Transmitting on the COM-radio.
"Standard coaxial transmission lines. When this type of line is working without unwanted radiation, all currents are inside the line. The outside world is isolated from the inside of the cable by the skin depth of the shield. Voltage from the shield to "ground", or the environment around the line, ideally is zero."
Refering to the attachment, my understanding is:
This means that if the BNC connector (shield) at the back of the COM-radio, and the COM-antenna BNC connector (shield) has the same GND-potential, there will be no external radiation from the coaxial cable.
Think of it as a hose filled with water. If there is no flow of water, the water levels at the ends of the hose are equal. Lower one end of the hose and water will start to flow.
If there is a GND-potential (Voltage) difference between the BNC-connector (shield) at the COM-radio and the BNC (shield) at the antenna, a Current will
flow in the OUTSIDE of the coaxial shield.
The coaxial cable will now radiate a magnetic field and act as an antenna.
In modern aircraft there are lots of wires that are carrying 0,5-4,5 V.
If those sensitive wires are located close to a Coax cable that are carrying
a current on the outside of the shield, there will be erronous readings
on the affected instruments.
One would think that there would be no Voltage differences in a metal aircraft. There are good reasons to have only one GND-bus and have it connected to the aircraft skin.
Ideally all GND-wires use this GND-bus. (not intercom or headset GND).
If for some reason it's disired to have more than one GND-bus, it's important
to have a well sized GND-wire between the GND-buses.
Do I have to rebuild all my wiring ? No, just be aware that there may be a radiating field of some proportion arround a COM Coax cable.
Then this can be corrected or canceled with a metal braid that is grounded.
https://www.w8ji.com/coaxial_line_and_shielded_wires.htm
Good luck
"Standard coaxial transmission lines. When this type of line is working without unwanted radiation, all currents are inside the line. The outside world is isolated from the inside of the cable by the skin depth of the shield. Voltage from the shield to "ground", or the environment around the line, ideally is zero."
Refering to the attachment, my understanding is:
This means that if the BNC connector (shield) at the back of the COM-radio, and the COM-antenna BNC connector (shield) has the same GND-potential, there will be no external radiation from the coaxial cable.
Think of it as a hose filled with water. If there is no flow of water, the water levels at the ends of the hose are equal. Lower one end of the hose and water will start to flow.
If there is a GND-potential (Voltage) difference between the BNC-connector (shield) at the COM-radio and the BNC (shield) at the antenna, a Current will
flow in the OUTSIDE of the coaxial shield.
The coaxial cable will now radiate a magnetic field and act as an antenna.
In modern aircraft there are lots of wires that are carrying 0,5-4,5 V.
If those sensitive wires are located close to a Coax cable that are carrying
a current on the outside of the shield, there will be erronous readings
on the affected instruments.
One would think that there would be no Voltage differences in a metal aircraft. There are good reasons to have only one GND-bus and have it connected to the aircraft skin.
Ideally all GND-wires use this GND-bus. (not intercom or headset GND).
If for some reason it's disired to have more than one GND-bus, it's important
to have a well sized GND-wire between the GND-buses.
Do I have to rebuild all my wiring ? No, just be aware that there may be a radiating field of some proportion arround a COM Coax cable.
Then this can be corrected or canceled with a metal braid that is grounded.
https://www.w8ji.com/coaxial_line_and_shielded_wires.htm
Good luck