On the back of the Icom IC-7300 there's a ground connector:
The manual goes on to say this:
Is this an electrical or RF ground?
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It's all of the above:
The manual says to connect it to a ground rod, to prevent TVI, BCI. If you used an end-fed antenna without a ground or counterpoise, the mains wiring (through your power supply) would become the RF counterpoise, making the house wiring carry a lot of RF current. This might interfere with your TV and audio electronics.
As a 12 V ground, it will (likely) be connected to the 0 V terminal.
As a lightning ground, it may help a little with lightning current on the coax. Of course not the whole strike, but if there is a small induced current after your earthed entry plate, the current will all flow on the coax braid. Earthing the chassis with a thick, wide, short conductor will reduce the voltage drop on the coax, reducing the current transferred to the centre conductor and into the radio.
Finally, switch mode power supplies are often floating, with the negative or 0 V terminal not earthed. This leads to all the equipment floating at about half the supply voltage (strictly limited to << 1 mA, so irritating and painful, not dangerous). This current also flows in the audio or USB cable shield, if you connect the radio to your PC. A solid ground of the chassis will prevent this 50 Hz buzz.
You could get much of the same benefit by earthing the coax braid as it enters the shack, except that 1) the coax is sometimes disconnected, as you change antenna, it's good that the chassis is still earthed for the 50 Hz buzz, and 2) The ground strap should be thicker than the coax, for lightning purposes.
It's merely a bolt through the case. Under normal operation it shouldn't carry any current, so insofar as grounds come in neatly categorized "kinds", I'd say it's for safety.
It is not part of the RF system, or shouldn't be under normal circumstances. If the feedline currents aren't balanced, then this ground connection would be one possible path for those common-mode currents. But it is much better to address those issues at the feedpoint. With a properly designed and installed antenna there should be no common-mode current, and thus no current that would use the ground lug.
It can improve safety. Anything connected to earth by a low impedance can't have a voltage much different than earth, and thus, can't present much of a shock hazard. Many electrical appliances are grounded through the 3rd pin on the wall outlet for this reason1, but the IC-7300 may be powered by a battery or isolated 12 V power supply with no earth connection. If through some fault (frayed wiring perhaps, or a powerline that's fallen on the antenna outside) the chassis were to come in contact with a dangerous voltage, nothing bad may happen until someone touches the radio, completing the circuit with meat. If the radio is earthed, such a fault will instead blow a fuse or circuit breaker.
It's often the case that for reasons of lightning protection or antenna design the coax shield is earthed anyway, so the ground lug is redundant as long as the coax is connected. However given the above safety concern it may be prudent to connect the ground lug anyway so the chassis remains grounded even when the coax is being moved about. To avoid creating a low impedance path for surge currents, you'd want the ground lug connection to follow the same path, and terminate at the same grounding panel as the coax.
1 Appliances that don't use the earth pin are usually class II or double insulated appliances which take extra precautions to reduce the possibility of such a fault occurring.
It's an electrical ground. The idea is that you connect devices to a common ground point (the electrical ground of your house for example) so that the chassis of your devices are at the same electric potential to reduce/eliminate the potential for an electric shock
Connecting that to an earth ground can invite damage from a lightning strike. See http://w8ji.com/station_ground.htm.
I used to have lots of annoying audio and CW feed back through my speakers, headphones, computers, etc. My voice and CW came through all of that whenever I transmitted. But when I bonded my tuners, amplifiers, speakers, wattmeter, and other shack equipment to that terminal on the back of my IC-765 transceiver, that put a screeching halt to that problem because all of that equipment is now at the same RF potential.