What's going on in the 900MHz band?

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by KE7IZL, Aug 8, 2019.

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  1. KE7IZL

    KE7IZL Ham Member QRZ Page

    I live in Seattle, and something weird is happening in the 33cm UHF ham band. The entire band is filled with very short pulses (10th of a second or less) of what look like FSK modulated signals (when viewed with a spectrogram). They are not all using the same tone separation. Some of the FSK pulses have up to 100kHz between the mark and space tones. It's like the entire band is fille with some kind of frequency hopping spread spectrum signal, where it's an FSK signal being hopped, and not only is the transmission frequency being hopped, but so is the separation between the mark and space tones. I'm using my AirSpy SDR to tune around, and it appears that this FHSS FSK signal fills the entire 33cm band.

    Anybody know what the name of this signal type is? It's certainly not standard RTTY.
  2. N5RFX

    N5RFX Ham Member QRZ Page

    It is most likely frequency hopping spread spectrum from utility meters in your area communicating.

    Mark N5RFX
  3. W6RZ

    W6RZ Premium Subscriber QRZ Page

    Correct. Here's what it looks like in Silicon Valley with just an indoor antenna.

  4. KE7IZL

    KE7IZL Ham Member QRZ Page

    Cool. Thanks for the info.

    I wonder if they are actually hopping, or if it's just many different meters communicating, maybe transmitting once every minute or so, but so many of them (each with a slightly different timing) that it seems like one transmitter hopping around. What kind of made me wonder is there tend to be a wide variety of different frequency separations between the mark/space tones. Usually FHSS just hops the transmit frequency, not other parameters of the signal. So it could be multiple systems in use nearby, each with slightly different signal parameters (such as baud rate and mark/space tone separation).

    And something else I wonder is this. Does the electric company have a ham radio license? This is clearly a ham radio band. Why not use an ISM band (such as the 433/434 MHz band) instead for this purpose? Wireless outdoor thermometers and other low power RF devices use this ISM band quite frequently. It seems they are just wasting ham-band by transmitting where they are now. And if the electric company doesn't have a license to transmit here, they are braking the law.
  5. KK6YAE

    KK6YAE Ham Member QRZ Page

    900 mhz is ISM in the US. Those could be LoRa signals from IOT devices
  6. K7JEM

    K7JEM Ham Member QRZ Page

    The 900 MHz band is a shared band. It has been ISM much longer than it has been a ham band.
  7. KE7IZL

    KE7IZL Ham Member QRZ Page

    Most wireless outdoor thermometers that and other similar devices I've seen transmit in the 433/434 band, even in the US (and I'm not talking about US customers buying cheap foreign ones on eBay that work according to the ISM band plan of whatever country they were made in). So there's both a 900MHz ISM band and 433/434MHz ISM band in the US? Or only 900MHz ISM band (such that ISM devices using the 433/434MHz band in the US are actually violating the law)?
  8. KK6YAE

    KK6YAE Ham Member QRZ Page

    433 mhz is ISM in US too *edit*
  9. K7JEM

    K7JEM Ham Member QRZ Page

    Both the 420 and 900 MHz bands are "shared" in the USA with other services. In some parts of the USA, part 90 LMR is used in the 420-430MHz area.
  10. N5RFX

    N5RFX Ham Member QRZ Page

    Yes many meters can communicate at the same time. Look your electric meter nameplate, you might get a clue as to what type of system it is. In Seattle I would guess Itron.

    Mark N5RFX

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