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Thread: VHF P25 system going "Robot"

  1. #1
    carterblumeyer No Longer Registered

    Default VHF P25 system going "Robot"

    Here is the issue...The system is giving a "Robot" sound when either keyed up from Console or from units in the field. Conversation starts out good then in the middle it goes crazy. I enclosed mp3 of the sound. System is Moto, Quantars, AtroTac3000 and DIU's... All with the latest firmware and CPS.. V.24 is stun tunneled thru Cisco 2900's routers and the IP runs on T-1 or Microwave..I have a stand alone repeater tunneled to a single DIU the other channels are running thru Compare AstroTac3000. The sound is heard from Dispatch keying up(Mcc5500 via DIU) and will not stop till unkeyed. This is also the same from units in the field. It seems the tunneled quantar and DIU without AstroTac is working much better or I have hardly herd it today. There are 5 DIU's per channel and I have ranked them.. The logs of the AstroTac3000 is empty and shows no loss of data.. Also the microwave is showing no loss of packets or connections. Radio Flash 16.00 and UCM 5.7.XX.. P25 VHF with AES encryption. Any help would be great...

    Carter Blumeyer-Contractor
    P25 Upgrade project RGV
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  2. #2
    Astro Spectra's Avatar
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    I think you posted this on the Batboard and you got suggestions from MattSR and myself. Have you followed those? We are both reasonably experienced in this area and it's not very rewarding providing advice on forums without any feedback.

    I assume you've isolated the consoles and listened directly at the DIU?

    If there are no CRC errors at the AT3k then it is going to be a clocking issue between it and the DIU. As in the post I referenced you need to check each item in the system for clock configuration and draw out the clocking scheme checking for asynchronous operation. Here is a simple example of a Quantar to AT3k link via microwave showing a good way to draw a clock plan which must have footnotes showing the config for the Quantar (in this case External Transmit Clock: Disabled), the AT3K (Link Type: V.24 Link - Internal Transmit Clock), etc:

    astrotac.png
    Last edited by Astro Spectra; Feb 02, 2013 at 11:53 AM.
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  3. #3
    carterblumeyer No Longer Registered

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    No issues overnight with the DIU directly to quantar... As I was tossing last night I am thinking the issue is in the Comparator and the "Parallel Audio" enabled.. There are 5 dispatch locations here and I am thinking the packets are colliding with that many diu's...

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    Listening to the mp3 it sounds like the dispatch is ok but the unit responding is "encrypted (robot sound). This could be caused by a timing issue in the system where the front porch is lost. AES should allow late entry. You may have to resort to using a clear sequence of test transmissions to confirm proper P25 operation. If these work fine and you dont loose P25 decode then its a matter of looking at the encrypted settings and possibly keys.

  5. #5
    carterblumeyer No Longer Registered

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    To give a late update on this... The cause was the Cisco 2900 firmware in the os causing the issue.

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    What IOS version was bad?
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  7. #7
    carterblumeyer No Longer Registered

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    It was one of the first releases that came with the 2900's when introduced

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    Quote Originally Posted by carterblumeyer View Post
    To give a late update on this... The cause was the Cisco 2900 firmware in the os causing the issue.
    Well at least you gave an update 2 and half years later!
    Hopefully it was fixed 2 and half years ago.

    I kind of feel taken advantage of, and I was not even involved in this thread. LOL
    Radio Referenced...Those who think they know it all are very annoying to those of use who do.

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