[Lowfer] That 8KC 'Phantom Loop' Antenna.

[hvanesce at comcast.net]

John,

All good points including:

Completely reliable: disconnect.
Transformer matches resistive component (of complex impedance)
Reactances will compound difficulty of finding lightning protection
components capable of adequate protection
The more power you run, the harder it'll be to find a suitable protector

Manual disconnect when not in use and when cell approaches would be a (very)
good idea;
 ... but for 8 kHz DX, hundred-hour continuous transmission is often
desirable so I will look into a backup auto-disconnect (self-contained,
battery powered).
The sensor and control portion of a backup auto-disconnect might be
straightforward given a small PIC processor that watches stroke range,
intensity and cell approach rate, but: the big question would still be
something like: 5-year 3-sigma I-peak and V-peak at the interrupter. I'll
try to estimate 5-year 3-sigma I-peak and V-peak at the interrupter for
lightning and soil type in David's area, at 2-foot cable depth; in any case
it definitely wouldn't hurt to know those two numbers (5-year 3-sigma I-peak
and V-peak).

John, was the cable that you used a buried cable?


Independent of the above, a 3.12-mile cable could be a very valuable asset
for VLF and ULF experiments (skywave and groundwave communications, TTE
communications, antenna modeling, imaging)

For several years I've been looking in TX and AZ for a site for a ten-acre
or larger buried loop. I've operated a 1-acre buried loop at VLF for some
time in Arizona and results suggest that a 10-acre buried loop could be
interesting. I think that David's 3.12 mile cable would be far more
interesting.   

73,

Jim AA5BW





-----Original Message-----
From: lowfer-bounces at mailman.qth.net [mailto:lowfer-bounces at mailman.qth.net]
On Behalf Of JD
Sent: Thursday, June 22, 2017 2:15 AM
To: Discussion of the Lowfer (US, European, & UK) and MedFer bands
Subject: Re: [Lowfer] That 8KC 'Phantom Loop' Antenna.

> We get storms here in NE Texas with nasty lightening.  Any strike even 
> remotely close to this cable is going to set-up some hefty surge 
> currents in it.  Any recommendations of how best to protect the amp from
these?

The only completely reliable way, particularly with a solid-state amp, is
going to be to disconnect the cable entirely every single time a convective
cell moves in or begins to form within 20 miles of you.

Having done similar experiments 35 or so years ago with a significantly
shorter cable run, I predict you'll find your setup to exhibit between
several tens of ohms to a few hundred ohms resistance (maybe more, depending
on the cable and ground systems) in series with a more inductive reactance
than you'd suspect.  You'll probably use transformer matching for the
resistance, in series with a bank of capacitors to resonate the system, and
those reactances will further compound the difficulty of finding lightning
protection components capable of adequate protection.

In my setup with a tube type amplifier running under 100 watts, I was
seemingly able to avoid damage with a few heavy duty industrial MOVs.
(That was for backup more than primary protection, though. I still
disconnected when I knew a storm was approaching, because I once had the
experience of vaporizing a fuse rated for 100,000 A interrupt that I'd left
connected between two similar grounds during a lightning storm.)  A solid
state amplifier is going to be far less tolerant of transients, and the more
power you run, the harder it'll be to find a suitable protector that can
guarantee removing those transients while not clipping your audio RF.

John

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