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Field Aligned Irregularities

  1. Wath is F.A.I
  2. Geometry of F.A.I.
  3. Signal Characteristic
  4. Height of Scatter
  5. Known Scatter
  6. The Best Season
  7. The Europe Map
  8. IC8FAX 's experience on the F.A.I

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- Wath is F.A.I -

The F.A.I. (Field Aligned Irregularities) is due to irregularities E-Layer ionization aligned to the earth magnetic field. The irregularities E-Layer ionization grows a zone of scatter where the Vhf emission are reflected. The propagation was short lived and disappeared when the heaters were turned off.
Several condictions are requiered to establish a F.A.I. radio link:
Suitable ionospheric condictions must be available. Furthermore, a suitable scatter geometry must be set up by the locations of the transmitter, receiver and scatterer. In particular both the transmitter's and receiver's antenna must be directed at a common scatter volume. These requirements were furfilled for the observations in concern, otherwise these QSO's couldnot have been made. ,

- Geometry of F.A.I. -

A radio signal illuminating FAI will be scattered back to ground in a cone shaped pattern with the apex at the irregularity and the axis aligned to magnetic field line. The intersection with the earth of the scattering cone, having an angle a2 to the magnetic field line, gives the contour of the maximum reception which is also labelled a2. Contacts may take place between stations located on supplementary countors(their sum is equal 180 deg.)

- Signal Characteristic -

F.A.I is different from Sporadic E or Tropo for the following main charatteristics :
- Signal offset from the great circle bearing.
- Rapid flutter, it is similar to auroral propagation in sound, but not as disruptive. Frequency components of 30 to 100 Hz are tipical. Ssb is quite intellegible when signals are somewhat above the noise.
With qsos in CW is preferable low speed .

- Heigth of Scatter -

The heigth of E-Layer is about 100-140 Km. Therefore the proper elevation of the antenna is decreasing with increasing of the distance of the station from the scatter point.
IW1AZJ Silvio in Turin at 150 Km. distance of the scatter use 35 � of antenna elevation.
IC8CQF Lino in Island of Capri at 800 Km distance of the scatter use 6� of antenna elevation.
So the station near the scatter point that do not have an antenna system elevation could use one fix antenna with a just elevation.

- Known Scatter -

Scatter at Brussels (CL/CK) :
This scatter is non available for me, please send me info about charatteristics of this point
Scatter at Budapest (JH) :
Scatter at Geneva (DG) :
Scatter at JN92 :
Scatter at JN41/42 :
This scatter is available for me but I have not direct info about this. Pse EA3ADW send me,tks.

- The Best Season -

The European F.A.I season generally starts at beginning of May and ends in the middle of September. Openings have been more frequent from the 16:00-19:00 Utc. In the last 1996 I have worked many openings, with good signals, betwen 20:00-22:00 Utc. I have had in the log only 3 stations from France. Usually during the previous seasons have worked about 45 several station. This is modification of the scatter point or low activity from France ?

- The Europe Map-

- IC8FAX ' s experience on the F.A.I. -

I am located in Capri Island in JN70CN, my first qso in F.A.I was in the May 1990 with Didier FA1MXE in JN05GQ with 100 watts and 17 element Tonna. The scatter point was Geneva at 330 �.

Now my work conditions are :

Yaesu FT736/R with Mutek Front-End,
Pa Eimac 8930 about 300 watts,
Shark 20 Element long yagi 9.50 mt. boom; 30� beam width.
Later on, I have had many qsos in different scatters points (Geneva, Budapest, Brussels, JN92) and have worked the following squares :

JN 03-04-05-06-16-18-34-35-45-46-54-55-65-66-75-85-86
IN 78-91-93-94-95-96-97-98-89
KN 04-05-06-12-13-22-23-32-33-68
KM 17

The phenomenon of the F.A.I. is more frequent in the period within May to September to 16 at 22 utc.
Experience tends to confirm the link between F.A.I in 144 MHz and sporadic E in the 50 MHz. The opening more frequent are on the Geneva scatter point, in June I have worked F.A.I. almost the evening-nitgh. At begin the best signal is from the West (France, Spain , Italy), at ended the signal for the Est is still very good. The signal is similar to auroral propagation in sound. but not as disruptive. Frequency components of 30 to 100 Hz are tipical. Ssb is quite intelligible when signals are somewath above the noise. In cw is preferable to use a low speed. When I have listen the F.A.I with distruptive signals, I have worked some squares not frequently. The scatter point on the Budapest is also much famous but on the it thare is not many activity. On the scatter point in JN92 I have worked only SV1BTR in KM17. JN92 is probably the some scatter point used in the Qso between 5B4/DL5MAE and IK6EIW and also I5 stations.


The K9SE have developed a programm that help to know the F.A.I phenomenology. He plot many contours lines ascribe at same scatter point. The contours represent the mathematical complement af the incident or reflected ray angle with respect to the scattering axis. When a station anywhere on the - 5 countor transmits toward the scatter, the reflected signal returns to earth not at one point, but along the antire arc of the +5 countor. A station on the 0 degree contour can work any other station on the 0 degree contour, including itself. (Ref. F. Kneisel K4GFG QST Jan 1982).



The square IN89 , at 02.09.95 14:46 utc, was probably worked around at the Brussels Scatter Point, in fact Allan ( GJ4ZUK ) had his antenna in direction of 80 � , my qtf was 335 �. This square is not ordinary for the my F.A.I openings.


References to :
Beyond line of sight by Emil Pocock
Ionospheric scatter by Field Aligned Irregularities at 144 Mhz by K4GFG
Dubus 3/86- Propagation at 144 Mhz by I3LDS
Dubus 2/88-Is there a Fai scatterer above Budapest ? by DF5AI
Software Fai from K9SE
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