27.975 MHz FM 27975 kHz FM Asian Fishing Fleet Fishery Radio Chatter 25 May 2023

[R4002]

Via UK based SDR.

27975 kHz FM 27.9750 FM [CSQ] 27.975MHz FM 27.975 MHz FM Asian fishermen radio chatter 1130 UTC May 25 2023. 
Fishing trawler radio chatter 27.750 MHz 27.75MHz 27.975MHz 27,975 27,750.  27.500 MHz FM 39.500 MHz FM.  Channel 20 frequency 27.9750 FM

SIO 222 to SIO 333, some dramatic fading.  Asian fishing radio fleet radio network 27.500 MHz - 39.475 MHz FM.  Often listed as 27.5MHz - 39.5MHz or 27.500 MHz - 39.500 MHz.  25 kHz spacing.  Fully channelized.  25 watt transmit power, 16K0F3E / 16K0G3E voice emission, 300 baud or 1200 baud AFSK / MFSK data transmission - 16K0F1D 16K0G1D emissions 16K0F2D / 16K0G2D GPS location ship to ship individual vessel call.  Channel 1 is 27.500MHz, channel 2 is 27.525MHz, channel 3 is 27.550MHz, channel 4 is 27.575MHz, channel 6 is 27.600MHz and so on. 

System is carrier squelch only, single frequency simplex.  No PL/DPL (CTCSS/DCS) tone squelch in use.  Just regular old simplex FM with carrier squelch, although the data based selective calling is apparently heavily used for individual vessel call and receiver muting (similar to the HF SSB SELCAL system, apparently). 

Lots of activity in the 29 MHz band, 30 MHz band, 31 MHz band...but now they're also showing up in 27 MHz.  Logged similar activity on 27.750 MHz FM (with pager POCSAG QRM, UK FM CB radio QRM 27.75125 MHz FM and SSB freeband CBer QRM).  Russian taxi dispatcher land mobile radio QRM.  Minor UK FM CB QRM from 27.97125 MHz FM as well.