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Mulitple Frequency-Shift Keying
Piccolo was a telegraphy system, used by the
Diplomatic Wireless Service (DWS) in the UK,
for sending and receiving digital data
in ITA-2 (5-bit baudot)
or ITA-5 (7-bit ASCII) format over narrow-band
Short Wave (SW) radio channels,
using Multiple Frequency-Shift Keying (MFSK) modulation.
Various implementations of Piccolo have emerged over the years:
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The first generation Piccolo dates back to 1962. It consists of
32 distincive tones, one for each character of the
ITA-2 alphabet,
10 Hz apart. It was intended for low-speed teleprinter signals
over HF radio links at 50 or 75 baud. This system is also known
as Muli-Level FSK (MFSK) or Polytone.
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#
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Tone
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Code
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0
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460 Hz
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00000
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1
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470 Hz
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00001
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2
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480 Hz
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00010
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3
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490 Hz
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00011
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4
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500 Hz
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00100
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5
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510 Hz
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00101
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6
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520 Hz
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00110
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7
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530 Hz
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00111
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8
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540 Hz
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01000
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9
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550 Hz
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01001
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10
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560 Hz
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01010
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11
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570 Hz
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01011
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12
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580 Hz
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01100
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13
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590 Hz
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01101
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14
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600 Hz
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01110
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15
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610 Hz
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01111
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16
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620 Hz
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10000
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17
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630 Hz
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10001
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18
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640 Hz
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10010
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19
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650 Hz
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10011
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20
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660 Hz
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10100
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21
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670 Hz
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10101
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22
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680 Hz
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10110
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23
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690 Hz
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10111
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24
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700 Hz
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11000
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25
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710 Hz
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11001
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26
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720 Hz
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11010
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27
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730 Hz
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11011
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28
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740 Hz
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11100
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29
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750 Hz
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11101
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30
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760 Hz
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11110
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31
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770 Hz
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11111
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The Piccolo II standard supports the same 10 characters per second,
but needs only 6 distinctive audio tones, each 20 Hz apart, starting
at 460 Hz. Two such tones, each 50 ms long, are sent in quick succession
in order to achieve ITA-2
compatibility. This way, 36 codes can be made.
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The matrix above shows the 36 characters (6 x 6) that can be generated
by creating tone pair from the table below, and how these characters
are translated to the ITA2 standard. As the ITA2 standard supports only
32 characters (25), 4 characters are unused. These tone pairs
(DD, DE, ED and EE),
shown here in grey, are used for synchronisation (SYNC) and
Multiple Ident (MI). Tone pair DD is not used at all.
The table above gives the Piccolo II tones for the
ITA-2 standard.
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A similar approach is used when using the Piccolo II standard for sending
ITA-5 compatible data (7-bit ASCII).
In this case, 12 distinct tones are
used, allowing a maximum of 144 characters to be defined (12 x 12).
At present, the translation matrix to 7-bit ASCII is not available.
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ITA2
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#
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Tone
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A
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400 Hz
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B
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420 Hz
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C
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440 Hz
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D
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460 Hz
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E
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480 Hz
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F
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500 Hz
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G
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520 Hz
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H
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540 Hz
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I
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560 Hz
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J
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580 Hz
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K
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600 Hz
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L
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620 Hz
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The Piccolo III standard follows the same scheme for ITA2 data as the
Piccolo II standard shown above, but uses higher frequency audio tones,
starting at 1900 Hz, each 40 Hz apart.
These scheme is used, for example, by the
FRM-4750
and the FRM-4780 Data Radio Stations.
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The specification of the Piccolo IV standard is currently unknown.
If you have more information, please contact us.
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Any links shown in red are currently unavailable.
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© Crypto Museum. Created: Thursday 16 April 2015. Last changed: Saturday, 06 March 2021 - 13:36 CET.
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