207 lines
9.4 KiB
Plaintext
207 lines
9.4 KiB
Plaintext
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[*][*][*][*][*][*][*][*][*][*][*][*][*][*][*][*][*][*][*][*][*][*][*][*][*]
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[*] sUBTERRANEAN tECHNOLOGIES mAGAZINE [*]
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[*] volume ()1, issue ()2 [*]
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[*] JULY-AUGUST 1994 [*]
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[*] [*]
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[*] ARTICLE 01/04 [*]
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[*][*][*][*][*][*][*][*][*][*][*][*][*][*][*][*][*][*][*][*][*][*][*][*][*]
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THE WORLD OF SATELLITE COMMUNICATIONS. PART #1
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by nEIL.s [v.1] HIDDEN SIGNALS
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There are thousands of signals transmitted via satellites that are hidden
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to the ordinary SKY TV viewer, yet these signals can be easily received
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with little or no modifications to your existing system. This file will
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explain how *YOU* can receive them.
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SOME OF THE HIDDEN SIGNALS AVAILABLE:
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* INTERNATIONAL TELEPHONE CALLS
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* TRAVEL AGENCY COMMS
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* RADIO STATIONS
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* LOCAL RADIO NETWORKS
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* SATELLITE CONTROL COMMS
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* PRESS AGENCIES
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* MONETARY AGENCIES
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* TV NEWSROOMS
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* DATA TRANSMISSION SYSTEMS
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[note: some of these signals will be encrypted]
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HOW TO RECEIVE THESE SIGNALS.
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Reception of most of the signals mentioned is a relatively easy task, with
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some of the signals requiring very little additional equipment. If you just
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receive ASTRA signals via a fixed dish, you are well on your way to
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accessing the thousands of others available.
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Before you begin to try & receive these signals, it would be best to
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understand the basic fundamentals of the signal formats.
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Your dish and LNB (low noise block) convert microwave signals, Ku, C, S or
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any other band into a standard IF of 950 to 1750 Mhz. Inside your reciever
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[thats the thing next to the vcr] one or more conversions take place,
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downconverting to 70mhz and finally to baseband, all so you can watch MTV.
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The BASEBAND signal is the key to accessing the hidden signals, it is the
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final product of all the previous conversions, ranging from 0 - 10.7Mhz and
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contains all the information required. Not only does it contain video &
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audio subcarriers, but all the signals listed at the beginning of the file.
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In the event that the channel tuned does not carry any video information, it
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can be utilised for placing thousands of *SINGAL CARRIER PER CHANNELS*
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To give some idea of the amount of information that a single transponder
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baseband can carry...
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On a channel that doesnt contain video information & is 36Mhz wide (normal
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size), there is space for 9000 4Khz wide audio or data channels (SCPC SSB),
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each of these can operate at the same time & each one can carry seperate
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information.
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** In this file, i will be covering the reception of:
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SCPC SSB FDM SCPC FM FDM SCPC DATA
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---------------------------------------------------------------------------
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1.0 SCPC SSB FDM
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As you have probably noticed, there are two main formats, SCPC SSB & SCPC FM
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The first one is used primarily within the baseband portion, as each signal
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occupys only 4Khz, the latter is based around the 70Mhz loop, each carrier
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being 60Khz wide.
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RECEIVING SCPC SSB FDM Signals.
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* NO MODIFICATIONS WHATSOEVER ARE NECESSARY TO YOUR EXISTING EQUIPMENT
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To receive the SCPC SSB signals is very easy [providing your receiver has a
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baseband output] most people already have the equipment needed.
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EQUIPMENT:
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1. SMALL CABLE WITH A PHONO SOCKET & OTHER END STRIPPED BACK ABOUT 5+ CM
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2. SHORT WAVE RECEIVER
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Connect the phono socket to the baseband output of your receiver & connect
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the stripped end to the aerial socket of your short wave receiver.
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BASIC RADIO RECEIVER REQUIREMENTS:
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1) LSB (lower side band) & USB (upper side band) switch
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2) Relatively stable (freq. doesnt drift)
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3) tune with NO gaps between 0.1Mhz and 30Mhz (10.7Mhz needed)
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4) Digital display is best.
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__________________________
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- - Now you can access loadsa new channels..
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- SATELLITE RECEIVER - Tune through the bands of your SW radio
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- - from 100Khz to 10.7Mhz, on each satellite
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-------------------------- channel there are likely to be thousands
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| of hidden signals. If you hear a tone of
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| BASEBAND upto 2Khz, or just a blank carrier, this is
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| TO probably an internaional telephone signal
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| AERIAL Data can be recognised by fast streams of
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| warbling tones.
