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