in my system. I don't think the published frequencies are always exact, but if I look at half a dozen beacons at say 3700.5 MHz and most are on the same frequency, I assume those are actually at 3700.5 MHz. I'm using a Titanium PLL LNB and when I used this technique in the past found the error was about 12 kHz, so that is what I used to correct the frequency in the image I posted. But I haven't checked that in many months, so I could be off some.

A SDR is a great tool for looking a beacons. I haven't done that in a while and don't recall seeing so many birdies. Have you tried turning down the gain in SDR#, to see if they go away?
seaveysky

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Reply with quote  #23 
wejones - The 2 beacons are still there. That's a nice receiver you have with your screenshots.

On my SA,  I see beacons V - 3701 and H - 3700 rounded out to nearest.

Earlier in the day,  someone was keying up RF right next to the main mux for a split second several times then quit.  Came back 20 seconds later with the same thing. Went on for several minutes. This looked similar to when one sees an add'l carrier with music on it for lets say an IFB but much more attenuated. Was weak to say the least. Gone now.
wejones

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Reply with quote  #24 
Re my 2nd image, which has a bunch of signals in the bottom vertical trace. I had said that all but one signal either didn't go away or got bigger when I moved the dish.  Well it turns out that most of those signals were coming from AMC9, next door.  When I went way off the sat, a collection of peaks, actually a center carrier with 2 sidebands that were a collection of multiple peaks,  got bigger and bigger, and peaked when I got to AMC9.  Interesting thing is the group of peaks just left of center DID seem to have modulation.  Sounded like an old modem.  It was about 600KHz off freq from where the AMC9 beacon should be, but again, it may be the LNB drift. 
   I then tried to find another beacon on AMC21, since I can switch to that sat via a diseqC switch.  I didn't find any signal where the beacon should be, but then I remembered that that LNB was actually from a fixed 1M dish which has a cheap LNBF on it, and it often drifts by a couple MHz.  I then found a signal almost 2 MHz off, that was very interesting.  Similar to the one from AMC9, it was a center carrier with 2 sidebands and the sidebands obviously had data, and the data was coming in beats at exactly 1 second intervals, as if maybe it was a time signal or something.  I had to shut down tonight, but I want to investigate that one more tomorrow. 

But anyway, I think most of the extra signals I was seeing weren't birdies, but coming from adjacent sats.  It's been many months since I've used this SDR thing.  I've played with gain before, but today I forgot where that setting was on the program I'm using.  It does seem like the gain is kind of non-linear, in that the low bleed from the adjacent sats must be amplified more than the stronger signals from the sat I'm on.  I'll play with the gain tomorrow.   The SDR I'm using is a very cheap one. I think I'm going to look into getting a better one. 

Quote:
Originally Posted by lost_mesa
No, the list doesn't mention modulation. I have heard modulation on some beacons, that was gone when I looked again a few weeks later. I've also seen some completely disappear for a time, apparently turned off. But mostly things are pretty stable.

Looking at your first image, there is no modulation on it. If I have time tonight, I'll look at Arsat-2 again to be sure both beacons are up. I'll also try to find a few examples of beacons with modulation.

The two Arsat-2 beacons should be exactly 1 MHz apart, but with opposite polarity. With your separate LNBs, each with its own LO error, that exact spacing won't be apparent, so it's hard to pick them out among the birdies. But if they don't go away after moving the dish a few degrees, they aren't beacons.

I use the beacons to calibrate the LO errors in my system. I don't think the published frequencies are always exact, but if I look at half a dozen beacons at say 3700.5 MHz and most are on the same frequency, I assume those are actually at 3700.5 MHz. I'm using a Titanium PLL LNB and when I used this technique in the past found the error was about 12 kHz, so that is what I used to correct the frequency in the image I posted. But I haven't checked that in many months, so I could be off some.

A SDR is a great tool for looking a beacons. I haven't done that in a while and don't recall seeing so many birdies. Have you tried turning down the gain in SDR#, to see if they go away?
wejones

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Reply with quote  #25 
Quote:
Originally Posted by seaveysky
wejones - The 2 beacons are still there. That's a nice receiver you have with your screenshots.

On my SA,  I see beacons V - 3701 and H - 3700 rounded out to nearest.

...


What you say seems consistent with what lost_mesa said.  I'll have to look closer at that tomorrow.  I had forgotten that the LNB drift would be different for my 2 LNBs, and I've been having problems with one of my LNBs, just can't remembe which one.  I did notice that one one of the 2 LNBs, I saw signals drifting across the spectrum, while other signals were constant, so maybe one of my LNBs is going bad.
 
   re the SDR receiver, it was something I got as a gift a couple years ago. I looked it up, and I think it only cost about $20.  I've noticed that it does tend to have a lot of birdies, and does some strange things depending upon how I change the settings in the FFT setup.  I really don't know what I'm doing. I'm pretty much learning how to use it by experimenting.


lost_mesa

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Reply with quote  #26 
Both beacons on Arsat 2 are still there, along with the original signal at 3789 MHz. Looks like I was a bit off on the beacon frequencies, they are probably more like 3700.25 and 3701.25 MHz. I think they might have some modulation on them, judging by the two sidebands. Here is a scan where I flipped the polarization from V to H, halfway through.

Also a couple of beacons with much more noticeable modulation.

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boblop

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Reply with quote  #27 
Here is a picture that many of you can do with your own current equipment. The scan shows both polarity of this Arsat-2 position. It looks almost the same with the Avcom 37XP except that first on the left side "cluster" of signals is constantly changing as to whether any of it is present or not. Like it is made up of several very narrow pulses of energy at several different freqs.

Of course a sat and its signals are made up of the up link signal/data and the down link which is what we are always looking for to extract some audio and video from. There is also the control info in both up link and down link for each sat up there.

