Due to software changes with DirecTV HD receivers if a slimline 5 LNB is used with the receiver set to slimline 3 an error code results,Here is updated information on how to make the small HD dish.
How to build your own small HD dish for DirecTV:
LNB heads that work well when mounted to a phase 3 dish (18" X 20"),this is for 99 (HD),101 (SD),103 (HD) operation.
Slimline 3 LNB (SWM/SWiM versions OK) with receiver set to slimline 3. "Best all around operation
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WNC AU9 5 LNB (white caps) with receiver set to slimline 5. "Good operation but 771 errors for SD locals on 119 satellite and possible guide data issues "
Eagle Aspen (clear covers) 5 LNB with receiver set to slimline 5. "Good operation harder to mount LNB head also 771 errors for SD locals on 119 satellite and possible guide data issues ""
Use slimline setup numbers to do course alignment of 101 signal, use 99(c/a/b) and 103(c/a/b) meter readings to fine tune and balance Ka band HD operation (The 14 transponders group for 99 and 103 is the key), signal numbers will range from the low 70s to the mid 90s for 99-101-103.
Adjust the tilt a little till 99 & 103 are balanced,Your going see low numbers on it initially probably in the 50s-60s then go back to the elevation adjustment and find the highest signal numbers for 103 & 99, signal numbers from the low 70s to the mid 80s are normal.
Use the normal screws/nuts in the pre drilled holes of the arm and LNB assembly, this alignment occurs when the LNB is inserted about half way.
The highest Ka signal numbers so far is when the LNB is fully inserted and flush in the arm tube,drilling new holes in the tube arm at the correct place and using the normal hardware to secure the LNB works well.
The key on the bottom of the LNB must pass to the inside of the dish arm tube,this can be done with a flat blade screw driver or metal nipper to make a notch for the key to fit into.
FYI: I don't recommend the use of the 18" round or any round dish,you will end up with missing transponders.
Disclaimer : This dish is experimental and not supported by DirecTV.
Having said that we have many successful setups working out in the real world