Many thanks to SWLing Post contributor, Dan Robinson, for the following guest post:
UPDATE NO 3: Malahit DSP-2 (August 18, 2021)
A few weeks ago, I wrote about my experiences with the Russia-made Malahit DSP-2 receiver, and made a recommendation that potential purchasers of the receiver hold off until the design team in Russia made some changes.
Weak points included the SMA antenna connector – specifically the short cable going from the antenna to the PCB board, and sharp noise spikes seen at numerous locations throughout the spectrum from mediumwave up to 30 MHz.
My particular DSP-2 unit went dead after an update to an early version of the 2.10TEST firmware. At the time, I had spoken via Skype with Georgiy on the Malahit team and kept up a string of communications on the Malahit Telegram channel.
It was not clear to me whether the problem with the first DSP-2 was primarily due to SMA antenna issues or also due to a problem with the firmware update I had applied at the time (it was an early version of 2.10TEST).
My appreciation goes to Georgiy who decided to send a new DSP-2 to me. This took about 3 weeks from the end of July until just recently when the receiver arrived (though the U.S. Postal Service made the end of that journey quite interesting).
Here are some observations that I hope will help current and prospective owners of the DSP-2:
The Malahit team has made a change in the SMA cable – whereas before an extremely short length of wire attached the antenna to the PCB board, there is now a longer, though it appears even thinner, length of wire making that connection.
The new cable appears to be far more flexible than the old one, which was forced up against the inside of the receiver’s metal cabinet placing strain on the antenna connection to the PCB. I have been unable to ascertain, from the numerous messages going back and forth on the Malahit Telegram group, whether the development team intends at some point to replace SMA with BNC, which would obviously be a better choice. There is some useful discussion of the antenna connector issue on Telegram, and various persons are experimenting with BNC options. Georgiy and the team seem to be working on various physical changes to the DSP-2 cabinet and other firmware versions that are likely to be seen in coming months.
An excellent location to see firmware changes clearly, for those not yet hooked up via the Telegram group, is on this excellent site which contains links to the latest FW updates and change log information.
As can be seen from the change log, from July 24th the Malahit team took steps to address some key issues, including the failure of the battery icon to accurately reflect remaining voltage, and internally-generated noise. Improvements were also made to Synchronous mode – the receiver now enables lower and upper SYNC.
Another change, implemented in the 2.10TEST FW version issued on August 16th, according to the Malahit team,“improved suppression of interference from the display. Now in SSB, AM, NFM modes, noise reduction is automatically turned on. This slows down the speed of the user interface, but greatly reduces the clutter! This function is not used in WFM mode.”
REDUCTION OF INTERNAL NOISE
The major problem with the Malahit has been internally-generated noise. My first DSP-2 unit had numerous noise spikes, some appearing at inconvenient places in the middle of shortwave bands. One example was on or around 6 MHz where Radio Havana, Radio Mali and other stations are located.
So, recent changes in firmware appear to have tackled this noise problem, to a degree. However, starting at the low end of the DSP-2 tuning range which is 50 kHz, noise spikes are still present, for example at: 445, 625, 800, 980, 1160, 1340, 1875, 2055, 2230 and so on up through the lower part of the HF bands.
After installation of the August 16th 2.10TEST firmware, the really loud noise spike seen at 6 MHz seems to have disappeared as has the noise spike at 12 MHz. Yet, noise spikes are still seen at 6,155 kHz, 6330, 6510, 6690, 6870, etc. at 180 kHz to 200+ kHz intervals.
So, my conclusion is that while the changes to the firmware may have reduced the noise problems slightly, they still have not been able to resolve this issue and this is something that anyone contemplating a purchase of the DSP-2 needs to take into account.
I have noticed what appears to be an increase in body sensitivity on the DSP-2 – signals improve sharply when hand touching the cabinet, and conversely fade fairly sharply without hand contact.
As I said, this is more noticeable than before, especially when not using the PRE-AMP feature. With PRE-AMP engaged, signals are more audible when the receiver is left on its own. With PRE-AMP off, for example when listening to the usually strong signal on 12,160 kHz, programming can barely be heard.
This video shows a comparison between the DSP-2 and Afedri LAN-IQ Standalone receiver. Both units were placed in roughly the same receiving location, with the Afedri using a BNC-connected whip. The DSP-2 was using a somewhat shorter whip along with a 50 ohm impedance module, with the HI-Z setting on the DSP-2 set to OFF.
