VFO and Amplifiers

Most of the components for this section come from Bag 5 and 6. Use a VOM (volt-ohm meter) or DVM (digital volt/ohm meter) to measure resistance values on the resistors (do not trust the color codes) and a small magnifying glass to read the numbers on the small capacitors.

You can go through and mark the parts in both Bags, or look for the parts as you put them in, marking those you measure and don't need right now.

Wire size does make a small difference on the VFO coil. Tests show that using wire size #20 on the toroid gives the best stability. Wire size with the kit will be #24 or #22, but if you have the larger size wire it would be the best to use.

____Wind the VFO coil. Use the large toroid, T68-6 (Bag 6, Yellow color, outside diameter 11/16"), and cut a length of wire 16" long. Start with 1" of wire on the end where you start. Wind 18 turns on the toroid and put a 30 degree gap between the ends of the winding. A turn is counted each time the wire passes through the center of the core.

____Wind one of the FT50A-75 ferrite cores (Black color, Bag 4) that is used at the 5V input to the VFO. Measure 8" of wire and put 7 Turns on the ferrite core. Wind evenly around the core with a 30 degree space between the ends of the winding. This is the VFO RF Choke.

____After winding the cores, trim the excess length, and scrape the enamel off the wire on the ends as close to the toroid/ferrite core as possible. Then flow solder onto the wires.

Please Note!: Pre-tinning the wires shows where you missed scraping the enamel and makes a good solder connection on the board.

____Mount spacers on each side of the board on the four corners to provide support for insertion of parts and easy soldering. Picture

Begin each section by filling in the parts that have the value inside their footprint. They are the following:

____1 - Large RF Choke (Bag 3), Footprint on PCB is a rectangle with square edges, "Large RF" inside the rectangle. Choke is a wirewound choke about 1/2" long with black plastic ends.
____2 - .01 capacitor (Bag 3), Footprint on PCB is rectangle with rounded edges, ".01" inside the footprint. One is in the picture above and the other is next to the photodiode at the bottom of the board.

Resistors:

____1 - 39K (Bag 6), below FET (2N5486) Remember, square edges for resistors, do not put the resistor in the 39pf NPO capacitor footprint.
____1 - 1M (Bag 4), Next to photo diode in lower right hand corner.

Capacitors (Going left to right on the board):

Note: The 68pf capacitor next to the 10.545 relay is not installed. The capacitor marked 10pf above the trim cap marked 14.068 is replaced with a 47pf NPO capacitor. Picture

____1 - 47pf NPO (Bag 5), Orange colored, small square, labeled "470, JCC". Placement of this capacitor depends on whether you are using the stabilizer. If using the stabilizer, capacitor goes inside the stabilizer parts box as shown in the picture above. If not using the stabilizer, capacitor is put in the bottom footprint outside the box.

Second one is located at the tuning capacitor, leave one end unsoldered until the tuning capacitor has been mounted. Bend the capacitor toward the large hole so that most of the lead length is underneath the board. The short lead will barely reach the main tuning capacitor if mounted flush with the board. Push unsoldered lead against the PCB to keep out of the way. Picture

Solder

Note: Be careful not to splash solder on the Poly capacitors. Do not remove the solder if you get any on the poly caps. It will be very difficult to remove and could destroy the capacitor. Just check to make sure the solder is not touching one of the lead wires.

Solder

Note: The higher value of this cap allows the VFO to be lowered to 13.5 MHz and provides a 500Hz bandwidth - 13.5 to 14.0 MHz, to cover two SWL bands.

Solder

Other Parts:

____2 - LEDs (Bag 3), Red color, next to relays. Match flat of 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, one can be placed next to the 1N914 diode. See Modifying the LEDs.
____2 - Yellow Trim caps (Bag 1), Next to relays, note flat area on body and match to the flat on the footprint.

Note: The Yellow Trim cap at the 10.455 text tunes the 41 meter band. With no modifications, the VFO will tune the 41 meter band from 7.300 to 7.6 MHz. If the lower end of the 41 meter band is desired, 7.100 to 7.300 MHz, solder a 20pf NPO (SWL parts bag) capacitor across the two unmarked holes next to the yellow trim capacitor. See picture below:

Bend the leads about 1/8" away from the body of the diode for easy insertion into the PCB.

____1 - 2/8 Ceramic Trim cap (Bag 1), Note arrow over one leg, match the arrow on the trimmer to the arrow on the footprint. Clean and tin the leads to make sure of a good connection before soldering on the board.

