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Originally Posted by Iceberg
the reason 11720 is low is because right next door is 11724 V on Dish 121 which is overpowering it. If you had a dish like the cable companies use (15 feet or larger) you wouldn't notice a difference. But because we have smaller dishes, the Dish121 signal interferes with G10.
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I know that it's 90% likely that the nearby Echo sat is responsible, but I'm not completely convinced that the 11720 problems are due to the 11724 signal next door. First of all, when I run a spectrum scan of G-10, it does show that the 11720 peak is not quite as strong as the other peaks on the sat, although it is definately strong enough that it shouldn't give the reception problems that people report.
But a few months ago, there was a discussion in another forum about this, and some were suggesting that it was due to the drift of the sats, bringing G10 and Echo9 closer together ( I didn't beleive this, however people's problems seemed to clear up when the 2 sats were brought back to their 2 deg spacing, so I don't know about that...) . However, to investigate, while tuned to 11720, I bumped my dish a bit to the west (still receiving G-10 on
C-band), expecting to see the reception improve from getting it further from Echo9, if the problem was due to 11724. If I remember correctly, this didn't happen, so I started to suspect that maybe people were having polarity problems. I reversed polarity, and did a blind scan. The blind scan picked up a strong signal at 11720/26800 ! At first I thought that I had discovered a new signal on the sat, but I decided to check nearby sats. What I found was that this signal was actually on G-13, ie 4 degrees away from where I was aimed!
As it turns out, my dish ie pretty bad with respect to side lobes, and apparently one of the side lobes is apparently approximately 4 degrees out.
Now, I know this still seems a bit illogical, but I think it is possible that interferrence from G13 is actually involved here. First, the SR on the G13 sat is much closer to the SR of the 11720/27692 on G10, plus the freq is right on. I know that the G13 signal is of the wrong polarity, however, I think that is is possible that polarity might be rotated somewhat for side-lobes (I have no evidence for this, but I think it is possible), plus it doesn't take being off much in polarity before you start getting significant amounts of signal, ie the polarity null is quite sharp compared to being off peak.
Now I have no idea of whether side lobes are a function of dish size or are more a function of frequency, so I don't know if side lobes on a 3' dish would be spaced the same as those on my 10' dish. I know that people don't complain about side lobes on small dishes, but I think that may be because the resolution is so poor that they kind of blend into the shape of the main lobe.
Another aspect is, why do I see this 11720 signal slightly lower in my spectrum scans. I wonder if they are voluntarily reducing the signal strength to help avoid interferrence with the Dishnet superdish people, who have less resolution than the FTA'ers.
Anyway, the odds are, that you are right, and it's due to the 11724, however I think there are other possible explanations, and I'm not quite sure how to tell what is causing the problems.