[NJARC] question regarding long wire antennas

Sat Sep 2 07:37:14 EDT 2017

Thanks guys for all the helpful tips and tricks.
My only concern with using the remaining antenna wire as the lead lead wire
down to the radio down in the basement is interference. Between ballasts is
LED light bulbs, WiFi signils and cordless phones, I was worried about
stray signals making their way into my receiver. Now I know that my WiFi
and phones are in the GigaHertz range, but I'm sure that there are outer
household sources of interference.

Between this and the tuned loop I hope to build with my Scott SLRM, I hope
to finally be able to enter next year's DXpedition and maybe, just maybe,
be competitive.

Thanks again!
Joe

On Sep 2, 2017 1:35 AM, "Gerry Steffens" <gsteffens at bevcomm.net> wrote:

> Lightning Current
> Williams says that a typical lightning bolt may transfer 1020 electrons in
> a
> fraction of a second, developing a peak current of up to 10 kiloamperes.
> According to Uman, the German scientist Pockels discovered that basalt rock
> in the vicinity of lightning strikes was magnetized and deduced currents on
> the order of 10,000 amps in 1897. Ampere's law allows you to deduce the
> current in a wire from the measurement of the magnetic field at some radius
> from the wire. Pockels presumably had measured the magnetizing effects of
> large currents on basalt and was able to scale those experiments to
> estimate
> the current associated with the lightning. Based on that principle,
> magnetic
> links are widely used for the measurement of the lightning currents. Most
> measurements have been in the range 5,000 to 20,000 amps but a famous
> strike
> just before the Apollo 15 launch in 1971 was measured at 100,000 amperes by
> magnetic links attached to the umbilical tower. Currents over 200,000 amps
> have been reported.
> One could envision a magnetic detector based on both Ampere's law and
> Faraday's law which could give you an estimate of lightning current
> provided
> you had a measurement of the distance from the detector to the lightning
> strike point. If you set up a coil of wire in a vertical plane, then the
> rate of change of magnetic field through the coil would generate a voltage.
> If you could sum (integrate) the current generated by that voltage, you
> could calculate the charge transferred in the lightning strike. With
> several
> such detectors in an area, you could model the location as well as the
> charge associated with the strike.
> Most commonly, the lightning current ceases in about a millisecond for a
> given stroke, but sometimes there is a continuing current on the order of
> 100 amps following one or more of the strokes. This is called "hot
> lightning" and it is the cause of lightning fires according to Uman. The
> temperatures of lightning are 15,000-60,000°F for both "cold" and "hot"
> lightning - it is the continuing current that starts some 10,000 fires per
> year in the U.S. in the estimation of Uman.
>
> The above is both in one of my text books and at one time I also found it
> online.
>
> I am an electric utility engineer and have worked in EHV electric
> transmission design and in utility operations.  When lightning strikes
> hardware on poles or houses in electric distribution, it usually rips the
> conductors to pieces or at least rips it loose from its mountings on the
> poles or buildings, leaving a charred track where the cables had been.
> Utilities employ expulsion arrestors (which operate differently than gap
> static arrestors) to protect such facilities and they do some of the time.
> However, let's think about even #10 or #12 wire in the face of the
> amperages
> involved.  These conductors don't stand a chance with that kind of energy,
> even for milliseconds.
>
> I did experience one case out on the farm where I had a radio and an
> antenna
> which was hit with a strike.  I had previously lost a couple of antenna
> coils in radios and was unable to explain that the radio that experienced
> the hit was OK after the strike.  I am guessing that the strike was at the
> windmill end (175 feet away) and the antenna wire simply melted or
> vaporized
> before the currents could travel the length of the antenna to the radio.
>
> The one thing of which I am certain, however, is that in 45 years in the
> utility business, I have run across many, many unexplainable incidents
