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The operation of the ADT-200A

The ADT-200A is an amateur radio. Accordingly, it is designed for amateur-specific applications. But he still has a small heart for the shortwave listener or for radio amateurs who want to listen now and then in the shortwave radio bands. On the back it has all sorts of antenna inputs and outputs, as well as connections for the audio and PC connection. Nice is, for pure receiving purposes the ADT-200A has a separate BNC antenna connection. This antenna input allows the reception of 10KHz - 30MHz. This is repeatedly protected against overvoltage. The receive signal then passes through a high-quality, tracking preselector (BP) before it is digitized in the ADC (analog-to-digital converter). It is then fed to the DSP where demodulation and filtering takes place. Then it goes on to the DAC (digital / analog converter), where it is analogized to make it audible.

After switching on the device, a self-test is executed first. There are some relay clicks from inside the unit. The ADT-200A has a built-in fan that runs permanently. Luckily it is quiet and therefore hard to hear. After pressing the volume control, I was astonished to note that the device does not have a built-in speaker! At first, a matching rear speaker had to be connected. After connecting the active speakers of the computer, I noticed rattling noises coming from the speaker. So I provisionally took a passive loudspeaker of my stereo to exclude that the sounds came about because of a ground loop. Unfortunately, the rattle was still there! So it came from the ADT-200A. But in the receiving operation, the disturbance is not heard. Since I make reception tests practically only with headphones, a problem got in the way! The ADT-200A has no regular headphone jack on the front panel. It has a Lemo socket that combines all the connections for headphones and microphone. So I had to ask Mr. Zahnd to send me a Lemo plug, so I could make an adapter with a 3.5mm jack. So it happened and the reception tests and comparisons could begin.
The ADT-200A does not have a ten-key keyboard for direct frequency input. Instead, he has band select buttons for the amateur radio bands and even for the radio bands incl. LW and MW. Press the selection button, select the desired band with the "Select" button and press the Select button. In addition to this, you can also select the desired frequency in MHz steps in the same way. Thereafter, the desired frequency is boosted with the silk soft VFO button. The same applies to the choice of operating modes as well as to the bandwidth selection. The step sizes can be selected with the two buttons above the VFO button. Unfortunately, the ADT-200A does not remember the last step of the operating mode. The operation of the ADT-200A is a bit confusing, because everything is organized in menus and submenus. It takes a certain amount of time for the training.
The ADT-200A can also be controlled from a computer using the ADAT Commander. The installation under Windows 10 is quite fast. The connection to the device is made via a USB2.0 interface. The communication between the ADT-200A and the ADAT Commander worked right away. As soon as the control program is started, the memories of the ADT-200A are read out first. These can then be labeled in the integrated memory manager and reloaded to the device.
If you place the mouse pointer on the tuning knob and turn the mouse wheel, the frequency should actually change. But nothing happened! Under "Edit" you get to the direct frequency input. Frequency entered and Enter pressed. Nothing happened here either. So the program was reinstalled and released in the Windows Firewall. Unfortunately without success. Certain functions, such as change the VFO worked. The guess was that the ADAT Commander was not 100% Windows 10 compliant or contained a bug. So the experiment had to be stopped.
You still have the option of displaying a spectrum with a viewing width of up to 2MHz on the PC screen. The connection to the device worked without problems. Unfortunately, the Spectrum Analyzer was not really fun either. Everything worked, unfortunately only very slowly. The ADAT-200A could not be addressed by the inputs to the Spectrum Analyzer. Only when you turn on the device VFO, the frequency changes in the spectrum. The PC control of the ADT-200A is not the same as other SDR's. Unfortunately, you can not run the ADAT Commander and the Spectrum Analyzer at the same time, which greatly limits the functionality.

ADAT-Commander

ADAT Spectrum Analyzer

The reception with the ADT-200A

In order to determine the reception power of a receiver, a comparison device is necessary. For this I took the Icom IC-R8600. He comes closest to the ADT-200A. It is also a standalone SDR with a 14bit ADC. Various antennas were used: Stampfl Active Dipole, Reuter Kreuzloop / RLA4 / 2E and the old Datong AD370.

