Dual DAB 4

I have recently bought a portable radio receiver called Dual DAB 4. It supports DAB (MP2), DAB+ (AAC) and the analog FM. It is equipped with a monophonic speaker and a telescopic antenna (although it is too short for the FM reception). Frontier Silicon Verona FS2052 tuner module contains Apollo 2 RF front-end IC and Kino 3 DSP. It is possible to use an included external 7.5V switching power supply or 6x AA batteries. 

According to the datasheet, the FM sensitivity (for 40 dB SNR) is typically -106 dBm (1.4 µV) and -97 dBm (3.9 µV) for DAB. Unfortunately there is no stereo de-noising or blending, but the mono sensitivity is fine. There are no conventional analog IF filters, signal is processed on the DSP. Sometimes there is an audible sound gap during switching between filters. The ±100 kHz selectivity is poor, but ±200 kHz is quite good – it performs better than my old JVC KS-833R car-radio with 2×180 & 1×110 kHz filters, but of course the performance is not like a famous XDR-F1HD. Nevertheless I have to admit that results are excellent for such price. I paid only 15€ for a refurbished unit!

Now let’s see what could be improved. I have removed the telescopic antenna and soldered a BNC connector for an external 75 Ω antenna input. Stereo noise decreases noticeably with an external preamp. I haven’t heard any intermodulation, even using a 18 dB preamp, so the AGC performs very well. Audio quality is very poor with the stock speaker. I replaced it with another one which was advertised as a neodymium speaker, but I’m not 100% sure about that. It is somewhat bigger (see photos below) but thankfully it fits inside the receiver case. Now I can enjoy much better sound with more bass and treble.

The battery life is a noticeable issue due to a 3.3 V linear voltage regulator. The input voltage varies depending on a supply. 6×AA batteries give 9 V, so the losses are the worst. 6×1.2 V rechargeables give 7.2 V, so losses are somewhat lower. According to the datasheet, tuner module has the highest power consumption in FM/RDS mode (317 mW). Listening to DAB/DAB+ takes respectively 227 mW and 245 mW. I have replaced the stock regulator with a step-down power switching module based on a L5973D. I can’t hear any interference coming from the switching supply, but there is some coming from the tuner itself. Just try to keep the antenna a bit away.

For some real-world tests I connected Körner 19.3 antenna to Dual DAB 4 with an external wideband preamp PAR-825U (25 dB gain, 47-862 MHz range, 2 dB noise figure). I recorded some aircraft scatters, mostly reflections via Airbus A380. RDS decoder seems to be sensitive enough on weak signals.

• 89.9 Ö2 – Radio Wien 537 km RDS
• 97.0 Ö1 & 89.4 Ö3 568 km RDS 
• 96.3 SRo 1 535 km RDS
• 88.8 Hitradio Antena 486 km RDS
• 94.1 F1 & 102.9 Impuls 566 km RDS
• 89.1 CRo 1 546 km RDS
• 99.4 Bayern 3 & 90.7 Bayern 1 621 km
• 89.5 hr3 & 101.7 hr4 700 km

What about DAB? Polish broadcast operators, Emitel and INFO-TV, are testing the DAB+ emissions. In Warsaw, the capital of Poland, there are 3 transmitters:

I don’t have any 174–240 MHz antenna, but the reception is possible all the time with Körner 19.3 (Emitel, H) and 2x 5-el (INFO-TV, V) at a distance of about 100 km.