Thank you Richard! I'll try to explain.

II. I have a decent RF and DC ground near the antenna site on top of
the building (huge masses of steel), but not in my shack, which is
some 120 ft. below. This is not unlike having the antenna out on the
lot, and the shack somewhere up in the attic.

Yes, after a fashion. What you mean to say is you are still far from
earth ground, but have plenty of metal.

Yes, it sounds weird, because it is. I have to thank another ham,
I2FZX, for the almost ideal situation.

On the TOP of my building there's a 50 ft steel lattice tower
(HF/VHF/UHF beams) and a tornado-proof 20 ft dish (1/2 kW UHF
moonbounce). They are some 80ft apart, both grounded.

Right now, I still have no real grounding in my flat - I just have a
virtual ground connecting all the conductive material in the shack,
which does help reduce noise and hazards. I intend to at least bring
the wiring up to regulation. That won't help with lightning safety,
though.

I intend to string the T2FD between the fixed part of the tower
(~40ft) and the base of the dish. I could use either for grounding,
but I'd opt for grounding at the dish, which is right atop my place.



EMP
Certainly are for those who aren't signatories of the
Nuclear Test Ban Treaty.

This is a bad neighborhood. Nuke blasts are an almost daily
occurence. As they are not meant for testing purposes, I am afraid the
NTB treaty does not apply. Also, there's a known focus of Al Qaeda
activity just a mile away (go to www.tuttocitta.it and plonk in Milano
/ Viale Jenner 50) but it can't be closed because it would hurt
certain people's sensitivities. I wear lead pants all the time.



IV. Also, I'd like to avoid as much as possible any hums that may
derive from poor double grounding. After all, we mostly do HAVE to
ground stuff inside the shack as well, for electrical safety.

Anticipating what follows, perhaps you should simply loop couple all
of that steel at the top of the building. No ground issue there. No
direct connections. No HV problems.

Please elaborate. Do you mean turning the warship atop my bldg into a
ground reference loop?



2) Ground the middle of the high-Z winding to the locally available
ground. NOT ground the low-Z winding - I'll just connect it to the
coax.

Here is where the part about doing it right raises its ugly head.
Ground is not simply a matter of being bulk metal. At least not RF
ground, and not always safety ground.

Well, not exactly.

A large bulk of metal is usually a pretty good capacitive sink at HF.
In fact, even an insulated structure works decently as a RF ground. I
even built crystal radios in which very few square inches of sheet
metal were enough to provide a cap sink that had a large effect when
worked against a wire antenna.

As for safety ground, NEVER "assume" that a bulk of metal is grounded.
If you did, you could easily be found guilty of manslaughter in court.
In some jurisdictions you have to get an an electrician to sign you
off that, among other things, a piece of eqpt is properly grounded.

In professional radio installations, one sees a "ground reference"
system which is indeed DC-grounded, but for RF purposes, most of the
sink effect comes from strapping together everything in sight,
including cabinets, metal furniture, building structures, drains,
floor support etc etc.



Route internal wires for maximum insulation. Fill the balun
case with either epoxy or urethane foam. Keep the two leads (coax,
ground) well separated.

This is more a matter of cosmetics and personal preference than
engineering consideration.

I would like to maximize the chance that any burst of energy will take
the ground path rather than the coax path. Why should putting, say,
3kV insulation between the antenna and the coax not matter?
Incidentally, you do find kV-range insulation in commercial products
as well.



Lead dressing is adequate and mounting
does the rest.

What do you mean?



3) Insert EMP dischargers right into the balun:
- One across the high-Z winding, for transversal mode.
- One between each high-Z lead and ground, for common mode.
- One across the low-Z winding, a'shunt the coax, for
transversal-mode.
And also one across the top resistor, also for transversal.

The resistor is already going to snub any "EMP" the rest is window
dressing. It takes quite a few KV to jump an inch.

So it snubs any EMP but not an RF signal. What is the spectrum of an
EMP? Is it more like DC or more like all across the RF spectrum?



4) Put one or more large iron-core chokes on the coax, as to dampen
EMP that could possibly travel on the outside of the coax shield.
(This would also ensure that RF power or noise will not travel on the
outside of the shield, of course)

8 turns of 6 inch diameter loops will do just as well, as would a
simple 1:1 Current BalUn. You are too much concerned with Nuclear
Blast. If you suffer EMP, you've got far more to worry about.

Now I understand. FYI, what gets you in a lightning near-hit _is_ an
EMP.

I once had an audible arc in an antenna due to a 1-lightning
thunderstorm. That single hit happened in the midst of a city, and
took out several power stations and countless other equipment. My
antenna was 8 miles away.



a) For HV DC insulation in the balun, I intend to use as large a
PVC-insulated conductor as I can fit, wind the high-Z winding, wrap it
in insulating tape, and wind the low-Z winding on the top of the
insulating layer.
- PVC is said to be lossy. Is it a dramatic loss or not?
- What tape should I use?
- Is the insulated core of a coax a decent alternative to HV wire?
- What is the implication of making a low-Z winding ATOP the high-Z
one & the insulating layer, instead of interleaving them?

10W is not going to generate any potentials to offer such prospects of
arc or corona - unless you are constructing a very small loop or
dipole. You have already described you are using a T2FD which
obviates that headache.

Great! But what about losses?

I NEVER saw baluns with windings atop each other
- they were always directly wound on the core.
And I don't know why.


b) For receiving, small 90V neon bulbs should already provide some
protection.

And maximum noise generation if they should ever fire. How's that
going to happen? Is this massive metal structure at the top of your
building an AM transmitter tower with a 50KW signal?

Nothing but EMP. Lightning arrestors, if not MOV, are mostly gas
discharge devices. All of yesteryear's professional toob radios and
many consumer ones included a tiny neon lamp in their front end.


c) For the coax shield choke, I am considering 20 tight turns on a
5in. plastic pipe,
the steel core being made with pieces of thin,
insulated rebar - enough to fill the pipe.

Excessive²

OK!


- Any reason to vote for either major party candidate in the coming
election?

Vote Status Quo and wait for the night of the Long Knives.

OK! Will do.



- Any reason to use FLAT steel instead of cheap, easy to find rebars?
Lead may help with the issues of thermonuclear events.

Great! But lead will lead to lead poisoning litigation too.

I don't want to litigate a lead-poisoned nuclear-armed jihadi.

Lead poisoning is also rumored to lead people to insanity
- see Goya (the painter, not the beans).

So, I don't want to litigate a lead-poisoned nuclear-armed
totally-out-of-his-mind jihadi either.



In fact, you would probably get just as
good a signal out if you simply ran 20 feet of coax to a 100 foot wire
going up and tying off (or not) to all this metal.

I had thought about that too, esp. for LF! Problem is, between moi
and the warship up on top lie crouching and waiting a few tens of TV
sets and just as many PCs. I already have a wire going up to the 5th
floor (out of 9). Works great, but only after 1 am, and only because
energy-conscious Italians always switch off their gear at night.

73

N1JPR/I2