At 11.9KHz the alpha signals from Russia could be heard again for a long time. These broadcasts are used for radio navigation of aircraft, ships and submarines. The ADT-200A brought the transmitter to the headphones with almost the same audibility as the IC-R8600. However, Icom had to switch on the preamplifier. Both devices were placed on CW with a bandwidth of 100Hz. On the long wave BBC4 can be heard here on 198KHz with quite strong signal every day. This time the transmitter was disturbed by a local disturbance, a kind of rattling. The Noiseblanker of the ADT-200A could eliminate the rattling completely, so that the transmitter was to be taken up properly. Here, the excellent AM reception of the ADT-200A was noticeable. Very low noise and a great voice reproduction. In comparison, the IC-R8600 had a rather dull playback and rushed a bit more. But his Noiseblanker could eliminate the disturbances completely. On the medium wave in the late afternoon at 531KHz. Jil FM from Algeria started to make an impact. Quiet and with heavy fading. Even with the flexibly adjustable AGC of the ADT-200A fading could not be removed. What was missed here was a synchronous detector. This is switchable with the ADT-200A, but is not implemented in the device firmware, which is a pity. By contrast, the IC-R8600, with its synch. Detector, was able to deliver the transmitter much quieter to the headphones. But also not completely free from fading. So it went on towards shortwave, directly on the 80m amateur radio band. With correctly set AGC at 2.4KHz bandwidth on LSB, rendering the ADT-200A is simply awesome! Lowest noise and a completely round and clear speech intelligibility. The Icom was also very low noise, but still did not come quite close to the clarity of the ADT-200A. There was a lack of brilliance. At very weak stations on the sward, both were pretty much on par. In the early evening at 4885KHz, Echo of Hope from South Korea was in fade-in. With this signal, the IC-R8600 brought the better understandability to the headphones. This is due to the Synch.- detector. Because the ADT-200A has none, the typical AM crackling prevented a better understanding. The 49m band in the late afternoon. The band is slowly filling up with channels and the adjacent channel interference is increasing. It depends on steep edge bandwidth filters. Of course this is not a problem for the ADT-200A. The digital filters separate the transmitters from one another. Unfortunately, the bandwidth filters can not be controlled steplessly. They can only be adjusted roughly in 1KHz steps in AM. This feature is better done on the more modern IC-R8600. The bandwidth can be set in 100Hz steps with very high selectivity. Here is the IC-R8600 at an advantage.
Virtually all reception situations in AM and SSB up to 20MHz offered the same picture. The ADT-200A usually had a slightly better speech intelligibility than the IC-R8600. Except for weak stations in AM. Since the IC-R8600 had the nose slightly forward because of the Synch.- detector. The sensitivity was purely auditory on both devices at the same level. Only above 20MHz did the ADT-200A show slightly better sensitivity than the IC-R8600. The DK0TEN beacon transmitter at 28257KHz was slightly better on the ADT-200A. In order for the IC-R8600 to keep up with this, the preamplifier had to be switched on. Gross signal problems or intermodulation were not detected during the test sessions.

Conclusion:

Although the ADAT ADT-200A comes from the beginning of the SDR amateur equipment, it convinces with its excellent receiver! The playback in AM is very clear and absolutely low noise. That reminded me of the Cubic CDR-3250. This had a similarly excellent reproduction. Unfortunately, no synchronous detector is available, although it can be selected in the menu. Here is a lot of potential given away! In SSB, the ADT-200A leaves no doubt. Audio reproduction, sensitivity and selectivity are in no way inferior to the more modern Icom IC-R8600, surpassing it in the clarity of audio playback.
A little cause for criticism was the operating concept of the ADT-200A. This is not very server friendly. Control via PC with the ADAT Commander turned out to be a big hurdle! The device could not be controlled properly. There may have been compatibility issues with Windows 10. In the past there was talk of offering a pure receiver variant. Unfortunately, nothing came of it.

posted: 19.01.2019