PI4

PI4 – PharusIgnis4 is a digital modulation (MGM) for beacon purposes.

It is an ideal digital modulation that is compliant with the IARU Region 1 VHF Committee accepted 1 minute mixed mode beacon sequence.

The name PharusIgnis4 comes from the ancient words for beacon, lighthouse and fire – Pharos (from Greek to Latin pharus and coming from the Lighthouse of Alexandria on the island of Pharos), Ignis (Latin: fire) and 4 for the four FSK tones.

Decoding PI4

The OZ7IGY Next Generation Beacons transmit in a 1 minute cycle starting at the full minute. The colored line below illustrates the mixed mode sequence where P indicate pauses. The CW is sent at 60 LPM/12 WPM.

PI4 P CW ID P Carrier P

First it sends PI4 (call sign), that last 24 1/3 s, a subsequent pause of 2/3 s, then at the 25 s sending CW identification (call sign and locator), followed by a 500 ms pause and carrier until the 59,5 s followed by a 500 ms pause until the end of the cycle. The resulting waterfall and decoding in PI-RX will look like the screen dump below. To decode a PI4 signal you will have to set your receiver to the same frequency as of you would do to receive a beacon with an 800 Hz carrier. The receiver bandwidth should not be less than 1 kHz. On most receivers you will have to set your USB dial 800 Hz lower than the nominal frequency, e.g. OZ7IGY is assigned to transmit on 50,471 MHz thus the receiver must be tuned to 50.470.200 to show a 0 Hz frequency deviation. When you receive the carrier at exactly 800 Hz then you know how accurate your station is.

To decode PI4 you can use PI-RX by Poul-Erik, OZ1CKG  or MSHV by Christo, LZ2HV, that runs on both Linux and Windows. Michael, DG0OPK, has MSHV running on a Cubieboard2 decoding PI4.

PI4 decoding of OZ7IGY and carrier measurement using PI-RX by Poul-Erik, OZ1CKG.

Why PI4

The reason for using PI4 + CW + carrier for the OZ7IGY beacons is:

  • The analog part of the identification must be frequent both to identify the beacon but also to “handle” QSB
  • The beacon, must be readable even when the path is distorted i.e. by rain scatter, aurora etc. Who says we have finished detecting new propagation techniques? So the beacon must also be “forward compatible”
  • It must be possible to decode the MGM part even if the receiver is not frequency locked
  • Today most beacons identify themselves every 30-45 seconds. But waiting for the identification “always” seems to long. Like waiting in a telephone queue always seems to long. The perceived time when waiting always seems to be to long
  • A 2 min sequence is to long and the shorter the better
  • Identical sequence every minute
  • It should be possible to calibrate to the beacon. Thus a carrier is needed to zero-beat on. Today this is specified to be about 20-30 seconds
  • The analog identification should be readable by “all of us” not just the very high speed CW operators. Thus 12 WPM/60 LPM as already specified seems to make sense
  • Must fit into the current 1 kHz beacon to beacon spacing structure
  • The MGM must be transmittable via a class C amplifier to save power

PI4 is specifically designed with beacons and VUSHF propagations in mind. It is far more robust to path irregularities and equipment inaccuracies than e.g. WSPR and JT9 that both also would require a long sequence. JT65 modes are in-between WSPR/JT9 and PI4, and JT4, when it comes to robustness but cannot fulfil an identical sequence every minute without other sacrifices unless using the JT65B2/C2 submodes. The JT4 submode JT4G has better path robustness than PI4 but takes about twice as long to transmit thus it will not fulfil the sequence requirements. PSK2k, FSK441, JT6M, JT9-fast, MSK144 and ISCAT are all “fast modes” but are not as sensitive as the other modes. Because of this is PI4 the MGM used by the OZ7IGY Next Generation Beacons.

The PI4 + CW + carrier sequence has also been chosen as the sequence for the IARU 50 MHz Synchronized Beacon Project.

PI4 + CW + carrier/Next Generation Beacons platforms

Click here for VUSHF beacon lists in general.

BeaconLocatorFrequencyNotes
4O0BCGJP92PK70,048 MHz
DB0HRFJO40FF144,475 MHz and 3400,975 MHz
DB0IHJN39HJ432,447 MHz
DB0JGJO31HS432,412 MHz
DB0LTGJO31TB1296,7435 MHz
DB0MMO JN49RV 144,455 MHz, 432,425 MHz, 10 368,840 MHz and 24 048,825 MHz
EI0SIXIO63VE50,005 MHzSBP 5/0
EI1KNHIO63VE60,013 MHzSBP timeslot 0, 1 and 2
GB3CFGIO74CR70,027 MHz and 1296,905 MHz
GB3FNMIO91OF2320,920 MHz
GB3GCTIO91IJ10368,935 MHz
GB3MCBIO70OJ50,005 MHz and 50,443 MHzSBP 5/1 and 3
GB3MHZJO02PB2320,830 MHz and 10 368,830 MHz
GB3NGIIO65VB50,006 MHz and 50,462 MHz
144,482 MHz, 432,482 MHz and 1296,905 MHz
SBP 6/2 and 4
GB3SEVIO82UI144,432 MHz
GB3UHFJO01EH432,430 MHz
HB9FJN37RA50,420 MHz
IW9GDC/BJM78SD50,006 MHzSBP 6/0, 1 and 3
KG4BYN EM75RV 28,2368 MHz
OH7VHFKP52HL 144,433 MHz
ON0EMEJO21JG10 368,875 MHz and 24 048,875 MHz
ON0SNWJO21BE10 368,965 MHz
OX4MHQ90AL70,047 MHz
OX6MHQ90AL50,047 MHz
OZ7IGYJO55WM28 MHz to 24 GHz
PA0AGJO32GH70,095 MHzPersonal beacon, 07-21 UTC
PI7SIXJO21FV50,005 MHz and 50,425 MHzSBP 5/2
SK3SIXJP73HC 50,468 MHz
SK4MPIJP70NJ144,412 MHz
SK3VHFJP73HC144,421 MHz
SR9RMFKN09GL70,060 MHz
SV3BSF/BKM08VA50,450 MHz
TF1VHFHP84WL50,457 MHz and 70,057 MHz
UA1ZFG/BKP69AK144,425 MHz
UT4UWJ/BKO50FK144,482 MHz
VA2NQFN35NL50,295 MHz, 144,491 MHz, 222,295 MHz and 432,302 MHz
YM4SIXKM66AO50,003 MHz and 50,403 MHzSBP 3/2

In the pipeline: GB3ANG (144 MHz and 1,3 GHz),  OH1DB (10 GHz), PI7RTD (1,3 GHz and 2,3 GHz), TF1VHF (144 MHz), WA1ZMS/4 (70 MHz and 144 MHz), YM4 (28 MHz and 144 MHz) and ZS0BET (144 MHz).

Next Generation Beacons – PI4