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Thread: msf5000/narrowbanding opinion

  1. #1
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    Default msf5000/narrowbanding opinion

    I need some advice. Im in the process of getting a commercial uhf 450-470 repeater pair. We currently have an msf5000 repeater, which i know is not narrow band capable. I cannot afford to purchase a Quantar or an mtr2000 (especially @ ebay prices). Is it worth it, to purchase 2 cdm's, either a 1250s or a 750s (one for recieve, one to excite the msf5000 amp), a decent controller and construct my own repeater that is narrow band compliant? Ive read up alot on using the msf5000 amp as a standalone unit, i just have no clue if it would hold up to being used fairly heavy a few nights a week.

    Would there be a big difference in using a cdm on the recive end, versus using an actual repeater for the recive?

    Any ideas/opinions would be helpful.

    Brian


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    CDM's *CAN* handle continuous duty, no question. I have a repeater that is built from a pair of CDM 1250 mobiles that is in near continuous keydown, and it hasn't failed yet (after over a year of use), knock on wood.

    The key to longevity is this: Remove the black plastic housing from the radio so you have the metal chassis exposed. Have a fan on top blowing air ACROSS the heatsink, and one underneath doing exhaust duty.

    Ideally you'd want to use low power radios that you can program down to a reasonable output level to drive your MSF 5000 amplifier. Doing this is fine, you shouldn't have a problem. If you're only running ~5-10 watts and cool the radio as I've described above, you won't have any problems. Using a timed, PTT controlled fan interface is wise too, as it'll save you from replacing fans all the time.

    There isn't anything wrong with using CDM 750's as well, you don't really need a multichannel radio for repeater use. As far as receiver performance, they aren't on-par with real-deal repeater receivers as there's significantly less filtering ahead of the receiver, and the CDM series operates over a wider bandsplit than say an MSF 5000 or Quantar. If you are using the correct type of duplexer (BpBr) and perhaps have a properly tuned pass-only cavity between the receiver and duplexer, you should be fine.

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    UHF MSF5000 PA decks take 3-5 watts drive.
    Adjacent channel rejection for CDM's is 75dB at 25Khz spacing.
    MSF5000 has 100 dB at 25Khz.

    I am new to the forum and haven't figured out how to post pictures, yet, or I would post scans of the spec sheets.

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    See the bad thing is the msf5000 doesnt do narrowband... and thats my problem. I need a repeater that will do narrowband, but also be 100watts.

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    Quantars aren't THAT expensive these days. One can be had for ~$1500 if you're patient. MTR 2000's are also an option, though for some strange reason they seem to go for MORE than a Quantar does, on average. You could also use a Kenwood TKR-x50 series, those are $700 or so on the used market. You could couple it with an external amplifier and have a continuous-duty 100W repeater.