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An old Television Antennae
An old Television Antennae

Signals from the Moon !

2 comments Technology

1984, LA Olympics.
Those were the days when satellite and DTH TV had still not come to India and television broadcast was limited to major Indian cities and "larger" second tire cities. Raipur was two hundred KM from Korba and had a regular TV broadcasting center.

There was no TV broadcasting either from Korba or from Bilaspur, which was some 100 KM from Korba en-route to Raipur. Thus there was no TV at Jamnipali. Newspapers and magazines weren't easily available items. Google was still some two decades away. Telephones were on land lines and mobile phones were still many years ahead. News was only from radio. The year was 1984 - the year of Los Angeles Olympics. The only way any one could watch TV was to travel to Raipur or some other place during the Olympics days.

200 Km from the nearest TV transmitting tower we decided we will build an antenna that will catch signal from moon - let alone from Raipur. Over a weekend evening of beer and music, four of us, - two electrical and two mechanical engineers decided we will see Olympics right here in Jamnipali. Weekend beer, excitement of doing something new and the possibility of taking a marooned township closer to LA made a heady exciting mixture.

200 Km from the nearest TV transmitting tower we decided we will build an antenna that will catch signal from moon - let alone from Raipur.

We bought a locally available antenna from Raipur and a commercial "signal booster". This is a device that works well in fringe areas where the signal level is acceptably low - for places that are not more than 40km from the transmission tower. We borrowed an old "box" TV from the executive club that was used for running movies from a VCR. Tuning a mechanical TV tuner was kind of tricky - so JP the RF guy took charge of that. The antenna was erected on the field hostel rooftop, the booster was hooked up and the TV was switched on. Excepting some static noise and snowy screen we could not see or hear anything from the TV.

There were several variables working together. The direction of the antenna, the gain of the booster, the tuning of the TV tuner. The direction could be fixed with a magnetic compass once we knew the direction of the line joining Jamnipali and Raipur on a local map. The gain or amplification of the booster was constantly varied. The tuner was the most difficult to manage - because with near zero signal level, it was virtually impossible to find the best possible tuning. Another significant factor was the weather condition on which we had no control. Sometimes rain and thunderstorm was helping the signal level, on other days, it was killing the signal. After three days of trial and error, we hit "sound" on a late evening. JP - the tuning department, was told not to disturb the tuning of the particular channel any further.

Some common sense to understand the story.

As the strength of a TV signal begins to deteriorate, the colors vanish first, the picture becomes black and white with no deterioration of sound. As the signal further deteriorates, the black and white picture gets worse. The last thing to suffer is the audio. To put in the reverse order, when you try to boost the TV signal, first you get sound, next video, next color of the video. So getting the audio signal was very logical and also inspiring. For the next several days, we had no luck and no further discovery other than some intermittent bursts of audio.

We realized, we are trying to amplify a signal which is so low that it was getting masked below the noise level. Noise is what you see when there is no signal given to a TV - like when you disconnect the antenna cable from the TV. It appears as a random flicker of "dots" or "snow", and is the result of electronic noise and radiated electromagnetic noise picked up by the antenna.

Noise and signal.

Consider the following.
snrSuppose we have an amplifier whose gain (the factor by which it amplifies) can be adjusted to any required value. With this amplifier, when the signal becomes weaker we can increase the gain and keep getting an acceptable output. This method will work well till the input signal level is well above the noise level of the source of the signal. When the signal level falls below the noise level, the amplifier will amplify noise as much as it amplifies the signal. This will result in an output which will be an amplified version of the input but will be noisy and useless. That is why it becomes necessary to improve the quality of the signal - or the signal to noise ratio (called SNR) before any further amplification will be useful.

This told us that we cannot just go on boosting the signal that the antenna is picking up. We need to pick up a better/stronger signal and then use a booster before feeding it to a TV. This meant, We need to have a better antenna. Those days there was no Internet to Google around for such info. Some old electronic magazines were available but they were not helping us. Morale was getting down. JP's fingers were tired of tuning the mechanical tuner. Staring at that snowy noise on the screen we started imagining ghosts and animals, but excepting bursts of audio we had very little excitement and encouragement. There were jokes around the township that - if not this time, we will see the next Olympics at Jamnipali.

