Trunked 900 mhz MSF500 to Quantar conversion problem. Help

[tonyknox]

We have a 900 mhz trunked system with 28 channel controller. We are using 100% Msf5k analog stations. We are trying to upgrade to Quantro. We found five stations and bought them. All five appear perfectly operational. I tried to swap out the control channels and ran into a small problem. With all Msf's, all mobiles and portables will work from my bench(approx 40 mi. from site). When I put in a Quantro for control channel, Maxtracs quit accessing the system out here, but you can physically drive closer to the system and they will start to work at about 30 miles away. They are hearing the OSW and trying to access, red tx light flashes numerous times before giving out of range tone. I finally reinstalled the MSF's as control channels and the quantros as voice, and everything is working, even at 40 miles away.

I keep thinking I've done something wrong in the setup, but can't figure it out. Anybody have any ideas?

[RKG]

Bench one of the Quantro receivers; my guess is that you'll find the sensitivity less than spec and they need to be tuned.

[tonyknox]

Actually, I did before I took them down there. The Msf's will do 12db. at about .25 microvolts, and the Quantro's will do it at about .20 microvolts. I'm thinking now that I might need to enable companding since the Quantro is all digital until the final audio output conversion. I'm pretty sure the controller would be looking for analog audio to decode connect tone, and the output to local audio is about the only place where they could find analog in the Quantar. I'm guessing that's what they used. What do yall think?

[MSS-Dave]

Another thing you might want to check is RX noise at the site that could cause desense. MSF has a real good filtering system in the front end. I have had issues in the past with Quantars being more susceptable to desense, especially in a hi RF level site, even more so receiving low in the band (896-897 MHz). This happened at a site with RX bandpass filtering at the RX multi-coupler but not on the tower top. Addition of a TTA with filtering AND properly balancing the gain in the RX system cleaned it up. If your site has upper and lower filters, check the gain (pads) in the system. You are looking for no more than 1-2 dB gain overall. I've had plenty of problems at sites where folks have removed the pads thinking "more gain the better" when actually it can degrade your sensitivity by 20-30 dB.

Real easy for the ISW to get hashed in high noise...

Good luck with it. Post back with what you find.

Dave

[RKG]

Strictly as a guess (I have no experience with 900 Quantars), I doubt companding would have any effect, since I believe that the AF range manipulated by companding does not drop down as far as < 300 Hz.

[tonyknox]

We use a Celwave TT and distribution amp. The TT does have a pre-selector filter built in to it. I have adjusted the pads to the point of diminishing return as they should be.

I consulted with system support, and they suggested varying the tiiming on the IRB (thinking it had something to do with the timing of the ISW). I went two settings in both directions and it had no effect. As of right now, they're scratching their heads just like me.

I just keep thinking it has to be something I've missed in the programming of the Quantros, but don't know what. The point about the freq response of the compander circuit is well taken, hadn't thought of that.

[Pwematt]

We have had the same problem switching from the MSF to the Quantars. I bet you will find that they will do voice channels but not control channels. We are still working on this problem but we think that if you use version 13 on the RSS you will see that you can change the RX disc audio from Quantar to MSF. Also make sure that the csc is labeled with the correct channel number. Let me know what you find since we are still working to correct the problem.

[wavetar]

There is a timing parameter you can adjust in the controller, but the name of it escapes me at the moment. It essentially adjusts the timing window of the OSW/ISW, to allow for units working from further distances the time to respond before the window closes. I'm willing to bet it has to be adjusted when switching from an MSF based system to a Quantar based. I think it's called "T-Zero" adjustment. I know in the newer MTC3600 it's a software setting, but it might even be a physical switch in the 6809 controllers. Maybe someone else can chime in with a little more detail, but it just may be your problem.

Todd

[tonyknox]

Ok guys, for SURE, the companding needs to be turned on in the repeaters. Works fine now.