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Antenna Heights for 6m Sporadic-E

Antenna Heights for 6m Sporadic-E. Steve Kavanagh, VE3SMA CSVHFS 2004, Mississauga, ON. Introduction. What is optimum height for 6m antenna to be used for Sporadic E contacts ?

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Antenna Heights for 6m Sporadic-E

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  1. Antenna Heights for 6m Sporadic-E Steve Kavanagh, VE3SMA CSVHFS 2004, Mississauga, ON

  2. Introduction • What is optimum height for 6m antenna to be used for Sporadic E contacts ? • Question triggered by looking at pictures of VHF contest Rovers, mostly with fairly low antennas, and recalling my dissatisfaction with 6m results in my own June contest Rover experience • Methodology • Approach is same as used by Jim Lawson, W2PV, for F2 propagation at HF (Yagi Antenna Design, ARRL, 1986) • Determine elevation angle range of Sporadic E signals • Determine elevation patterns of 6m antennas at various heights • Compare – which antenna heights give best gain over the necessary range of elevation angles ?

  3. h = approx. 110 km (for sporadic E) Earth radius Re = 6378 km Distance = paRe/90 Can work out angle b with trigonometry Elevation angle is b - 90 degrees Sporadic-E Geometry

  4. Characteristics of Sporadic E • Maximum distance is 2352 km • single hop • 0 degrees elevation angle using geometry on previous slide • Minimum distance typically about 1000 km • limited by degree of ionization

  5. Elevation Angle vs. Distance

  6. A is between 1000 and 1800 km distance (3 to 10 deg.elev.) B is between 1800 and 2352 km distance (0 to 3 deg.elev.) Area of A is about the same as Area of B Potentially same number of stations to be worked in areas A and B Area Covered vs. Elev. Angle

  7. Elevation Angle Results • Elev. angle range of interest is 0-10 deg. • 0-3 degree and 3-10 degree ranges are of about equal importance regarding number of stations (and grids) available to be worked • disregarding variations in population density, oceans, etc.

  8. Elevation Patterns (from YA)

  9. Observations • Over flat level ground there is no antenna height which gives optimum performance over 0-10 degree range • Best single height is probably about 50 ft. • Higher antennas give more gain at low angles but have nulls at the upper end of elevation angle range • A choice of two antennas should work well, with one at about 30 ft., the other above 60 ft.

  10. Observations, cont’d • A rover with antenna at 10 ft will be 12 dB down (2 S-units) compared to a fixed station with the same antenna at 40 ft. • A dipole at 20 ft. is as good as 3 elements at 10 ft. • A 20 ft. high antenna will be 10 dB louder (at 2 degree elevation) over 5 degree sloping ground than over level ground.

  11. Limitations of Analysis • Real ground may not be flat or level • Could use terrain analysis software to evaluate performance at a particular site • Real ground may not be smooth • Compared to HF, smaller obstacles will be significant at 6m • It would be interesting to use software such as NEC to examine the effect of power lines, buildings, cars, etc. on radiation patterns of 6m antennas over ground • Applies only to sporadic E • Very high antennas will work well for tropo, troposcatter, line-of-sight signals which propagate only at very low elevation angles • Applies only to horizontal polarization

  12. Conclusions • A single antenna at about 50 ft over flat level ground will work quite well for Sporadic E • But a choice of lower and higher antennas should be better • Most Rovers’ 6m antennas are too low to be competitive – some extra height will make them much louder on Sporadic E

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