Perhaps one more thing to check: could it be interference from the TV or monitor on
which you are viewing the receiver? A explained in another thread in the forum,
I had a similar problem but on a much lower frequency and that turned out to be the
hdmi cable. The only problem with that explanation is that the interference was
at much lower frequency, but it was extremely strong, despite decent coax, and
affected reception in another room of the house.
The tests to rule it out are simple: Some ways to check
-move the receiver to another place (e.g., outside or well away from its current location;
if you can reroute the cable, or perhaps some other cable)
-and/or connect another tv/monitor
-and/or change the screen resolution of the receiver
-if the receiver allows it: watch the channel using streaming on a pc (and fully disconnect the TV)
Another not too expensive diagnostic tool could be one of those cheap Chinese portable battery
powered dvbs-S2 meters. Connect them outside after disconnecting all other cables from the lnb.
In that way you isolate the test setup completely from the house.
If you have picture then you know the problem must be inside the house. If you then connect connect the other cables and the picture disappears then you will know the interference travels through the cables from inside
(but the opposite is not true).
Another test would be to connect this meter to the cable end point in the house.
These meters also have a spectrum analyser screen, but the picture is tiny. However, if there is
interference on that meter (i.e., it has picture problems on 11307), a simple test is to cover the
cover the lnb with something blocking reception (alu-foil?). If the spectrum still shows a peak, then the interference must be at 1.547 Mhz approximately, otherwise at 11307MHz (unlikely).
A pc tuner card, e.g., tbs5927 is a more expensive solution, but it would allow inspecting spectra
and has many other uses.
Or you could find out if there are some amateur radio operators near by (they may have equipment
for testing).
About LNBs: many LNBs have a metal casing inside the plastic, so covering the side with aluminium
foil will not do anything. Covering the front with a wet cloth or some foil is a good way to simulate
reduced/absent signal strength, but I think it will simultaneously reduce interference, should that be
picked up by the lnb (which I doubt).