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
The construction requirements for SMRs in the 220, 800, and 900MHz band across the 1990s and 2000s led to some interesting scenarios. One that I saw in the Lansing, Michigan area in the late 1990s was an 800 MHz 5 channel LTR system that used 5 Realistic analog scanning receivers set to a single frequency each, with 5 EF Johnson 8600-series mobile radios set to talkaround on the repeater output frequency. The scanners and mobile were each wired to an LTR controller panel to make a functioning trunked repeater system. This actually worked, but was certainly not to the RF performance of a dedicated repeater design. This was done after the SMR licensee lost 5 of their original 10 channel license due to failure to meet construction requirements.
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.