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900 MHz FM -- what deviation steps to use?

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by K3RW, Apr 26, 2020.

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  1. K3RW

    K3RW Ham Member QRZ Page

    I have an Alinco G-29T and the RT Systems programming cable and software. I can do queries from it and see Repeater databases. At least so far it appears the usual value for deviation on repeaters is 5. Though I understand in different regions the deviation may be something different, and may even use nbFM for some repeater pairs. Problem here is knowing which is which, and that's not always clear. Repeaters here seem to use a deviation of 5.

    But for simplex 927, this radio can do nbFM and FM. If I understand nbFM on 33cm, it is reportedly a deviation of 2.5, not 5. But the radio itself (per the manual) only has steps from 5 and above. Even the software won't let me put in a lesser value than 5. And on 903.2, this is supposedly not the nbFM part, so it gets a deviation of 5... am I on the right track?

    So what I have thus far is a conundrum with 927.5--where I'd like to hit people simplex in VHF contests, SOTA, etc. Should this be nbFM with a deviation of 5, or 'regular' FM with a deviation of 5? Is there a problem that the deviation might be expected as 2.5, but I can't do the radio at that value?
  2. W6KCS

    W6KCS Ham Member QRZ Page

    It sounds like you're confusing frequency stepping values in VFO mode with the deviation setting (actually the modulation bandwidth setting that affects both the transmitter and the receiver). For frequency steps, try 12.5 KHz since that's how far apart the channels are. You might need to dial in an even frequency like 902.0000 before you make the selection, for the numbers to be correct as you step through the channels.

    For deviation, you need to be setting narrowband "NFM" or regular "FM". See page 52 of the manual.

    In Northern CA virtually all of the repeaters are narrow (+/- 2.5 KHz) deviation. I'm not sure about what people are using for simplex but I assume it's also narrowband since almost everyone uses surplus gear that is narrowband anyway.
    Last edited: Apr 26, 2020
    KB0MNM and K3RW like this.
  3. K6CLS

    K6CLS Ham Member QRZ Page

    ... it is narrow FM in norther n CA. tripped me up a few times. had my Alinco DJ-G29 set to wide FM, couldn't hear anyone...

    that said, it seems 900MHz FM conventions are regional. What's the calling frequency? What's the repeater offset? Wide or narrow FM? All that changes depending on local noise etc.
    K3RW likes this.
  4. K3RW

    K3RW Ham Member QRZ Page

    Ok--that makes sense. Its the way RT Systems shows it in their software, to make me think 'step' doesn't mean 'tuning step' but rather 'deviation'. It does appear that switching to FM Narrow also switches the deviation to 2.5, whether that is visible in the programming or not.


    Its where it says "Step" on the far right that I think I'm getting confused--tuning step vs deviation. Seems redundant to need a 'tuning step' in the memory.

    Per the manual it appears that FM is a default deviation of 5kHz, and FM narrow is by default 2.5kHz, so that's that. So for this software, I should have 000-8 and 000-9 correct, since those are our local simplex calling frequencies, and FM narrow is only at 927, and 903 is for the regular FM transverter crowd.

    As for my TK-981, if I understand this correctly, since it is a converted 900 rig, then it should only be running narrowband FM, on simplex and even to its repeater pairs. I can hit most of these repeaters on the 981 (15w and a yagi), but I can only hit one with the G29 (on 'regular' FM)--so it may be that some or all of the repeaters above are FM narrow. That's not data I have seen in the repeater directories, so I'll have to experiment and see. It may be some repeaters can deal with the deviation and others can't.
  5. KA9JLM

    KA9JLM Ham Member QRZ Page

    Most all analog FM amateur radio repeaters are still wide band. And you will sound a lot better transmitting wide.

    As for some modified radios, Some may be narrow band only. Using these on a wide band repeater, Your audio will be cut in half and sound very low.

    Using narrow on a wide band repeater can make your receiver audio cut out, Because the repeater goes out of your limited Passband.

    Wide FM works very well, And I am glad that the FCC still allows us to use it. :)

    Have Fun.
    K3RW likes this.
  6. ND5Y

    ND5Y Ham Member QRZ Page

    Some radios allow you to manually tune the frequency up and down from a memory channel (in a VFO-like mode).
    A band (or sub band) could need different VFO tuning steps.
    That's why you need tuning steps in memory channels in some cases.
    K3RW likes this.
  7. W6KCS

    W6KCS Ham Member QRZ Page

    Do you also mean on 900? Northern CA 900 is almost all narrowband, but I don't know about elsewhere.
  8. AI3V

    AI3V Ham Member QRZ Page

    Explain again why you can't hear 2.5khz deviation transmissions when your receiver is set to 5khz.

  9. W6KCS

    W6KCS Ham Member QRZ Page

    You have it backwards. A narrowband signal received on a wideband receiver will be heard, but the detected audio will be slightly lower. Conversely, a wideband signal on a narrowband receiver may have voice peaks lost because of the reduced IF bandwidth.

    So, as KA9JLM pointed out, if the repeater transmitter is wideband and your portable's receiver is narrowband, the portable's receiver may squelch on voice peaks.

    What you need to remember is that setting a radio for narrowband not only reduces the TX deviation, it also selects a narrower IF filter.
    Last edited: Apr 27, 2020
  10. AI3V

    AI3V Ham Member QRZ Page

    Recall you posted that you had your rx set to 5khz...


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