ACSSB and 220 MHz two-way radio
The 220 MHz ACSSB two-way radio system in the USA was a remarkable last gasp of analog technology trailing off as DMR, NXDN, P25, and other digital modes began to dominate the land-mobile radio landscape. ACSSB squeezed into 5 kHz channel spacing in contrast to the 12.5 - 25 kHz common for two-way radio FM channels. Digital two-way radio modes achieve 6.25 kHz effective channel spacing via TDMA (DMR, P25 Phase II) or FDMA (NXDN). A vital contemporary use of 220 MHz band is for data telemetry (e.g. SCADA via GE Vernova / MDS radios) and Positive Train Control (PTC).
Technical deep dive links:
- 220 MHz ACSSB system design manual fascinating with good LTR and conventional system design info applicable to common radio systems.
- 220 MHz assignment map
- SEA ESP-1000 repeater manual
- SEA equipment brochure
- SEA ESP504 test procedure
- hacking SEA ESP-504 to plain SSB
- ACSSB standards
- Manufacturers of ACSSB radios said to include: Securicor / Intek, Linear Modulation Technology, Inc., SEA, Uniden.
- FCC test procedure for LMP4213 ACSSB radio
- Cornerstone SMR document index
- While many UHF intercoms (e.g. RTS BTR-800) use wideband (40 kHz deviation) FM, there is a design house that made ACSSB intercoms for nuclear power plants due to the uniquely severe multipath and RF environment
- Political analysis on FCC spectrum auctions including 220 MHz band
An attempt to provide a 220 MHz LTR-Net system and data telemetry network across 80% of the continental USA and 2/3 of the population was made by Cornerstone SMR, who was one of the 220 MHz auction 72 winners, but adoption stalled and Cornerstone SMR was denied a waiver on their 220 MHz license construction requirements in 2018. Cornerstone SMR aimed to raise about $5 million in 2003-2004 from investors to build out the wide-area 220 MHz LTR-Net network. Civil theft litigation due to an employee stealing nearly $500k led to an appeal ending in 2015 (Cornerstone SMR, Inc. v. Bank of Am., N.A. , 163 So. 3d 565, 568 (Fla. 4th DCA 2015)) and set a precedent in Florida case law. Cornerstone SMR’s idea to use their 220 MHz spectrum for a nationwide IoT network and proposed business merger to make innovative IoT hardware ultimately led to litigation filed in Delaware in Sept. 2025.