Rpi3

RPi3

• Quad Core 1.2GHz Broadcom BCM2837 64bit CPU
• 1GB RAM
• BCM43438 wireless LAN and Bluetooth Low Energy (BLE) on board
• 40-pin extended GPIO
• 4 USB 2 ports
• 4 Pole stereo output and composite video port
• Full size HDMI

General notes about grounding

There are four types of grounds in ham radio [1]:

(1)  Safety

• All grounds to be bonded together per the National Electrical Code (website).
• Use the electrical safety ground (green-wire ground) for overcurrent protection.
• “The conductive case of equipment is required to be connected to the bonding system, which is also connected to earth ground at the service entrance, so someone who is connected to “earth” (for example, standing in bare feet on a conductive floor) that touches the case won’t get shocked”.

(2)  Antenna

• Create a common reference point potential.
• Minimizes RF current flowing between equipment.
• Must be bonded to safety ground!

(3)  Chassis

• Difficult to achieve equipment bond to an RF (antenna) ground because the wire will have a higher impedance as its length is increased.
• The chassis of equipment should be connected so that no RF current is carried between them at all.

(4)  Lightning

• Low inductance and resistance are required.
• Must be able to handle 20-30 kA.

It seems to me that the antenna and chassis grounds are very similar in function/design.  Here is a visual representation from of a chassis ground (also called a station ground):

When it comes to lightning protection, I think it is easier to disconnect all radio equipment from AC and also disconnect the antenna feedline when not in use.  The topic of lightning protection is very complex and further research is needed (see ARRL Handbook 2014/2015 sections 28.7 Lightning Dissipation Ground, 28.1.10 Antenna Discharge Units, and 28.1.11 Lightning/Transient Protection; The ARRL General Class License Manual for Ham Radio Chapter 9 Electrical and RF Safety).

Update

The primary purpose in lightening protection is to reduce the risk of fire and damage to radio equipment and “the best protection is to disconnect all cables outside the house and unplug equipment power cords inside the home before a storm [2]”.
That is easy to do.  I’ve seen many products that claim to offer lightening protection but I’m not so sure these work as well compared to disconnecting feedlines and power cables.  An example of such a product:

I’m not convinced that a lightning strike is going to be diverted with this device.  Still, this has me thinking that it isn’t enough to simply disconnect the feedline to the radio.  Where should the feedline go after that?  If it is left in the house it could start a fire if a lightning strike were to hit the antenna system.  All that electricity and energy has nowhere to go except the end of the feedline and into whatever else is in the way.  Clearly the ideal solution is to disconnect the entire feedline from both the antenna and the radio, as the ARRL General License manual mentions.  Would it be possible to simply disconnect the radio feedline, and then plug it into something that goes back outside to ground?  Here is what I’m thinking:  The feedline to the radio is disconnected and then connected to another piece of coax that is sent some distance out of the house, to a ground rod.

Some make the argument that a station ground is not necessary. W8JI doesn’t use an RF ground except in certain circumstances [3].  Club station KF6GDJ writes that RF grounds are needed at the HF frequencies but not VHF/UHF [4].  Something interesting to note on the last link is that there is a hypothetical ham radio operator using the second story of his home to operate from.  From there he has a low resistance braid coming down to earth ground connected to a ground rod.  The problem with this is that the ground connection is “not short and direct as possible”.  At some 33 ft, this grounding wire may actually affect other wiring in and around the house.  So what is the solution?  According to the article the operator should have his station placed on the ground floor.  Yes, that is obvious but what do amateur radio operators do when they live in apartments or condos?

Sources
[1]  Lux, Jim. “Chapter 28 Safety” In The ARRL Handbook for Radio Communications: The Comprehensive RF Engineering Reference 2015, edited by H. Ward Silver, 28.6. 92nd ed.
[2]  Silver, W. (2015). The ARRL General Class License Manual for Ham Radio (8th ed.). CT: American Radio Relay League.
[3]  http://www.w8ji.com/rfi_rf_grounding.htm
[4]  http://www.ve3sqb.com/hamaerials/kf6gdj/

Decibels

A Tutorial on the Decibel