A summary of considerations by ON7FU.

• RF noise (as received on an antenna system and considered annoying) consists of different contributions.
• There is radiated noise (noise directly incident to the antenna) and conducted noise (noise transported in a conducted way over cables).
• Both are present, but either of them can be dominant.
• Radiated noise consists of atmospheric noise (depending on atmospheric conditions) and man-made noise radiated directly from all possible appliances and digital equipment.
• Conducted noise mostly consists of all kind of disturbances originated in the receiver vicinity and brought into the weak signal wanted signal path by conduction over cables an penetration into it, e.g. directly due to shielding effectiveness limitation or by Common Mode to Differential Mode conversion.
• Radiated noise can convert into conducted noise, and conducted noise can convert into radiated noise.
• Radiated noise or interference can only be lowered by eliminating the source of noise, or by increasing the distance to the disturber. (Remember that the field strength lowers by the square of the distance).
• Conducted noise can be effectively lowered by inserting choking in the unwanted cable paths.
• Conducted noise issues are experienced during reception (increased noise floor) as well as during transmission (RF feedback disturbing the radio).
• RF feedback into the radio transceiver during transmission is a typical example of conducted interference.
• The first cause of conducted interference is often a non ideal transition of symmetrical to a-symmetrical media.
• This mainly occurs at the antenna feed point.
• At that point differential mode signal (the RF signal transmitted) is converted into unwanted common mode signal (the sheath current flowing on the outer surface of the coaxial cable) and the common mode (the noise current present on the outside of the coaxial cables during reception) is converted to differential mode signal adding up with the wanted low signal.
• So the use of BALUNs with a good common-mode rejection is the first thing to be considered.
• Next, a low impedance “clean” grounding of the coaxial cable outer shielding  on the antenna side is considered good practice. Together with adequate choking it adds a “second order” to the Common-Mode filtering.
• The safety ground (and wiring) of a house electricity installation is intended for safety purposes and has too high a impedance at RF frequencies to be able to drain RF noise to ground so it is “polluted” with RF interference originating in all equipment connected to it.
• A clean RF ground consists of several ground rods interconnected with heavy gauge earthing cables placed some distance (e.g. 10m mimimum) away from the polluted safety grounding so that RF noise cannot couple into it via coupling through earth. It can also serve as antenna or tower primary lightning protection.
• The clean RF ground needs to be isolated by all means from the polluted safety ground by installing common-mode chokes (line isolators in coaxial cables and chokes in earth bonding wires and control cables) between them.
• Station equipment (e.g. transceiver, RF amplifier and antenna tuner) needs to be bonded together as to for one common apparatus. (Use an earthing bar or the heaviest and shortest possible earth interconnection wires or straps).
• Do not install ferrite cores or sleeves on those earth bonding interconnections.
• Ferrite chokes can be installed on interface cabling between individual equipment (e.g. on control and communication wiring). There it makes sense.
• Even though electrical safety ground is not RF clean, station equipment needs to be connected to safety ground obviously for electrical safety reasons.
• As long as the shielding integrity of the radio equipment and cabling shielding effectiveness is good enough this does not harm its noise behavior. The common-mode disturbances stay on the outside of the shielding enclosures.
• However, as stated before, care should be taken that this common-mode noise does not convert into differential mode noise and couple into the weak signal wanted signal path.
• Therefore, use coaxial cables with the best possible shielding effectiveness and pay attention to coaxial connector shielding connections.
• Coaxial line isolators and RF chokes on the cables leaving the shack or house are an additional means of protection.
• Attempts to lower the RF impedance of the electricity safety ground mesh, by adding ground rods right at the shack position can be of help, as long as they are not too close to the clean RF grounding system, however, often this is not the perfect solution.
• Isolating the clean RF ground and the safety ground by means of common-mode chokes often yields the best results.
• Remember that, as a rule of thumb, a straight wire or cable (e.g. grounding cable) has an inductance of in the order of 1 nH per mm, meaning that 1m of grounding cable can easily have an impedance of 20 ohms or more on 3 MHz and 200 ohms or more at 30 MHz. (This is not to be considered as a low impedance to ground).
• Placing an additional mains filter into the incoming shack AC mains cabling can be helpful to supplement the mains filter in the equipment. A dedicated additional mains filter in the mains circuit of typical equipment knowing to cause interference like those with a switched mode power supply can also be considered but need to be evaluated on a case-by-case basis.
• If mains filtering is deployed, additional ferrite core common-mode choking is an overkill as mains filters already include adequate common-mode filtering.