Rocky Mountain Ham Radio continues to investigate alarming problems with recently released low-cost DMR Tier II radios. This article focuses on the Baofeng DM-5R Plus and Baofeng DM-5R with Tier II firmware update. A later article will examine the Radioddity DM-55 / Tytera MD-398.
Our tests find that the Baofeng DM-5R is unfit for DMR use and degrades the repeater network. We will continue to forbid the use of it on our systems.
Here are our findings.
The short version:
“Does the DM-5R transmit a legitimate digital voice signal on timeslot 1?” Yes.
“Does the DM-5R transmit a legitimate digital voice signal on timeslot 2?”
Uncertain. Baofeng says no, but we have been able to activate talkgroups which are only carried on timeslot 2. This requires more research. The radio transmits a copy of the TS1 signal on TS2. It is not supposed to do this. (Updated Jan 5 2017)
“When transmitting on one timeslot does the DM-5R jam the other timeslot?” Yes.
“What does the jamming signal look like?” It
appears to be is a duplicate of the intended signal. This requires more research. (Updated Jan 5 2017)
“Are you sure you weren’t using the radio in Tier I mode?” DMR Tier I FDMA and Tier II TDMA are completely incompatible. If the radio were in Tier I it would not be able to activate DMR repeaters or work with other Tier II radios in digital simplex. Our DM-5R with the Tier II update is able to do both of those things.
“Has the Baofeng DM-5R been tested and approved by the DMR Association?” No.
“Will Rocky Mountain Ham Radio allow the DM-5R to be used on its amateur DMR repeaters?” No.
“What if I ignore your ban and use the DM-5R on the RMHam network anyway?” You will raise the noise floor at the repeater for anyone attempting to use the other timeslot. This is called jamming. It is poor practice at best. If you choose to do this anyway it could be interpreted as deliberate interference which is forbidden under FCC regulations.
“Isn’t ham radio just a fun toy? What am I hurting by using the Baofeng DM-5R?” We cannot speak for other DMR networks but Rocky Mountain Ham Radio has prioritized robustness and reliability from the beginning. We want our repeater network to perform flawlessly in the case of a disaster and this philosophy shapes every decision we make. This radio is more than a nuisance, it poses a direct threat our ability to respond to a disaster.
“Are other DMR networks banning the DM-5R?” Yes. Hoosier DMR is known to have banned them in late November. There are likely to be others.
“Will you be able to identify hams who are using the DM-5R?”
We’re working on it. Yes. (Updated Jan 5 2017)
“Will Baofeng update this radio to allow correct use of both timeslots?” Given their responses to date this seems unlikely. Some teardowns indicate it may be impossible due to inadequate switching speed of the RF section, although we have not verified this.
“What has their response been?” Baofeng and Radioddity have consistently stated that if you wanted a two-timeslot radio you should have purchased one.
“Have they addressed the issue of jamming?” Not that we have seen.
“Are there any other issues with these radios I should know about?” The Baofeng DM-5R frequently glitches while reading or writing memory channels. This causes them to receive and transmit incorrect talkgroup parameters.
“Are the ARRL or FCC doing anything about this?” Not yet. They took effective action on bad GFCI outlets and grow lamp ballasts once enough people complained. Consider writing some polite letters.”
“Motorola radios and the software to program them are really expensive! I don’t even know if I will like DMR. Are there good, affordable entry-level radios?” The Connect Systems CS750 is an excellent performer at $180. The Tytera MD-380 at $120 is pretty good. Programming software is free for both of these.
“Are those radios dual band?” No. At this time there are no other dual-band DMR radios on the market. Connect Systems has announced one with an expected availability in early 2017.
“What am I missing by having a single-band DMR radio?” Mostly you lose the ability to operate DMR while traveling to regions where another band dominates. In the Colorado Front Range nearly all DMR activity is on 70cm. Rocky Mountain Ham Radio will be deploying 2m DMR to Colorado’s Eastern Plains in the near future.
Test procedure and results:
For testing we acquired a Motorola XPR 6550 VHF, Tytera MD-380 VHF, and Baofeng DM-5R Dual Band with Tier II update.
We set all of these to 145.790 Digital Simplex (timeslot 1, color code 1, destination contact 16777215). Each transmitted directly into a Rigol DS1102E Digital Storage Oscilloscope at low power (nominal 1W) through 40 dB of inline attenuation. Screen captures were taken with identical settings on all tests (10ms/div x 50mV/div).
A well-behaved DMR Tier II radio should alternatingly generate RF for 30ms then switch off for 30ms. This is exactly what we see with the Motorola:
The Tytera is also well-behaved, although a chirp is evident:
Contrast the Baofeng DM-5R:
All screenshots were taken with identical settings on the oscilloscope. Repeated tests gave the same results, and settings were double-checked.
The only possible conclusion is as stated above: the DM-5R with Tier II update happily transmits full amplitude RF during both timeslots. The DM-5R Plus can be assumed to do the same.
(If you doubt this last point and wish to loan us your radio we will test it and report here. Contact us at email@example.com to arrange shipping.)
A simpler test.
If you do not have an oscilloscope there is a simpler test you can do.
Place your DMR Tier II radio on a dummy load and tune it to a digital simplex channel and an analog FM receiver to the same frequency. Transmit a low-power test message from the DMR radio. A proper DMR simplex transmission has a characteristic staccato sound when heard on an FM analog radio. Take this example from our XPR 6550:
Or this from our MD-380:
However the DM-5R produces a grinding sound:
The RF on timeslot 2
Initially we believed the RF in the second timeslot was random noise. However we encountered several credible reports of these radios keying up both repeater timeslots simultaneously so decided to look more closely.
We created four new channels in the Baofeng: two correctly programmed for a talkgroup on each timeslot, and two incorrectly programmed by swapping the timeslot parameters.
On the first attempt all four channels on the Baofeng activated the timeslot 2 talkgroup. This seems to indicate that not only was a digital voice signal present on both timeslots, the radio had glitched and was sending incorrect talkgroup parameters.
The four test channels were deleted and re-created. On the second test they did not glitch. The intended talkgroup was activated in all tests, including when timeslot parameters were deliberately reversed. This reinforces the idea that the digital voice signal is present on both timeslots.
In order to verify assumptions the same test was performed using the Motorola XPR6550. With timeslot parameters reversed the talkgroups were not activated. The XPR6550 exhibits correct behavior.
Added on Jan 5 2017: CBridge logs confirm the DM-5R activates both timeslots simultaneously.