Saturday, March 19, 2011


 The new happening thing in the Ground-Station control room this month is the cacophony of unique sounds. These sounds are nothing but beeps interwoven into the complex pattern of dots and dash used for wireless communication to transmit and receive Morse signals.

In reality, this entire buzz is to decipher the Morse coded satellite beacon signal that will be transmitted by 'Pratham'. The Morse coded beacon signal acts as an identification for the satellite confirming its pass over the ground station.

Most of us are familiar with the sound …--… which is nothing but Morse for SMS.
Also,  …---… is the Morse for the Emergency SOS call.

Devised by Samuel Morse in late 1800, Morse is a language in itself wherein each English alphabet has a characteristic sound which is a unique combination of dots and dashes, arranged in a definite rhythm.  Morse code speed is measured in words per minute (wpm).Higher the skill of the operator, more is his speed. Speed of 72 wpm has been recorded during world war2. The general Morse transrecieving speed is about 18-25 wpm on the international High-Frequency (HF) band.

Being a code in itself, Morse has a special exclusivity. It is intelligible music to the ears of someone trained in Morse but to the untrained ear, it is a rhythmic noise.

Signal to noise ratio of Morse code is appreciably high. This means in long distance transmission (DX), modulated audio signals may die out and get unreadable at the reception because of atmospheric noise. In most DX, the audio transmitted over radio frequencies will be reliably received only over a particular distance. But the carrier can travel even beyond this distance. Such fading of audio signals puts a limit on the reach of your communication system. In such conditions Morse code being a timed transmission of bursts of the carrier signal, it has a better chance of being received without an error.

Perhaps due to this reason, the first satellite transmission to earth, done by Sputnik was Morse coded.
In order to acquire the skill of Morse coding, the character must not be remembered as a combination of dots and dashes (this is the most common mistake of beginners) Instead, the characteristic sound, rhythm of each letter must be registered.
Discover the Morse code for yourself using this simple software.

Monday, March 14, 2011

The case of the Unforeseen radiator

It was not until we studied the technical paper released by PRATHAM team on
ground station set up that we realized something very obvious.

“The antenna should be as far away from any radiating systems as possible
(at least 20 meters away)”

‘Radiating sources’ reminded us of the walkie-talkies used by the security
guards. And a minisecond later it reminded us of the transmission line tower
that stands just across the road…

We rushed out of the control room into the adjoining terrace to check out
the giant metal structure… it was there always…so inconspicuous….it was only
now that we were looking at it with a sense of awe.

“But the lines have a frequency of 50Hz whereas our reception signals are in
the UHF VHF range, so how does it interfere with our project?“ enquired Anuj

Saurabh had the answer ready “Although the frequency is 50 Hz, the voltage
is of a gigantic value-around 33kv…KILOVOLTS…. So the transmission tower acts
as a giant radiating source emitting spurious signals much like how the sun,
a hot body, emits a range of value of radiations…”

The new discovery consolidated the need of accurate satellite tracking (read
antenna rotor)

Quote of day “Radio reception can be impaired under a power line, due both
to shielding of a receiver antenna by the overhead conductors, and by
partial discharge at insulators and sharp points of the conductors which
creates radio noise.”