Batboard

My agency recently installed a Motorola ASTRO UHF conventional system. The system is make up is the following. 1 UHF Quantar repeater, 1 DIU3000, 1 Astrotac 3000 comparitor, 3 Quantar Astro receivers V.24 linked to the repeater via 4 wire FDDA lines via Paradyne Modems. The system is linked to a Centracom II Gold Elite console. Subscriber units are a combination of XTL2500 and XTL5000 mobiles and XTS2500 portables.

The problem is that the audio quality is not what we expected. The repeated audio, mobile to mobile and portable etc. is acceptable but not great. The console seems to be where most of the issues are. The console transmit out audio seems warbly at times and very bassy. The receive audio at the console is also warbly and at times hard to understand. We have had our shop back several times to look into this but they have not found anything wrong that stands out.

Does anyone know if there are any adjustments that can be made to the DIU or any jumper settings to the BIM that may have been overlooked or anything else that may resolve this issue?

Thanks,
Don

drp10275 wrote:My agency recently installed a Motorola ASTRO UHF conventional system. The system is make up is the following. 1 UHF Quantar repeater, 1 DIU3000, 1 Astrotac 3000 comparitor, 3 Quantar Astro receivers V.24 linked to the repeater via 4 wire FDDA lines via Paradyne Modems. The system is linked to a Centracom II Gold Elite console. Subscriber units are a combination of XTL2500 and XTL5000 mobiles and XTS2500 portables.

The problem is that the audio quality is not what we expected. The repeated audio, mobile to mobile and portable etc. is acceptable but not great. The console seems to be where most of the issues are. The console transmit out audio seems warbly at times and very bassy. The receive audio at the console is also warbly and at times hard to understand. We have had our shop back several times to look into this but they have not found anything wrong that stands out.

Does anyone know if there are any adjustments that can be made to the DIU or any jumper settings to the BIM that may have been overlooked or anything else that may resolve this issue?

Thanks,
Don

You did not say if the system was running in the digital or analog mode. The description
you have provided, might indicate that the system was being used in the digital mode.
If this is the case, I would guess that maybe there is a possibility that your having a
combination of a signal multi path distortion and or audio levels on the transmitters
being too high.

Let's see if there are other comments and where they may guide the solution.

Jim

Yes the system is running in digital.

3 Things:

- Is this a recent move from analog to digital, and perhaps digital isn't what you expected? That would answer the mobile to mobile aspect. If you talk simplex from radio to radio, is the audio better, worse or the same than the system?

- The radios talking to themselves is ok, but the console does not sound good. Does it sound like it's 6db louder (more than twice as loud and slightly distorted?) than the subscribers? Was the equipment bought used / refurbished? If so, what is the firmware of the DIU?

- Lastly, I will disagree with Jim. This isn't a simulcast system with multiple transmitters. Transmitter overlap doesn't apply. Although the possibility exists that the transmitter is set too high, I'm curious on the above 2 comments and questions.

Although no one will be able to say for certain what the problem is on a message board, hopefully we can give you some options to check and steer you in a direction.

Hope that helps,

tpg

I'd be checking the clocking of your V.24 connections to the DIU and possibly to the remote receivers. Regular clock slips caused by improper clocking can introduce a kinda stuttering audio effect.

Also as tpg is suggesting, are the console to DIU line levels set correctly and not double terminated?

Rule of thumb...with digital, lower input levels often result in better sounding audio. I've found the same thing with P25, MotoTRBO, and Kenwood's NexEdge products...settings which work fine in analog do not sound optimal in digital. Your transmit issue could be as simple as backing the mic gain at the console(s) down until the audio sounds more like mobile-to-mobile. Of course, if you also use the same console(s) to talk out on analog channels, you may have to make the level change at another point such as the levels into the DIU. Or keep the mic low & pump up the levels into the analog radios...it can be a bit of a balancing act.

As far as the field units, you might want to play with the AGC levels with a few test units to see what works for your fleet to make things sound better...or perhaps AGC was turned off by the programming shop...who knows?

To all,

Thanks for the suggestions and comments.

Yes we did move from a VHF analog to a UHF Digital system. All the equipment is new delivered in Febuary and installed in July of this year by our local MSS.
The mobiles and and portables do sound better direct than they do going throught the system. But again at the console. The console audio is pretty much the same level as the mobiles and portables going out of the repeater. Like I said, at times warbly but all the time bassy and muffled.

As far as the V.24 clocking, I know the shop was looking at that but I have to check with them what they found. I have been around radio for a long time and can hold my own but this digital stuff is all new to me so bare with me. They did discuss taking the clocking from my Spectracom Net clock and port it into the Quantar repeater if that tells you anything.

I did look into the level settings and brought it down slightly at the BIM. No difference. Maybe I should look at the DIU settings. The only thing that stood out to me on that was that there is a headset level setting not a console mic setting unless I missed something. I only have the one channel operating on digital and all the others are analog which all sound great. So I would rather not play with the mic gain if I can help it.

Again thanks

I always get concerned when I hear people say that they're going to 'try' something when it comes to clocking.

You might want to ask the shop to show you the clocking plan for your system, as often there is no plan. Such a plan looks at what equipment is the clock master (sometimes the telco leaves you no choice with T1 facilities but sounds like everything is under your control as you're using back to back analog modems) and how the clocking flows from there.

Put simply what you want to avoid is one device clocking out data referenced to one clock and another device receiving that data but using a different clock. As the two clocks will always have slightly different frequencies the clocks slip relative to each other and while for a time you get good data periodically (depending on the clock slip rate) you get bad data or in this case errored HDLC frames.

I know this might sounds kinda arrogant but it is the most common issue in these types of networks. Also ask them to check the ASTRO-TAC comparator CRC error counts these will often show clock errors in an otherwise 'working' system.

With ASTRO devices the synch data input, receive data (RXD), has an associated receive clock input (RCLK). However each data output, the transmit data (TXD), can be (usually) set to output data referenced to either a transmit clock input (TCLK) to the device or by providing a clock output (external clock). Things get complex quickly because the terms transmit and receive are a bit relative. With your Paradyne Modems for example the TXD is an input to the modem while the RXD is an output.

When I set up ASTRO Voting, I always try to use the AstroTAC as the clock source and everything else references that. If I recall correctly (it's been a while), the Paradyne 3810 modems also require one to be set to master, and the other modem references that... Or am I wrong...

The only thing I can see them trying to use the Spectracom Netclock for is 1PPS reference, and unless you're running simulcast, it's not necessary and it's not going to fix the problem. The only other possibility is that they may use the 5 or 10MHz reference out of the Netclock (if it provides that, mine here at home doesn't and I don't recall seeing anything but the very high end units that do) to lock the Quantar transmitter to an external reference. Again, this is nice and is good practice, but that's not going to fix the problem either.

Although it may not be an issue in this case, it could be the quality of the phone lines themselves. We are having constant issues with a brand new system where we are getting noise in the lines when it has rained for several days ( ) Of course the phone company says "It all checks out OK."