National Interagency Incident Communications Division

May 22, 2012

To: Radio Users

From: Stephen M. Jenkins, Chief, National Interagency Incident 

Communications

Subject: Relm BK EPH/EMH Radio Interstitial Frequency Safety Issue

Issue: The Relm BK EPH/EMH radio will not tune to FCC-issued interstitial 

frequencies in use by state and local agencies. If a technician uses the PC 

programming software to program a channel to an interstitial frequency, that 

channel will contain a random frequency, with no indication that an error occurred 

from either the PC programming software or the EPH/EMH radio. The affected 

radio will appear to function on that channel, but the transmitter and receiver will 

be on the wrong frequency, jeopardizing the safety of the radio user. The only way 

to know that an error occurred is to inspect the radio configuration via front panel 

programming or to read the radio configuration back into the PC programmer. The 

channel that was programmed with an interstitial frequency will have a different 

frequency than the one entered. If a technician attempts to program an interstitial 

frequency via front panel programming the radio will not accept it. If an interstitial 

frequency is cloned into an EPH radio, the radio will program itself to the next 

valid frequency.

Identifying interstitial frequencies: An interstitial frequency is any frequency in 

the FCC public safety band (150 - 162 MHz) that has a five in the fourth decimal 

place. For example 155.7525 is an interstitial; 155.7450 is not. Note that federal 

frequencies (162 to 174 MHz) with a five in the fourth decimal place are not 

interstitial (e.g. 166.6125) and are compatible with the EPH/EMH radio. 

Discussion: The issue of interstitial frequency radio incompatibility was first 

identified in 2007 and information was posted to the National Interagency Fire 

Center (NIFC)/National Interagency Incident Communications Division (NIICD)

NIFC/NIICD Hot Sheet. It was noted in the Hot Sheet that the EPH was incapable 

of tuning to FCC-licensed interstitial frequencies and that interstitial frequency 

assignments would increase over time. The problem with the PC programmer was 

not discussed because it had not yet been identified. It was recommended that 
EPH radios be replaced as soon as budgets allow. The DOI lifecycle replacement 

of portable radios is 7 years and the US Forest Service lifecycle replacement for 

radios is 10 years. Relm/BK states that the last EPH radio was shipped in 1998. 

State and local agencies are completing the FCC-mandated migration to 

narrowband. Consequently, interstitial frequency assignments are

increasing. Since the EPH/EMH cannot be programmed to these frequencies, it 

can no longer be considered an effective tool for interagency wildland fire

communications. Continued use of the EPH/EMH will create problems with 

interoperability, complicate frequency management, and impede mutual aid. 

Outcome: Effective January 1, 2013 the EPH/EMH will be removed from the 

NIFC/NIICD Approved Radio list. Wildland fire contractors who are required to 

provide radios from the NIFC/NIICD Approved Radio list need to plan 

accordingly for the 2013 fire season.

Recommendations:

1. Radio management personnel need to identify any incompatible FCC-licensed 

frequencies being used as part of mutual aid agreements with state and local 

entities and make radio users aware of the limitations of EPH/EMH radios. 

2. Communications unit leaders need to identify on their Incident Radio 

Communications Plan (ICS 205) any incompatible FCC-licensed frequencies being 

used on the incident and make incident radio users aware of the limitations of 

EPH/EMH radios.

3. Ensure EPH/EMH radios are replaced with newer radio models no later than 

January 1, 2013. After this date, only radios which are fully compatible with 

interstitial frequencies will be placed on the NIFC/NIICD Approved Radio list.

Questions concerning this issue can be directed to the Communications Duty 

Officer (208-387-5644) cdo@fs.fed.us.

/s/ STEPHEN M. JENKINS

Chief, NIICD/NIFC