Marconi Wireless Station Clifden

[peter scott]

I was looking at the location of this station that was in Galway between 1907 and 1922. In addition to the wireless station this location is also famous for being the landing site for Alcock and Brown in 1919.

There isn't much today to show where the wireless station was but maps show the huge condenser shed with wires radiating out from it eastwards. The photo below is looking towards the backside of the condenser shed with the masts and wires on the far side.

The landing site of the Vimy is marked with a bullet shaped monument and if the location is accurate then it was within the span of the aerial wires. There is no mention in the accounts that I've read of any collision with the aerial. I wonder if they flew in beneath it?

The Google "Aerial View" is compared with the Wireless Station map.

Peter

       

[ppppenguin]

Makes you wonder how close they came to getting caught in the aerial array.

[peter scott]

I have taken the Bing Aerial View and superimposed it on the Wireless Site Map.

   

Peter

[peter scott]

There's no fool like an old fool!

Most people would think that I'm old enough now not to take everything at face value but to question everything.

My first mistake was with the Marconi Wireless Site map. The aerial system was not as wide as the map suggests because the outer rows of points described as masts were not masts at all. They were anchor points for guy wires supporting the inner rows of masts.

My second mistake was to accept the map location described as the landing site of Alcock and Brown's aircraft. It was probably a good vantage point from which to witness the landing and it was also a nice place to site a monument but that was as far as it goes.

Peter

[peter scott]

The aerial system did start out with a mast beyond the position of the Alcock and Brown monument. As on the right hand side in the coloured sketch but the whole array was later reduced to a width bounded by the centre two rows of masts.

   

As for the monument, it started out with a sign on the top saying "Landing Site 500 metres" however, the sign did not survive the weather or the subsequent refurbishment. My red arrow starts approx. at the monument and ends about 500 metres distant in the general direction.

Peter

       

[peter scott]

I don't how widespread the knowledge was but it was known locally that the flight was taking place and that it was expected to land at Galway.
Watch this video from 5.26

The radio station was really a very different world. The Condenser House was 350 ft long containing an air spaced condenser comprising 1800 galvanised steel plates 30' x 12' spread on either side of the transmitter and receiver in the centre section. Initially the connections to the aerial system were on the opposite side from the masts but later the aerial was redesigned and fed from the same side as the masts.

               

The transmitter used spark techniques to pulse a resonant circuit coupled to the aerial. Power came from a high voltage DC generator (or a high voltage battery) that alternately charged two capacitors in series where each has a spark gap that connects through the resonant circuit. A form of electro-mechanical multivibrator. The generator or battery voltage was about 12kV so I would not have wanted to go anywhere near the plates in the Condenser House. The capacitors alternately discharge pulsing the resonant circuit. This generated a fairly continuous wave instead of the rather random pulsing of a simple buzzer type of spark generator and therefor didn't fill the entire RF spectrum with as much noise. That said, in order for the operator at the receiving end hear a tone rather than a simple on/off click a further refinement was added such that the timing of the spark discharges were forced to occur with a regular frequency. The carrier generally used was 45kHz and the tone imposed on the sparking around 8kHz. You can see Marconi's description in the Nobel Lecture he gave. The transmitter is shown in Figure 24.

I think the simple spark spectrum would have been like the first screen shot and the toned one more like the second screen shot.

At the receiving end the detector used was the famous Marconi Magnetic Detector that passed a continuous loop of soft iron wire through two concentric coils. One coil was connected to the tuner or aerial arrangement and the other to a headphone. The wire loop was driven round by clockwork and as it entered the coils it was magnetised by a horse shoe magnet but the received signal in the tuner/aerial coil acted to degauss the magnetism depending on the amplitude of the received signal. A second magnet was also arranged at the point where the wire exited the coils. I have no idea what it did.

               


Peter

[peter scott]

To someone like me who knows very little about aerials the system used at Clifden was also interesting. It consisted of a set of masts 200ft tall that supported aerial wires running horizontally away from the direction of the receiving station across the Atlantic at Glace Bay. Apparently most of the transmitted radiation came from the vertical parts rather than the long horizontals. If you have a simple vertical aerial then towards the top the current tends to zero but the horizontal additions add capacitance to the aerial and increase the current flow at the top and add to the effective length or height although also increasing the optimal wavelength.

Peter

       

[peter scott]

the tone imposed on the sparking around 8kHz.

Correction 500Hz not 8kHz.

[peter scott]

I've been trying to get my head round some of the numbers.  According to Sir J.A. Fleming in his book "The Principles of Electric Wave Telegraphy and Telephony" the capacitor at Clifden was 1.16uF and was charged up to 80kV. (Page 255.)

Both these numbers are puzzling. We know that in the "Condenser House" there were 1800 plates 30' high by 12' wide with 12" spacing. The shed was 360' long by 75' wide. Well that would certainly fill most of the shed allowing some space for the actual spark transmitter. An air spaced multiplate capacitor with those dimensions would have a capacitance of 1.76uF which doesn't fit with the Fleming figure but we need to partition this total between the three capacitors in the diagram and we also need to account for the 80kV voltage from the 12kV generator. I think that the capacitors K each charge up to 6kV on sparking but transfer their charges to E in opposite senses so each of K imparts 40kV on E so the ratio of each K to E must be 6.66. With a total size of 1.76uF E must be 0.123uF and the two Ks 0.818uF each.

So where does Fleming's 1.16uF fit in? Someone got something wrong somewhere and I don't imagine it was Fleming. 

Peter

   

[peter scott]

The previous post is garbage!

Peter