ASMAX2 (AM DDS) C-QUAM Stereo Transmitter
ASMAX2 is a C-QUAM compatible Stereo, or Mono capable AM Medium Wave DDS-based (better than PLL stability) radio broadcast board for educational or similar use that offers great audio quality, 1KHz frequency step selection (for both 10KHz US and 9KHz EU steps) using only four keys. You connect left-and-right audio and send it wirelessly using a whip antenna, distance varies with surrounding conditions, RF PEP output 100mW [according to US FCC Part 15.219] or 600mW PEP [EU] (at 50 Ohm) maximum over the entire band. FULL BROADBAND DESIGN, no variable caps to adjust! RF power adjustment is done via the keypad (no trimmer). Reception is either on a regular AM radio (mono) or a stereo C-QUAM compatible radio set anywhere from 530KHz to 1700KHz (special model available for 510-2000KHz covering 160m band) and minimum step of 1KHz.

It has two independently adjustable audio inputs, for Left and Right channels with modified 50usec or 75usec pre-emphasis and low-pass filtering (depending on country).

You can change the broadcast frequency, stereo/mono mode, and other functions using the settings menu. After ENTER is pressed the DDS is re-programmed with the new transmission frequency. The power-on frequency and all other settings are saved to the built-in non-volatile memory when exiting the settings menu.

ASMAX2 is an upgraded version of the older ASMAX1 with several enhancements and improvements, some of them being: better stereo separation up to 40db, clearer audio and RF signal, left-and-right mono audio component output to drive a high-level modulator circuit (if needed), RS232 TTL level port (TX, GND, RX) for complete configuration of all parameters from a PC terminal. To do so, you need either an RS232 level translator adapter (example: rs232adpr.htm). You can also use an optional external Ethernet module to connect it to the Internet for remote management from anywhere in the world.

The firmware is periodically improved and/or enriched with additional features.
The latest firmware (for bootloader v1.20) can be found here:

For the 20x4 LCD model: Board ASMAX2 firmware.
For the boxed 8x2 LCD model: Boxed ASMAX2 firmware.
For other variants or custom configurations, please contact us.

IMPORTANT: If your device was purchased before 2022 please do NOT rush to upgrade its firmware lest you end up with a temporarily unusable device. If the update fails (due to incompatible bootloader version), you won't be able to go beyond the bootloader terminal screen (nothing shows on the LCD). (Don't worry. Your device isn't bricked.) However, in that case, you'll have to contact us with the details of the INFO terminal command so we can send you the correct update for your specific device.

One important enhancement is that on the LCD you can see the real-time modulation percentage and bar-graph, giving you the possibility to correctly adjust the final modulation of the transmitter to keep it within specs, and avoid over-modulation peaks that may lead to distortion.

The unit meets all FCC Part-15 requirements for AM transmitters. It has an excellent spectral purity with harmonics rejection better than -50dBc (upper half band) as can be seen in a Spectrum Analyzer, out-of-band spurious output better than -60dBc, and accuracy of the lock-on frequency better than +/- 0.5Hz. You can manually turn the RF output on/off, or use the built-in real-time clock to set a daily or weekend schedule for automatic on/off at a specific time. With this option, one can leave the unit at a remote site and have it operate only for the specified hours.

A C-QUAM Stereo encoding system is built-in and provides crystal clear audio up to 15KHz and with a channel separation of up to 40dB. Optionally, stereo encoding can be de-activated via a menu selection in case you need to use the device as a Mono AM transmitter.

The board is also capable of DRM transmission by selecting the appropriate mode and using appropriate (PC) software for the independent I and Q base band encoded signal. For more info, please contact us.

The device requires 13.8VDC (FCC compliant USA model), 24V (EU/International) @350mA maximum.

Disclaimer: Although this unit meets FCC Part 15 requirements for AM transmitters, this does not mean it has been FCC certified.

Available as board (dimensions 102mm [front] x 117mm) with 20x4 white on blue LCD.
Product Details
Download User's Guide
Download Schematics
Available as board with 20x4 LCD (for boxed version, see ASMAX2 NV product)
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