Sherwood TD130SB AM Stereo Receiver - C-QUAM
The Sherwood TD130SB is an AM Stereo / FM Stereo component tuner receiver. Its most prominent feature is the ability to decode stereo AM broadcasts that use the C-QUAM (Compatible QUadrature Amplitude Modulation) system.
Features include: auto/manual tuning, 6 user preset stations per band. Attractive blue fluorescent display of station frequency. Built-in AM bar antenna, connections for external FM and AM antenna. FM antenna connections include 75 ohm and 300 ohm inputs, suitable for connection via coaxial cable to a roof antenna and indoor dipole antenna respectively.
Decline in Australian AM Stereo broadcasting
As of 2010, there are almost no Australian AM stations broadcasting in stereo. Exceptions include 2CA on 1053 kHz in Canberra.
AM Band limits - Australian models
Units sold in Australia are factory preset to European settings:
- FM: 87.5 - 108.0 MHz, 50 kHz tuning step
- AM: 522 - 1611 kHz, 9 kHz tuning step.
As of 2008, more and more community stations are narrowcasting in the extended AM broadcast band from 1611 to 1710 kHz in Australia. Unfortunately, most older receivers (especially the PLL/digitally tuned ones) are not able to tune past 1611 kHz. A TD130SB from the factory is subject to this limitation.
Modifying the TD130SB to receive the extended AM band
Fortunately, it is easy to modify the TD130SB to receive the extended AM band. The secret lies in the Tohiba TC9147BP IC chip. This chip is a multifunction IC that incorporates a PLL, input control and display outputs. Two control pins on this IC (wired to jumpers on the PCB) dictate the frequency bands and tuning steps. It supports Japanese, European and US bands. An interesting (and vital) key point is this IC has a 9 kHz tuning step mode for the US 522-1710 kHz bandplan.
TC9147BP US band limits:
- FM: 87.5 - 108.0 MHz, 100 kHz tuning step
- AM: 522 - 1710 kHz, 9 kHz tuning step or
- AM: 530 - 1710 kHz, 10 kHz tuning step
The US setting with 9kHz steps is suited to Australia (and Europe as well), and it has a 100 kHz tuning step for FM. This is more convenient because in Australia, no FM broadcast station is allocated a frequency that is a multiple of 50 kHz. All stations are a multiple of 100 kHz.
The two pins, E1 and E2, correspond to pins 30 and 29 respectively. From the factory default state, E1 is held high (via a 100 kOhm pullup resistor to the +5v bus) and E1 is grounded (via a jumper wire link). To activate the US 9kHz bandplan, the logic state of E1 and E2 needs to be swapped.