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

[w8au at sssnet.com]

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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