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P25 digital rcvr sensitivity

Have a question or information regarding interfacing or interoperating Motorola digital radios with models from other manufacturers? Here's the place to do so.

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Bill_G
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Joined: Thu Sep 17, 2009 5:00 am

P25 digital rcvr sensitivity

Postby Bill_G » Thu Dec 09, 2010 6:47 am

I'm finally dipping my toe into a 700M P25 system that I will have full hands-on time with rather than be a construction contractor (bolt it down, wire it up, git out of Dodge - someone else works out the bugs and maintains it). What are you seeing for RSSI values with clear communications (no bubble)? My initial reports show we need -108dbm to have good comms despite the mfg spec of -120dbm for 5% ber. I wasn't expecting the radios to actually function well at -120, but I was hoping they would work well at -115. But, the "squelch" doesn't open below -110 so far on field units (portables and mobiles) as displayed on the front panel diagnostics. At -115dbm displayed on the front panel, the receivers are fully muted. At -110db they open with bubble. Kind of a broad difference between the spec and real life, but maybe this is normal. Any thoughts?

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Wowbagger
Aeroflex
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Joined: Tue Dec 10, 2002 10:46 am

Re: P25 digital rcvr sensitivity

Postby Wowbagger » Thu Dec 09, 2010 8:20 am

How are you making the sensitivity measurements?
This is my opinion, not Aeroflex's.

I WILL NOT give you proprietary information. I make too much money to jeopardize my job.

I AM NOT the Service department: You want official info, manuals, service info, parts, calibration, etc., contact Aeroflex directly, please.

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Bill_G
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Joined: Thu Sep 17, 2009 5:00 am

Re: P25 digital rcvr sensitivity

Postby Bill_G » Thu Dec 09, 2010 5:41 pm

From the front panel Qos and RSSI indicators built into the radios. They seem to track each well. That is, all radios agree on the RSSI and the percentage of error correction applied. I'll bring it up with the OEM reps when they arrive next week. But, I am curious if anyone else has similar experience with P25 units in the field.

MOEtorola
Posts: 49
Joined: Wed Feb 27, 2002 4:00 pm
What radios do you own?: APX7000, All XTS and XTL

Re: P25 digital rcvr sensitivity

Postby MOEtorola » Thu Dec 16, 2010 7:19 pm

You really cannot use the RSSI values as a reference, for one thing they are programmable. I am assuming you used a P25 service monitor like the aeroflex's 2975 super nice monitor to reference the RSSI values to dbm readings. If that is this case, it really tough to come up with an accurate dbm reading due to the range between values.
In my experince p25 is outperforming analog. Believe me the radios meet or exceed the 5% BER.
My radio starts dropping at an RSSi value of 34.
You mentioned something about when the squelch opens,in digital there really is no squelch.

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Bill_G
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Joined: Thu Sep 17, 2009 5:00 am

Re: P25 digital rcvr sensitivity

Postby Bill_G » Thu Dec 16, 2010 7:38 pm

These Tait radios actually state rssi in dbm in a diagnostics screen along with a percentage of fec being applied. In the 1011 rx test, they will also display ber. I have not done a sanity check with a 2975 to see how well calibrated they are. But, all of them are agreeing. I am not seeing wildly different rssi levels between individual radios in a given area. That said, during 1011 tests and voice script loops (canned messages played back from a pc over the air), the rssi can get down to -115db before bubble and muting occurs which is much closer to the published spec. We'll see how it goes.

MOEtorola
Posts: 49
Joined: Wed Feb 27, 2002 4:00 pm
What radios do you own?: APX7000, All XTS and XTL

Re: P25 digital rcvr sensitivity

Postby MOEtorola » Fri Dec 17, 2010 3:24 pm

Ok, sorry I was speaking Motorola never messed with Tait


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