[600MRG] TM1LY and TM100LY Lafayette Stations on the Air.

Sat Dec 19 00:41:35 EST 2020

Yes, it's more like a Marconi L than a Marconi T but the front section
would have made me write "Marconi T" also, but it's just a wide feeder
for a Marconi L.

Very interesting antenna.

73
DR

On Sat, Dec 19, 2020 at 12:34 AM Bart Lee <bart.lee.k6vk at gmail.com> wrote:
>
> Correction to previous post:
>
> DR, A photo at the bottom right shows the antenna for the megawatt arc at Bordeaux circa 1920+.  It looks like a radiating vertical lead system, a narrow "V" --  into the leading edge of a large rectangular capacity hat, like a Marconi [inverted]  "L" but spread out. So the towers look to be isolated from ground and so did not radiate. The direction of emission would be to the observer (and camera). For U.S. Mid-Atlantic (e.g., Annapolis, MD), the direction would be East-NorthEast of Bordeaux (great-circle). This could be verified if there were a lay-out map available of the transmitter and antenna, but that's what it looks like in the small diagram. There had to have been a very large ground-screen under the antenna system.
>
> 73 de Bart, K6VK ##
> -- --
> Bart Lee
>
> Texts only to: 415 902 7168
>
> www.bartlee.com
>
> {Bart(dot)Lee(dot)K6VK(at)gmail(dot)com}
>
>
>
> On Fri, Dec 18, 2020 at 8:51 PM <w8au at sssnet.com> wrote:
>>
>> Fhanks, Dave, for the ARC info. Interesting engineering for that era
>>
>> Perry  W8AU
>>
>>
>> > Arc transmitters couldn't be keyed for on/off keying because it took a
>> > moment to strike the arc, so frequency shift keying was used.
>> >
>> > See below,
>> > 73
>> > DR
>> >
>> > See this article from Wikipedia
>> > <https://en.wikipedia.org/wiki/Arc_converter#Keying>.
>> > Keying[edit
>> > <https://en.wikipedia.org/w/index.php?title=Arc_converter&action=edit&section=3>
>> > ]
>> >
>> > Since the arc took some time to strike and operate in a stable fashion,
>> > normal on-off keying <https://en.wikipedia.org/wiki/On-off_keying> could
>> > not be used. Instead, a form of frequency shift keying
>> > <https://en.wikipedia.org/wiki/Frequency_shift_keying> was employed.[8]
>> > <https://en.wikipedia.org/wiki/Arc_converter#cite_note-8> In this
>> > *compensation-wave
>> > method*, the arc operated continuously, and the key altered the frequency
>> > of the arc by one to five percent. The signal at the unwanted frequency
>> > was
>> > called the *compensation-wave*. In arc transmitters up to 70 kW, the key
>> > typically shorted out a few turns in the antenna coil.[9]
>> > <https://en.wikipedia.org/wiki/Arc_converter#cite_note-9> For larger arcs,
>> > the arc output would be transformer coupled to the antenna inductor, and
>> > the key would short out a few bottom turns of the grounded secondary.[10]
>> > <https://en.wikipedia.org/wiki/Arc_converter#cite_note-10> Therefore, the
>> > "mark" (key closed) was sent at one frequency, and the "space" (key open)
>> > at another frequency. If these frequencies were far enough apart, and the
>> > receiving station's receiver
>> > <https://en.wikipedia.org/wiki/Receiver_(radio)> had adequate selectivity
>> > <https://en.wikipedia.org/wiki/Selectivity_(electronic)>, the receiving
>> > station would hear standard CW when tuned to the "mark" frequency.
>> >
>> > The compensation wave method used a lot of spectrum bandwidth. It not only
>> > transmitted on the two intended frequencies, but also the harmonics of
>> > those frequencies. Arc converters are rich in harmonics. Sometime around
>> > 1921, the Preliminary International Communications Conference[11]
>> > <https://en.wikipedia.org/wiki/Arc_converter#cite_note-11> prohibited the
>> > compensation wave method because it caused too much interference.[4]
>> > <https://en.wikipedia.org/wiki/Arc_converter#cite_note-Little_1921_125-4>
>> >
>> > The need for the emission of signals at two different frequencies was
>> > eliminated by the development of *uniwave methods*.[12]
>> > <https://en.wikipedia.org/wiki/Arc_converter#cite_note-12> In one uniwave
>> > method, called the *ignition method*, keying would start and stop the arc.
>> > The arc chamber would have a *striker* rod that shorted out the two
>> > electrodes through a resistor and extinguished the arc. The key would
>> > energize an electromagnet that would move the striker and reignite the
>> > arc.
>> > For this method to work, the arc chamber had to be hot. The method was
>> > feasible for arc converters up to about 5 kW.
>> >
>> > The second uniwave method is the *absorption method*, and it involves two
>> > tuned circuits and a single-pole, double-throw
>> > <https://en.wikipedia.org/wiki/Contact_terminology>, make-before-break
>> > key.
>> > When the key is down, the arc is connected to the tuned antenna coil and
>> > antenna. When the key is up, the arc is connected to a tuned dummy antenna
>> > <https://en.wikipedia.org/wiki/Dummy_antenna> called the *back shunt*. The
>> > back shunt was a second tuned circuit consisting of an inductor, a
>> > capacitor, and load resistor in series.[13]
>> > <https://en.wikipedia.org/wiki/Arc_converter#cite_note-13>[14]
>> > <https://en.wikipedia.org/wiki/Arc_converter#cite_note-14> This second
>> > circuit is tuned to roughly the same frequency as the transmitted
>> > frequency; it keeps the arc running, and it absorbs the transmitter power.
>> > The absorption method is apparently due to W. A. Eaton.[4]
>> > <https://en.wikipedia.org/wiki/Arc_converter#cite_note-Little_1921_125-4>
>> >
>> > The design of switching circuit for the absorption method is significant.
>> > It is switching a high voltage arc, so the switch's contacts must have
>> > some
>> > form of arc suppression. Eaton had the telegraph key drive electromagnets
>> > that operated a relay. That relay used four sets of switch contacts in
>> > series for each of the two paths (one to the antenna and one to the back
>> > shunt). Each relay contact was bridged by a resistor. Consequently, the
>> > switch was never completely open, but there was a lot of attenuation.[15]
>> > <https://en.wikipedia.org/wiki/Arc_converter#cite_note-15>
>> >
>> > On Fri, Dec 18, 2020 at 9:37 PM J Mcvey <ac2eu at yahoo.com> wrote:
>> >
>> >> Wow that must have been LOUD. I suppose all the plumbing was to vent the
>> >> ozone?
>> >> How did they key it?
>> >> That setup is a lost art for sure.
>> >>
>> >>
>> >>
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