VHF Interoperability Channel Naming
Wednesday, March 30, 2011 | Comments
By John S. Powell
The first documented use of interoperability channels is in the early 1960s shortly after the two-channel, VHF FM mobile radio was first marketed. Art McDole, long-time Northern California Association of Public-Safety Communications Officials (APCO) International frequency advisor and communications director for Monterey County, Calif., saw a dramatic increase in requests for secondary VHF frequencies by law-enforcement agencies coupled with a lack of interoperability. Working through what was then the California Disaster Office (CDO), the state of California licensed the state agency-only frequency 154.92 MHz for what became known as the California Law Enforcement Mutual Aid Radio System (CLEMARS).
The VHF channel is still widely known by CLEMARS even though the name was recently updated to follow the intrastate version of the American National Standards Institute (ANSI) channel naming standard, and with expansion to other bands, a dozen CLEMARS channels are used across California. The fact that this was a simplex channel enhanced its usability because its limited range made it incident specific. Pairing with any other VHF channel for repeater use would have left it unusable whenever the other channel was located adjacent to an incumbent VHF channel because the FCC doesn’t formally pair channels in that band. Currently, channels in the UHF, 700 and 800 MHz bands are all paired by FCC rule, allowing the use of tactical repeaters with relative ease. Unfortunately, this lack of pairing left the VHF band without any designated repeater channels for interoperability. With VHF continuing nationally to be the most heavily used band for public-safety communications, the need for standardized repeater pairs to provide wider coverage is a significant requirement.
In April 2010, work began independently in Minnesota and Texas to pair existing FCC Part 90 national VHF interoperability channels for use in on-scene tactical repeaters. Formal proposals were developed and discussed within Minnesota’s Allied Radio Matrix for Emergency Response (ARMER) group and Federal Emergency Management Agency (FEMA) region VI’s regional emergency communications coordination working group (RECCWG), with coordination through the Department of Homeland Security (DHS) Office of Emergency Communications (OEC) by its regional coordinators and Ross Merlin, author of the national interoperability field operations guide (NIFOG) at DHS/OEC headquarters. A formal proposal subsequently was submitted by the state of Texas to the National Public Safety Telecommunications Council’s (NPSTC’s) interoperability committee for consideration as an addition to the ANSI Naming Standard (APCO/NPSTC ANS 1.104.1-2010: Standard Channel Nomenclature for the Public Safety Interoperability Channel).
ANS 1.104.1-2010, initially approved by ANSI June 9, 2010, contains two parts. The normative part describes the formula and supporting logic used to implement the standard, and the informative part lists the application of the formulas to existing FCC-designated Part 90 nationwide interoperability channels in the form of tables listed in channel name and frequency order. Changes to the normative part of the standard require a full re-vetting of the standard, while updates to the tables — without changing the formula — are considered minor and can be made without a full re-vetting of the standard. Thus, it was desirable to implement these changes by only addressing the names themselves using the existing formula.
The proposal from Texas was designed to pair the existing VHF general use tactical channels (VTAC11 to VTAC14) to provide maximum separation between receive and transmit (RX/TX) frequencies for ease of implementation. The proposal strictly addressed transportable repeaters with low transmit power (typically 20 watts output or less) designed for on-scene use in support of an incident, either emergent or planned. Three pairs were identified with RX/TX separations greater than 4.25 megahertz that could, using high-quality receivers and transmitters, be implemented without requiring a duplexer if antennas were properly located. In fact, this implementation could be accomplished using an interconnect net on an audio bridging device or gateways that are considered standard equipment in most mobile communications vehicles (MCVs) with proper adjustments and antenna placement.
In examining the Texas proposal from a nationwide perspective, it was determined that none of the proposed pairs were usable in Puerto Rico (PR) and the U.S. Virgin Islands (USVI). If these pairs were to be truly nationwide, at least one of them needed to be usable in the Caribbean.
Texas officials initially expressed a need for two statewide interoperability channel pairs. Follow-on discussions were subsequently held by NPSTC with VHF stakeholders in other states, including California, Minnesota, Montana, Nebraska, Nevada, Oklahoma, Wisconsin and Wyoming, with consensus quickly reached. Although too late to include in the initial publication of the APCO/ANSI/NPSTC channel naming standard, a best practice determined by appropriate stakeholder representatives could be given national exposure in the upcoming 2011 revision of the NIFOG and then submitted to ANSI as the first revision to the naming standard.
An unofficial opinion from key personnel in the FCC’s Public Safety and Homeland Security Bureau (PSHSB) indicated that the use of these channels in a repeated mode at temporary sites (temporary mobile relay, FCC station class FB2T) wasn’t prohibited by current Part 90 rules and regulations. While there appears to be no FCC restriction on licensing of these interoperability channels at fixed sites (FCC station class FB or FB2), such use could be problematic, particularly with the potential for high-power base/repeater stations — 60 watts or more, often at high elevations above average terrain — causing interference to on-scene users of these tactical channels across a wide area. The intent for tactical repeater use within the local/state public-safety practitioner community was solely for low-power use at 20 watts output or less for incident-based deployable systems, and then only as designated by an incident’s communications unit leader (COML) or incident commander on that incident’s radio communications plan ICS Form 205.
