It's not likely that your antenna system or mine would survive a direct lightning strike. A direct lightning strike will deliver an overwhelming amount of energy, capable of melting fusing and vaporizing consumer grade equipment. Surviving a nearby strike or contact with a power conductor is a more realistic goal.
A lone ground rod is unlikely to provide much protection. The reason is, few ground rods make enough contact with the earth to be able to conduct more than a few amps of current in the event they are connected to power line voltage (in N America, typically 120 VAC).
To illustrate, I am just finishing installation of a sub panel in an out-building. the local adopted code says that if there is no grounding electrode system at the outbuilding, I am supposed to install one and connect the frame of the new panel to it. If I use a single 8' ground rod as the grounding electrode, it must have no more than 25Ω of resistance... Failing that, I am supposed to add a second 8' ground rod at least 6' away from the first.
I don't have an accurate test set to measure my ground rod resistance, but I can estimate it by connecting a known voltage that is referenced to the presumably low resistance ground from the local utility. My nice new copper clad rod has an approximate resistance of 1100Ω.
Not really a big surprise, given the sandy soil I'm on. After driving the second rod, and redoing the test, I measured an approximate resistance of 550Ω which seems to give some credence to my methodology.
Stop and think about this... If I connected 120 VAC to a resistance of 550Ω, the current flow would be E/R=I or, 120V/550Ω=0.218Amps. Then, lets say I added several dozen 8' rods to my system... As a result, I manage to get a ground resistance of 25Ω as mentioned in the NEC (250.56). If I connect 120 volts to a resistance of 25Ω the current flow is 120V/25Ω=4.8Amps. Huh... A 15 amp fuse or circuit breaker will never trip in either case, will it?
My point is that an isolated ground rod (one that's not connected to the rest of your grounding electrode system and the utility company's grounding system) can't be counted on to carry enough current to trip a breaker if a power conductor comes in contact with the rod or any thing it's connected to. You could have 120 volts connected to your antenna coax shield and never trip a breaker... even when someone happens to touch the cable and something else grounded to the rest of your electrical wiring system.
Now, think about the much higher voltage you would expect if lighting struck close by... If there is only a high resistance path between your antenna system and the rest of the grounded items in your house, isn't it reasonable to suppose that a few thousand volts could be developed between the coax of your antenna system and the wiring in your house? A surge protector connected to the antenna coax and building ground to could be expected to make a really bright flash as it vaporized.
If you bond the antenna ground rod to your existing electrical service as called for by NEC 250 and 810, you'll greatly reduce the chance of a large voltage difference between items that should be at ground potential. (The NEC defines - "Bonded (Bonding). Connected to establish electrical continuity and conductivity" )
So what's the purpose of grounding (connecting to earth)? Per the NEC, "Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operation." I understand this to mean that if no one grounded anything, we would expect static buildup to occasionally cause unexpected arc-over between systems that are insulated from each other. In fact, early in the development electrical utilities, systems were not grounded and they had a variety of problems due to static, lighting and lack of a common reference. Grounding does not stop lighting, but it does mitigate the damage it can cause. Grounding works in large part, because your ground rods are connected to your neighbors via the utility company system... everyone that makes a ground connection improves the total system and it's connection to earth.
I would run a #10 AWG copper (or larger) from the mast to the electrical service ground. I would also route the coax from the antenna to a location close to the electrical service ground. At a location that was 10' or less from the electrical service ground, I would install the coax grounding block. From there I would feel comfortable running the coax to wherever it needed to go.
This method avoids adding a rod that is difficult or impossible to bond to the existing electrical service grounding system. It avoids the need for expensive #6 AWG bonding cable between a new rod and existing. More importantly, the connections and wire called for by the NEC can be expected to conduct enough current to trip a breaker quickly if by some odd chance, a power conductor comes in contact with your antenna system.
