VHF/UHF WSPR Propagation Study

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Observations of Radio Propagation above 50 MHz using Dr. Joseph Taylor's WSPR (Weak Signal Propagation Reporter)

by Dr. Carol F. Milazzo, KP4MD (posted 14 June 2012) last update 21 Nov 2020  E-mail: kp4md@arrl.net

Check William Hepburn's Tropospheric Ducting Forecasts for current VHF propagation conditions.

Propagation Study Paths

1. California coastal range mountains that obstruct the initial 80 mile radio path under study include the Sugarloaf Ridge immediately east of Santa Rosa, California and the Berryessa Blue Ridge Mountain area, both with elevations ranging from 1,600 to 2,000 feet.

View 2 meter WSPR Propagation Study in a larger map

2. WSPR Propagation study paths.  W7PUA-N6KOG 482 miles from NW Oregon to the central California valley.  N6GN/K6PZB-KC6KGE 292 miles over coastal range summits.  N6KOG-N3IZN 385 miles through central California valley and over San Bernardino Mountains.  Interactive map link  Google Earth KML file

3. The Radio Mobile Online application produced this combined coverage map for the West Coast 2 meter WSPR study group stations.  At least one of our stations should be heard on 144.4905 MHz at locations from Southwest Washington state through California from Redding to the Grapevine and to San Diego.   The expected signal to noise ratio is greater than -20 dB in the yellow areas and less than -20 dB in the orange areas.

4. Northern California Stations in 144 MHz WSPR Propagation Study. The path distances between Sacramento (KP4MD-WW8L), Santa Rosa (K6PZB-N6GN) and Milpitas (KI6STW) are similar. There are no apparent high elevations obstructing the path from Santa Rosa to Milpitas. Mt. Allison (Elev. 2664 ft) in the Monument Peak Ridge is 3 miles away from Milpitas and directly obstructs the path to Sacramento. The Sugarloaf Ridge and Blue Ridge-Berryessa areas average 1800-2000 ft elevation and obstruct the path from Santa Rosa to Sacramento.

5. 6 June 2012 - N6GN WSPR signals received at KP4MD. The steep diagonal traces on the waterfall are reflected signals from passing aircraft subject to Doppler shift.1  N6GN has observed that Doppler reflections near the signal frequency for about 20% of each two minute transmission window often cause WSPR signal decoding failure.

6. Time lapse screen captures of contacts among 144 MHz WSPR propagation study stations. All spot reports consisting of time, signal to noise ratio, time segment shift, frequency and drift received at the study stations are uploaded to a database at WSPRnet.org.2

Tropospheric Propagation Phenomena

7. 11 June 2012 0700 UTC - N6GN signals tonight are up to -10 dB SNR, after the winds have calmed, I suspect we are now seeing some tropospheric enhancement predicted by Hepburn on http://www.dxinfocentre.com/tropo_wam.html3

8. Hepburn Tropospheric Index 1200 UTC June 14, 2012.

9. Hepburn Tropospheric Index 1200 UTC June 15, 2012.

N6GN Spots 11-17 June 2012

10. WSPRnet Spot Reports of KP4MD Signal to Noise Ratio (SNR) at N6GN June 11-17, 2012. Compare with the previous Tropospheric Forecast Maps for those dates. The dip in signal strengths on 15 June appears to coincide with the absence of tropospheric enhancement over the signal path on that date. 

11. Early morning heating of the upper troposphere over a valley as a source of propagation enhancement.4 The temperature inversion at the boundary of the warm air and the cool air can support VHF and UHF radio wave propagation to hundreds of kilometers beyond the line of sight.

12. A view from 5,500 feet elevation in the Sierra Nevada Mountains of a temperature inversion over the San Joaquin valley in central California.

13. The circuit between KP4MD in Sacramento and KI6STW in Milpitas is usually blocked by a ridge of mountains near KI6STW.

14. Monument Peak, Mt. Allison (2700 ft elevation) and Mission Peak are 3 miles away from KI6STW and lie directly in the path toward Sacramento.

KI6STW Spots 7 July 2012

15. On 2 July 2012 KP4MD's 144 MHz WSPR signals at KI6STW were up from -28 at 0216 UTC peaking to -19 dB SNR at 0500-0700 UTC, concurrent with Hepburn's forecast predicted tropo enhancement in the Sacramento Valley at 0600 UTC.

16. 2 July 2012 0000 UTC - Tropo forecast before enhancement event.


17. 2 July 2012 0600 UTC - Tropo propagation enhancement forecasted in the Sacramento valley at the time KP4MD signals peaked at KI6STW.


18. 2 July 2012 1200 UTC - Tropo propagation enhancement in the Sacramento valley abated concurrent with the decline of KP4MD signals received at KI6STW. http://www.dxinfocentre.com/tropo_wam.html

19. 4 July 2012 - First 144 MHz WSPR contacts established over 290 mile circuit with KC6KGE in Taft, California.

20. 5 July 2012 - Further 144 MHz WSPR contacts established with KC6KGE in Taft, California.

21. 19 July 2012 - Strong 2 meter WSPR signals received at KP4MD from KC6KGE in Taft, CA 265 miles away. Hepburn predicted tropospheric enhancement around station KC6KGE in Taft, California at 1800 UTC on 18 July and again at 0600 UTC on 19 July.

KC6KGE Spots 19 July 2012

22. 18 July 2012 - KC6KGE's 144 MHz WSPR Signal to Noise Ratio at KP4MD was up from -33 dB at 1040 UTC peaking to -18 dB SNR at 1726 UTC, and again to -10 dB at 0314 UTC on 19 July 2012.

