elevision is a method of reproducing fixed or moving visual images by the use of electronic signals. There are numerous kinds of TV systems and different standards have been adopted around the world. Moreover, TV standards are in a state of flux since there is a worldwide push to adopt a new high-definition television (HDTV) standard.
 

Broadcasting Standards

ITEM                                                               FCC Standard

Channel Bandwidth                                           6 MHz

Visual carrier frequency                                    1.25MHz±1000Hz above the lower boundary of the channel

Aural carrier frequency                                     4.5MHz±1000Hzabove the visual carrier frequency

Chrominance subcarrier frequency                    3.579545MHz±10Hz

Aspect (width-to-height ratio)                           Four units horizontally for every three units vertically

Modulation type visual carrier                           AM with negative polarity

Aural carrier                                                     FM with 100% modulation being deltaF=25KHz, usinh 75 microseconds preemphasis

Visual modulation levels

Blanking level                                                   75%±2.5% of peak real envelope level

Reference black level                                        7.5%±2.5%

Reference white level                                        12.5%±2.5% of sync tip level

Scanning

# of lines                                                           525 lines/frame, interlaced 2:1

Scanning sequence                                            Horizontally:left to right;Vertically:top to bottom

Horizontal scanning                                           15,734,264±0.044Hz

Frequency f_h                                                    15,750Hzmay be used during monochrome transmission

Vertical scanning                                               59.94Hz

Frequency, f_v                                                   may be used during monochrome transmission

Rated Power

   The rated power of a TV visual signal is the effective isotropic radiated peak envelope, EIRP, and is usually called simply the effective radiated power, ERP. The EIRP is the power that would be required to be fed into an isotropic antenna to get the same field strength as that obtained from an antenna that is actually used as measured in the in the direction of its maximum radiation.

The actual equation is

                                  P_ERP= P _PEP Ga G_L

Where

Ppep=peak envelope power out of the transmitter

Ga= power gain of the antenna

G_L=total gain of the transmission line system from transmitter output to the antenna

For a VHF TV station operating on channel 5, a typical value is ERP of 100Kw, which is the maximum power licensed by the FCC for channels 2 to 6. For a UHF station operating on channel 20, a typical value is ERP of 500Kw.

Color TV

Color television pictures are synthesized by combining red, green, and blue light in the proper proportion to produce the desired color. This is done by using a color CRT that has three types of phosphors-one type that emits red light, one that emits green, and a third type that emits blue light when they are struck by electrons.

The National Television System Committee (NTSC) compatible color TV system was developed and adopted in the United States for U.S. transmissions in 1954.

U.S. Television Channel Frequency Assignments

The U.S. channel frequency assignment is as follows:

Channels 2 to 13 (VHF)                                   54MHz to 216 MHz

Channels 14 to 83 (UHF)                                 470 MHz to 890MHZ 
 

TV MARTI   

    TV Marti is one of the most powerful weapons against Castro. Castro has had a complete

embargo of information over the Cuban people. As they say, a picture is worth a thousand words. To inform the Cuban people, daily, via TV signals, of the true world, what is happening, how is life in the United States, in the rest of the world, is something Castro cannot afford and what he fears most.
 

REALITY

    To interfere TV Marti, Castro uses AM radio signals, like the signals transmitted in the United States by your local AM stations. In Miami, signals like WQBA, WAQI, etc. Why? Because analog TV video signals are transmitted using AM radio signals, at a higher frequency and bandwidth.

   Instead of voice or music, the signal used to interfere TV Marti is called a “tone” that can be compared to a whistle or the sound that we hear on the radio when they simulate an emergency situation as a test. However, the Cuban government uses a sequence of tones distributed over the bandwidth of the TV Marti signal

   The maximum power allowed in the United States by the FCC to radio stations is 50,000 Watts. And even so, very few stations get so high because it costs money to do so. This is, by the way, also an international regulation, to avoid interference of stations.

