This data highlights why you need to calibrate your receiver if you’re doing any kind of serious work. The OMNI-VI is also about 5 dB per S-unit down to S4, but then takes a radical jump of 10 dB from S4 to S3īelow S3, the S-meter on all receivers is only 2-3 dB per S-unit. The TS-180 and the FT-747 exhibit approximately 5 dB per S-unit down to S3. The other two receivers are off by 7 dB (one is higher, one is lower). The TS-180 comes closest to the anchor point of S9 = -73 dBm. Three conclusions can be made from this data. These three receivers do not have a separate preamp switch, so all that is noted is the setting of the attenuator.
How do the 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 my receivers on 20-Meters.
Unfortunately a recommendation has no teeth to it. In 1981 the IARU (International Amateur Radio Union) even adopted the Collins standard as a recommendation. I believe 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. It’s true that Collins did have those values as a standard a long time ago. This anchor point is generally accepted to be S9.īut why do we have to go through a calibration procedure? Didn’t Collins Radio make 6 dB per S-unit and S9 = 50 microvolts (-73 dBm into 50 ohms) a standard? It also means having an anchor point in terms of absolute power. What does “calibrating your S-meter” mean? It means knowing exactly how many dB there are between each S-unit. On the other hand, if you’re doing scientific research (for example, monitoring signal strength during a solar eclipse like the one that occurred on August 21 of this year) or comparing antennas on the air, then it’s important to make sure your S-meter is calibrated. This also applies to contesting, as the signal report for most contests has evolved to 59 for Phone and 599 for CW. If you only do casual operating, you probably don’t need to calibrate your S-meter.
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