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 bothLinux 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 and Next Generation Beacons platforms

4O0BCG in JP92PK – 70,048 MHz

DB0HRF in JO40FF – 144,475 MHz

DB0IH in JN39HJ – 432,447 MHz

DB0JG in JO31HS – 432,412 MHz

DB0LTG in JO31TB – 1296,7435 MHz

EI0SIX in IO63VE – 50,005 MHz, SBP 5/0

GB3CFG in IO74CR – 70,027 MHz and 1296,905 MHz

GB3MCB in IO70OJ – 50,443 MHz and 50,005 MHz SBP 5/1 and 3

GB3MHZ in JO02PB – 10 368,830 MHz

IW9GDC/B in JM78SD – 50,006 MHz (Later SBP 6/4)

KG4BYN in EM75RV – 28,2368 MHz

ON0EME in JO21JG – 10 368,875 MHz and 24 048,875 MHz

ON0SNW in JO21BE – 10 368,965 MHz

OX4M and OX6M in HQ90AL – 70,047 MHz and 50,047 MHz

OZ4BHM in JO75KB – 50,005 MHz, SBP 5/4, later also 50,466 MHz

OZ7IGY in JO55WM – 28 MHz to 24 GHz

PE1MXP in JO32GH – 70,095 MHz (personal beacon, 07-21 UTC)

SK4MPI in JP70NJ – 144,412 MHz

TF1VHF in HP94AC – 50,457 MHz

UA1ZFG/B in KP69AK – 144,425 MHz

VA2NQ in FN35NL – 50,295 MHz, 144,491 MHz, 222,295 MHz and 432,302 MHz

In the pipeline: DB0MMO (144 MHz, 432 MHz and 1,3 GHz), GB3ANG (144 MHz and 1,3 GHz),  GB3NGI (50 MHz, 144 MHz, 432 MHz and 1,3 GHz), GB3UHF (432 MHz), IW9GDC/B (144 MHz), OH1DB (10 GHz), OZ4BHM (144 MHz), PI7SIX (SBP 5/2), TF1VHF (70 MHz and 144 MHz) and WA1ZMS/4 (70 MHz and 144 MHz).

Next Generation Beacons – PI4