LTR Problems

[syslinux]

We have a 4 Channel portable LTR system using Trident Raider Controllers and are experiencing unreliable call setup when more than 2 channels are bussed together?

When 4 talk groups are keyed up and have gone to channel, 1 or more talk groups drop out?

We are using Motorola GP328 LTR Radios (Firmware R05.09.13 and R05.08.07) as our portables with the Raider Controllers (Firmware FEREV 2.27 TCP REV 1.23 BOARD REV 1.0). We have harnessed the repeaters with duplexers (tuned broadband) on all channels dual isolators on transmit leg and hybrid coupled the outputs from the duplexers to the antenna, we have spec tested the performance specifications of the repeaters and have checked for desensing between repeaters.

The system seems to be reliable with just one call, the more simultaneous calls the less likely the call will connect.

Here are some pictures of the LTR waveform:





We do have some concerns about the transmit data from the raider (Also measured at pin 5 of the DB25 Plug) as it does not appear to be as clean as the handheld transmit data? Can you verify if this is acceptable waveform?

Is the trident raider capable of driving 600ohms on the TX Data port is there an optimum that you would suggest.

We would appreciate any help that you could give us, we have a Motorola trained technician and suitable test equipment but we do not have experience with the LTR system.

[MSS-Dave]

I'm assuming that the pictures show the TX waveform from the repeater. What repeaters are you using? The waveform shows distortion on the data. The long flat part of the waveform should be straight across. Depending on the equipment, this can be adjusted. MTR 2000 has a modulation compensation adjust in the menu. Looking like this, the problem might be when the LTR bus loads up, the radios quit decoding properly. I also had a problem with channel assignments and talkgroup assignments. Trident recommended that channels in the system be assigned evenly across the 20 allowed. My 4 channel system was on 1,3,5 and 7. Talkgroups were the same way across the 250 per home channel allowed. It seemed to help.

The TX waveform definitely needs to be fixed first, this may cure your problem up front.

Dave

[ve3nsv]

I'm assuming that the pictures show the TX waveform from the repeater. What repeaters are you using? The waveform shows distortion on the data. The long flat part of the waveform should be straight across. Depending on the equipment, this can be adjusted. MTR 2000 has a modulation compensation adjust in the menu. Looking like this, the problem might be when the LTR bus loads up, the radios quit decoding properly. I also had a problem with channel assignments and talkgroup assignments. Trident recommended that channels in the system be assigned evenly across the 20 allowed. My 4 channel system was on 1,3,5 and 7. Talkgroups were the same way across the 250 per home channel allowed. It seemed to help.

The TX waveform definitely needs to be fixed first, this may cure your problem up front.

Dave

The MTR adjustment will be for the reference modulation in the service menu and once adjusted properly the horizontal portion will be as straight as possible. Before adjusting I had problems handshaking between a PR400 and MTR2000 with a Raider controller, after adjustment it was rock solid. I also have noticed that the controllers don't like RF very much so be sure to slap the lid on the controller during testing and use a dummy load on your portable.

Last but least are you sure all your controllers are talking to each other? If you log into the master controller and look at the real time display does it show all the Home Repeaters idle that are connected to the Master. Any chance the controller is trunking you off to another channel but that channel isn't programmed into the user equipment? Exhausting all that I would be looking at your controllers to see that they are all set to the proper baud rate and are in sync with the master.

[syslinux]

Thanks Dave-MSS & ve3nsv for your help.
We have been learning alot about Two-Point modulation and the importance of a flat waveform as you mentioned.

We have been trying the controllers with various repeaters including motorolas & some taits for comparison. We have now squared up the waveform by adjusting the modulation and now have Rock Solid Performance on a 4 Channel system.

Philip Steel