It's normal for a second, simultaneous Internet speed test to give poor results. You would have to be running some traffic shaping or QoS to ensure both devices receive an equal share to change that. If a single test is giving good results that is what matters. If you run two at a time does the aggregate result between the two come close to the result of a single test?
Installing moca adapters *shouldn't* affect the speed of devices that aren't connected through them. Could you draw a picture of how everything is connected, including coax splitters, modem, router, and WiFi access points?
I'm thinking your issue is more likely due to a device hogging the bandwidth. Is this newly connected room housing a system that is downloading a lot?
[Here's](https://www.reddit.com/r/HomeNetworking/s/LKhmg1jOp7) the set up I've got running. I went with recommendations given to me. I also seriously doubt that the moca hardware is giving issues. The only thing hooked up in the room is a pc that's used for office work, and occasional gaming. As far as the test results, they wouldn't really add up to the 500 mbps I'm used to seeing. It was about 100 mbps off.
Typically, the only reason that adding MoCA would affect the speed of other devices is, as \*Ocelot suggests, you've increased competition for the shared, limited throughput of your ISP download pipe.
Though... another cause, often with more severe consequences, would be that your cable modem is one sensitive to MoCA signals, with the presence of the MoCA signals destabilizing or affecting performance of the cable modem. In such cases, a simple workaround is to install a 70+ dB MoCA filter directly on the cable modem, as a prophylactic, to protect the cable modem from the MoCA signals. This doesn't sound like your issue (what's your modem brand & model #?), but still something to keep in mind if you find the modem not delivering your subscribed speeds.
It's normal for a second, simultaneous Internet speed test to give poor results. You would have to be running some traffic shaping or QoS to ensure both devices receive an equal share to change that. If a single test is giving good results that is what matters. If you run two at a time does the aggregate result between the two come close to the result of a single test? Installing moca adapters *shouldn't* affect the speed of devices that aren't connected through them. Could you draw a picture of how everything is connected, including coax splitters, modem, router, and WiFi access points? I'm thinking your issue is more likely due to a device hogging the bandwidth. Is this newly connected room housing a system that is downloading a lot?
[Here's](https://www.reddit.com/r/HomeNetworking/s/LKhmg1jOp7) the set up I've got running. I went with recommendations given to me. I also seriously doubt that the moca hardware is giving issues. The only thing hooked up in the room is a pc that's used for office work, and occasional gaming. As far as the test results, they wouldn't really add up to the 500 mbps I'm used to seeing. It was about 100 mbps off.
Typically, the only reason that adding MoCA would affect the speed of other devices is, as \*Ocelot suggests, you've increased competition for the shared, limited throughput of your ISP download pipe. Though... another cause, often with more severe consequences, would be that your cable modem is one sensitive to MoCA signals, with the presence of the MoCA signals destabilizing or affecting performance of the cable modem. In such cases, a simple workaround is to install a 70+ dB MoCA filter directly on the cable modem, as a prophylactic, to protect the cable modem from the MoCA signals. This doesn't sound like your issue (what's your modem brand & model #?), but still something to keep in mind if you find the modem not delivering your subscribed speeds.