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--------------------------
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- -
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- SHORT WAVE RADIO -
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- -
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--------------------------
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RECEPTION PROBLEMS:
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A) IF THE SAT RECEIVER HAS AN 'AGC' SWITCH, TURN IT OFF
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B) IF THE RECEIVED SIGNALS DROP OFF AFTER 4.2Mhz, YOUR SATELLITE RECEIVER
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HAS A VIDEO FILTER IN HTE BASEBAND CIRCUIT, THIS IS NOT TRUE BASEBAND,
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SO CHUCK IT IN THE BIN & BUY A DECENT RECEIVER.
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C) MAKE SURE THE BASEBAND IS CLAMPED, THIS WILL REDUCE THE 30Mhz BUZZ
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-----------------------------------------------------------------------------
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1.1 SCPC FM FDM
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OK, for services that require full audio spectrum siganls, such as music,
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and high speed data, another method is employed, this is called SCPC FM/FDM.
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This process is propably one of the fastest expanding services available &
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should be available on all satellites and channels.
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Your existing satellite system already provides a convenient output for all
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of these signals, providing that it has a 70Mhz loop on the back, most
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GOOD QUALITY units do. This loop can be recognised simply by a small section
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of cable with two F-type connectors protruding out of the back of the unit.
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One of these is labelled OUTPUT & the other is INPUT. The SCPC FM signals,
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are as you probably guessed available via the OUTPUT, in the freq. range of
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50Mhz to 90Mhz. SCPC FM signals have been fairly standardised, they are 60Khz
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wide, which is twice the amount needed for CD quality audio, and are spaced
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200Khz apart. For a satellite channel that does not have any video
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information, this means that 180 channels are available at all times.
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The 70Mhz loop is called so because its centre freq. is 70Mhz, however a
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standard transponder bandwidth is 40mhz, etc... etc..
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This means that the tunable range is from 50Mhz to 90Mhz, per satellite
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channel.
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RECEIVING THESE SIGNALS.
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In order to receive these SCPC FM signals, a receiver or scanner is required
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that is able to tune between 50Mhz and 90Mhz. A standard FM radio is not
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suffucient as it tunes only from 88 - 108Mhz, also the audio bandwidth
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is normally quite wide. For SCPC FM reception, an FM narrow switch is
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necessary, variable is even better.
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The min. SPECS for SCPC FM reception:
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a) Good freq. stability, digitally synthesised
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b) FM Narrow bandwidth
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c) Digital readout
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d) tuning in 1Khz steps
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e) Frequency range covering 50 - 90Mhz at least
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Connect your system as in the below diagram, the T piece simply feeds the
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70Mhz IF loop back into your satellite receiver, so you can see the video
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signals, be sure to check channels with no video as well as ones with video.
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______________________________
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- -
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- SATELLITE RECEIEVER -
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------------------------------
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| |____________+++++++++++ ----------------------
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|_________________+ T-PIECE +-------------- SCANNER/RECEIVER -
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+++++++++++ - 50 - 90Mhz -
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----------------------
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-----------------------------------------------------------------------
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1.3 MORE ADVANCED FORMS OF DIGITAL TRANSMISSION
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Both SCPC formats are used for sending digital inforamtion, and you
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have probably already tuned into what sounds like high speed warbling.
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These are the transmissions we are now going to look at.
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As mentioned earlier, SCPC SSB can be utilised only to send either
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telephone circuits, any voice only transmission and low speed data, due to
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the bandwidth of only 4Khz. SCPC FM however can deliver us with high speed
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data.
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The data arrives at various speeds & in different formats (RTTY, BAUDOT,
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ASCII, PACKET, SITOR, AMTOR.. and many others. Units to decode and send the
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data to your PC are relatively cheap (or expensive). Maplin stock some good
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ones. Maplin also supply PC software.
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--------------------------------------------------------------
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OK, thats it. Hope you have some fun listening to the hidden signals.
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Most of the information above was obtained from:
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* SATELLITE TV EUROPE magazine
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* Design Technology ltd. [who produce various documents, see one of their
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adverts in SAT TV EUROPE].
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Look out for THE WORLD OF SATELLITE COMMUNICATIONS. PART #2
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coming real SOON.
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note: this file was written with european broadcasting in mind, but it
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would probably apply to anywhere.
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typed/edited/put together by nEIL.s
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[end of file #1]
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++++++++++++++++++++++++++++++++++++++++++
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