BFO and Amplifier, Product Detector and Audio Amplifiers


Approximate time to complete 0:40 - Picture | Picture | Picture


Modifications for AM SWL Reception

Most of the BFO components are installed on the board except for the 7805 BFO voltage regulator, the 35pf BFO panel mount tuning capacitor and 3.3pf output capacitor. This allows easy addition of the BFO in case SSB/CW reception is desired after the kit is built.

The output from the 455kHz IF filter is routed to the input of the BFO amplifier. The BFO amplifier is used as an additional IF amplifier to give the AM detector enough drive to operate.

The Product Detector is modified by removing one diode, which makes it an AM detector. Then a 10K resistor is paralleled to the first .047 capacitor at the output of the detector, which serves as a load resistor for the AM Detector.

The output of the AM detector is much higher than the original product detector, so the audio pre-amplifier is bypassed. The 1K resistor which supplies 12 Volts to the pre-amplifier is removed along with some other components. Picture


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

____7 - .01 capacitors (Bag 3)

Note: The .01 capacitor below the footprint for the SFU455A is not completely installed. Only the top lead, connecting to the 455kHz filter, is soldered to the board. The other lead of the capacitor is soldered to a 2 1/2" wire that is soldered to the right hole in the 3.3pf capacitor footprint connecting to the input of the BFO amplifier. Picture

Solder

____Solder a 2 1/2" length of hookup wire in the 3.3pf capacitor footprint at the input of the BFO (right hole).
____Solder one lead of a .01 capacitor capacitor to the upper hole in the .01 footprint just below the 455 kHz filter.
____Solder the other lead of the .01 capacitor to the hookup wire from the 3.3pf capacitor of the BFO Amplifier input. Picture

Solder

____3 - 100 ohm resistors (brown, black, brown) (Bag 3) Be careful, rectangle footprints only, there is a 100pf capacitor in the area.
____3 - 100K resistors (brown, black, yellow) (Bag 3)

Resistors:

____1 - 12K (Bag 4), Located above the MOSFET on the right side.

Solder

Capacitors (Going left to right on the board):

____1 - 100pf NPO (Bag 3), Located to the left of the 2N5486. Orange color, short leads flared out, labeled "101".
____1 - 47pf NPO (Bag 5), Located to the left of the Minicircuits T1-1T transformer. Orange colored, small square, labeled "470, JCC"
____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.

Other Parts:

____1 - 50A03 455KHz IF can, Black core (Bag 6), Located below the text "455 kHz BFO". After inserting into the board, touch the soldering iron to the IF can pins first, and make sure the pin is accepting solder before flowing solder onto the PCB.
____1 - 50A01 455KHz IF can, Yellow core (Bag 6), Located next to the product detector. After inserting into the board, touch the soldering iron to the IF can pins first, and make sure the pin is accepting solder before flowing solder onto the PCB.
____1 - 2N5486 (Bag 4), Spread the end pins slightly so they fit through the holes. Do not force all the way down onto the PCB and stress the pins. Note flat side of part and match to the flat side of the footprint.

Solder

____1 - 100K trim pot (Bag 5), located above the MOSFET, Black or Blue color, marked "EXP 104" on side. Blue color are smaller than the 10K blue trimmers, marked "104Fd5" on side.

Note: Turn adjustment screw all the way counterclockwise - this gives maximum gain for initial testing and use.

____1 - LED (Bag 3), Red color. 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, one can be placed here. For details, check Modifying the LEDs.

____3 - HP5082 diodes (Bag 4), Blue band, on a reel strip all together. Note the band on the part and match it to the band on the footprint. Note: Only three are installed. The lower right diode is left off the board for AM detection. Picture

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

____1 - T1-1T Minicircuits 1:1 transformer (Bag 4), Note the dot on the part and match it to the dot on the footprint. A dot is outside the footprint so that you can double check your work after it is mounted.
____1 - L40 B2 455KHz Filter (Bag 6), White color, another part with fragile pins, do not bend the pins when mounting/soldering the part to the PCB. Tin the leads with solder to get a good solder joint on the PCB.

There are two footprints for 455KHz IF Filters, only one is used. Use the footprint that fits the pins of your part. This is because we have several types in stock and the one included in the kit will change as more kits are made.

Solder

____1 - MOSFET (Bag 2), (Picture) static sensitive part, touch a ground wire before taking it out of the bag, notice the dot on MOSFET (may be difficult to see, hold at an angle to a light source and you can see the shadow of the dot), the dot is located to the left of the second line of the text on the MOSFET. 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

Audio Amplifiers

Approximate time to complete 0:45 - Picture

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

____2 - .01 capacitors (Bag 3)

Resistors:

Several resistors are not installed. See Picture for details. Only install the resistors listed below.

____1 - 1.5K (Bag 6), Located to the right of the Audio Pre-amp.
____1 - 560 ohm (Bag 5), Located above the 1.5K resistor.
____1 - 5.6K (Bag 6), Located above the 2N3904 on the right.
____1 - 39 ohm (Bag 5), Located above the 330mfd electrolytic.
____1 - 220 ohm (Bag 6), Located on the right of the 39 ohm resistor.
____1 - 2.2 ohm (Bag 6), Located below the 220 ohm resistor.
____1 - 10 ohm, 1 Watt (Bag 6), Located above the TDA2002. Part may be too large for the footprint. Curl the leads underneath the resistor and then bend them down to fit into the holes.
____1 - 1 ohm (Bag 6), Located below the 1mfd cap on the far right of the section.

