- --ICOM M506

--Standard Horizon GX5500

--SAILOR 6216

We will start with the ICOM and the Standard-Horizon. Here are the manufacturer's specified receiver sensitivity data:

ICOM M-506

Sensitivity (at 12dB SINAD) 0.22µV typical

Standard-Horizon GX5500

Sensitivity

20 dB Quieting = 0.35 μV

12 dB SINAD = 0.30 μV

Squelch Sensitivity (Threshold) = 0.13 μV

We compare at the common specification, input signal to give 12-dB signal to noise and distortion ratio. This is easy because both use the same unit of measurement, microvolts at the 50-Ohm antenna input. The results is that ICOM rates their receiver to be 0.08-microVolts more sensitive, but qualifies that as "typically." The difference in sensitivity looks small. Now let's look at the difference in signal power. First we convert the two signals to be in dBm.

ICOM = 0.22 microVolt

ICOM = 20 LOG Eµ - 107

ICOM = 20 LOG (0.22) - 107

ICOM = -120.1515 dBm

SH = 0.3 microvolt

SH = ICOM = 20 LOG Eµ - 107

SH = ICOM = 20 LOG (0.3) - 107

SH = -117.4576 dBm

The difference in signal power for same sensitivity is (-117.4576 dBm -[-120.1515 dBm]) or 2.69 dBm in favor of the ICOM. That is more impressive that I thought it would be with only a 0.08-microVolt difference in sensitivity.

In order to appreciate a 0.08-microVolt or 2.69 dB difference in sensitivity, the desired signal would have to be just at the threshold of being detected. That means the squelch circuit would have to be backed off to no-squelch and the signal was just barely above the noise floor. I don't know where you can get signals like that to perform tests, unless you have a signal generator. You don't get signals like that by randoming tuning around the marine band.

The Standard-Horizon specifications are more informative. They show that with an increase in signal to 0.35-microVolt the recovered modulation will have a very nice 20 dB SINAD--that means the recovered signal is 100-time stronger than the noise.

ICOM does not give us any data on how fast its receiver quiets down with increasing signal strength.

Now let's throw the SAILOR radio into the comparison. For their 6216 radio the sensitivity is rated as:

Receiver Sensitivity < -119dBm Typically @ 20dB SINAD CCITT Weighted

First, we see the SAILOR is rated at a 20-dB SINAD. Whoa--we must keep that in mind, as we are getting a much better signal-to-noise output than with the other two sensitivity ratings at only 12-dB SINAD. And we have to convert dBm to microvolts at 50-Ohms; that's not too hard. The relationship is

microVolts = 10^(dBm +107)/20

microVolts = 10^(-119 +107)/20

microvolts = 10^-0.6

microvolts = 0.25

Heya--that is a rated sensitivity of 0.25-microVolt for a 20-dB SINAD, so that is actually better than both the ICOM and the Standard-Horizon. However, the SAILOR radio probably costs more than either the ICOM or the Standard-Horizon.

ASIDE: for the math behind the conversion of dBm to microvolts, see my derivation at

http://continuouswave.com/whaler/reference/dBm.html

ASIDE: you can also compare the sensitivity in dB using the two voltages. The power ratio in dB for two voltages is

dB = 10 log (V1/V2)^2

For 0.3 and 0.22 microvolts, that works out to

dB = 10 log (0.3/0.22)^2

dB = 20 log (1.3636)

dB = 2.69