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33cm 927MHz bandpass filter

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by K3RW, Mar 18, 2020.

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  1. K3RW

    K3RW Premium Subscriber QRZ Page

    I have a couple of Kenwood 900 rigs I'm hoping to use more regularly during contests on 927 simplex. My Elmer has a couple of 900 amps I might use at some point.

    I'm not far from a big retirement community and assisted living/nursing home places. So I am a wee bit sensitive to knocking off medical devices and whatnot.

    Does anyone make a tight bandpass filter suitable for 927?

    Ideally I'd like a very tight filter but I haven't seen one yet.
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    "Very tight" at that frequency may well be +/- 50 MHz.

    What frequency are you trying to avoid, with respect to RFI?
  3. AI3V

    AI3V Ham Member QRZ Page

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  4. K3RW

    K3RW Premium Subscriber QRZ Page

    Yep, that is the problem... I'd like to not knock off a bunch of medical devices down the street just get my 927 signal through the trees. And when I'm up 4500 feet I don't want to be a nuisance with an amp on a whole city.

    We have no 902 FM activity. But a relaticely tight filter doesn't seem to exist for ham use, that I'm finding so far.

    With the wide split for TX/RX it wouldn't help me with calling up repeaters to solicit interest, but I wouldn't run an amp for that and could switch the filter out of line.
  5. K7JEM

    K7JEM Ham Member QRZ Page

    A bandpass filter is probably not going to help much. There shouldn't be a lot of off frequency components in a typical transmission. You could probably easily find a commercial 900 MHz cavity, depending on power level needed, if you really want a filter.
    K3RW likes this.
  6. K3RW

    K3RW Premium Subscriber QRZ Page

    Thanks... I had overlooked that completely.

    I just found one. 5MHz bandwidth--thats good for my use at 927, not killing off 915 devices, and its retunable within the 33cm band, etc. Its an ISM one but can be tuned all over.
  7. W6KCS

    W6KCS Ham Member QRZ Page

    No need for a filter, off-channel noise/spurious will only be something like -76 dBm/Hz conducted, and maybe -120 to -150 at the old folk's home. Your carrier might do something since it's inside the ISM band (M=Medical).
    Last edited: Mar 18, 2020
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  8. K3RW

    K3RW Premium Subscriber QRZ Page

    That was more my fear, that running 100w simplex on 927.5 on a beam from way up high could blast things all around the whole city. Or at least the potential exists. At least I figured I could put a 5MHz wall around my signal I could at least not blast the entire band.

    My garage door opener, CPAP, keyless entry, a other devices in the house are all 900 band. Granted, they are sometimes 915, 904, etc., so I won't be able to prevent all chaos, but if I could chop a nice slice away for RX (and TX as a bonus) I'd be happy for that. I'm also not required to go to extraordinary lengths for the unlicensed users, but if I nuke them I am also somewhat nuking myself too :) I'm sure some of my 2 and 5GHz experiments have reset some routers :rolleyes:
  9. W6KCS

    W6KCS Ham Member QRZ Page

    The stuff you will hear in your receiver are on-channel, no bandpass filter will help with that.
    K3RW likes this.
  10. W6KCS

    W6KCS Ham Member QRZ Page

    I should qualify that, if you have anything nearby that puts a strong enough signal into your receiver to block its front end, a bandpass filter might help. The levels would probably need to be -30 dBm or so to do that, which I wouldn't expect into an antenna up on a tower away from other devices, but if you had something nearby like a Point to Point ISM band radio, maybe it could happen. But you'd need a pretty narrow filter to be effective since that stuff might cover the whole band.
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