THE BURGLAR ALARM.

By David J. Hussey.

The group of explorers on the first Martian expedition were discussing the problems of communication between the roving machines that were doing the hard work and Base Station One. The trouble, it seemed, was the background noise. Despite erecting aerial masts on the high ground within ten miles of the base, our transmissions seemed always to be swamped by a signal that appeared on all frequencies. "That in itself was unusual" said the Physics Officer, starting on one of his boring lectures. "Radio frequencies usually stick to separate bands and were either amplitude modulated or frequency modulated. Nowadays," he went on, "digital signals are 'all the rage' but this is something that I haven't come across before".

"Why didn't we hear it down on Earth?" It was an obvious question.
"Maybe it's too weak to reach Earth". This was agreed upon as being the most likely reason as measurements were almost impossible to make.
"Check all our equipment again." The station commander told us. We did - although it was a standard task that we had done countless times before.
"Maybe we are too close to the problem" someone said. But when asked what he meant, he could only answer. "I don't know, but what if this signal is ground hugging within, say a mile of the surface, and disappears above that height?"
"What would be the use of that?" someone wanted to know.

The talk continued each night after the tasks for the day had been completed but nobody had any solutions.
The noise was annoying, there is no doubt about that and, after a few arguments had turned into fights - putting the safety of the dome into question, the commander called everyone together and told them that all other work would be suspended until the problem had been attended to.

Signals were sent to Earth - with great difficulty, as the interference modulated the base's transmissions. That gave a clue to its shape. "It's a pure square wave!" said the Physics Officer. "That would account for it being on all frequencies." But when he was asked why it was there at all, he made no reply.
New equipment was designed and constructed and seemed capable of measuring the noise with some accuracy. Progress was being made.

Expeditions were sent out to the high ground all around and, on the hour, every hour, they communicated with the base by light signals that were not affected by the interference.
At last, meaningful measurements could be taken. After some weeks these were co-ordinated by a simple computer programme that was not blurred by the 'noise'.

"It seems as though we are being tested" someone said with a nervous laugh. "You know: at first we couldn't overcome the problem but now we at least have made some progress!"
The commander took this more seriously than anyone expected.
The next project was to send balloons up from the same high points - so that again we could communicate by light - and detectors were sent up to measure the strength of the signal at various points. The results were plotted on a grid-like map system. It seemed that, using a triangulated plot, the noise was slightly louder from an area about five miles from the base.

After much thought, the commander fitted out a large expedition with all the equipment that could be spared from the base.
Within three days we decided that the signal seemed to emanate from a large glass-like escarpment about twenty feet up the side of a large hill. When the dust had been cleared away the bulk of the mass appeared to be opaque. Using high powered microscope equipment we thought we could see a pulsating light within the block of glass.
"Rubbish!" said one of the technicians. "How could that be? It can only be a reflection. The equipment must be faulty".

A message was sent to the base station for the opinion of the commander and his instructions.
It was decided that the light from the sun must be powering the strange transmitter and, that if we could remove some of the material surrounding the source of the light, perhaps we could learn more.
"Wait a minute," someone asked, "if that was so then why is the signal still there at night? Does it have a sort of storage device?" We couldn't answer that one.
On the next hour, a signal came from the base to cover up completely the alien transmitter, to keep the sun off it.
It was agreed that this was an excellent idea and we proceeded to do just that.
The signal faded away from our immediate area and, just as we were congratulating ourselves, a message came from the base to say that the signal was still as strong there.
"There must be other transmitters on the other side of this d---- planet!", was the collective groan. "Mind you, this proves that it is sun-powered" said the Physics Officer. "Another step forward."

"Right!" said the commander, in his next message, "Cut it open!" It took some time to devise a method to cut into the glass covering. Our best laser was used and eventually made some progress. The signal grew in intensity as we progressed, peeling the layers off the protective covering like an onion.
Eventually the last thick sheet of glass-like substance was removed and immediately the signal increased briefly a million fold, burning out all our measuring equipment.

When we contacted the base, they told us that the signal had now ceased completely. There was nothing to be heard except a panicky signal from Earth asking "What the blazes was that?"
"That," said the commander when we had all returned to the base, "really was a test. "Whoever had set up the transmitter was waiting for visitors to this planet who, obviously, had conquered space travel, had the intelligence to overcome the annoying signal and had also developed equipment capable of detecting it and then cutting into its hardened covering."

"Why did the signal cease?" someone wanted to know.
"That is just it. It isn't needed anymore. They know! It is just a matter of waiting."
"Blimey!" said someone, "Now we've done it!"