Hello,
I'm building an antenna tuning unit for a 1/4 wavelength vertical antenna for the 40m band.
The ATU will require me to use a frequency synthesizer connected to a VCO to generate frequencies between 7.0 and 7.3 MHz. After a frequency sweep is done a directional coupler will determine the lowest VSWR through a ESP8266EX ADC. This will read out VSWR and the resonant frequency of the tuned circuit. I have this design completed, Arduino code written and have ordered parts off Digikey and am now building the first part of the circuit which is a crystal oscillator used as a reference oscillator for the frequency synthesizer.
The 8MHz oscillator is to be fed into a CMOS MB87014A Fujitsu synthesizer. The required output of the oscillator is to be High + 3.5V and Low - 3.5V.
In LTspice I managed to get the simulation oscillating please see below but when constructed on copper board I could not get an oscillation. This is my first time building a crystal oscillator. Here are the multimeter values after probing:
Voltages:
Node 1 (Node after RFC to V+) 1.67v
Q Collector 1.61v
Q Base 660mV
Node 2 (Voltage divider node to crystal) 550mV
Currents:
THrough collector resistors 3mA
THrough R2 1mA
THrough R9 &R6 1.65mA
THrough L5 & R8 292mA
(Assumed current through crystal 1.65mA - 292mA = 1.43mA
Assumed power through crystal 786 uW - Under 1mW drive level)
Continuity check revealed no connections between grids at the time of board cutting. All capacitors were checked with Ohm meter and respond good.
It appears the RF gain is staying at roughly 1 when probed with oscilloscope.
My assumption is that the toroid core for the impedance matching transformer is unsuitable for a 8MHz frequency. I believe I need a core with a low permeability. The material for this toroid was L8.
Any assistance would be appreciated.
I'm building an antenna tuning unit for a 1/4 wavelength vertical antenna for the 40m band.
The ATU will require me to use a frequency synthesizer connected to a VCO to generate frequencies between 7.0 and 7.3 MHz. After a frequency sweep is done a directional coupler will determine the lowest VSWR through a ESP8266EX ADC. This will read out VSWR and the resonant frequency of the tuned circuit. I have this design completed, Arduino code written and have ordered parts off Digikey and am now building the first part of the circuit which is a crystal oscillator used as a reference oscillator for the frequency synthesizer.
The 8MHz oscillator is to be fed into a CMOS MB87014A Fujitsu synthesizer. The required output of the oscillator is to be High + 3.5V and Low - 3.5V.
In LTspice I managed to get the simulation oscillating please see below but when constructed on copper board I could not get an oscillation. This is my first time building a crystal oscillator. Here are the multimeter values after probing:
Voltages:
Node 1 (Node after RFC to V+) 1.67v
Q Collector 1.61v
Q Base 660mV
Node 2 (Voltage divider node to crystal) 550mV
Currents:
THrough collector resistors 3mA
THrough R2 1mA
THrough R9 &R6 1.65mA
THrough L5 & R8 292mA
(Assumed current through crystal 1.65mA - 292mA = 1.43mA
Assumed power through crystal 786 uW - Under 1mW drive level)
Continuity check revealed no connections between grids at the time of board cutting. All capacitors were checked with Ohm meter and respond good.
It appears the RF gain is staying at roughly 1 when probed with oscilloscope.
My assumption is that the toroid core for the impedance matching transformer is unsuitable for a 8MHz frequency. I believe I need a core with a low permeability. The material for this toroid was L8.
Any assistance would be appreciated.