(Updated Apr 3 2017 to include the Radioddity GD-55.)
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, Baofeng DM-5R with Tier II firmware update, and the Radioddity GD-55 (a rebranded Tytera MD-398).
Our tests find that the Baofeng DM-5R Plus and Radioddity GD-55 are unfit for DMR use and degrade the repeater network. We will continue to forbid the use of these units on our systems.
Here are our findings.
The short version:
“Do these radios transmit a legitimate digital voice signal on timeslot 1?” Yes.
“Do these radios transmit a legitimate digital voice signal on timeslot 2?” The radio transmits a copy of the TS1 signal on TS2. It is not supposed to do this.
“When transmitting on one timeslot does the radio jam the other timeslot?” Yes.
“What does the jamming signal look like?” It is a duplicate of the intended signal.
“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. These radios are able to do both of those things.
“Have these radios been tested and approved by the DMR Association?” No.
“Will Rocky Mountain Ham Radio allow these radios to be used on its amateur DMR repeaters?” No.
“What if I ignore your ban and use these radios 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 by FCC regulations.
“Isn’t ham radio just a fun toy? What am I hurting by using these radios?” 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 these radios?” Yes. Hoosier DMR is known to have banned the Baofeng DM-5R in late November 2016. There are likely to be others.
“Will you be able to identify hams who are using these radios?” Yes.
“Will the manufacturers update these radios 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, causing them to receive and transmit incorrect talkgroup parameters. The Radioddity GD-55 has a particularly confusing menu system which buries common actions several levels deep.
“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/MD-390 at $120 is 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 previously announced one with an expected availability in 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. However 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, Baofeng DM-5R Plus (Tier II capable from the factory), Radioddity GD-55 UHF, and Motorola XPR 6550 UHF.
VHF radios were set to 145.790 DMR simplex (timeslot 1, color code 1, destination contact 16777215). UHF radios were set to 446.200 DMR 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 inline attenuators. DSO captures were taken and are presented here. Scope settings were 10ms x 50mV / div for VHF, 100ms x 200mV / div for UHF.
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 (Radioddity GD-55 has identical behavior):
Repeated tests gave the same results, and DSO settings were double-checked.
The only possible conclusion is as stated above: the DM-5R with Tier II update, DM-5R Plus, and GD-55 all transmit full amplitude RF during both timeslots.
A simpler test.
If you do not have an oscilloscope there is a simpler test you can do with your own radios.
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.
Added on Jan 5 2017: CBridge logs confirm the DM-5R activates both timeslots simultaneously.