   The radio signals that Castro uses to interfere TV Marti have a power of 500,000 Watts. This is ten times more powerful. Castro has 7 stations dedicated to interfere TV Marti. Three of them “donated” by the former Soviet Union, and 2 purchased in Japan, 2 given by the PRC.

   Five antennas are used. They are located at: Hotel Habana Libre, Hotel Triton, Guanabo, Alamar, and Mirador de Lawton. They also use the equipment located in the Antenna Farm, located in El Wajay, near La Habana. In this “farm” the Cubans work together with PRC’s personnel. The Center of Operations is located in Paseo, between 11 and 13, in El Vedado, La Habana. They also cooperate here with military personnel from PRC.

   TV Marti is presently transmitted in VHF, that is, in the range of frequencies occupied by channels 2 to 13., as indicated in the Table above. TV Marti transmits in Channel 13, that is, in the 210 to 216 MHz band UHF are the channels from 14 up, as indicated also in the Table above. Castro also has in place some special equipment to interfere UHF signals. Castro purchased these equipments in the late 90s, from the PRC, anticipating the change of frequency spectrum of TV Marti to UHF. TV Marti is also transmitting in Channel 20.

   Castro needs, in order to have an efficient interference signal, one station per approximately 70,000 inhabitant neighborhoods or geographical regions.

    What is needed to transmit TV Marti in order to be seen in  Cuba properly?

Analysis

I.                   VHF

    For channel 13, 210 to 216 MHz, the frequency band behaves as any other VHF propagation waves, which travel beyond the horizon, taking into account or assuming 5,278 miles/8494 Kms, which is 4/3 times the actual earth radius to correct for atmospheric refraction.

In practice, it has been experienced that the high frequency channels, upper levels, 7 to 13, will not be absorbed or totally attenuated by the water, but it will be reflected mainly when using directional propagation antennas.

An antenna about a height of 1000 to 1500 feet range will reach Cuba territory with no fading or with very small one. The code of Federal Regulations ( 47, parts 70 to 79) specifies parameters for distance separation between FM and TV coverage contours.

However, the effective radiation power, which is limited by ERP and height above the average terrain (HAAT), is an important parameter to not interfere with other stations. For example, 98.3 MHZ located on the channel 4, which belongs to NBC/RCA, when modified from class A to class C, or 100Kw ERP, required to change frequencies for FMs located in Arcadia and Immokalee, with distances from channel 4 tower which are respectively 252 Kms and 127 Kms.These data indicate the reach of a signal over terrain.

II.                UHF

The antenna height above the average terrain is an important parameter to determine the directivity of the signal to the desired zone (Cuba) so as the number of elements that comprise the antenna in order to orient the signal properly.

Consequently, the VHF and the UHF bands are practically with a radiation beyond the curvature of the earth. Also, the ionosphere plays an important role on the reach of the signal by the line of sight mainly.

In both cases of VHF and UHF they are increased by approximately 15% beyond the optical line, which also helps the signal to reach beyond the horizon. The elevation of the antenna and the inclined angle of the elements are factors to direct and reach the desired point of reception (Cuba).

III. Equations

For VHF, we have

                 Distance, d, in miles = 1.41 (H)^1/2

Where H = combined receiver and transmitter antenna height, feet

Sky waves apply to VHF and UHF

For UHF, we have

Depression angle of radio horizon and distance to radio are:

                            A, angle = 0.0153 (H)^1/2

                            D, miles = 92.1518 A

Needed

One option

1. Three transmitters, 20 Kw each. Approximately total cost, $ 200,000.

2. Three antennas, 2,500 feet high each, directional. Approximately total cost           

$ 150,000

3. One antenna in the center. The other two, one on the left, one in the right. To cover the west, central, and eastern zones of Cuba

Other costs: wire installation, engineering design, etc,.

Transmission medium: Video,Vestigial sideband, VSB; audio FM, video AM.

Change of frequency spectrum from VHF to UHF, or keep channel 13,VHF

Optimum option

    A plane flying either over international waters along the north coast of Cuba, or, around a U.S. key (like Sand Key) near Cuba. This option would project a visible signal over Cuba, which could be more difficult to interfere.