The California Emergency Services Net (CESN) is a major element in California's disaster preparedness. The net meets every Wednesday morning at 10 AM on 40 meters (7.230 MHz). 60 emergency communication stations from all over the state regularly check in each week. The stations include Emergency Operation Centers (EOCs), state health facilities, the California Highway Patrol (CHP), numerous Caltrans sites, municipal utility districts, Army, Navy, and Air Force MARS locations, NASA Ames Research, National Weather Service, and the Nevada State Division of Emergency Management. Checking into the net is strictly limited to amateur radio emergency stations located at government and approved agency facilities.
Last December we applied for and were granted permission for the East County Sheriff's Station (ECSS) to become a member of the net. We check into the net each week from our ARES/RACES radio room at ECSS. Our tactical call sign on the net is Ventura County EOC. As a condition for becoming a member we were requested to conduct a 4 month study to determine how well we could receive the other stations checking into the net. The net uses a 6 level (0 to 5) Circuit Merit (CM) reporting structure in which CM-5 is perfect reception, CM-3 is the minimal level for acceptable communications, and CM-0 means that the station can not be heard. Bruce Elbert, K6ZB, and I began collecting data in January and are now into our 8th month of what has turned into a long term study of HF Regional Communications.
We have considerably expanded the study beyond its original intent. In addition to recording how well we receive each of the station checking into the net, we also record how well each station reports receiving net control and how well net control receives them. Net control is located at Patton Hospital in San Bernardino. Without this additional information, our records of how well we received each station would be of limited use. What we really want to know is how well we received each station relative to net control. If we receive Caltrans San Diego poorly and net control does as well, then we know that the problem is most likely poor band conditions. However, if we receive Caltrans San Diego well but net control does not, then perhaps our location and antenna configuration puts us in a favored position to receive San Diego. This information is very valuable to net control during an actually emergency since it allows them to designate key locations as relay stations ensuring that the net is totally connected.
Bruce and I have taken the study a step further by recording the condition of the Ionosphere each week at net time. This information is readily available on the internet. The information that we collect consists of the 10.7cm Solar Flux, Boulder A Index, Boulder K Index, X-ray Flux from the GOES earth satellites, the Ionosphere Critical Frequency over California determined by government radio sounders (in particular for us the one located at Vandenberg AFB), estimated F2 Layer height, solar activity reported by NOAA, geomagnetic field analysis, and any abnormal D Level absorption. In addition, we down load the Wednesday image of the Sun showing where the sunspots are located on the Sun's photosphere. This image is needed to understand the NOAA solar activity reports. We also record the signal strengths of WWV (Boulder, CO) and WWVH (Kauai) on 2.5, 5.0, 10.0, 15.0, and 20.0 MHz.
Bruce and I have learned a great deal about regional communications by comparing the Ionospheric data with the Circuit Merit levels reported on the net. Those of us in the California Emergency Services Southern Region (from Bishop and San Luis Obispo south to San Diego) rely on Near Vertical Incident Skywave (NVIS) propagation to communicate with net control in San Bernardino. NVIS is very sensitive to critical frequency. We have learned that a critical frequency of 7.0 MHz and higher, see Figure 1, provides excellent communications among Southern Region stations and with net control. However, communications within the Southern Region and with net control is very difficult, if not impossible, if the critical frequency is below about 6.0 MHz. In contrast, communications between the Southern Region and the Tahoe and Burney relay stations in Northern California is good for critical frequencies down to about 4.5 MHz. So if the critical frequency is too low to communicate directly with net control, we can still communicate via the Tahoe relay station. Through our study we have become quite good at accurately predicting prior to the net when direct communications between Southern Region stations and net control will be possible and when the Tahoe or Burney relay stations will be needed.
Communications between the Northern California stations and net control in San Bernardino can be severely impacted if heavy D Layer absorption occurs. Predicting D Layer absorption is more difficult than the critical frequency analysis. We have found that one good indicator of D Layer absorption is the 5.0 MHz WWV signal from Boulder, CO. If we can clearly hear WWV prior to the net then we know that all is well and net control should be able to communicate with the Northern California Stations. However, if we can not hear WWV on 5.0 MHz then D Layer absorption is probably high meaning that net control may have trouble communicating with Northern California.
One cause of sever D Layer absorption is a solar flare. The X-ray Flux measured by the GOES satellites provides a direct indication of solar flare activity. The normal X-ray Flux has been running in the A and B bands of the chart shown in Figure 2. A sharp spike into the C, M, or X bands means that a solar flare is occurring. A large flare, Figure 2, occurred on July 13 at about 1430 UTC and was still at a level of C9.0 at net time (1700 UTC). Most flares last for 30 minutes or less. This one lasted considerably longer. Figure 3 shows that the flare caused severe D Layer absorption over most of North and Central America with the "epicenter" over Mexico. The epicenter, the point on the Earth where the affects of the flare are most strongly felt, is the location where the Sun is directly overhead at the time of the flare. The flare produced a major disruption of the net. Circuit Merit reports from all over California were mostly in the 0 to 2 range, unacceptable for reliable communications. The comment from Tahoe Relay was "Very unusual morning, best range is 100 miles". While it was unusual, it was not a mystery. We were being hit with a solar flare. Armed with the GOES X-ray Flux data, Bruce and I knew what was happening and had an idea of how long it would last. In an emergency situation this type of information would be critical.
The web sites for the Ionospheric data that we are using are listed in the links section of the CVARC web site. To access the Ionospheric data go to www.cvarc.org, click on the Links tab and scan down the links list to the Ionosphere section.
This has been a very exciting project which we plan to continue well into the future. Understanding what the Ionospheric conditions are, why they are that way, and what to do about it to achieve successful HF communication is a very gratifying feeling. We would like to get more radio operators involved in the project. If you have an interest in learning more about HF Ionospheric communications, and are available Wednesday mornings from 9:30 to 10:30 AM, talk to either Bruce or myself at the CVARC club meeting. We would love to have you join us Wednesday mornings at the East County Sheriff's Station.