Solder

Capacitors:

____2 - .047 (Bag 5), Located to the left of the text "Audio Pre-Amp". Orange colored, small square, leads flared out, labeled "473, C1J".

____1 - 10K resistor (Special SWL Bag) Solder across the first .047 capacitor coming from the detector - the left one that you installed above. Solder underneath the board to protect the small mono .047 capacitor from heat. Picture

Solder

NOTE: There is an optional "Gain Adjust" electrolytic capacitor in the pre-amplifier. This cap is not installed. This cap adjusts the gain of the pre-amplifier, which is not used in the SWL version.

____2 - 10 mfd 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. Orange colored, with three short pins. Located near the box labeled "Audio Control", one above and one to the right.

Do not put one in the footprints above or below the 2N3904. The one below is the input to the audio pre-amplifier, which is disabled for AM SWL reception. Picture

Solder

____1 - 2.2mfd Electrolytic (Bag 4), Next to the TDA2002 audio IC, please notice that the negative (-) side of part is marked. The + (Plus) side is marked on the silkscreen.
____2 - 330mfd Electrolytic (Bag 4), Note: - (Minus) is marked on the part, and the + (Positive) is marked on the board. One is above the box labeled "Audio Control". The second one is to the right of the TDA2002.
____1 - .1 (Bag 6), Located right next to the "C" on the 2N3904. Blue colored, labeled "K5M, 104"
____1 - 100pf NPO (Bag 3), Orange color, short leads flared out, labeled "101". Located above the 330mfd Electrolytic.
____1 - 1mfd Film (Bag 6), Located next to the box labeled "Speaker". Large red rectangle, labeled "105".

Solder

Other Parts:

____1 - TDA2002 Audio Amplifier and Heat Sink(Bag 6), Be careful mounting on the board so that all five pins go into the PCB. Sometimes the pins may be bent out of place from shipping. Note mounting picture below.

Be careful mounting the heat sink, it is a slip on part. Use a small screwdriver to hold back the clip to help it slip on easily. Best to put the heatsink on the IC before soldering to the PCB.

Some kits may have a LM383 or a house numbered part "9779", which are identical to the TDA2002, both in dimensions and electrical properties.

Solder

Audio Control Potentiometer

There is a place below and left of the Audio Control Square that has ten holes that will accommodate most PCB mount potentiometers.

The pot supplied with the kit has five pins and matches the five holes in the forward part of the square. The pins are slipped through the holes and then soldered. (Picture)


Wiring the Potentiometer

____1 - 10K Potentiometer (Bag 6), A small white pot labeled 10K. Install into the five holes at the bottom of the footprint below the labeled holes (1, 2 and 3). Solder the pins underneath the board. (Picture)
____Use a 1 1/2" jumper wire and connect the Gnd hole to the Gnd hole in the "Audio Control" square.
____Use a 1 1/2" jumper wire and connect the hole labeled "1" to the bottom hole in the footprint of the 3 pin, 10 mfd tantalum capacitor and as shown in the picture above.
____Use a 1 1/2" jumper wire and connect the hole labeled "2" to the hole labeled "2" in the "Audio Control" square.

Hole "1" in the "Audio Control" square will not be used.

S-Meter

____The resistors that are used at M1 and M2, to the left and above the S-Meter Square at the AGC Detector (Picture), are set up to use a 50uA meter. (Picture)
____If the plastic S-Meter was ordered with the kit, make sure you put a 22K resistor at "Mtr1" for proper operation of the meter. (This resistor is not supplied with the kit.)

You can use any meter with a value between 50 uA to 250uA, by changing the M1 and M2 resistors. Values for different meters are given in the S-Meter page. Circuit theory is included to help you properly set up the meter any way you like.

____The S-Meter, if board mounted, is glued to the top or bottom of the board where the text "Audio Amplifier" and the "Designed by...." is located at the bottom right of the board.

Silicon Rubber Sealant was used to secure the S-Meter on all the prototypes, and allows you to pull the meter off the board if you transfer the receiver to a case, where you will be mounting the S-Meter on a front panel. Picture

____Solder a wire from the + hole in the S-Meter square on the PCB to the + connection on the S-Meter.
____Solder a wire from the - hole in the S-Meter square on the PCB to the - connection on the S-Meter. Picture

Double Checking Your Work

____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 MOSFET.
____Check the flat on the 2N3904.
____Check the blue bands on the three HP5082 diodes. Make sure the lower right one is missing.
____Check the dot on the Minicircuits T1-1T transformer.
____Check the flat on the LED and make sure it fits the flat on the footprint.
____Did you remember to turn the "Gain Adjust" (100K Black or Blue trim pot) all the way counterclockwise?
____Make sure the 2.2mfd, and two 330mfd Electrolytics are mounted correctly, located right next to the regulator, and at the Audio Amplifier.


If you have already tested Board 1, go to Mounting/Testing Board 2.

Mounting/Testing Board 1

Mounting/Testing Board 2

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Last Update: 10/15/12
Web Author: David White, WN5Y Free Website Translator