The 900 MHz Radio Shack (model 43-3102, FCC ID
AAO4303102) intercoms are an example of the long range possible.
Several hundred feet range between intercoms is possible with 1 milliwatt RF output and wideband 75 kHz FM modulation.
These intercoms are specified at -109 dBm 20 dB SINAD sensitivity (very good).
However, intercom squelch is set a bit too tight in my opinion from the factory. The CTCSS/PL squelch system uses several of the same frequencies as standard two-way radios. Lowering the squelch threshold allows weaker RF signals to be heard without falsely opening the squelch on static.
Squelch adjustment tradeoffs
For this intercom, the squelch potentiometer makes the squelch “tighter” with counterclockwise turning and “looser” with clockwise turning. On this intercom, when the squelch is open (but with no/incorrect CTCSS) the middle RX LED will flicker once per second. When the squelch is set just tight enough to stop the RX LED from flashing with no incoming RF signal, the RF RX sensitivity is maximum (maximum range).
If the squelch threshold is set too low, there can be occasional bursts of static (CTCSS false decode). Also, for battery operated intercoms, the battery consumption will be higher if the squelch is always open as it’s trying to find the CTCSS tone constantly, kicking the receiver into full power drain.