DMR Scanner programming, "NFM" or "FM"?

[RRR]

Hello all,

I was wanting other's feedback on monitoring DMR "syatems", this will be for my SDS200, though I presume it would apply to any DMR / Mototrbo scanner.

What have you had better success with, when monitoring DMR / Mototrbo, using "NFM" (12.5) or "FM" (25)? I understand when a DMR / Mototrbo repeater transmits on either slot 1 -or- slot 2, it keys up on both slots (making it 25 wide), even though no traffic may be passed over the other slot.

So, in theory, DMR / Mototrbo would be 25 wide, correct?

I know portables and mobiles transmit in 12.5, and I can't get my SDS's to pick them up (My TRX-1 will, though)

I appreciate any opinions or assistance!

 

[GTR8000]

I understand when a DMR / Mototrbo repeater transmits on either slot 1 -or- slot 2, it keys up on both slots (making it 25 wide), even though no traffic may be passed over the other slot.

So, in theory, DMR / Mototrbo would be 25 wide, correct?

DMR channels are 12.5 kHz, not 25 kHz. The whole point of TDMA is to divide the 12.5 kHz channel into two alternating time slots.

In fact, DMR is actually licensed with 7.6 kHz emission designators, so it's actually quite a bit less than the full 12.5 kHz "narrowband" channel width.

 

[chief21]

So, in theory, DMR / Mototrbo would be 25 wide, correct?

As noted, a complete DMR signal is 12.5 kHz wide. DMR slots are time-based, not frequency-based (TDMA vs. FDMA).

 

[RRR]

Thank you for the replies, I was under the impression that a mototrbo repeater was 25Khz wide, but got around the "Narrowbanding" by the FCC, due to the use of timeslots, to have 2 channel talkpaths. I guess I was wrong.

So, with what y'all are telling me, it would be appropriate to set the scanners to 12.5 Khz for DMR repeaters, correct?

 

[nd5y]

Set it to what you think works best. It might not make any difference. Does anybody even know if filter bandwidth on scanners actually works for digital modes or is it fixed at wide or narrow?

 

[Ubbe]

The two different filters in a BCD536 works as well as the two in the TRX and switches with the FM and NFM settings and BCD536 also change the audio level so it sounds the same. But TRX doesn't do any audio level compensation, it justs switch filters and NFM then have a lower audio level as it modulates less. Upman once recommended to use FM mode with DMR signals. Don't know if that was to compensate for some irregularities in some specific firmware version as NFM should be the proper setting.

/Ubbe

 

[RRR]

I had the actual filter modifications done to my BCD996T scanners, and it really helped with "Narrowband" Is this same filter modification available for the BCD996P2's?

 

[XTS3000]

I had the actual filter modifications done to my BCD996T scanners, and it really helped with "Narrowband" Is this same filter modification available for the BCD996P2's?

Yes, same 455Khz filter mod for the 996P2. All Uniden scanners starting from the 396T to the 996’s use the same exact filter, including the HP1 and HP2.

I’ve done the filter mod to my 396XT and HP1. Works great. One side effect I’ve noticed after the filter mod is you need to turn up the squelch from 1-2(original 25Khz filter) to 5-6 with the narrow band 12.5Khz filter.

 

[Ubbe]

It was some other anomaly that happened during normal use, so read the filter modification thread carefully.

/Ubbe