I ran across a really strange constellation pattern on amc21 at approximately 12025H. I was not able to lock the transponder (if it IS a transponder).
When I did a blind scan, I came up with transponders at ~12023H1200 and 12028H1215.
Both are ACM/VCM. 12023 seems to be using about 16 different modes, but mainly QPSK,8PSK and 16PSK. {Note, the LNBF I'm using here is 2 MHz low, so the 12020.8 shown is actually 12023.)
![AMC21-12028H.jpg]()
Now, since there was space for another signal between these two, I moved the freq above to 12025H {12023 with my drifting LNBF}. I couldn't lock a transponder there, however I got the following constellation patterns:
![amc21-12025H.jpg]()
which is the same pattern, but tilted to the left instead of right.
Then, I just let the constellation pattern run out longer, and got:
![amc21-12025H3.jpg]()
The initial two patterns seem to really be two QPSK patterns, shifted off each other at 45 deg angles either left or right. The third pattern just seems to be a combination of the first two.
The reason I included the patterns from 12023 and 12028 was that I thought that one possibility was that this wasn't a combination of two nearby signals, but I don't think there is any way you could get this pattern from those other two signals.
So, assuming that this is a real pattern, then the question is, what in the heck IS this. It doesn't seem to be any modulation mode I've seen before. Like I said the only thing I can think of is that it might be two QPSK patterns on the same signal, but separated so that they can be decoded separately.
EDIT: Or, since there are 16 spots, perhaps this is another experimental version of 16APSK??? But this wouldn't explain why they seem to show up as about 2 different versions of dual-QPSK at any point in time. If a type of 16APSK, you'd think the spots would be randomly equal.
When I did a blind scan, I came up with transponders at ~12023H1200 and 12028H1215.
Both are ACM/VCM. 12023 seems to be using about 16 different modes, but mainly QPSK,8PSK and 16PSK. {Note, the LNBF I'm using here is 2 MHz low, so the 12020.8 shown is actually 12023.)
Now, since there was space for another signal between these two, I moved the freq above to 12025H {12023 with my drifting LNBF}. I couldn't lock a transponder there, however I got the following constellation patterns:
which is the same pattern, but tilted to the left instead of right.
Then, I just let the constellation pattern run out longer, and got:
The initial two patterns seem to really be two QPSK patterns, shifted off each other at 45 deg angles either left or right. The third pattern just seems to be a combination of the first two.
The reason I included the patterns from 12023 and 12028 was that I thought that one possibility was that this wasn't a combination of two nearby signals, but I don't think there is any way you could get this pattern from those other two signals.
So, assuming that this is a real pattern, then the question is, what in the heck IS this. It doesn't seem to be any modulation mode I've seen before. Like I said the only thing I can think of is that it might be two QPSK patterns on the same signal, but separated so that they can be decoded separately.
EDIT: Or, since there are 16 spots, perhaps this is another experimental version of 16APSK??? But this wouldn't explain why they seem to show up as about 2 different versions of dual-QPSK at any point in time. If a type of 16APSK, you'd think the spots would be randomly equal.