Thermal Floor (Boltzmann noise, et al) for 1,000 Hertz bandwith is
-174dBm + 30 dB = -144dBm
What the voltage level, across 50 ohms from a standard RF interface, for -144 dBm?
Given 0dBm across 50 ohms is 0.632 volts peakpeak, and -120 dBm is down by 1,000,000 to 0.632 microVolts PP, and -140 dBm is down to 0.0632 uV (or 63 nanoVolts), the extra 4 dB drops the level another factor of 2.5X to 25 nanoVolts PP
Summary: the input signal, for 1,000 Hertz bandwidth signal at 0dB SignalNoiseRatio, is 25 nanoVolts PeakPeak.
Thus some amplification, at RF or in an active-mixer or in the Intermediate Frequency filtering stages, occurs prior to feeding the 14-bit ADC.
Or some signal-processing methods are used. Read on.
If you use a transformer to stepup the signal, converting from 50 ohms to 5,000 ohms impedance and then BUFFER (Unity Voltage Gain) to feed the ADC, you'll have 10X higher voltage or 250 nanoVolts into the ADC.
Still a factor of 40 too low.
You can dither the ADC sample amplitudes (random noise is one ditherer). Then post-process digitally, collapsing the samples from 100,000,000 per second (for example) down to 100,000 per second and pick up a factor of SQRT (1,000) = 31X improvement, which is getting close to the factor of 40x.
[by the way, this averaging, this collapsing of frequency from 100,000,000 to 100,000, is exactly what a MIXER does, in downconverting to a much lower IF frequency.]
Note the original energy level of -144 dBm produces ZERO dB SNR; assume you want 10 dB SNR, which raises the voltages by sqrt(10) or 3.1X, requiring -134 dBm from the Antenna.
Now..... is this what iCOM 7300 uses? You have some of the fundamental limits to muse over.