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Thread: Whats all the fuss about uplink noise?

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    Default Whats all the fuss about uplink noise?

    Officer Ogletree Officer Ogletree Officer Ogletree SIR Officer Ogletree Officer Ogletree PLEASE!

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    I had a situation where a TX-RX class B amp was installed and turned on before it had been optimized. The nearby simulcast site went deaf. A comment on class A BDA amplifiers. They have additional group delay so TDI at the periphery of the building and at ingress points will be worse. Perhaps ideally Class A on uplink, class B on downlink?

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    I see this alot. Continually finding bda that aren't even permitted and we had zero clue they were there. I find alot of guys crank the gain or even leave at factory levels and it causes issues. I'm big in turning these down when possible. We had one the other day that was wide open 166 rssi on my apx in a garage. I had him cut it 5db at a time while I walked the garage. We were able to drop the gain by 15db and not affect the signal only very slightly (3-5pts rssi)

    We're not seeing tdi issues with any of the systems we have in the city. I believe we're allowed up to 80us. With a well designed system this shouldnt be a big issue.
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    EM - Since you seem to be familiar with Comba product, have you ever worked on one that carried mixed modes in the same band?

    We determined they could not pass Trbo and P25 at the same time. They could pass conventional and P25, or conventional and Trbo. But, whichever digital envelope was passed last, was entirely corrupted. And since the local PS MOT trunking system always had a control channel up, the customer's Trbo did a toilet swirlie.

    We have a Silicon Forest customer (that shall remain nameless because of the NDA) that replaced all their aging TX/RX BDA's with Comba, and had a series of issues until our engineers discovered a problem in the signal processing code of the Combas. After many iterations of firmware, Comba resolved the problems. They may or may not have rolled it into their most recent production, but we now stay away from Comba despite the cost advantages.
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    Quote Originally Posted by Bill_G View Post
    EM - Since you seem to be familiar with Comba product, have you ever worked on one that carried mixed modes in the same band?

    We determined they could not pass Trbo and P25 at the same time. They could pass conventional and P25, or conventional and Trbo. But, whichever digital envelope was passed last, was entirely corrupted. And since the local PS MOT trunking system always had a control channel up, the customer's Trbo did a toilet swirlie.

    We have a Silicon Forest customer (that shall remain nameless because of the NDA) that replaced all their aging TX/RX BDA's with Comba, and had a series of issues until our engineers discovered a problem in the signal processing code of the Combas. After many iterations of firmware, Comba resolved the problems. They may or may not have rolled it into their most recent production, but we now stay away from Comba despite the cost advantages.
    No mixed mode here so havent seen this. Hearing this doesn't surprise me though. It's a cruel world dealing with fw and sw issues.
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    You mean full smoke is not the correct setting for BDA's ??
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    Well, Combas can do an almighty +20dbm uplink to the donor.
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    Quote Originally Posted by Bill_G View Post
    EM - Since you seem to be familiar with Comba product, have you ever worked on one that carried mixed modes in the same band?

    We determined they could not pass Trbo and P25 at the same time. They could pass conventional and P25, or conventional and Trbo. But, whichever digital envelope was passed last, was entirely corrupted. And since the local PS MOT trunking system always had a control channel up, the customer's Trbo did a toilet swirlie.

    We have a Silicon Forest customer (that shall remain nameless because of the NDA) that replaced all their aging TX/RX BDA's with Comba, and had a series of issues until our engineers discovered a problem in the signal processing code of the Combas. After many iterations of firmware, Comba resolved the problems. They may or may not have rolled it into their most recent production, but we now stay away from Comba despite the cost advantages.
    That is indeed a frighting situation. Does this mean that if for example a co-channel or adjacent depending on BW setting, DMR signal enters the system that all the subsequent P25 calls will be trashed?

    That sounds like a public safety critical bug.

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    Quote Originally Posted by RFI-EMI-GUY View Post
    That is indeed a frighting situation. Does this mean that if for example a co-channel or adjacent depending on BW setting, DMR signal enters the system that all the subsequent P25 calls will be trashed?

    That sounds like a public safety critical bug.
    Yes. The Comba seemed capable of only doing one digital mode at a time. So, if a Trbo call was the first in process, a subsequent concurrent P25 call would be treated as Trbo, and vice versa. Our guys noticed it during the deployment. In staging, it all worked perfectly, but they were injecting one mode at a time. Once it got into RL, it immediately manifested itself because it faithfully passed the constant never ending P25 control channel, but not the customer Trbo.
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