On the IC-746PRO mailing list, a fellow asked, “On the 2m band, why doesn’t the S-meter reading on my IC-746PRO match the S-meter reading on my 2m mobile radio?” My answer was that while there is a standard (it’s actually a recommendation), it’s rarely followed, so it’s not a surprise that the two readings don’t agree.
Mark, K5LXP, corrected me, noting that the recommendation specifies one value for an S9 reading below 144 MHz, and a different value above 144 MHz. The recommendation reads:
STANDARDISATION OF S-METER READINGS
- One S-unit corresponds to a signal level difference of 6 dB.
- On the bands below 30 MHz a meter deviation of S-9 corresponds to an available power of -73 dBm from a continuous wave signal generator connected to the receiver input terminals.
- On the bands above 144 MHz this available power shall be -93 dBm.
- The metering system shall be based on quasi-peak detection with an attack time of 10 msec ± 2 msec and a decay time constant of at least 500 msec.
This corresponds to a voltage of about 50 microvolts below 144 MHz and a voltage of 5 microvolts about 144 MHz.
It would be interesting to know how the software of the IC-746PRO handles this. I say software because the S-meter on the IC-746PRO is a digital meter whose readings are controlled by the rig’s microcontroller. Theoretically, the software could calculate the S-meter readings differently based on the band that the rig is set to, but I don’t know that the programmers would go so far as to do that.
Dave New, N8SBE says
Elecraft goes to the trouble. It was discussed on their mailing list. Since the K3 is considered a state-of-the-art transceiver for use with transverters going up into the microwave region, the K3 can be calibrated for the power gain of the transverter, as well, so you can get a ‘true’ S-meter reading on all bands (including HF+6m), with all transverters.
73,
— Dave, N8SBE