BER testing in Mototrbo

[efc]

Hello,I have got a 6 repeater Mototrbo Linked Cap plus system which I have checked the transmitters,antennas,receivers,and the system appears to test good,450 Mhz,until the customer gets busy.In other words,they say that they get busy at nights,then they get no communication ,especially in one area,which of course tests good for me except here and there,and I would like to do a BERT test with the Turbo system,but not really sure how,my R8000 does a BER test,but this is fairly new to me so I am not sure.Any helpful thoughts appreciated.

Thanks.

[efc]

By the way,I understand how to do the BER test for Tx and Rx ,directly to the radio with monitor,but isn't there a way to test BER in a real life situation,whereas the medium,the distance between the portable and repeater is considered.

Thanks

[FMROB]

You have issues to look at my good sir. 6 channels of LCP at one site, or 3 each at two sites? Two things jump out at me that often are culprits, proper system and subscriber programming and RF issues at the site.

With this in mind, you need to narrow down what "busy means" and why and how they are getting them. 6 channels is a lot of capacity so I would be inclined to figure that they are not actual systems busies due to capacity. With that said, are the repeaters properly rolling over when the rest channel is pushed? On CP+ and LCP+ if you have issues with network or the NIC card the system will behave strangely. Unless you are at the site with a bunch of radios keyed simultaneously you wont' catch it, but you will get busies. For example, I had an MTR with a crappy nic card that puked when it felt like it. When it puked, it disrupted the 5 other repeaters. Although units could access the system, busies happened often because the rest channel wouldn't roll over between repeaters. The only way I was able to track it down was with 6 portables on different talk groups and key and hold the radios to watch the system operate.

You checked the sites RF wise. Is something lighting up at night causing intermod or raising your noise floor at the site. Maybe its not happening during the day time. If you are combined down, if two or more transmitters are coming on, is it causing you grief?

I am going to catch hell for this, forget all the BER crap. Analog! Take one of your repeaters off the air digital and dump it to analog. Program up some test units and go at it in the bad coverage areas. The ear can tell you a lot in analog. If its not working in analog, digital is not going to make it better and testing is so much easier.

On the programming side, are the units set to color code or channel free for access? You most likely need to use color code free, rather than channel free. Depending on your licensing FB6, FB8, trunking, etc. you may have no choice but to use busy channel lock out, but if you have a lot of co channel chatter your system may suffer?

Hope this helps a bit. Rob

[efc]

Hello,

Thank you for your input,the interference you were talking about I have thought of,have not checked yet.Went the yesterday afternoon,could not get but 2 failures in offending area.Yes ,the busies I got were not the portable loosing the Repeater,but not getting in,no orange light on top of radio in other words.Let me give you a breakdown of system layout :

2 sites,Linked cap plus,both sites in a casino boat,which is unorthodox should have been a BDA in lower levels to capture portables.
6 repeaters in site 1,4 down in hold area site2.Combiners used and multicouplers,the combiner company,name escapes me,did an intermod study for the frequencies and all was good.I am also using GW3 to monitor the system.The portables are xpr 3500,350 of them.

Thanks.

[FMROB]

Wow, ok that changes a bit of the situation. So there are repaters on the upper level and a set of repeaters on the lower level, linked together. So if I read your reply correctly, 4 repeaters in the hold area, leaving 2 in the upper level of the vessel?

Covering a metal vessel can be challenging, to say the least. Remember with the trbo, the repeaters RX is just as important as the portable hearing the output of the repeater. If the wake up is not acknoldged, or the radio desn't properly follow the beacon the radio is must likely going to get busies. Seems to me that the output of the system may not be able to be heard throughout the vessel, and that could be your problem.

Don't ever count on the combiner company doing thier "due diligence" in system design. We had tx rx design a 7 channel combiner, and the paperwork came back with some funny notes that didnt make snese to us. It was along the lines tat 4 or 5 trasnmitters were theorized in the calcualtions. We called up and asked them what that exactly meant. There answer was that they didn't check all channels transmitting within the combiner system. We explained that this was crazy, and explained that in public safety system it would be easy to have all 7 channels in use at the same time. This caused them to change thier internal engineering practices and it turned out that the combiner would work with all seven channels. There were lots of hits on low number harmonics. We wound up getting some new channels and worked it out. If we didnt happen to catch that little snibit of notes we would have ordered and installed the unit not knowing the pitfalls. We would assume that they did the calcs and ran it out 20+ in order with all transmitters. Just an fyi.

My suggestion would still be to fully vet out RF side of the system and see where the coverage issues really area. Rob

[efc]

Thanks for the input,and i will remember that.Just to clarify,of my 2 sites,site 1 upstairs has 6 repeaters,downstairs has 4 repeaters.Plus these folks are HEAVY users,so I am keeping an eye on GW3 because it is possible,since the system is not balanced,that site 2 gets so much traffic that it busies the entire system out.

Thanks

[wavetar]

That certainly is a unique application for LCP. A couple of things to look at that pop into my head:

RSSI Threshold- by default, this is set for -108 dBm per site in the portable programming. It's likely that as people roam around the ship, their radios will stay on one site or another because the portable can still 'see' the site, but cannot reach it. They may be in good coverage of the other site, but won't roam to it. I would change this setting to -100 or maybe even -95, to allow for more responsive roaming.

If you want to put some science behind it, a helpful tool on MOL is the MotoTRBO Site Survey tool. Using this tool, you program a portable for a single site at a time and roam around the ship, keying a repeater every "x" seconds and you'll be able to see that in some sections of the ship the portable will be able to key the repeater at say a received RSSI of -103, but others where it may not be able to key at -98. It can also vary a lot between hip level & head level. You should test using the hip level that the customer is likely using.

Doing the above for each site will allow you to map out the actual "usable" coverage for each site. This way you can determine the best RSSI threshold to use for best roaming between sites. You might even find a few spots where neither site works properly in terms of portable reach back, and deal with those.