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NBFM--what rigs work, and what bands?

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by K3RW, Sep 8, 2019.

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  1. K3RW

    K3RW Ham Member QRZ Page

    Read a couple of guys on the PNW boards discussing NBFM equipment for 900 MHz. I've got several repeaters nearby, and if I could program my KW rig I'd be on them. But as I understand it, that's not a NBFM rig (TK-941).

    Apparently the Alinco G29 handheld (that now sells for more used than it did new!!) was capable of 900 FM and NBFM. I'll admit I'm new to the concept of NBFM and not familiar where it is used and what the implications are. Not sure if NBFM folks can receive a wideband signal, for example, or if they can be received on a wideband radio. That's where I get lost.

    Other than this white whale of an Alinco HT, what other equipment for 900 is capable of NBFM? Is this just a 900MHz thing for amateurs, and not an issue on say 23cm and above?

    I've got the bug to run a 33cm transverter to pick up some of the 902/3 crowd on SSB and maybe try to catch them on FM on the low side--though I am not sure if my FT-817, IC-7100, or IC706MKIIGs (as IF radios for the transverter) are capable of NBFM. I may just splurge and get a 30w Motorola and just run that for FM simplex on 927.

    Sort of related...

    I'm guessing that 927 FM simplex is dedicated to 'regular FM' and the lower 902/3ish FM is for the narrowband FM?

    And finally, is any of the commercial-convertable stuff (KW, Motorola, etc.) NBFM?
  2. K7JEM

    K7JEM Ham Member QRZ Page

    About 30 years ago, the 900MHz commercial LMR band was established, it covered 896-902 and 935-941 Mhz primarily as a trunking repeater band, due to the fact that the 800MHz LMR band was filling up fast, especially in metro areas. Since this band was new, the FCC decided that radios operating there would be what you call NBFM (but reality is that all of the FM used by amateurs is NBFM). It consists of transmitters that have deviation set to 2.5KHz maximum, instead of the 5KHz max that all of the other LMR services were using at that time.

    Since these radios were coming available as surplus, hams that wanted to set up repeaters in the 900MHz band decided to use that narrow FM, to remain compatible. Thus, any commercial 900MHz radio designed for that band, is already narrow capable, and probably only has narrow band mode anyway. A wide RX can hear a narrow TX just fine, you just have to crank up the volume somewhat to compensate for only half of the deviation being available. A narrow RX will hear a wide TX fairly well, sometimes there will be some distortion, but it pretty much works. Have the guy TXing back off the mic a little, if it is a problem.

    If you want to use a wide radio on narrow, just reduce the deviation, by whatever method is available to do that. The PL tones on narrow usually run 400-500 Hz of deviation, on wide they are usually 600-750 Hz of deviation, but either one will work to the other, since most RX's, either narrow or wide, will respond to 200+ hz of deviation.
    K3RW likes this.

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