I was kind of waiting to see how this thread pan'd out, since I was using my dish for other sats the last couple days, and also waiting to see if the OP would respond to Ice's question of whether the PBS programming was actually coming in on 12180. \
However I checked MY AMC-21 reception, and there does seem to be an anomoly with respect to 12140, despite the fact that it's coming in error free for me.
I'm using a fixed Primestar dish on AMC-21, and it's giving me quite strong signal AND quality on 12180. On 12140, the signal level is about the same as 12180, however the quality is SIGNIFICANTLY lower. Not bad enough to stop me from getting a lock and getting good reception on the channels, but the quality is much worse.
I ran a blscan spectrum, and the two signals (12140 and 12180) look pretty much the same hight and shape, so it would seem that the only explanation would be interferrence that's degrading the quality on 12140.
Lyngsat listed a Hughesnet channel on 12140V/30000 on the adjacent G13, so I think it is likely that it could be interferring with the PBS channel of the same freq/SR on AMC-21. Ice had mentioned a hughesnet signal on 12180 , but I'm not seeing that, nor do I see it listed in Lyngsat.
Anyway, I checked with my 90cm dish (which is partially blocked by my garage on that sat), and the Hughesnet signal is still there at 12140V/30000. So I think that interferrence from the Hughesnet signal is probably responsible for 12140 having worse quality than 12180.
My C-band dish happened to be sitting on G13 at the time, so even though it does a terrible job on Ku, I decided to look at the spectrum from the Ku side of it. I could see the 12140 Hughesnet signal, however there was an extremely strong narrow band spike right in the middle of it, which is strange. It's possible that I'm seeing a birdie in my system that just happens to be right at 12140. I then looked at a spectrum from my 90CM on G13/H1, and it also shows the same spike. The spike sort of looks like the center of an analog channel, or perhaps an unmodulated carrier, but it's superimposed right on top of the 12140 signal.
I am getting the Ku signal from both the BUD, the 90CM, and my Primestar all through the same 4x1 DiseqC switch, so it's possible that the birdie is actually coming from something else in there (actually the circular port of my Invacom Quad also feeds into that switch.
Anyway, short of removing the switch, and looking for the source of this narrow signal, I'm wondering if anyone with a spectrum analyzer is seeing this narrow peak at 12140V on G13/H1? It's probably in my system, and it's probably responsible for MY low quality on the PBS HD channels, and the Hughesnet transponder is probably responsible for the poor signal for the original poster.
ANYWAY, is anyone else with a spectrum analyzer seeing a narrow signal on top of the Hughesnet signal???
EDIT: Additional data point. THe 12140 spike is NOT visible when I view the AMC-21 V spectrum from my fixed Primestar, which comes through the same DiseqC switch, however I recorded that before moving the 90CM to 127, and before powering up the Ku lnb on the BUD. All ports from the diseqC switch go through first my Diamond, then the Twinhan before being spectrum scanned by my Broadlogic, so there is plenty of potential for birdies appearing from the multiple connections, but I only saw them on the 90CM and BUD ports.
