Re: G8 signal strength meter

jim_kr1s <jkearman@...>

--- In ultralightdx@..., Antonios Kekalos wrote:
> Would someone mind explaining how to interpret the readings on the signal
> strength meter on the G8? The numbers don't really mean anything to me.
> Unless I missed it, the manual doesn't explain this. Thanks.

The decibel is a way of representing the relationship between two electrical quantities of the same type and units. For example, you may be comparing two powers, two voltages or two currents.

The meter on the left compares the voltage across the input to the LNA to 1 microvolt (uV). On AM, FM or SW, the radio's antennas are not efficient, and their response is not uniform across any band. The signal strength required to generate 1 uV on one frequency may be much different than that at another frequency. So the meter is not absolutely accurate for comparing signal strengths on different frequencies or bands. You couldn't accurately say, "WGR is 10 dB stronger than WWKB," because they are on opposite ends of the band. Thus, it's called a Relative Signal Strength Indicator (RSSI).

The meter on the right is marked "SN," an abbreviation for "Signal-to-Noise." This is a misnomer, as the proper term is "Signal-plus-Noise-to-Noise." In testing and comparing receivers, this measurement is done as follows: The receiver output is connected to a meter. With no signal applied, the noise output is measured. Then a signal of known strength is applied and the measurement is taken again. The noise measured at first is still present, thus "signal-plus-noise..."

On a PL-380 (and I assume PL-310) where you can adjust the selectivity, for a given signal strength, the SN meter reading should increase as you narrow the bandwidth. Noise is aperiodic; that is, it is random in frequency. You can hear the reduction in noise on an unoccupied channel when you decrease the bandwidth. For a given, constant signal level, reducing noise improves the "SN" result.

If you can increase the signal level without also increasing the noise, or if you use an antenna that, while it may not pick up as much signal as the internal one, reduces noise pickup even more, you can improve the SN number and make the signal easier to hear.

In actual use, however, the meters are not so helpful. That's because they don't respond quickly to changes in signal level. The reason is the need to reduce processor functions that would drain the batteries more quickly, and could increase digital noise radiated into the antenna.

Hope this helps. You can learn more about decibels from Wikipedia. To narrow the bandwidth I skipped over how they are calculated. :)


Jim, KR1S

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