SIGNAL INTENSITY MEASUREMENTS IN TECSUN PL 310et, PL 380 AND OTHER RADIOS OF THIS BRAND
On the display of these radios, in the upper right corner, 2 magnitudes related to the received signal are indicated: signal strength on the left and signal/noise ratio on the right (as shown in the image).
1.Signal strength indicator – Related to the old S-meter, in Tecsun the unit of measurement is the dBµ (as it is on the display for short), or more correctly dBµV (dB = decibel, a way of expressing magnitudes of value as the voltage logarithmically; µV = microvolts) ). On those radios that use DSP technology, this indicator is also called RSSI. In the images is the table of readings made by the DSP SiLabs chip used in Tecsun in dBµ, and its relationship with the “S” unit. The columns in dBm and µV are also presented.
Let's see this in practice on my 310et: I tune to R. Alcaraván at 5910kHz and (on average) the indicator in dBµ shows 28; checking this quantity in the table, it corresponds to S8. The reception is very poor and I would gladly give an S3. There is a good discrepancy, that is, the table does not match. But in this case we could give a discount and establish a different table, with the reality of our subjective values of the “S” scale. So I tested it at 5055kHz, there was no station and the indicator showed 22dBµ = S7; it seems that this radio takes these readings without distinguishing the modulated signal from what is just noise. In that case an S1 would be the maximum tolerated. So I considered this Tecsun signal strength indicator a goner.
2. Signal/noise indicator – In Tecsun the measurement unit is in dB (decibel) and in the images, there is a drawing that illustrates this quantity well; is the ratio between the desired signal and background noise S/N = signal to noise ratio or SNR (S=signal, N=noise, ratio=ratio, proportion). According to some texts, 15 – 25dB would be considered a minimum range of magnitude to establish connectivity but in Tecsun, observing in practice, the total range of magnitude in AM is 0 – 25dB. On FM this range can be overridden. The SNR is an interesting signal analysis unit of measure because in practice, we can establish the level of intelligibility, or the ability to copy a content in the signal, using a better term related to radio. In practice (on my 310et), this measurement is very consistent with what happened: noisy signals have low dB and vice versa. I listened on 08/13 at 0917ut, R. 4940 at 4940kHz with S/R = 12dB regular and noisy signal; on the same day at 0922utc to R. Alcaraván 5910kHz with S/R = 5dB weak signal and also noisy.
Probably this Tecsun measurement of S/N indirectly establishes the magnitude of signal strength as well, because if the signal is noisier it is generally weaker.
This text has as its main source the page: https://radio-timetraveller.blogspot.com/2015/01/the-ultralight-db-mystery-s-meters-and.html?m=1
In this research, I saw a video in which it is stated that these Tecsun measurements are negligible; I agree with the one related to Signal Strength but not with the SNR measurement.
73
LOB
Brazil
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