> involving lightning.  The most fun to watch was seeing a lightning strike
> to
> ground where the lightning actually crawled along the surface of the ground
> for a couple hundred feet before it disappeared into the ground.  I was
> sitting on a tractor about 1/8 mile away at about age 16.
>
> I am not familiar with the unit you pictured.  The arrestors I used were
> the
> old porcelain gap type from Allied, BA, McGee and others back in the 1960s.
> However just from the physical size, these units are not dealing with the
> currents of the scale of lightning strikes.
>
> Gerry
>
>
>
> -----Original Message-----
> From: Chuck [mailto:cpaci1 at verizon.net]
> Sent: Friday, September 1, 2017 9:45 PM
> To: Gerry Steffens; 'Joe Giliberti'; 'New Jersey Antique Radio Club'
> Subject: Re: [NJARC] question regarding long wire antennas
>
> Hi Gerry,
> I'm not an electrical engineer like yourself, but my experience of the
> extent of the spark arrestor's capabilities went a little further.
> I am a software engineer and my knowledge of the subject comes only from my
> limited experience.
> My antenna took a direct strike from a HUGE bolt of lightning, according to
> my neighbor who saw it happen. It felt like a truck hit my house!
> The antenna is mounted on a 25 foot aluminum flagpole mounted at the top of
> the gable of my house and is the highest object in the area at 48 feet
> high.
> So I guess it's a prime target for a lightning strike!
> Somehow the spark arrestor saved it as well as the radio, even though the
> radio was connected to the antenna at the time.
> The antenna was not trashed and the radio was still intact. Go figure??? I
> would think it should have all been burnt to a crisp.
> I only had damage to the spark arrester itself! After changing it out for a
> new one, I found, to my surprise, everything still works fine???
> I guess I just got a really good spark arrestor - - - or I was really
> lucky!
> I attached a picture of the spark arrestor I had (and replaced it with), in
> case anyone one would like to get the same one for their antenna.
> Now days, I keep a spare in the shop - lol
>
> Chuck
>
> -----Original Message-----
> From: Gerry Steffens
> Sent: Friday, September 01, 2017 5:09 PM
> To: 'Joe Giliberti' ; 'New Jersey Antique Radio Club'
> Subject: Re: [NJARC] question regarding long wire antennas
>
> Just remember
> Reply = Poster
> Reply All = Everyone
>
> _________________________________________________________
> The analogy to a spark plug is a good one.  However, maybe I am just a
> wording junky but, if lightning strikes your antenna, the antenna is
> trashed
> and so is the radio, TV or what have you.  The function of a (miss-named)
> lightning arrestor is to bleed off static charges which can develop by
> wind,
> rain, snow, etc. blowing or falling by the antenna.  The thinking, by some,
> was that the charged antenna attracts lightning, maybe so maybe not, I am
> an
> electrical engineer, not a meteorologist and more.  But, static charges and
> sparks can and do wreck antenna coils in radios and more.
>
> My first time, taking arrestors seriously was in the early 1950s as a kid
> with a shortwave radio and antenna (Allied supplied an arrestor with the
> antenna kit).  I was sitting in the living room and I kept hearing a snap
> every few seconds.  After much searching for the cause, I found it.  The
> night before we had experienced the beginning of a pretty wild storm (snow
> storm - ice crystals and high wind).  Dad had disconnected the TV twin-lead
> from the TV set and even unplugged it 'cause up front there had been a
> couple of lightning flashes.  The snap was a static spark between the
> exposed wires of the 300 ohm twin-lead of the TV antenna.  The next time at
> the auto garage where dad worked I got to talk with the radio repairman
> employed there.  He explained the definition of "snow static".  I went home
> and installed the arrestor with a good ground!
>
>
>
> -----Original Message-----
> From: njarc-bounces at mailman.qth.net [mailto:njarc-bounces at mailman.qth.net]
> On Behalf Of Joe Giliberti
> Sent: Friday, September 1, 2017 7:44 AM
> To: New Jersey Antique Radio Club
> Subject: [NJARC] question regarding long wire antennas
>
> Just remember
> Reply = Poster
> Reply All = Everyone
>
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