23. 18 July 2012 - Hepburn predicted tropospheric enhancement around KC6KGE's area on 18 July 2012 at 1800 UTC. http://www.dxinfocentre.com/tropo_wam.html

24. 19 July 2012 - Hepburn predicted tropospheric enhancement around KC6KGE's area again on 19 July 2012 at 0600 UTC. http://www.dxinfocentre.com/tropo_wam.html

Aircraft Scatter

25. 12 July 2012 - On http://planefinder.net N6GN noticed a FedEx flight, southbound on a path that took it about 8 miles east of Santa Rosa at about 13K feet. The plane took a turn to the east, starting about Petaluma on this path.

26. 12 July 2012 - When the FedEx plane flew overhead at 0444 UTC, a trace from KI6STW shows such a strong aircraft scatter (ACS) component that it didn't decode. Furthermore, the reason for the lack of decode was that the ACS components were quite close to transmitted frequency for a significant portion of the 2 minutes, particularly at the start. Since this aircraft was flying almost exactly along the path between the two stations, the indirect path length wasn't changing much. As the turn progressed, the path started getting longer to both N6GN and KI6STW from the aircraft and the ACS (Doppler) component dropped in frequency.

27. ‎12 Aug 2012 - 0725 - 1430 UTC - 144 MHz WSPR Study (Perseid Meteor Shower) A few very bright, long and steep descending Doppler echoes at 0726 and 0758 are probably aircraft scatter (ACS). The much shorter duration traces at 0916, 1052 and 1138 may be meteor echoes. The ACS echoes increase rapidly after 1250 due to local air traffic.

Aircraft Wingtip Vortices

28. 11 Aug 2012 - Suspected aircraft wingtip vortex echoes detected at station KE6GLA at 2058 and 2108 UTC on 2 meter WSPR signals.

29. Suspected aircraft wingtip vortex echoes detected on 2 meter WSPR signal at station N6GN.

30. 02 Oct 2012 1338 UTC - Spectran analysis of the final 80 seconds of a 2 meter WSPR signal showing the discrete tones.  This signal did not decode due to the 25 Hz negative frequency drift over the period. Moving symmetric side images 35 dB down from main signal are observed. The corresponding WSPR waterfall segment is on the right.

Frequency stabilization

31. N6GN engineered this GPS disciplined frequency reference for selected stations in our West Coast VHF/UHF WSPR Study Group.  It provides a 10 MHz reference as well as a GPS disciplined substitute for the master oscillator or local oscillator of various commercial transceivers or transverters.  The discussion thread can be read here. Leo Bodnar Electronics now sells a similar device.

32. A typical Elecraft XV144 transverter modification for the GPS10V frequency reference. The 47Ω resistor suppresses the 116 MHz crystal oscillations and Q1 functions to amplify the external 116 MHz reference signal.

33. The Elecraft XV144's internal local oscillator with crystal oven option had exhibited 3-4 Hz frequency drift during 2 minute WSPR transmissions and long term frequency instability with ambient temperature variation. This frequency instability and drift was eliminated with the GPS10 frequency reference.

Study Group Station Antennas

The KC6KGE station antenna in Taft, California. 

Cushcraft A144-11 Yagi at 20 feet with 15.3 dBi gain. 

Effective isotropic radiated power: 526 watts (57 dBm)

The KI6STW station antenna in Milpitas, California. 

Two stacked M2 HO loops at 20 feet with 10.14 dBi gain. 

Effective isotropic radiated power: 62 watts (48 dBm)

The KP4MD station antennas in Citrus Heights, California. 

Two stacked halos at 14 feet and 18 feet with 7.88 dBi theoretical gain.  Effective isotropic radiated power: 212 watts (53 dBm). 

5 element 432 MHz Yagi with 10 dBi gain (not shown).  Effective isotropic radiated power: 315 watts (55 dBm).

The K6PZB station antenna in Graton, California. Cushcraft A13B2 13 element Yagi at 20 feet with 15.8 dBi theoretical gain. Effective isotropic radiated power: 1,734 watts (62 dBm).

The KE6GLA station antenna in El Dorado Hills, California. M2 EB-144 Eggbeater (at left) at 30 feet with 6 dBi theoretical gain. Effective isotropic radiated power: 32 watts (45 dBm).

The N6GN station antennas in Santa Rosa, California. 4 element 144 MHz Yagi (at right) at 20 feet with 9 dBi gain. Effective isotropic radiated power: 40 watts (46 dBm). 

6 element 432 MHz Yagi (at left) 10.2 dB gain.  Effective isotropic radiated power: 315 watts (55 dBm).

The WA6LIE station antenna in Salinas, California. Cushcraft A13B2 13 element Yagi at 40 feet with 15.8 dBi theoretical gain. Effective isotropic radiated power: 380 watts (56 dBm).

The KD6RF station antenna in Livermore, California. VTenn UltraWide Band Vivaldi at 22 feet with 6.5 dBi gain at 144 MHz. Effective isotropic radiated power: 89 Watts (50 dBm).

Above it is an Arrow 4 element 144 MHz Yagi antenna.

2m WSPR Activity

World Wide 2 meter WSPR daily spot report activity has increased 100-fold since this study commenced in June 2012.



VHF/UHF WSPR Slideshow Presentation

from the Pacificon/ARRL National Convention 13 October 2012.


VHF/UHF WSPR Slideshow Presentation #1

from the ARRL Pacificon Convention  12 October 2013.


VHF/UHF WSPR Slideshow Presentation #2

from the ARRL Pacificon Convention 12 October 2013.

VHF/UHF WSPR Study Stations

VHF/UHF WSPR Study Group

*EIRP = Effective isotropic radiated power