I havetwo MA2500D but there‘s something wrong withit the speed, I want to know the reason. Should I buy a better capble?
Just an update for you...I did finally track down and fix my issues which were the same as yours. As suspected, there were several non-MoCA splitters in the network. Once I replaced all of them, including the main splitter at the entry-drop, my speeds are up to the 3.4 to 3.5Gbs (PHY) rate.
I do have one MoCA adapter that is still hanging around 2.4 to 2.7Gbs (PHY) rate but that adapter is the furthest location in the house. A MoCA amplifier would most likely fix this slightly lower speed, but I don't feel that it's worth the cost to me. Best of luck on your journey!
There are so many possible variable for why you are seeing low link speeds. Some of the things to check for are:
Excessive number of splitters
Using non-MoCA compatible splitters
Poor cable connections (e.g. cables not fully tightened)
Interference from your cable/internet provider
Excessive line loss for a number of reasons (too many outlets on the extension, poor splicing, etc.
Tracking down the reason for the poor link speed can be time consuming, but will pay off when you get everything to work correctly.
I am actually going through this same issue as well. I have 4 MoCA 2500Ds and 2 of them have poor link rates. I am currently replacing all of the splitters with MoCA compatible splitters, placing resistors on all non-utilized outlets and splitter ends, and checking the cables as well as possible. Fun times....