As designed, these new names would be additions to the ANS 1.104.1-2010 name tables and a minor change to the standard not requiring a lengthy public comment period. In selecting the recommended pairs, the following points were considered:
1. Which frequencies to pair, frequency separation and PR/USVI restrictions;
2. Continuous tone-coded subaudible squelch (CTCSS) use; and
3. Operating practices
• Primary and secondary pair
• Shared use and priority
After considerable deliberation by NPSTC’s interoperability committee with public-safety communications practitioners across the United States, the following proposal was presented to the NPSTC governing board at its June 15, 2010, meeting:
1. Available pairings — low-in/high-out for repeaters, and shown as subscriber radio TX/RX pairing were:
• VTAC11/VTAC14 — 151.1375/159.4725 — this pairing has the maximum separation possible for the VTAC channels: 8.335 megahertz
• VTAC12/VTAC13 — 154.4525/158.7375 — separation is 4.285 megahertz
• VTAC11/VTAC13 — 151.1375/158.7375 — separation is 7.6 megahertz
• VTAC12/VTAC14 — 154.4525/159.4725 — separation is 5.02 megahertz
• VTAC13/VTAC14 — 158.7375/159.4725 — separation is 0.735 megahertz — duplexer required, but usable in PR/USVI
2. Available names for VHF tactical repeater channels:
•VTAC15, VTAC16, VTAC18 and VTAC19 were considered. However, with hope for the future addition of national VHF channels (including designating 155.1600 MHz for national SAR), these were kept in reserve.
• VTAC33 to VTAC38 were also available. Because selected pairs can be operated either way (repeater low-in/high-out or high-in/low-out), both are provided.
3. Final name proposal. NPSTC proposed the following six pairings and associated names:
Name                    Pair (subscriber RX/TX)
VTAC33 = VTAC14/VTAC11 separation 8.335 megahertz
VTAC34 = VTAC13/VTAC12 separation 4.285 megahertz
VTAC35 = VTAC14/VTAC13 separation 0.735 megahertz (for PR/USVI only)
With many parts of the country following the federal standard of high-in/low-out for repeaters, the following pairing was also proposed to support co-siting these channels with federal users: 
Name                    Pair (subscriber RX/TX)
VTAC36 = VTAC11/VTAC14 separation 8.335 megahertz
VTAC37 = VTAC12/VTAC13 separation 4.285 megahertz
VTAC38 = VTAC13/VTAC14 separation 0.735 megahertz (for PR/USVI only)
Because channel resources within subscriber radios are often limited, NPSTC recommended that the primary frequencies for tactical repeaters be VTAC36, VTAC37 and VTAC38 for two reasons:
• A preferred national standard for deciding which channel pair sets to use is highly desirable, as is following the federal standard for high-in/low-out, and 
• The direct or simplex mode for these pairings — transmitting on the repeater output — are VTAC11, VTAC12 and VTAC13 respectively. For subscriber radios using a button to select repeat or direct mode (if CTCSS and channel names on the radio display can be appropriately programmed) this configuration relieves the requirement to dedicate three added channel slots to support both direct and repeated modes, an important consideration for radios with limited capacity.
4. CTCSS recommendation. To provide for controlled repeater access, and to keep two repeaters within range of each other, but paired oppositely (such as one on VTAC33 and the other on VTAC36) from locking up, the following tone recommendation was made:
• CTCSS 136.5 hertz on repeater input, CSQ on repeater output.
5. Operational use.
• To preserve simplex channel availability, designate a primary and secondary repeater pair. For example, if one transportable repeater is used, it should be on VTAC36 (VTAC11/VTAC14 paired). If a second is needed, it should be on VTAC37 (VTAC12/VTAC13 paired) with the understanding that there would remain no available simplex VTAC channels. VTAC13 and/or VTAC14 could be used as talk around in either or both use cases, at the risk of being interfered with by repeater users who can’t hear the talk-around transmissions.
• VTAC35/38 (VTAC13/VTAC14 paired) should be used as a repeater pair only in PR/USVI where VTAC11 and VTAC12 are unavailable.
• Repeater use should have no priority over simplex use of the involved channel(s).
• It is strongly recommended that tactical repeaters be activated only when called for by a COML as documented on an ICS Form 205 for an incident.
The NPSTC governing board approved this proposal June 15 with an added 45 days of public comment before the report was to be submitted to APCO’s Standards Development Committee (SDC) for adding to the standard. During the 45-day period, only positive comments on the proposal were received and the completed proposal, including modifications to the APCO/NPSTC ANS 1.104.1-2010 tables, was transmitted to APCO’s SDC Aug. 2.
The proposal was considered by APCO’s SDC and approved Nov. 19. It’s pending reformatting and submittal to ANSI as Revision 1 to the published standard. The final recommendations and tables have been included in the recently released revision of the NIFOG and by several states in revisions to their own communications field operations guides (FOGs).
Editor’s Note: This is the expanded version of the April 2011 “Spectrum Monitor” column on Page 10 of MissionCritical Communications.

John S. Powell is chair of the National Public Safety Telecommunications Council (NPSTC) Interoperability Committee. E-mail comments to editor@RRMediaGroup.com

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