Naked hardware #12: USB Audio Transmitter

USB Audio Transmitter teardown

This time I decided to teardown a little bit different hardware as usually - radio transmitter.

unbranded USB Audio Transmitter

USB Audio Transmitter

Key components:

Holtek HT82A821R
Quintic QN8027

General info

It is cheap noname USB audio transmitter, that is supported beginning from the Linux Kernel 3.4. Kernel driver name is radio-keene, done by Norwegian V4L superman Hans Verkuil.

Device has a USB ID 046d:0a0e assigned. That ID seems to belong Logitech, but likely company has nothing to do with device itself. Maybe the ID is just chosen because Logitech uses it on some USB speakers?

Device starts transmitting just after it is plugged on 95.160 MHz. Use of device is very easy as it implements itself as USB speaker - just plug it to the USB port and select proper audio output from volume control. There is some extra controls available via V4L2 interface, like a frequency setting and TX power. Check and tune using v4l2-ctl tool, "v4l2-ctl -d /dev/radio0 --all" lists all settings.

Hardware internals

PCB top side

All components are assembled to that side of the PCB. Bigger chip is HT82A821R and smaller is QN8027.

HT82A821R is USB speaker chip that supports standard USB audio profile.  The other chip, QN8027, is of course FM transmitter. Two similar looking metal tubes are clock sources. Unfortunately I forget to check clock frequencies, but according to datasheets HT82A821R supports 6 & 12 MHz and QN8027 supports 12 & 24 MHz.


Black wire is antenna, which is physically connected to the metal side frame giving physically a little bit more length.

PCB bottom side is almost empty

PCB bottom side

No components on that side, but still something. There seems to be about half of the antenna wired directly to the PCB.

BL-UAT82 V 1.0 ?

USB interface

IDLE current drain without a driver: 38mA

lsusb -vvd 046d:0a0e Bus 003 Device 010: ID 046d:0a0e Logitech, Inc. Device Descriptor: bLength 18 bDescriptorType 1 bcdUSB 1.10 bDeviceClass 0 (Defined at Interface level) bDeviceSubClass 0 bDeviceProtocol 0 bMaxPacketSize0 8 idVendor 0x046d Logitech, Inc. idProduct 0x0a0e bcdDevice 1.00 iManufacturer 1 HOLTEK iProduct 2 B-LINK USB Audio iSerial 0 bNumConfigurations 1 Configuration Descriptor: bLength 9 bDescriptorType 2 wTotalLength 135 bNumInterfaces 3 bConfigurationValue 1 iConfiguration 0 bmAttributes 0xa0 (Bus Powered) Remote Wakeup MaxPower 500mA Interface Descriptor: bLength 9 bDescriptorType 4 bInterfaceNumber 0 bAlternateSetting 0 bNumEndpoints 0 bInterfaceClass 1 Audio bInterfaceSubClass 1 Control Device bInterfaceProtocol 0 iInterface 0 AudioControl Interface Descriptor: bLength 9 bDescriptorType 36 bDescriptorSubtype 1 (HEADER) bcdADC 1.00 wTotalLength 40 bInCollection 1 baInterfaceNr( 0) 1 AudioControl Interface Descriptor: bLength 12 bDescriptorType 36 bDescriptorSubtype 2 (INPUT_TERMINAL) bTerminalID 1 wTerminalType 0x0101 USB Streaming bAssocTerminal 0 bNrChannels 2 wChannelConfig 0x0003 Left Front (L) Right Front (R) iChannelNames 0 iTerminal 0 AudioControl Interface Descriptor: bLength 10 bDescriptorType 36 bDescriptorSubtype 6 (FEATURE_UNIT) bUnitID 13 bSourceID 1 bControlSize 1 bmaControls( 0) 0x03 Mute Control Volume Control bmaControls( 1) 0x00 bmaControls( 2) 0x00 iFeature 0 AudioControl Interface Descriptor: bLength 9 bDescriptorType 36 bDescriptorSubtype 3 (OUTPUT_TERMINAL) bTerminalID 3 wTerminalType 0x0301 Speaker bAssocTerminal 0 bSourceID 13 iTerminal 0 Interface Descriptor: bLength 9 bDescriptorType 4 bInterfaceNumber 1 bAlternateSetting 0 bNumEndpoints 0 bInterfaceClass 1 Audio bInterfaceSubClass 2 Streaming bInterfaceProtocol 0 iInterface 0 Interface Descriptor: bLength 9 bDescriptorType 4 bInterfaceNumber 1 bAlternateSetting 1 bNumEndpoints 1 bInterfaceClass 1 Audio bInterfaceSubClass 2 Streaming bInterfaceProtocol 0 iInterface 0 AudioStreaming Interface Descriptor: bLength 7 bDescriptorType 36 bDescriptorSubtype 1 (AS_GENERAL) bTerminalLink 1 bDelay 1 frames wFormatTag 1 PCM AudioStreaming Interface Descriptor: bLength 11 bDescriptorType 36 bDescriptorSubtype 2 (FORMAT_TYPE) bFormatType 1 (FORMAT_TYPE_I) bNrChannels 2 bSubframeSize 2 bBitResolution 16 bSamFreqType 1 Discrete tSamFreq[ 0] 48000 Endpoint Descriptor: bLength 9 bDescriptorType 5 bEndpointAddress 0x02 EP 2 OUT bmAttributes 9 Transfer Type Isochronous Synch Type Adaptive Usage Type Data wMaxPacketSize 0x00c0 1x 192 bytes bInterval 1 bRefresh 0 bSynchAddress 0 AudioControl Endpoint Descriptor: bLength 7 bDescriptorType 37 bDescriptorSubtype 1 (EP_GENERAL) bmAttributes 0x00 bLockDelayUnits 0 Undefined wLockDelay 0 Undefined Interface Descriptor: bLength 9 bDescriptorType 4 bInterfaceNumber 2 bAlternateSetting 0 bNumEndpoints 1 bInterfaceClass 3 Human Interface Device bInterfaceSubClass 0 No Subclass bInterfaceProtocol 0 None iInterface 0 HID Device Descriptor: bLength 9 bDescriptorType 33 bcdHID 1.10 bCountryCode 0 Not supported bNumDescriptors 1 bDescriptorType 34 Report wDescriptorLength 22 Report Descriptor: (length is 22) Item(Global): Usage Page, data= [ 0x00 0xff ] 65280 (null) Item(Local ): Usage, data= [ 0x01 ] 1 (null) Item(Main ): Collection, data= [ 0x01 ] 1 Application Item(Global): Logical Minimum, data= [ 0x00 ] 0 Item(Global): Logical Maximum, data= [ 0xff ] 255 Item(Local ): Usage Minimum, data= [ 0x00 ] 0 (null) Item(Local ): Usage Maximum, data= [ 0x01 ] 1 (null) Item(Global): Report Count, data= [ 0x08 ] 8 Item(Global): Report Size, data= [ 0x08 ] 8 Item(Main ): Output, data= [ 0x02 ] 2 Data Variable Absolute No_Wrap Linear Preferred_State No_Null_Position Non_Volatile Bitfield Item(Main ): End Collection, data=none Endpoint Descriptor: bLength 7 bDescriptorType 5 bEndpointAddress 0x81 EP 1 IN bmAttributes 3 Transfer Type Interrupt Synch Type None Usage Type Data wMaxPacketSize 0x0008 1x 8 bytes bInterval 48 Device Status: 0x0000 (Bus Powered)

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