Extreme Radio Services operate on the 902-928 MHz ISM (Industrial, Scientific, Medical) band. It is actually a service mark for a specific walkie talkie that was manufactured by Trisquare, which operated in a similar manner to other handheld radios using frequency-hopping, spread-spectrum technology, but in order to price their product competitively, it wasn’t assembled in a robust housing. This led to premature failure, and eventually the company went out of business.
The 902-928 MHz band is used for a variety of devices, including computer access points. This makes the band far too noisy for analog FM communications, but the nature of frequency-hopping, spread-spectrum technology overcomes noisy environments, and enables private conversations because the signal moves throughout the band according to a discrete algorithm.
Because of the shorter wavelength, the 902-928 MHz band is ideal for cuise ship applications. The signals have a tendency to reflect against walls and pass through small apertures. This means the radios provide communication where others fail to do so.
Another advantage of the license-free 902-928 MHz band is that it is authorized throughout Region 2, which includes the Americas, Caribbean, and some Eastern Pacific islands. This means it can legally be used in the United States, on the cruise ship, and in foreign ports.
Although Sprint decommissioned the Nextel cellular network in 2013, many of the phones are still usable in the Direct Talk mode. Unlike Direct Connect, which requires the network for operation, Direct Talk can be used to communicate between two (or more) phones directly, using the 902-928 MHz unlicensed ISM band. Nextel introduced this mode in 2004, to help alleviate the problem of their subscribers being unable to communicate with each other at jobsites which were outside the coverage area of their network.
As mentioned previously, shorter-wavelength transmissions have greater penetration in confined spaces, because the signals can move through smaller apertures, and reflect when striking metal surfaces. For these reasons, eXRS is well-suited for personal communication on cruise ships.
When Nextel ceased operations. a huge number of their phones found their way to the used, surplus market. They can be found on eBay and other marketing websites at discounted prices. The following is a list of specific Nextel phones which support the Direct Talk feature:
| ic402 | ic502 | ic602 |
| ic902 | i275 | i315 |
| i325 | i335 | i355 |
| i365 | i425 | i560 |
| i570 | i580 | i615 |
| i670 | i760 | i776 |
| i850 | i870 | i880 |
This list has been sourced from others who have successfully used the Nextel Direct Talk feature, and is believed to be accurate. However, you should always verify that this function operates with the model prior to purchase. Also, a Nextel SIM card must be installed in order for the feature to work as it contains the identification data necessary for the phones to communicate with each other.
Another option for unlicensed communication on the 902-928 MHz band is Motorola’s DLR and DTR handheld radios. Although these are designed for the business and commercial market, they can be found on the used on eBay for a reasonable price.
Although they are also manufactured and designed by Motorola, and use the same frequency-hopping, spread-spectrum scheme in the same wireless band, they are incompatible with the Nextel Direct Talk feature since they use different software.