Note: Placement depends on whether you are using the stabilizer. If you are using the stabilizer, the trimmer goes inside the stabilizer parts box as shown above. If you are not using the stabilizer, the trimmer goes next to the 14.068 text.

Solder

Solder

Solder

Solder each one individually

Important Blue Relay mounting information!

1. Clean and tin the pins with solder before mounting on board to ensure a good solder joint. The pins can be difficult to solder without pre-tinning.

2. Be sure to mount the relays flush with the board. If mounted slightly off the board, the relay will flex back and forth while handling the board, and break the pins between the relay and PCB.

Solder one pin to the PCB, then hold the relay against the top side of the PCB and remelt the soldered pin to set the relay against the board. Then solder the other pins.

You can use a tie wrap, using the center hole and any hole around the core, or use a screw and nut with a 3/16" rubber grommet inside the toroid. (Parts not provided in kit) Picture

A small 3/16" grommet can be cut to fit inside the core, and with a 3/4" long screw and nut (4-40's), use the hole in the middle of the footprint to hold the ferrite core onto the board. (Parts not provided in kit) Picture

Solder

Solder

If you are not using the stabilizer, skip this section and go to "VFO Amplifiers".

The arrows show the parts that should already be installed and their locations. Continue by installing the following parts:

Solder

Note: If you are going to test the VFO before the stabilizer is installed, use a clip lead and place it to the connection labeled Stabilizer and the output of the 5 volt regulator. This will approximate the output of the stabilizer (which is between 4 to 5 volts at startup). See below:

If you would like to use a Rotary Switch instead of manual switching see Instructions for using a Rotary Switch.

Schematics for Manual Switching

Solder

Pictures/Instructions - The switches are mounted on VFO PCB shielding. When drilling the holes for the switches, make sure they don't interfere with the adjustment of the 10.455 yellow trim cap.

The above instructions are just guidelines. Individual layouts may be used depending on your layout or personal preferences.

Mount the parts that have the values inside the footprint. They are the following:

____1 - RF choke (Bag 3), Off the 12 Volt connection on the PCB, Footprint on PCB is a rectangle with square edges, "RF" inside the rectangle. Choke is about the size of a 1 watt resistor with rounded edges.
____11 - .01 capacitors (Bag 3)

Solder

Solder

Resistors:

____2 - 2.2K (Bag 4), Next to the 1:1 and 1:4 transformers

Capacitors:

____1 - 39pf NPO (Bag 4), small, blue colored, short leads, labeled "390J, 201". Located at the left of the second MOSFET.
____1 - 2.2mfd Electrolytic (Bag 4), Next to 7805 Regulator, please note that the negative (-) side of part is marked. The + (Plus) side is marked on the silkscreen.
____1 - 10mfd Tantalum, 3 pin (Bag 4), The center pin is positive, two outer ones are ground, this part is used in automatic insertion PCB work so that it never gets put in wrong, located below the second MOSFET near the LED. Orange colored, with three short pins.

Solder

Other Parts:

____1 - 100K trim pot (Bag 5), located above first MOSFET, black or blue color. Turn adjustment screw all the way clockwise for the Black trimpot; all the way counterclockwise for the Blue trimpot - this gives maximum gain for initial testing and use. Black color, marked "EXP 104" on side. Blue color are smaller than the 10K blue trimmers, marked "104Fd5" on side.
____1 - 7805 Voltage Regulator (Bag 5), notice the text "Front" on the silkscreen and place the front of the regulator (heat sink is back of regulator) as shown on the silkscreen. Labeled "L7805CV".
____1 - T1-1T Minicircuits transformer (Bag 4), Note the dot on the T1-1T transformer and match the dot on the silkscreen. The dot on the outside of the footprint can be seen after the part is mounted so that you can double check proper mounting.
____1 - T4-6T Minicircuits transformer (Bag 4), Same notes as above, be sure to get the dot in the right place.
____2 - LEDs (Bag 3), Red color. Match flat of the LED to the flat on the footprint. Note: If you ordered the Bright Red LEDs, install them now. Do not use Super Bright LEDs here unless you change the bias resistors. See Modifying the LEDs.

Solder

Solder

Solder

____Check the dot on the MOSFETs and the Minicircuits transformers.
____Put your VOM in resistance mode and check that the adjustment screws on the trim caps in the VFO are grounded. On the Yellow caps, stick the probe right down in the middle of the cap to get a good connection on the adjustment screw. The 2/8 cap adjustment screw is set above the cap and is easier to get a good connection.

Note: If you are using the stabilizer, the adjustment screw of the 2/8 trimmer will not be grounded.