Frequency Stabilizer
Construction

The new Rev 2 boards currently being sent with the kits have the parts for integrating the stabilizer with the VFO on the PCB. If you ordered the stabilizer with the receiver kit, the parts were installed when the VFO was built.

Connecting a cable between the stabilizer and the stabilizer parts in the VFO is all that is needed to have a working stabilizer.

The reason for the output being labeled "Relay" was that the original stabilizer setup used a relay mounted on the VFO toroid to control frequency. The current draw of the relay caused problems with overheating the output of the CA3140 in the stabilizer.

A fix was found for the problem, but using varicaps and integrating the parts on the VFO PCB made installation a snap and performance became consistently excellent. The magnetic coupling does work and for those that would like to experiment with magnetic coupling check out Frequency Stabilization using Magnetic Coupling.

The VFO coil is wound with 19 turns when using the stabilizer. If you wind it with 18 turns, just pull the windings together to get the 14 MHz VFO within range of the 8pf ceramic trimmer.

The varicap on the 8pf trimmer raises the 14 MHz frequency 300-400 kHz, so the VFO coil is wound with 19 turns, instead of 18 turns without the stabilizer.

Readjustment of the toroid windings will be necessary to get the 8pf trimmer in the 14 MHz range of the VFO. The addition of the varicap will raise the 14 MHz frequency and bringing the windings closer together will be necessary.

____Start with the resistors and capacitors. Picture You will not install a 2 meg resistor that will be left over in some kits. Be sure to get the 4.7K in the right footprint. If it gets in a 4.7 meg spot, the integrator will not work.

Be careful mounting the 7805. The front of the 7805 faces to the outside of the board. The bold line of the footprint indicates the location of the heat sink, the back of the 7805. Be sure to get good solid solder joints at the pins of the regulator to the PCB.

There are four jumpers (Picture) on the board:

There are two connections to Board 1 in the VFO section, one to the reset button and one to 12 volts and ground.

A box labeled "Stabilizer" between the VFO Amplifiers on the edge of the PCB goes to the "VFO IN" connection on the Stabilizer board.

At the VFO, above the main tuning capacitor, there is a box labeled "Stabilizer In" that goes to the box labeled "Relay" on the Stabilizer board.

Inside the "VFO IN" box are the connections to the VFO "Stabilizer" connection on the receiver board.

The lower one is the VFO connection (connected to the .01 input capacitor) and the upper one is the "Gnd" (ground) connection.

It is easier to make this connection first, mount the stabilizer board, then make the connection to the VFO "Stabilizer" box on Board 1.

____Solder the shield of a 6" length of miniature coax cable to the ground plane underneath the board.

____Solder the center conductor to the trace connecting to the .01 cable underneath the board. You might be able to get the center conductor through the hole on the top side but it is much easier to solder to the trace underneath.

The yellow arrow points to the connection between the VFO amplifiers that connects to the cable from the "VFO IN" connection on the Stabilizer board. Miniature coax is used for the connection.

If desired, wire loops can be installed at both the "Stabilizer" box and in the "Ground" box for easy connection points.

The output of the stabilizer is marked "Relay" and "Gnd". Both connection holes are in the box labeled "Relay".

____Connect the cable to the stabilizer first. Mount the stabilizer board, then connect the cable to the receiver board as shown below. Use about a 5" length of the miniature 75 ohm coax.

Note the ground and center wire connections. There is a "Gnd" label next to the Ground hole. Or solder the shield underneath the board on the ground plane.

____Mount and connect the "Reset" button to the stabilizer. The Reset button is a small push-button switch, closes on push.

Be sure to use enough wire length to reach where the Reset button will be mounted on the front of the receiver. Twist the wires together to keep them neat.

The picture above shows the connection of the output of the stabilizer to Board 1. The connection is made underneath the board. The shield is soldered to the ground plane and the center conductor is soldered to the pad underneath the board where the "Stabilizer In" hole is located. See the picture below.

This picture shows the connection on the top side of the board. Note the yellow arrow pointing to the connection hole. This hole and both resistors connect to the same pad underneath the board.

____Connect the B+ (12 Volts) and Ground to the stabilizer board.

Even though pictures of the receiver show the 75 miniature coax connecting to B+, regular hook-up can be used. Two pieces of wire twisted together work great.

There are enough holes here to install wire loops for connection points for the 12 volt and ground connections if desired.

The 12 volt power supply to the stabilizer should be filtered from the receiver. Make a connection to the receiver only at the BOLD 12 Volt connections, where the RF Chokes are located. Using an additional RF Choke at the 12 Volt connection to the Stabilizer PCB wouldn't hurt.

Have the stabilizer turn on at the same time as the receiver. The VFO will do some short term quick drifting, as the 2N5486 warms up from the operating current.

The stabilizer should lock very fast. The current integration of the stabilizer with the VFO has provided excellent stabilization. The stabilizer should be reset by pushing the reset button after about five minutes.

Depending on how fast the room temperature is changing, normal reset times are about two to four hours.

There will be a slight, short term drift when changing VFO frequencies as you change bands.

If the stabilizer does not lock up after 5 minutes of operation, then some troubleshooting is in order.

If the drift is in one direction, then one of the signals to the integrator is missing. Frequencies should be checked at the .01 caps going to the transistors.

Sudden drifting, with no jumping, is a bad solder connection at a ground or B+ pin at an IC. Check the connections to the transistors also.

Jumping of the frequency, around the stabilized frequency, can be a bad ground at one end of the miniature coax. A lot of movement during setup of the boards can cause the ground lead to break right at the cable where the tinned ground shielding ends against the insulation. Pull gently at the cable to make sure there is a strong connection.

All the readings below are with the VFO at 14 MHz.

It is very difficult to blow a CMOS chip, unless you put the 5 Volt regulator in backwards. Otherwise, your problem has to be a bad solder connection on the board. An unsoldered pin at one of the ICs is the most likely problem to occur. Check carefully!

Resistor/Capacitor Mistakes

Resistors too low in value at the integrator, the 4.7 meg values, will cause modulation in the output of the VFO. This modulation will be heard in the speaker. Remove the wire to the varicaps at the main tuning capacitor to test.

Check the integrator resistors - two 4.7 meg.

If there is no output at the .01 caps coming from the transistors, check the 22K resistors for correct value, and correct polarity of the diodes.