Topband: Reducing Noise in the Shack

As I mentioned in a post a few days ago, I am at the very beginning of
being able to operate on 160 and 80M’s.  (To date, I have only operated on
10, 15 and 20M.) I have been doing a lot of reading, primarily ON4UN’s
“Low-Band DXing.”

My rig (FT-dx5000) is located on a desk.  Immediately under the desk is my
computer, and just above the rig is a shelf on which sits 2 flat-screen
monitors.

One of the points made in “Low-Band DXing” is the necessity of reducing
noise in the shack.  The author states at page 7-75: “It is essential to
feed the equipment at the shack through high-quality mains filters.”  In
looking for such filters, I have come across the W3NQN AC Line Filter.  It
seems to be built with quality components, but I have not been able to find
any specs on the amount of attenuation it provides to EMI and RFI noise at
various frequencies (either common or differential mode).  Could someone
recommend a “high-quality mains filter” or comment on the W3NQN filter?

The author goes on to state: “The bottom side of the operating table in my
shack is completely covered with aluminum sheet.  This represents a lot of
capacitance and virtually zero inductance, which is just what you want!
Quality mains filters are bolted directly to those sheets and the mains
outlet to which the equipment is connected is connected as well.  The
ground plane is connected with very short low-inductance wide straps to
long copper ground rods.”  Would someone please explain to me the purpose
of this ground plane and how it helps reduce noise? How does “a lot of
capacitance and virtually zero inductance” under a transceiver help reduce
noise?

Thanks in advance for advice and help for a newcomer.