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Piccolo
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 ITA2 (5-bit baudot) or ITA5 (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:

Piccolo I
The first generation Piccolo dates back to 1962. It consists of 32 distincive tones, one for each character of the ITA2 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.

# Tone Code  
0 460 Hz 00000  
1 470 Hz 00001  
2 480 Hz 00010  
3 490 Hz 00011  
4 500 Hz 00100  
5 510 Hz 00101  
6 520 Hz 00110  
7 530 Hz 00111  
8 540 Hz 01000  
9 550 Hz 01001  
10 560 Hz 01010  
11 570 Hz 01011  
12 580 Hz 01100  
13 590 Hz 01101  
14 600 Hz 01110  
15 610 Hz 01111  
16 620 Hz 10000  
17 630 Hz 10001  
18 640 Hz 10010  
19 650 Hz 10011  
20 660 Hz 10100  
21 670 Hz 10101  
22 680 Hz 10110  
23 690 Hz 10111  
24 700 Hz 11000  
25 710 Hz 11001  
26 720 Hz 11010  
27 730 Hz 11011  
28 740 Hz 11100  
29 750 Hz 11101  
30 760 Hz 11110  
31 770 Hz 11111  

 
Piccolo II
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 ITA2 compatibility. This way, 36 codes can be made.

 
ITA2
# Tone
A 460 Hz
B 480 Hz
C 500 Hz
D 520 Hz
E 540 Hz
F 560 Hz

 

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 ITA2 standard.

ITA5
A similar approach is used when using the Piccolo II standard for sending ITA5 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.

 
ITA2
# Tone
A 400 Hz
B 420 Hz
C 440 Hz
D 460 Hz
E 480 Hz
F 500 Hz
G 520 Hz
H 540 Hz
I 560 Hz
J 580 Hz
K 600 Hz
L 620 Hz

 
Piccolo III
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.

 
ITA2
# Tone
A 1900 Hz
B 1940 Hz
C 1980 Hz
D 2020 Hz
E 2060 Hz
F 2100 Hz

 

Piccolo IV
The specification of the Piccolo IV standard is currently unknown. If you have more information, please contact us.

Further information
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Crypto Museum. Created: Thursday 16 April 2015. Last changed: Monday, 31 October 2016 - 17:17 CET.
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