Andy's receiver was built in 1973 by David Warshaw, A-1, who designed it and built it to try out the RCA new CA3035, one of the first operational amplifier integrated circuits to become available commercially. Dave liked to experiment with new electronics products. His interest in experimenting with them dates back to 1956 when he designed and built a transistor VLF receiver using the first Germanium transistors then just coming on the market. This came about when the National Bureau of Standards, NBS, donated four Brown strip-chart recorders to the AAVSO Solar Division to detect solar flares by the SEA (Sudden Enhancement of Atmospherics) method. Harry Bondy was then the Chairman of the Solar Division and knew Dave Warshaw and of his vast experience with electronics so he recruited him to design an SEA receiver for the Solar Division to set up an SEA program. This would make it possible for the AAVSO to participate in the International Geophysical Year, IGY. Dave worked for IT&T at their overseas communication short-wave radio station in Rocky Point, Long Island, New York keeping their radio equipment in good working order so he knew a lot about such things. He also talked IT&T into financing the construction of a quartz monochrometer he built to view the sun in its Hydrogen Alpha line. This was quite a project in those days because it used a series of quartz crystals followed by a final Iceland Spar crystal to separate the H-alpha line. The Iceland Spar crystal eventually cracked but Dave never got around to making a new one. Iceland Spar is difficult to work with. Now you know how the Solar Division got started in the SID business and the early history of the SEA and later the SES program.

On the last page of this SID supplement is a Schematic of Dave Warshaw's first SES receiver to use an op amp IC, the RCA CA3035. I publish this for historical reasons only because today much better Op Amps are available and the Miller slug tuned coils are no longer available. This SID receiver is as good as any as you can see from Andy's charts above, but Art Stokes's Gyrator II is a lot easier to build and tune. For a fixed frequency receiver however, Ferrite core coils are still a good choice. Although the slug tuned coils are no longer available you can get Merrett fixed inductance 20 mH coils from Digi-Key and tune them close with fixed capacitors and then tune them to final resonance at the desired frequency with variable trimmer capacitors that have a polypropalene dielectric. These come in small PC board mounted sizes up to 220 pfd. Two stages of RF amplification, each with a pair of inductively coupled 20 mH ferrite core coils provides enough selectivity to easily separate NAA on 24 kHz from the new 25.2 kHz signal or from NPG on 24.8 kHz

Many observers have remarked on how many of the SESs they recorded in April that were inverted. Both of Andy Clerkin's charts above show inverted SESs. His first chart made on 4 April shows what might be called a double inversion. It starts out rising in the normal way but then changes its mind and quickly inverts downward. Then it reverses direction again and rises more slowly to finish recording the SES. His second chart also shows an inverted SES. This one is almost completely inverted although in the very beginning it does start with a small rise before suddenly inverting. Inverted SESs are not unusual over short propagation paths like Andy's fromNAA at Cutler in the Northeast corner of Maine to Bedford, Massachusetts near Boston. What is unusual is distant observers recorded them inverted in April. Al McWilliams, A-94, in Minnesota and Jerry Winkler in Texas recorded inverted SESs and so did I in Florida. Art Stokes recorded one in Ohio and his are almost never inverted. Below is Art's inverted SES on 15 April. It is interesting to compare it with Andy's recording of the same SES on the 15th. Notice How Art's stays normal going up a bit longer than Andy's

Art also sent a schematic of a multiplexer he is using to record two signals. His schematic is below. For those hoping to record a gamma ray burst, GRB, it will be much more clearly defined if you have it recorded as two signals on the same chart. Danie Overbeek A52's, recording of GRB010222 was on a multiplexed chart of three signals, NAA in Northeastern USA, GBR in England and NWC in West Australia. The fact that the GRB produced an SES on all three of these signals at exactly the right time was what made it almost certain the SESs were the signature of GRB010222. I hope others will follow Art's example and build a multiplexer and record more than one signal.

A Two Input Multiplexer

SID Receiver for SES (Sudden Enhancement of Signal)

• Back to April Solar Bulletin
• Sudden Ionospheric Disturbance Report