There are several reasons behind this. The primary reason being that most amateur repeaters in this band are built from commercial equipment that has been modified to transmit and receive in the amateur 33 centimeter band and modification complexity increases rapidly as target frequencies are moved further from the original design frequencies. A 25 MHz split results in frequencies fairly close to the original frequencies this commercial equipment was designed for resulting in relatively simple modifications. As well, spectrum analyzer tests consistently show the noise floor to be considerably higher near the center of the band due to other non-amateur services making the quieter frequencies near the band limits more desirable . Finally, the 12 MHz split requires high quality and more expensive duplexer devices to isolate the repeater receiver from the repeater transmitter when sharing a single antenna (as most repeaters do) whereas the 25 MHz split provides sufficient frequency separation such that separate antenna for transmit and receive with 20 feet or more of vertical separation often works well and eliminates the need for expensive duplexers as long as the repeater transmitter is limited to 15 to 20 watts of output power. With the explosion in popularity of Nextel phones with a push to talk feature, the marketplace has seen a flood of newer 800 and 900 MHz commercial mobile radios that are designed to the following specifications: 800 MHz Radios: Transmit: 806 - 821 MHz and 851 - 870 MHz Receive: 851 - 870 MHz 900 MHz Radios: Transmit: 896 - 902 MHz and 935 - 941 MHz Receive: 935 - 941 MHz The receivers on many of these modern 800 MHz radios can be easily modified to receive higher than 870 MHz, to about 904 MHz with good sensitivity. In addition, the transmitters on many of the aforementioned 900 MHz radios can be easily modified to transmit lower than 935 MHz, to about 926 MHz with acceptable power output. With this in mind, many amateurs have opted to set up repeaters with -25 MHz splits using modified 800 MHz radios as receivers and modified 900 MHz radios as transmitters. A number of resources are available for amateurs to build repeaters that can be used on the 33 cm band. Resources are also available via several e-mail discussion groups (such as the Yahoo Groups: "AR902MHz" and "900mhz") where information regarding conversion of other brands commonly used (such