First Mixer, Post-mixer Amplifier, Crystal Filters

This section uses the remaining FT50A-75 ferrite cores (Black colored, Bag 4). Click on the link above for pictures and text on winding the coils for the mixer.

The center transformer of the mixer is only a ten turn bifilar coil. The coils at each end of the mixer are ten turn bifilars with a 5 turn secondary.

The 3.547 MHz crystals used in the 40/20 filter are extremely high Q. These crystals make excellent CW filters. The 100pf capacitors supplied with the kit for this filter will not receive SSB.

If SSB listening is wanted on 40 and 20 meters the capacitors used in the 3.547 MHz crystal filter need to be lowered. Any capacitor value between 27pf to 39pf may be used.

Four of the lower value caps are needed to replace the four 100pf that are normally installed in the 3.547 MHz crystal filter. At this time, lower value caps are not supplied with the kit. Email if you do not have any and wish to have SSB reception.

On the 4.000 MHz crystal filter, the 100pf capacitors work fine for SSB reception on 17 meters. The 4 MHz crystals have a lower Q than the 40/20 crystals and do not need lower capacitors to receive SSB.

Insert all the components that have their values inside the footprint. They are the following:

____4 - RF Chokes (Bag 3), Footprint on PCB is rectangle with square edges, "RF" inside the rectangle. Choke is about the size of a 1 watt resistor with rounded edges. Two are located next to the First Mixer and Amplifier and the other two are at the input to the crystal filters.

Correction: DO NOT install the RF Choke next to the "12 Volt" box above the VN0106N3 switching circuitry on this board. Install a jumper wire in place of the RF Choke. See the picture below:

Solder

Solder

Solder

Resistors:

____3 - 470 ohm (Bag 4), One is located at the top left of the first mixer, and the other two are located to the top and right of the IR LEDs.
____2 - 1K (Bag 3), Located at the top and bottom of the input to the crystal filters.
____1 - 2.2K resistor (Bag 4), at the left of the middle bifilar Ferrite Core in the mixer.

Capacitors (Going left to right on the board):

____8 - 100pf NPO caps (Bag 3), Orange color, short leads flared out, labeled "101". All located inside the crystal filters.

Note: The value of the capacitor you use in the filters determines the bandwidth. If you want all SSB, change the caps on the 40/20 (3.457MHz) filter to 39pf (not included in kit, any value cap between 27pf to 39pf will work) for best reception. The 100pf caps on the 30/17 (4.000MHz) work fine on SSB. If you are CW only, raise all the capacitors to 200pf, after you have the receiver working.

When raising the value of the capacitors, solder the new ones underneath the board to the existing capacitors. Taking out the existing capacitors can be a lot of trouble and you may want to revert to the old values at some time in the future.

Solder

Other Parts:

____6 - LEDs (Bag 3), Red colored, match the flat on the LED to the flat on the footprint. The short lead is on the same side as the flat. Note: If you ordered the Super Bright LEDs, you can place two of them at the input of the crystal filter, next to the IR LEDs. Use different colors to help crystal filter identification. If you ordered the Bright Red LEDs, they can replace the ones in the mixer. See Modifying the LEDs.

Solder

____2 - IR LED (Bag 4), Smoky colored, on a cardboard strip, do not cut the leads off the strip, tear the IR LEDs off the strip and clean the bottom of the leads. Located at the input to the crystal filters, right next to 100pf caps.

The short lead is on the same side as the flat. Mount as high as possible and match the flat on the LED to the flat on the footprint.

Bend the one shown above, in the middle of the board, toward the Phototransistor at the VFO board. Aim the phototransistor back toward the IR LED.

The IR LED near the outside of the board points to the phototransistor at the Crystal Oscillator on Board 2. Wait till you mount the boards to aim this IR LED.

Solder

____2 - VN0106N3 (Bag 2), static sensitive part, touch a ground lead before removing the part from the bag. Match the flat on the part to the flat on the footprint. Spread the outside leads slightly to fit the footprint. Marked "SI N, 0106, 8302".

Solder

Solder

Solder

Solder

Solder

Please Check!

Carefully inspect the wires on the bifilar side of the cores and make sure they are not shorted. There is no ohm meter check for this error, so you must look carefully. Make sure the bare parts of the wires are not touching!

Double check underneath the board to make sure there is not a solder bridge between the leads.

The second and third core (counting from the front) carry 12 Volts. If the bifilar leads are shorted there will be some burning (smoke) of the wires, the LEDs will not light up, and the RF Choke that feeds 12 Volts to that core will need to be replaced if it shows less the 6 ohms resistance.

A dot is placed outside the footprint so that you can double check your placement after it has been soldered to the PCB. The leads on each side of the part need to spread apart slightly to fit the footprint.

Solder

____1 - SPDT Miniature PC Mount switch (Bag 5), There is a switch footprint in front of the First Mixer. There are two hole patterns. Mount the switch in the holes that work. Picture

____Miniature Coax Cable, cut a 12 1/2" piece (Bag 6), The coax is used between the VFO OUT in the upper left hand side of the board, to the VFO IN at the lower right hand side of the board.

The coax supplied with the kit is Teflon 75 ohm cable. The best way to strip the insulation is to get a very sharp utility knife and slice a 1" section length wise, then fold over the cable and pull the shielding/center out of the insulation.

Pull back the shielding slightly to loosen, make a small hole at the bottom, and pull through the center wire.

Since it is Teflon, there is no of danger burning up the insulation on the center wire and causing a short while soldering.

Best to mount this jumper underneath the board for a cleaner appearance and avoid interfering with the IR switching at the bandpass filters.

When soldering underneath the board, solder to the traces and the ground plane. Saturate the ground braid with solder first, then solder the braid to the ground plane. Next solder the center wire to the output(VFO OUT)/input(VFO IN) pads. Pictures

____Miniature Coax Cable, cut a 10" piece (Bag 6). Strip and prepare as explained above.

____Solder the center wire to "XTAL FILTER OUT", solder the braid to the "Ground" box. Leave the other end loose at this time.

____Place the PCB in front of a bright light. If you see light shining through any of the soldering holes, you missed a solder connection.
____Check the dot on the Minicircuits T4-6T transformer.
____Check the primary/secondary leads on the ferrite cores in the mixer/amplifier for solder bridges or shorts between the wires.
____Check the dot on the MOSFETs.
____Check the flats on the LEDs and make sure they match the flats on the footprint.
____Check the flats on the VN0106N3s, they should both be facing to the right.
____Look at all the 100 ohm (brown, black, brown) resistors and check the size of the footprint underneath the resistor. It should be shorter than the length of the resistor body.
____Look at all the 100K (brown, black, yellow) resistors and check that the size of the footprint is as long as the resistor body. The yellow band is a dead giveaway to find these resistors.

Take the capacitor and put the soldering tabs into the holes on the PCB footprint. Then roll the capacitor onto the ground plane and solder in place. This will automatically mount the capacitor straight and leave plenty of room for soldering to the tabs.

Be careful, as the capacitor begins to lie flat, the tabs come out of the holes in the PCB.

After the capacitor has been mounted to the board, solder the 39pf capacitor to the middle tab, and the 10pf (or 6.8pf) to the back tab of the capacitor, as shown on the silkscreen.

Please note: When mounting the capacitor on a ground plane, without the holes for the soldering tabs, the tabs will be forcefully grounded on the ground plane because their length is as long as the mounting legs.

Bend the soldering tabs up and against the stator connections to keep from grounding the stator sections, when mounting on PCB ground planes other than the receiver's PCB. Picture