Then the following miracle happened.
The power plant was in urgent need of some spare parts from Mumbai. I traveled to Mumbai for getting these parts. While traveling in a bus in Mumbai, the bus was passing through Lamington Road, the electronic component whole sale market in Mumbai. The bus was crowded and I was standing around the middle of the bus. Since I am above six feet tall, my eyes were above the window level of the bus and I was bending down and straining myself for getting a clear view of the moving cityscape of the noisy and crowded street passing by. There were lot of people standing and the view I was getting was through a narrow window of a couple of inches between two persons standing across the window. For some reason the bus stopped for a few seconds and there on the street was a vendor selling old electronic books. One book, a small paperback, bright blue in color, caught my eyes. The book had rather a long name but two letters in that name caught my imagination. The letters were - TV in capitals. I looked as closely as possible. The name of the book was "Long Distance Television Reception (TV-DX) For The Enthusiast" - with the picture of a winged satellite above the earth. I thought this book must be the answers we are searching.

the book

This book, now out of print is still available on Amazon for some Rs.2500/-

I got down from the bus and walked over to the street vendor and pointed at the blue book. I was dying to see inside the book, but he took a good ten seconds to clean it up of the dust collected since the morning rush. The original owner had left no signature, no dog-earring, no highlighting or any underlining anywhere. The book was like new. I looked inside the book and saw design diagrams of long and exotic antennas for very long distance TV reception. On those pages I was already looking at scenes of upcoming Olympic. I asked him how much for the book and he said 12 rupees. I bought the book and came back to Jamnipali. I browsed through the book many times during the train journey from Mumbai back to the project.

rf beam

With the book in hand the project "Olympic" was back on track. We found out at what TV frequency channel Raipur transmitter was transmitting. With inputs from the book, we designed an antenna with dimensional accuracy down to fraction of a millimeter. The antenna was made out of aluminum pipes and steel supports.

Wiring, connections, clamping were professionally done. It was not an antenna, but a beautiful piece of art. The first day we hooked it up, crystal clear sound came out of the TV. Little more optimizing of direction and tuning, and we could see people on the screen in black and white although the quality of the video was poor. The news about this was out in the plant and township. Although we could hardly imagine human shapes, people were talking about their dresses. But beyond this marginal improvement we could not move ahead. The Olympic was only a week ahead. Coming back from plant every day we used to wonder till midnight - what next? We realized two other things that can possibly improve the signal strength. The first one was to take the antenna to a higher location. The second was to use a second booster in series with the first. The first was surely going to help. About the second, we were not sure. So we located a water tank in the middle of the township and decided we will install the antenna on the top of it. There was a narrow stair case inside the shaft of the water tank that was helpful in carrying and installing the antenna there safely and easily. The first booster was used near the dipole of the antenna. We started getting clear black and white pictures. Pictures were still not coming in color. News was out that we were going to see Olympics right here in our own township.

The last phase of the improvement was still pending. We hooked up the second booster near the TV. With two boosters in series, there were two gain controls to reckon with. For three days we were struggling arbitrarily to hit the sweet spot of overall control, but then we understood the magic of how the series combination worked. The following is an explanation of a rather complex scientific phenomena of signal conditioning.

Imagine you have two amplifiers of gain 50 each. Let's say we need a gain of 72. Then what combination of gains will yield best result? We found that for best results, the first one should be set to minimum possible and the second one to maximum possible. This happens because, amplifying a signal first by 22 and then by 50 will introduce less noise than compared to first by 50 and then by 22. Armed with this understanding, we trimmed the gain of the two boosters and managed to optimize the signal a little more and managed to get colored pictures.

1984, July 28 was a Saturday with a rainy evening. There was one 21" TV put on the open theater near a water-tank, in the middle of the township showing Los Angeles Olympics in full color. There were about 150 people standing in the rain, some with umbrellas, some under a sheet of poly and others out in the rain watching the Olympics. The smile on those happy faces was more valuable than anything that we could have asked for.

But for the four of us, the signal was not coming from Raipur, it was coming from the moon.

LA olympics 1984The Grand Opening Day Ceremony of the LA Olympics, 1984

Last modified onTuesday, 09 August 2016 18:04
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