Since 45mps (I think you meant Mbps) is well under 802.11g's range of speed you see these issues for far too many reasons.
Distance, a wifi system that can't decide on which protocol, and good old interference. Tell me how you scoped out the airwaves. I use my Android phone and WiFi Analyzer. Read http://www.howtogeek.com/197268/how-to-find-the-best-wi-fi-channel-for-your-router-on-any-operating-system/
Bob
When hardwired via ethernet, I'm picking up about 45mps. Wifi signal though drops it to 20 or less. I tried hooking a high-end dual band external wifi router up, but there's no improvement. What's going on here???

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