LENTUS means " Slow " (but also indolent, nonchalant, quiet…) in latin.
Baud rate : 0.1465 (4800/32768) or 6.827 seconds by 5 bits symbol
Messages: a message of 293.5 seconds duration (43 symbols) begins at t=4 sec of the UTC minute 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, or 55 (it is necessary that the PC may be synchronized on a “Standard” clock).
Note : in manual transmission, it can also start at 4+6.827=10.827 sec (42 symbols sent) or 10.827+6.827=17.654 sec (41 symbols sent) or 17.654+6.827=24.481 sec (40 symbols sent), to « pardon » the Ham operator for a delay to answer, but with reception probability a bit weaker.
The message is normally composed of 43 symbols (but can be reduced to 40 symbols, see above), each one with a length of 32768 audio samples (or or 6.827 seconds). The 9 first symbols carry a tone allowing the determination of the transmission central frequency. The 31 following "5 bits symbols" carry the message (allowing the Reed-Solomon coding of 75 bits). The last three symbols are transmission central frequency carriers.
Messages can be either plain text (13 characters, preceded by a bit “CQ de” and a bit “Beacon”) or formatted text according to different possibilities, listed below:
A standard CQ call composed of a bit “CQ” + a bit “Beacon” + complete call (with 3 characters max in the mantissa, as for example “AZ2/FL5XYZ/MM”) + optionally, a 6 characters Locator (accuracy +/-2.31 km in latitude and +/- 4.63 km in longitude).
Note: without the “CQ”, it is an information transmitted by the Ham answering to the CQ call,
A “Station description” type CQ call composed of a bit “CQ” + a bit “Beacon”, a 6 characters call + suffix (as for example “FL5XYZ/MM”), a “6 characters Locator” + Power level + “mW/W” bit + relative gain of HF antenna + directivity of the antenna.
Note: without the “CQ”, it is an information transmitted by the Ham answering to the CQ call,
A “Meteorological” type CQ call composed of a bit “CQ” + a bit “Beacon”, a 6 characters call (as for example “FL5XYZ”), a “6 characters Locator” + Temperature + Wind force + Type of weather + Humidity.
Note: without the “CQ”, it is information transmitted by the Ham answering to the CQ call,
A CQ call with precise geographical position composed of a bit “CQ” + a bit “Beacon”, a 6 characters call + a geographical position (latitude + longitude) in ° ‘ and 2 figures decimal (as for example “48-49.83N 002-22.02E”). The accuracy is equal to 9 m in latitude and in longitude (about 60000 times more precise than a Locator position).
Note: without the “CQ”, it is an information transmitted by the Ham answering to the CQ call,
An answer to a CQ with Locator 4 characters composed of a 6 characters Call 1 ( as for example “FL5XYZ”) + 6 characters Call 2 (as for example “FL5XYZ”) + Locator 4 characters (accuracy +/-55 km in latitude and +/- 111 km in longitude), in answer of Call 1 to a CQ done by Call 2,
An answer to a CQ with S/N ratio and drift composed of a 6 characters Call1 (as for example “FL5XYZ”) + 6 characters Call 2 + Suffix (as for example “FL5XYZ/MM”) + S/N ratio (12 to -37 dB) + drift (-4 to 4 by step of 0.1 Hz/mn), in answer of Call 1 to a CQ done by Call 2,
An answer to finish a QSO composed of a 6 characters Call 1 (as for example “FL5XYZ”) + 6 characters Call 2 + Suffix (as for example “FL5XYZ/MM”) + “73 GB SK”.
Moments of decoding :
Reception start: the reception normally begins at t=4 sec and lasts 40 or 43 symbols (see below). In case of failure of the operator, the reception can also begin at t=24.481 sec and lasts 37 or 40 symbols (it’s a degraded working).
Decoding start: the main decoding takes place after reception of 40 symbols (i.e. 273 seconds), which normally leaves about 25 seconds to answer. However, there is still a margin of 20 seconds (to reach 25+20=45 sec), the message being, in that case, truncated but being able to be decoded.
In case of failure of the main decoding, other decoding attempts are done after 41 symbols (280 seconds), 42 symbols (287 seconds) and 43 symbols (294 seconds). In this last case, it remains 6 seconds to answer. However, there is still a margin of 20 seconds (to reach 6+20=26 sec), the message being, in that case, truncated but being able to be decoded.
