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repeaters, gap between frequencies?

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by K6XRA, May 5, 2019.

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  1. K6XRA

    K6XRA Ham Member QRZ Page

    Is there a standard for repeaters, as to how far apart in frequency they should be?
    I just found that there are two near me, one at 447.640 Mhz and another at 447.620 Mhz. And with my cheap radio, the one at 447.620 will annoyingly break the squelch when I am listening a 447.640, although all you near is noise. This is in San Diego if you want to take a listen.
  2. ND5Y

    ND5Y Ham Member QRZ Page

    I think the standard repeater channel spacing in most of CA is 20 kHz (0.020 MHz) on 70 cm.
    What kind of radio is the problem occurring on?
    You should not have desense unless you are really close to one of the repeaters.
  3. KS2G

    KS2G Subscriber QRZ Page

    [QUOTE="K6XRA, post: 5056160, member: 912454] ...And with my cheap radio...


    As ND5Y posted, standard channel spacing in southern California is 20 kHz.

    Southern California Repeater and Remote Base Association 440-450 MHz Band Plan

    AI7PM likes this.
  4. K6XRA

    K6XRA Ham Member QRZ Page


    Yup, could be that, it was my first guess, but as a new ham I wasn't sure how much selectivity the radio should have.
    But now it isn't happening... so I'm not sure what is up.
    Thanks for the pint to the band plan. I know they show the open frequencies 20Khz apart, but I don't know how much physical distance they would require, if any, between repeaters that close in frequency. The repeater at 447.620 looks to be private and isn't on the bandplan of the scrrba... so...
    AI7PM likes this.
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    "Zero" separation distance geographically is required.

    Lots of repeaters are simply on the local mountaintops, so they're really all in the same place.

    Close to Sandy Eggo, that's likely to be Palomar Mtn. A bit farther north into OC, Santiago Peak. A bit farther north into L.A., Mt. Wilson or Mt. Disappointment (almost the same place). Etc.

    No authority determines where they're located and almost every hilltop has half a dozen amateur repeater systems...some more than that.
    Last edited: May 5, 2019
  6. K6XRA

    K6XRA Ham Member QRZ Page

    I guess I mean, is it typical to put to repeaters within 10 miles of each other 20Khz apart?
    At least in my VERY LIMITED experience, they are usually further apart than that. Of course if they are far apart, they are even placed on exactly the same frequency.

    But, I don't think it is selectivity from a nearby channel anymore. My nice Kenwood is picking up the noise too... I think there was just a lot of traffic on the other repeater and I was mistaken that it was simultaneous and thus the problem.
  7. ND5Y

    ND5Y Ham Member QRZ Page

    Yep. It doesn't bother real radios.
    Commercial/public safety repeaters can be 12.5 kHz apart on 450/700/800/900 MHz. Channels spacing on VHF is mostly 7.5 kHz. Geographically close repeaters can be 15 kHz apart on VHF.
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Yes. Actually, it's common for all repeaters on any frequency at all to be at the same location. The frequencies used are based on local coordination councils.

    "Ham" gear is often not terribly selective no matter who made it. The filtering used is a compromise between adjacent channel rejection and good recovered audio fidelity, and also allows users (simplex and repeaters) to be a bit off-frequency and still be intelligible.

    "Commercial" stuff can be "tighter" as they're more restricted with respect to being "on frequency" (amateur radio actually has no requirement at all regarding frequency accuracy or stability).
  9. K6XRA

    K6XRA Ham Member QRZ Page

    I'm not sure I understand that statement?
    N2SUB likes this.
  10. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    It's called "co-location:" Several repeaters in the same or different bands all at the same hilltop, sometimes on the same tower, sometimes with the equipment located in the same equipment cabinet or shelter.

    There's only so many mountaintops available for this stuff, so a place like Palomar or Santiago (just two of dozens of examples in southern CA) have dozens of repeaters on each one. Closer to me, Oat Mountain, Saddle Peak and Verdugo Peak are similar examples -- dozens of repeaters at each site. If the input-output frequencies are very close, they deal with that.

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