Can powerline adapter affect modem speeds

[#1]

Hi, would powerlines affect my modem sync speeds at all.

I have seen my speeds go from 68 last year to 45 and downstream from 17 to 11 - 12.

I did raise a fault after speaking to someone who said he could see a potential issue and i had a reply saying there had been a fault with my broadband service that would be raised to the supplier.

A week later I had another reply asking me do do a fault diagnosis "If the test is classed by the speed tester as failing,"however it never did show as failing again and now the question has closed after no reply for 14 days.

They are Devolo passthrough powerline adaptors and the modem and router were powered by an extention lead that was powered from the powerline adaptor. I have now disconnected my powerline adapters to see if that will help speeds at all.

[#2]

Moderator's note by Mike (Mav)

Empty post removed

[#3]

I've seen powerline adaptors drop the SNR which could I guess drop your speed if the modem resyncs whist they are in use as your SNR will go back to the target of 6dB, the result of which will be a drop in sync speed.

[#4]

I had powerline adapters that injected huge numbers of errors on the line. The SNRM didn't change if I remember correctly however the errors caused the interleaving depth to go very high and the overall speed to be reduced. The ping times also increased significantly.

I haven't used powerline adapters for some time and my connection has been solid with fastpath on the upstream and only an interleaving depth of 8 on the downstream.

I have, however, recently installed powerline adapters again but this time have changed to a different brand. So far so good but early days. I have read that a lot of people use powerline adapters with no issues so maybe it depends on brand. I suspect it also depends on topology of your mains wiring and how close it runs to the phoneline etc. My new adapters are in exactly the same location as the old ones so if they don't cause issues, it will the different brand that helped. 

[#5]

Thanks for taking the time to reply.
I guess i will leave them off for now then and see if things improve.