Mode of transmission: Lentus can be used to do QSO (two_way communication) or as a beacon. In that last case, no answer is required:
a beacon transmission could be done at minutes 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, or 55.
for a QSO, by mutual agreement , the Ham calling CQ will transmit at minutes 0, 10, 20, 30, 40, 50 and the Ham answering to the CQ call will transmit at minutes 5, 15, 25, 35, 45, 55.
Repeater: Lentus can also be used, for very specific use, as a repeater. As a repeater, it simply transmits what it is received so as to forward the message to other stations or to broadcast a message (with several repeaters).
Speed : 75 bits (or 13 characters maximum in plain text) by 5 minutes period (with only one message by period) or 0,43 wpm
Modulation : MFSK 32 tones (for 5 bits) with a shift between tones of 0.7325 Hz (5 x baud rate).
The synchronization tone transmitted during the 9 first symbols corresponds to the central frequency of the transmission bandwidth. It permits to determine this frequency (with a precision of about +/- 0.1 Hz) and the drift speed (up to 3 Hz/mn). The 32 possible 10th symbol (first data) frequencies will be estimated from these two pieces of information. The synchronization frequency search bandwidth tolerance is variable from +/- 20 Hz to +/-80 Hz, counted from the frequency clicked, by the user, on the waterfall.
Receive mode: USB. Each transmitting or receive period of 300 sec must start at t=4 sec of the UTC minute 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, or 55 with a maximum tolerance of +/-0.1 sec of the PC clock. A margin of 20 seconds is given as indicated in “Messages” above.
It is possible to introduce an advance (from 0 to 990 msec by 10 msec steps) to compensate from a possible transmission delay (due to a big distance to the zone to target or a delay due to a Wifi link or due to a SdR TX buffer, for example). Symmetrically, in reception, it is possible to introduce a delay (from 0 to 990 msec by 10 msec steps) to start decoding, for the same reasons as for the advance in transmissions (transmission delay, Wifi link, SdR RX buffer…).
The time to switch the transceiver is supposed to be very short (definitely less than to 100 ms).
Characters set (46) : ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789 <SPACE> / + - . ? ! @ % $
Shape of pulse : rectangular
Bandwidth: 23 Hz
Synchronization: using the very accurate time from an Internet Time Service as the NSIT, through a SNTP or NTP protocol (but not through the RFC-868 Time Protocol) so to have an accuracy widely better than 50 ms. The use of the “AboutTime” freeware is widely encouraged as the PC time error is determined by the soft, simply by setting time twice, the second time (and the followings) will give the PC time error.
Coding code: Reed Solomon (31, 15) or 31 symbols of 5 bits for 15 symbols of 5 information bits (so a yield of 0.48). The irreducible polynomial P(x) is equal to X^5+X^2+1.
The generator polynomial G(x) is equal to a product of (X+alpha^i) with i minimum=1.
Convolution code: no
Interleaving : no interleaving nor Gray coding is used.
Scrambling : each of the 31 Reed-Solomon symbols (which value is between V=0 and V=31), which order is defined by O=0 for the first transmitted symbol until O=30 for the last transmitted symbol, is associated with a XOR f(O). In other words, for each symbol, it is done the operation V = V XOR f(O). This is done to avoid that a carrier produces a suite of same symbols (suite which could be interpretable by the Reed Solomon coding as a correct code). At reception, the V initial is found again by doing Vinitial = Vreceived XOR f(O).
The f(O) function is random :
O f(O)
0 24
1 31
2 20
3 4
4 24
5 4
6 16
7 23
8 13
9 20
10 20
11 0
12 15
13 23
14 5
15 29
16 10
17 12
18 26
19 16
20 15
21 1
22 9
23 29
24 22
25 30
26 23
27 2
28 10
29 12
30 28
Pmean/Ppeak: 1
Drift tolerance : 2 Hz/mn (note that the performance in S/N ratio term is degrading with drift)
Lowest S/N : -34 dB (without any drift, for more than 90 % of the frames), however some frames are decoded from -36.5 dB. At -37 dB and below, no frames are decoded.
