Typically any RF synthesizer will provide a means to connect an external reference frequency in order to provide precise frequency and time synchronization. Most commercial synthesizers and signal generators will only work with 10MHz external references. The Valon 5009 Dual Frequency Synthesizer module will also accept external 10MHz references. However, a useful feature of the Valon 5009 synthesizer is that they will also lock to other external reference frequencies in the range of 10~100MHz or more depending on model. This can be a useful capability for some lab setups where the source to be synchronized to has a reference output that is something other than 10.0MHz.
In addition to having an external reference frequency input, the Valon 5009 synthesizers are provided with Electronic Frequency Control (EFC) input. EFC provides a means for adjusting the synthesizer’s internal VCTCXO reference frequency with a control voltage. The EFC voltage can be provided either from the internal DAC or through the application of an external voltage (pictured above with a classic Helipot).
In the case of the internal DAC the EFC voltage is set using the REFerenceTrim (REFT) command either from a terminal emulator or also from the GUI. The REFT command accepts any value from 0 to 255 (8-bit) with 127 being the nominal center point. This gives the user the ability to “spot” the synthesizer’s frequency in order to correct for slight internal reference oscillator frequency errors. The range is ±10ppm typically which would provide ±10kHz trim capability at 1GHz as an example.
The external EFC capability is very useful for those applications and setups that have an AFC or phase control voltage available. The EFC control voltage is applied to the same SMA port as the External Reference input. There is no conflict here since the EFC is only used with the internal frequency reference. The EFC input impedance is approximately 20kΩ and the bandwidth is limited to
Figure 1 5009 Reference Circuit
Restrict the input voltage to -3V to +6V maximum with 1.5V ± 1.5V being a good nominal starting point. Use internal DAC with the REFerenceTrim command to help center the tuning range to give the best results with the particular AFC or phase detector being used.