VERY SHORT ANSWER TYPE QUESTIONS

Q. 1. How fm transmitter differ from AM Transmitters?

Ans. The FM transmitters have a very large bandwidth as compared to AM transmitter. In FM transmission ground way1 and sky wave propagation is not possible, and signals in VHF and UHF bands are prpagated by line of sist propagation, which restricts the range upto 50 km.

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Q. 2. What are the methods of FM generation/modulaiotransmission?

Ans. We can generate FM signals by using various FM modulators. The basic requirement of fm modulator (FM signals generator) is to provide a variable output frequency with varying proportions to the instantaneous amplitude of the modulating voltage. The FM signals can be generated by two methods

1. Direct Method. The FM signals can be generated directly by frequency modulating the carrier

2. Indirect Methods. The FM singals can be generated indirectly by integrating the modulating and signal and then allowing it to phase modulate the carrier.

Or by using the modulating signal first to produce a narrow band FM signal and then by frequency multiplication, the frequency deviation may be increased to the desired level.

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Q. 3. What are the limitations of direct modulation methods?

Ans. The direct methods of FM generation suffers from the following limitations:

In the direct methods of FM generation, it is difficult to obtain a high order of stability in carrier frequency. This is because the modulating signal directly controls the tank circuit which is generating the carrier. The crystal oscillator cannot be used as it provides a stable but fixed frequency.

The non linearity produces a frequency variation due to harmonics of the modulating signal hence there are distortions in the output FM signal.

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Q. 4. Explain principle of indirect methods of FM generation modulation. Give the indirect modulation methods.

Ans. Indirect Methods of fm radio transmitter Generation. The indirect method removes the limitations of direct method.

The indirect method employs the phase modulation to obtain FM signal. It is only necessary to integrate the modulating signal prior to applying it to the phase modulator. The general block diagram for such a method is shown in figure 1. This is used in VHF and UHF radio telephony.

The indirect methods of FM generation/modulation are

(i) Armstrong method, (ii) RC phase shift method.

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In 1957 the Collins radio company launched the KWM-1 transceiver

Because of the possibility of receiving signals over a great distance, ten meter radio has a considerable following, including the ten-ten club, an international organisation for radio enthusiasts who enjoy the challenges and opportunities of the ten meter band. The ten meter band was opened to technician class licensed radio amateurs in 1987 and in 2007 the requirement for a Morse Code test as part of the licensing process was dropped. It is NOT part of CB radio which is unlicensed. CB is restricted to the 11meter band and to lower power transceivers. Arthur Collins, founder of the Collins best radio transmitter company, and a very prominent figure in the history of amateur radio, was one of two participants in the test General leMay carried out.
In 1957 the Collins radio company launched the KWM-1 transceiver, the first mobile transceiver and the first to use SSB. Collins radio placed all their emphasis on SSB rather than AM equipment, with the result that since 1957 SSB has been the effective standard for long distance radio transmission by voice. During World War II radio station equipment communications advanced quickly and the use of SSB spread to amateur radio operators. General Curtis leMay, who, in 1951, had become the youngest four star general in US history (since Ulysses S Grant), was Commander of SAC (Strategic Air Command) in the 1950’s. He was also an amateur radio enthusiast and well aware of the debate over the use of standard AM or SSB. SAC were planning to get rid of radio operators on their new aircraft and intending to use AM equipment, so General leMay had tests carried out to investigate the difference between the two modes of communication. In two flights, one to Okinawa and one to Greenland, SSB trounced the conventional AM systems leading SAC to adopt SSB as the standard for their new bomber, the B52. Single Side Band is a modification of amplitude modulation which makes more efficient use of power as well as bandwidth. Originally known as SSSC (single side band suppressed carrier) the technique was patented in 1915 and in 1927 a commercial radiotelephone service was set up to use SSB for transatlantic communication. The cost was $75 for three minutes, equivalent to more than $760 today.
The 10 meter wave band (frequencies 28 MHz to 29.7 MHz) is part of the shortwave spectrum where a great deal of Morse code transmission can be found. For those interested in voice transmission, SSB (single side band) is available on frequencies from 28.3 MHz to 28.5 MHz with 28.4 MHz the designated calling frequency. Many radio amateurs enjoy the process of contacting like minded individuals in far away countries, as well a sending and receiving QSL cards to show the extent of their contacts. With relatively small antennas, ten meter radio is a great ‘place’ to gain experience in antenna building and to practice for a higher class of amateur radio license. If you dream of far away places with strange sounding names, the 10 meterradio broadcast equipment may be exactly what you are looking for. Ten meters is primarily a day time waveband; in the USA it is often possible to hear Europe in the morning, all of the Americas midday and the Pacific and East Asia in the evening. Traffic varies considerably, but the major attraction of the ten meter band is that it is possible to make contact over very large distances, especially at times of high solar activity. 。