Batboard

Never one to miss out on a new forum...

Does anyone know if the Companding scheme in the MTR2000 and the X-Pand companding scheme in the Professional Series radios and GR1225 repeaters use the same audio processing curves, or are they substantially different?

In other words, in a narrow-band system full of Professional Series radios running X-Pand, will a base station running through an MTR2000 using companding have acceptable audio, in both directions, or will audio quality get screwy because they are alctually two different processing curves?

Thanks!!

Are you talking about putting a MTR 2K into a system that already has GR1225's running? I'm a little confused on the question. I maintain LTR UHF systems using both the 1225 and the MTR on narrowband using X-Pand but I do not have the systems mixed. I've been able to make both of them sound acceptable but I really had to futz with the compression settings on HT1250LS on the MTR system to get it there.

Dave

Dave:

The system will be VHF conventional, using only the MTR2000. No GR1225 (although there may be a couple of M1225s kicking around).

I apologize if I phrased my question unclearly. The basic question is:

What type of futzing, if any, will I have to do with the companding to get the MTR2000 wireline audio to play nice with the HT1250s/750s / CDM1550s?

Thanks again!

Since you are using conventional signalling (PL/DPL??) and not LTR, I would think the default settings on the radios would be OK. I have no experience running a narrowbanded MTR down the wireline so I can't comment on that.

I can only suggest you set the MTR up for narrowband, you can choose either 12.5 KHz or APCO 25 for bandwidth and set the TX deviation to 2.5 KHz. You have to align the wireline board anyway, do that and see what the recovered audio sounds like on both your console and the radios without using companding. If there is a problem, it will probably be recovered audio on your portables not being loud enough. If you do change to companding, use the defaults (full compression / full expansion) in the portables and switch on the compander in the MTR in RSS. I would suggest you realign the wireline board after you do this and see what happens. Hopefully, someone who has actually done what you are doing will post with their comments.

As far as "futzing" with the Pro series, I went back into my notes and found the problem was a customer mixing HT1250LS with P1225LS on a narrowband LTR system. Let's just say that it was a PITA for now..

Post back with your results!

Dave

All the different literature that I read from Motorola seems to indicate that they are doing the same thing in all their equipment (a 1 to 2 ratio I believe). All the way back to the MSF5000 where this feature is sort of an option. I think the only item they changed is the name for it; from “companding” to “Expand technology”.

Nand.

Thanks guys!!

I finally got the repater up and running, and the answer is that it works fine and souds GREAT once it has been properly aligned

When I first set the repeater up, it sounded like absolute crap, and the audio path gains were all over the place.

After some quality time with a service monitor, I got all of the audio paths aligned to unity gain, and the thing sounds terrific! It really sounds like you are talking simplex radio to radio. I have dealt with a couple of narrow-band GR1225s before (set up by others), and was not impressed with their audio quality. I guess I'll have to find some time to lug the old R2002/C over to see them next week...

The only down side to all of this is that I discovered that the duplex generator on the R2002 drifts like it was going out of style. I guess it's time to think about taking the hit for calibration / service.

Thanks again to all!