I wonder if this down link info I have in my picture and that changing "cluster" of info is likely the feedback from this sat about its present position and health status? I would think that on a beacon signal it would be normal to have sat ID info.

I can see we all "need more stuff" to help us better understand these great signals coming at us from above. Or we can just use all the look up charts to figure out where and what we are looking at.

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wejones

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Reply with quote  #28 
Quote:
Originally Posted by lost_mesa
Both beacons on Arsat 2 are still there, along with the original signal at 3789 MHz. Looks like I was a bit off on the beacon frequencies, they are probably more like 3700.25 and 3701.25 MHz. I think they might have some modulation on them, judging by the two sidebands. Here is a scan where I flipped the polarization from V to H, halfway through.

Also a couple of beacons with much more noticeable modulation.


Thanks. 
The AMC9 trace was just like what I was seeing.  I think I understand better what I was seeing on the new sat. 
These traces should help me calibrate to ajust for the LO drift of the LNBs, so perhaps I can calibrate via these knowns and then more easily find the unknowns.

I'm still intrigued by what I saw on AMC21.  Yesterday, I was looking at AMC-21-H, which is supposed to have a beacon at 12198.   Yesterday, I was using my 1M dish, which has a very cheap LNBF, which has a LOT off freq drift.  I can't remember what freq I found the signal at, but I posted that it was a couple MHz off. 
   So this morning, I went to that signal again, captured some images, then I swung the big dish over there, and compared what I saw with the big dish.  I expanded the waterfall display, in hopes of actually viewing the data bursts.
   Below, I attached the images from the 2 dishes.  The first one shows a modulated signal centered at about 1446. 43 {=12196.43), which is about 1.7 MHz off, not unusual for the cheap LNBF.  The 2nd image shows the display from my BUD.  It shows the signal centered at 1448.93 {=12198.93}, which is off by about .93 MHz, which is a lot for the LNB on my big dish.  I can't remember what the stability of that Ku LNB is....  I think it's supposed to be something between 150 and 250 KHz.
   However I just remembered, that the SDR itself tends to be a bit off freq.  Yesterday, it was a bit different from what I found with the ICOM-7000, but I can't remember how much different.  I'll try to figure that out.

    But anyway, on both images, you can see considerable modulation of the signal.  Exactly every second, a few of the sideband peaks seem to buzz with a data burst.  I had hoped that I could expand the waterfall enough to spread out that data burst enough to see the data, but I was already pretty much at the fastest rate.  But it's interesting.  It somewhat reminds me a bit of the GPS data bursts I get from a GPS dog tracking collar we have.  It sends out these very short data bursts at a rate of once every couple seconds.  That would be an interesting way for the controllers to have a real time view of where the sat is. 
    Anyway, I'm having fun playing with this.  Like I said, previously I thought all the beacons were unmodulated carriers, but that obviously isn't the case.  Thanks.


EDIT:  I just pulled up the signal with my ICOM, and it shows up at 1448.84, still off by about 0.84 MHz from where satbeams lists the beacon...   HOWEVER, I just noticed that the list lost_mesa posted yesterday shows this beacon at 12178.5, which is a LOT closer, ie only 0.34 MHz off.   That plus I've never really verified the accuracy of my ICOM at freqs above 1000 MHz.  Ie the 7000 does 25-1000 MHz normally, but kicks in a 1000 MHz crystal to cover the 1025-2000 MHz range.  It is right on in the range below 1000, but I've never verified it above 1000, although considering the cost of this receiver, it should be very close, even though it is over 25 years old.  


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boblop

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Reply with quote  #29 
Like I said----we all need more stuff.

It would make sense that a marker beacon would include sat ID data. I could be wrong. As hobby people just wanting to view some free audio and video most of use a look up chart after finding a tp to figure out what sat we are really on. I bet the pros use another receiver which can read the data "if there" from a marker beacon and thus they "know" what sat they are looking at.

My collection of RC2000 dish controllers all have an agc input where that signal strength is then used to control the output of the RC2000 to peak the connected dish. Pro equipment here.

For most of us hobby folks we just are peaking our under sized dishes for some free stuff. "we are cheap"
Thus we are using cheap and minimal equipment.

Thus I say again---we all need better and more stuff.
I long ago stopped buying the cheap stuff. I think there is a place to use low cost equipment but the pro gear is what one needs. They do make good lnbs that use a standard 10 MHZ input signal but for us that is a little "over the top". (all the lnbs get locked to a freq standard)

A hobby should be fun and help one to learn new things. The pros already know all this stuff and they have and use high quality stuff. (hobby folks may just play with cheap low cost stuff) We can get free tv with a nice $100 receiver and a free used dish.

Part of the skill of using test equipment is to understand what the displays are telling us about the input signals. That is the learning part of the hobby. As a hobby, well have some fun.

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wejones

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Reply with quote  #30 
Wow.....  I just decided to pull up the beacon on the vertical side of AMC-21, and boy is that full of a variety of modulations.  It's centered at 951.42 on the SDR and 951.38 on the ICOM (= 11701.42 and 11701.38 respectively).  But you can see (and hear) modulations in more of those sideband modulation peaks.  You can still see and hear that the bursts are timed at 1 second, but now it's more like the data is between the short bursts seen on the horizontal side.
   Boy, I'd like to figure out some way of decoding these.  I'll bet that this beacon has all sorts of satellite information.  This really goes against what I've always known to be the definition of a beacon, ie just an extremely narrow unmodulated carrier.  Maybe that's only the definition the FCC has for hams, and satellites have different rules.

I guess I'll swing the dish back to 81 again, and look for the beacon I missed on the other polarity.


AMC21beacon5.jpg

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