RF Synthesizer is a simple FM signal source. It is based on the Analog Devices ADF4360-series of integrated phase-locked loops. The entire circuit is on a bare (no enclosure) 2" by 3" circuit board and will run from 7.5V to 15V input. The total input current is about 100ma.

While the unit can be constructed for any freqeuncy from 50MHz to 1GHzMHz, the frequency range of any given unit is limited. The tuning range depends on the frequency. The following list gives some typical examples:

• 750MHz to 1GHz using ADF4360-7
• 400MHz to 500MHz using ADF4360-7
• 320MHz to 400MHz using ADF4360-7
• 200MHz to 300MHz using ADF4360-8
• 140MHz to 200MHz using ADF4360-8
• 120MHz to 150MHz using ADF4360-8
• 100MHz to 130MHz using ADF4360-8
• 75MHz to 100MHz using ADF4360-8
• 60MHz to 75MHz using ADF4360-8
• 50MHz to 65MHz using ADF4360-8 plus divide by 2
• 37MHz to 50MHz using ADF4360-8 plus divide by 2

Other features include a microprocessor (Atmel Mega8) to control the PLL and to provide modulation by means of an 8-bit R-2R DAC, a digital pot to vary the deviation, a power sensor to measure the actual output power, voltage regulators to provide stable operation, a temperature-compensated reference oscillator to provide +/-2ppm frequency accuracy, a 10db attenuator to provide additional output amplitude range over that provided by the PLL, and a by-2 frequency divider to extend operation down to at least 50MHz. Harmonic reduction filtering is provided on the divider output. Output is through an SMA coaxial connector.

Provided modulation includes 1200 baud Bell202, 1200 baud MSK, other AFSK modulations from 2400 baud down to 300 baud. Direct FSK at 9600 baud is also provided. Pseudo-random data is provided. Code can be customized to provide data in predetermined patterns. DTMF may also be possible. Single test tones (static, stepping up or down in frequency, smoothly varying) are provided. Deviation is adjustable from very low to rather high values. Twist or pre-emphasis can be added. All AFSK modulation is phase-continuous. A low-pass reconstruction filter is also provided for the modulation signal; this filter has a single pole and has one bandwidth suitable for most AFSK modulations and one for FSK. The filter bandwidth is changed manually. Modulation is highly dependent on code and can be customized to meet a variety of requirements.

Frequency can be set to a specific value withing the operating band. The frequency can be set to automatically scan between preset limits. It can also be set to increment or decrement on input of a specific character; the Terminal Interface outputs the frequency and the output signal amplitude at each step.

The microprocessor includes an ASCII serial RS232 interface with a ROM Monitor and a Terminal Interface with commands to vary PLL and modulation. It also reads the output amplitude and senses PLL lock status. A switch and an LED give additional control and status indication. The processor has a standard Atmel "in-system programing" connector. Source code is provided and instructions are included for operating the ROM Monitor and the Terminal Interface from a generic terminal program.

RF Typical Specs:

• Frequency range: as listed above
• Frequency accuracy: +/-2ppm (200Hz at 100MHz)
• Channel spacing: 2.5KHz, set from Terminal Interface.
• Frequency agility: can be ramped, hopped, etc, up to a rate of about 5us per point.
• Frequency scanning: between user defined limits at user defined rate. Manual up/down frequency change is provided. Both features are modifiable in software.
• Output power into 50 ohms without divide by 2: 0dbm, -3dbm, -6dbm, -9dbm, -10dbm, -13dbm, -16dbm, -19dbm, accuracy tbd; with divide by 2: 0dbm and -10dbm.
• Output voltage: directly read at RF output and reported by Terminal Interface
• PLL Lock Status: reported by Terminal Interface and indicated by LED; modifiable in software.
• Output connector: SMA
• 3rd Harmonic content: typ 20dbc at frequencies above 65MHz; estimated 10dbc below 65MHz.

Electrical Typical Specs:

• Input voltage: 7.5V to 15V
• Input current: about 80ma (independent of input voltage)
• RS232 interface: 9600 baud, N81 (changable in processor code)
• RS232 connector: standard female DB9
• Programming: Atmel AVR ISP interface; connects to a variety of Atmel and 3rd party programming devices.

Programming Typical Specs:

• ROM Monitor: allows examination and alteration of memory contents
• Serial Terminal Interface: allows setting operating frequency, channel interval, modulation, and read of output power
• EEPROM: holds frequency limits and other operating parameters for rapid power-up without terminal control.
• Source Code: Provided. Can be customized by ORE or customer. Atmel AVR "Studio" (tm) assembly-language or gcc c-compiler are usable.

Mechanical:

• Size: 2" by 3" (5.1 by 7.6cm)
• Enclosure: none

Uses:

• Receiver frequency calibration
• Filter tuning
• Receiver deviation calibration
• Transmitter exciter
• Receiver local oscillator

More detailed specs, prices, and availability will be available by late November, 2007. If you are interested immediately, e-mail ORE for details.

Thanks for stopping by.

James Wagner, Chief Engineer, Oregon Research Electronics

Updated September, 2007