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?>>>>
I'd worry about that later, and if I needed filters, I'd filter at the noise
source.
Unless you look at a Star Roamer or some other vacuum tube vintage receiver,
you'll find most radios are extremely good for internal shielding of mains
or power supply leads to the receiver RF system.
In my experience, most leakage problems are in marginal shield grounding
connections in phono plugs or poor external equipment design, and not in
radios at all. For example, plastic boxes with wires for jack ground leads
inside are hundreds or thousands of times worse than anything getting into
the radio. When external connections are cleaned up, with any modern solid
state radio I have owned or used, the issue becomes devices radiating out to
antennas, which then pick up the noise.
I had a particularly difficult computer supply. Rather than do extraordinary
and difficult things to a dozen points in the RX system, and move my
antennas further away from the house, I cleaned up that supply with a
filter.
A normal station with proper attention to common mode suppression on
feedlines at the antenna, and good connections on shields, should not even
need a desk ground. (One exception might be power line safety. My old
two-wire tube gear, like my Ranger II and HQ-120, has safety grounded
cabinets.)
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?>>>
The only cases I can think of, where a large desk groundplane might reduce
noise, are if:
1.) The antenna has significant common mode current that makes it all the
way into the house. For example, look at a longwire shack ground. An end fed
longwire antenna is a system with terrible common mode, as are "end-fed
dipoles".
http://www.w8ji.com/long_wire_antenna.htm
2.) There are poorly constructed 'boxes" in the receive path. The
groundplane and shield path integrity in receiving paths is critical.
3.) Internal shack cables have poor shield connections.
4.) Some device in the shack, or near the shack, is exciting terrible common
mode RF currents on wiring.
Personally, I'd never bother with an extraordinary desk ground. I'd fix the
real problem or problems.
73 Tom
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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