On 7/30/2025 8:08 AM, Michael Carter via Elecraft wrote:
The standoffs likely provide localized grounding in that section of the RF
board. I'll have to look at the corresponding top-side circuit area to know
which circuits might be affected by lack of a local return path for currents.
Hi Mike.
You misunderstand the nature of "ground" and how signals are carried on
a circuit board. Most circuit boards are multi-layer, where traces are
above a continuous "ground" layer, and the traces form a transmission
line with return current on the region of that layer directly them. This
prevents crosstalk between circuits, and is the equivalent of having all
of those signals carried on coax! It also prevents the radiation of
those signals. In the most sensitive equipment, the traces are
sandwiched between two "ground" layers, which provides even greater
isolation.
A connection to mother earth is not a sump into which problems are
poured. It's only functions are 1) Lighting protection -- absolutely
critical, and all earth connections and every chassis in our homes must
be bonded to it. 2) As a component of most receiving antennas. It has
nothing to do with how equipment works.
A connection to mother earth does NOT make transmitting antennas work
better -- indeed, it makes them work worse! That's because, while
end-fed antennas like verticals and long wires need a path for return
current, the earth is a big high value resistor that burns transmitter
power. That's why it's important to have radials or another form of
counterpoise for these antennas.
And it IS critical for all cable shields to be connected to the
Shielding Enclosure (the chassis) at the point of entry for the cable
shield to work. And a shield that is not connected to the chassis, but
goes through a hole in the chassis to the circuit board, carries shield
current into the box, and is a recipe for hum, buzz, and RFI (noise, RF
feedback). Failure to make this connection is called "The Pin One
Problem," because it was first realized by Neil Muncy, ex-W3WJE (SK), a
ham working in pro audio, and Pin One of the connectors used in pro
audio is the shield contact.
Before circuit boards, connectors were mounted to the chassis, and most
connectors had a shield connection to the shell. Unshielded wiring came
through a "feedthrough" capacitor, constructed so that the circuit
carried through, with capacitance to the chassis. I'm a very OF that
remembers them.
73, Jim K9YC
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[email protected]
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [email protected]
