2013-06-17

Naked hardware #11: unbranded RTL2832U + R820T

RTL2832U + R820T bulk DTV stick teardown

That stick is Realtek RTL2832U reference design with Rafael Micro R820T RF tuner . USB ID is 0bda:2832, which is chipset default reference design ID. Why there is still eeprom?

Linux support has been added since the Kernel 3.10.

unbranded RTL2832U + R820T

unbranded RTL2832U + R820T stick

Key components:

Realtek RTL2832U
Rafael Micro R820T

Hardware internals

RTL2832U + R820T stick PCB

All components are assembled to that side of the PCB. Very standard RTL2832U stuff with nothing extra. Main components from left to right are: power LED, IR-receiver, MCX antenna connector, A7 - BAV99 diode, R820T RF tuner, 28.800 MHz crystal, 24C02 serial eeprom, RTL2832U DVB-T USB interface + demodulator, FS1117 voltage regulator and type A USB connector.

28.800 MHz clock is shared with RTL2832U and R820T - saving one component. BAV99 diode is used for ESD protection. It protects RF tuner possible ESD coming from antenna connector. RTL2832U devices having that RF tuner are very popular currently, especially in SDR usage.

There is not much to explain as I have already teardowned two devices build upon RTL2832U, but having different RF tuner. Look these first:
Naked hardware #6: ezcap USB 2.0 DVB-T Stick
Naked hardware #7: TerraTec Cinergy T Stick Black

R820T RF tuner

That RF tuner is quite new as it appeared devices less than one year ago. It is the latest tuner added to the RTL2832U reference designs until now (what I know).

Tuner is designed for digital terrestrial standards. Frequency range is from 42 to 1002 MHz, but it is said to to perform far more over that. Wide frequency range makes this tuner interesting, otherwise it is rather similar than typical DTV RF tuners nowadays. Everything but crystal is integrated, which mean less external components. No need for external LNA nor SAW filters (SAW filters are not needed since 1st generation silicon RF tuners, QT1010, MT2060, etc.).

R820T differs from the trend seen during last few years as it is not direct conversion aka zero IF tuner. That tuner is so called low-IF tuner, which means it uses intermediate frequency (IF) 5 MHz or less. Over the years, IFs used by DTV tuners has gone down from the ~50 MHz to few MHz or even zero (baseband). Compared to traditional superheterodyne architecture, direct conversion has many advantages like simpler architecture, lower power consumption and no harmful image frequency. Whilst direct conversion has many advantages it has some disadvantages too, most notable DC offset.

R820T power consumption

As this RF tuner has different architecture than all the other modern tuners used with the RTL2832U I decided to take some measurements to see how much more power it consumes than those which are based of direct conversion architecture. I used live 634 MHz DVB-T signal which has 8MHz bandwidth. That is very typical DVB-T transmission condition.

Here are the results, measured from the USB, nominal voltage 5V:
fc2580: 183mA
e4000: 176mA
fc0012: 166mA
tua9001: 186mA
r820t: 313mA

Architecture complexity has a price. It seems to drain around 135mA more current than Zero-IF tuners compared. I could assume it is pretty much same for all the the other low-IF tuners too that are designed during last 3 years or so.

PCB bottom side is empty

a lot of room for components
There is not much to say from that side of PCB. Few wires and two hole arrays, under the RTL2832U and R820T chips located other side. Those are for cooling. That device has a lot of empty room :)

USB interface

IDLE current drain without a driver: 110mA



Pictures