Page 30 - EngineerIT December 2022

AMATEUR RADIO

Amateur radio contests could

become science projects

By Hans van de Groenendaal ZS6AKV

hroughout the year, almost weekly, there are amateur radio Carl Luetzelschwab K9LA makes three conclusions from this data.
contests where large numbers of radio amateurs participate 1. The TS-180 comes closest to the anchor point of S9 = -73 dBm.
Tover a 24- or 48-hour period. With very slight changes to The other two receivers are off by 7 dB (one is higher, one is
the rules governing these contests, particularly of some of the lower).
major international events, this could turn basic social events into 2. The TS-180 and the FT-747 exhibit approximately 5 dB per
scientific projects, greatly enhancing the study of ionospheric and S-unit down to S3. The OMNI-VI is also about 5 dB per S-unit
other more exotic propagation modes. The data collected in this down to S4, but then takes a radical jump of 10 dB from S4
way would be huge. to S3.
The objective of many of these contests is to contact as many 3. Below S3, the S-meter on all receivers is only 2-3 dB per S-unit.
radio amateurs, during the given contest period, in as many countries
as possible, mostly exchanging call sign, station location and a signal Back to turning contests into parallel science projects; if the
report. In some contests, the objective is to contact stations in as rules are changed and participants are compelled to log accurate
many grid squares as possible. A grid square is a small area defined S-meter readings, we are a step closer. Ok, but all S-meters are not
by longitude and latitude and designated by an international code, calibrated by the manufactures to the same standard, you may
for example the east of Pretoria is grid square KG43cg. rightfully argue. So what is the point? Firstly, we are a step closer
Because of the social aspect of contesting the signal report, to turning contesting into parallel science projects. Secondly,
sharing has become somewhat of a joke. Radio amateurs tend the difference in S meter calibrations could be taken care of by
to give each other 59 (readability 5 on a scale of 1 – 5 and signal applying a correction factor in the software.
strength 9, irrespective of how well the signal is received). This, however, is only the beginning of an idea. Many
The signal strength can be read from the s-meter on a algorithms would have to be developed to extract and interpret
receiver. The readability report is based on how well you could the information from the submitted log sheets. Perhaps the
write down the shared information. Proper S-meter readings biggest hurdle will be to convince contesters to look at their
provide more realistic information, provided that the S meter is S-meters and record the information accurately. It takes up
correctly calibrated. valuable time but the idea is worth pursuing! n
For any serious scientific work, for example monitoring signal
strength during a solar eclipse like the one that occurred a few years
ago, or comparing antennas on the air, it is important to ensure that
the S-meter is calibrated.
On the HamSCI website, an article by Carl Luetzelschwab K9LA
explains what calibrating S meters is about. It means knowing
exactly how many dB there are between each S-unit. It also means
having an anchor point in terms of absolute power. This anchor point
is generally accepted to be S9.
But why do we have to go through a calibration procedure?
Didn’t Collins Radio make 6 dB per S-unit and S9 = 50 microvolts Figure 1: Power in dBm vs S-meter reading
(-73 dBm into 50 ohms) a standard? Yes, they did. Collins did have
those values as a standard a long time ago. Luetzelschwab believes
that many individual manufacturers did adhere to 6 dB per S-unit
in the early years, but this fell by the wayside because there wasn’t
an official document that new manufacturers signed up to. In 1981
the IARU (International Amateur Radio Union) adopted the Collins
standard as a recommendation.
How do S-meters on modern receivers compare to the Collins
standard? Figure 1 gives tabular data (power in dBm versus S-meter
reading) for three of the receivers on 20 metres. Figure 2 graphs this
data. These three receivers do not have a separate pre-amp switch,
so all that is noted is the setting of the attenuator. Figure 2: Power in dBm vs S-meter reading

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