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Thread: XTS5000 - sensitivity tests - 25 vs 12.5 KHz

  1. #1
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    Default XTS5000 - sensitivity tests - 25 vs 12.5 KHz

    I have being doing some brief sensitivity comparison tests with my VHF Model 1 XTS5000.

    In general, the XTS5000 is very sensitive and compares well to, say, my VHF MCS2000 and MTS2000. On a very weak, practically unreadable signal, the MCS2000 maybe just has the edge....but I need to do more tests and audio adjustments.

    Usually, when you use 12.5Khz spacing (2.5Khz dev), the narrower filter (around 7.5khz IF filter vs 15KHz IF filter for 25Khz spacing) results in a 3dB improvement in sensitivity.

    However, with the XTS5000, 25KHz (5kHz dev) spacing is slightly more sensitive...why is this? On all my other (analog) Motorola radios I can hear weak signals better using 12.5 KHz spacing.

    Also, when using 12.5KHz spacing, the XTS5000 does NOT like even slightly over deviated signals. If the dev is more than 2.5Khz, you get filter rattling and clipping. With practically all my Motorola analog radios (MCS2000, CDM etc), I have found that they can handle very over deviated signals with no problem...a 5Khz dev signal still sound almost perfect using 12.5Khz spacing. With the XTS5000, a 5 KHz dev signal using 12.5KHz spacing sound bad and a weak 5KHz dev signal is unreadable using 12.5KHz spacing!!

    I also noticed that at the threshold where the analog to digital converter switches off and you get fake white noise,that using 25KHz spacing resulted in a "clean" transition from noisey weak signal to fake white noise whereas with 12.5KHz spacing, there was a lot of "poppling" noise just before the fake white noise came on??


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    Any thoughts on why 25KHz spacing (15KHz filter?) on the XTS5000 is more sensitive than 12.5Khz spacing(7.8KHz filter)

    On my XTS3000 (note 3000) , I've check the sensitivity at 25KHz (15KHz IF filter?) 20KHz (12.5KHz IF filter), 12.5KHz (7.8KHz IF filter) and 12.5Khz (5.76 KHz IF Filter). As expected, as you use narrower IF filters, the sensitivity improves..the best sensitivity is when you use the Ultra Narrow 5.76 KHz IF filter using 12.5KHz spacing.


    So why is the XTS5000 more sensitive using a wider IF filter with 25KHz spacing??

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    I am interesting about ASTRO CAI receive test info. (BER and eye diagram)