As you can see, the AFEDRI with its heavier metal cabinet is largely immune from touch conductivity, while the DSP-2 is sharply sensitive to touch and lack of same. By the way, this was true for the DSP-2 both with and without the 50 ohm impedance module.
I have observed in the past that most every portable receiver I have ever used exhibits touch sensitivity to a certain degree. Aside from the Afedri, the Belka DX has somewhat more immunity to this, likely due to its heavy metal cabinet construction. Even Tecsun receivers, especially the PL-990x and PL-368, have this annoying issue.
However, the fact that hand conductivity is so significant with the DSP-2 is a bit troubling since it brings into question the extent to which the receiver can be used for comfortable extended listening while not being hand held, necessitating use of something like a You Loop or other antenna to maintain listenable signals.
As to updating firmware – after navigating the YouTube videos and Russian language instructions provided by Malahiteam, using the STM32Cube software has, for me anyway, become fairly routine.
As long as one follows the instructions carefully, the updates succeed, though there is no appearance on the STM32 window of any “DFU” icon as one of the Malahit videos stated at one point. You do have to check to be sure that the receiver shows up in the Windows 10 or 11 devices list under USB devices.
At the end of my previous article on the DSP-2 I recommended that anyone considering a DSP-2 hold off for a while until the Malahit team was able to thoroughly iron out all hiccups with the receiver, whether in firmware or hardware. This included the question of the SMA connector, and voltage monitoring.
Georgiy and the Malahiteam continue to be amazingly responsive to input from users. Firmware updates have addressed one of the above issues, and have made other improvements.
Unfortunately, the problem of noise spikes has not been completely dealt with. I am not sure this issue can be eliminated without a significant re-design of the cabinet and internals to improve shielding, including making the cabinet itself thicker, which would, of course, add more costs of production.
One piece of advice I have passed to the Malahit team involves QC (quality control) issues with the screw holes on the cabinet. On both my initial DSP-2 and the replacement, one of the screws did not insert smoothly in the hole threads. This is something Georgiy is aware of and says will be dealt with in a re-design of the cabinet, though no timeline is provided.
For now, the Malahit retains enormous attractiveness for those in the radio hobby who appreciate the numerous signal processing features it provides – including its excellent noise reduction – as well as internal speaker, and replaceable 18650 cell power.
However, although recent firmware updates appear to have helped reduce the level of noise spikes from 50 kHz up through the shortwave bands, the receiver remains hobbled to a degree by this internally-generated noise. That is not something seen on direct competitors of the DSP-2, such as the Belka DX and Afedri LAN-IQ.
As I wrote previously, Georgiy has asserted that when using an external antenna, noise is not as serious adding that the Belka is a simpler device that concentrates only on shortwave, while Malahit is wide band receiver with more complex DSP and user functions.
Georgiy said that this problem is mainly linked to telescopic antenna antenna operation because of the antenna’s proximity to the display. But the solution suggested at one point of disabling the display to resolve the noise issue is a workaround that should not be necessary with a receiver costing $260.
I would continue to urge Malahit team to come up with a clearer English translation of the receiver manual, and to review and possibly revise instructions contained in YouTube videos showing the firmware upgrade process, as there are still many new users who seem to have problems with the updates.
I will continue to decline to issue any sort of recommendation to purchase the DSP-2. As I said, these continually evolving SDRs are something that are of interest primarily to those of us in the hobby who are willing to ride a roller coaster that can be full of thrills but also disappointments as new firmware rolls out, and faults are found. However, as many others have observed for a small design team in Russia, where supply issues are always a challenge, the Malahit receivers and software are an impressive accomplishment, so we should congratulate and thank Georgiy and his crew for this.
I will be looking ahead to likely more significant hardware changes in the Malahit in coming months. On the Malahiteam Telegram group, some of these have already been leaked out, though with little further detail.
For my personal interests, the combination of a Malahit, Afedri SDR, and Belka DX for now fill all of my needs for experimentation with these small standalone radios. It will certainly be interesting to see where things stand at about this same time in 2022.
FINAL NOTE: Anyone purchasing a DSP-2 from Malahiteam should make sure to ask them to be crystal clear in addressing the outgoing package. The U.S. Postal Service has some serious ongoing issues, and the addition of any Russian words to a U.S. address can cause problems, especially any words following the zip code.