ASMAX2 is a CQUAM 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 CQUAM
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,
clock date/time, 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
the exiting the settings menu.
ASMAX2 is an upgraded version of our 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 (as for example
or even a USB-to-RS232 converter. You can also use an optional
external Ethernet module to connect it to the Internet for
remote management from anywhere in the world.
One important enhancement is that on the LCD you can the see
the real-time modulation percentage and bargraph, 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
Analyser, 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 device requires 13.8VDC (US Model), 24V (EU/International)
Disclaimer: Although this unit meets FCC Part 15 requirements
for AM transmitters, this does not mean it has been FCC