ASSEMBLY MANUAL FOR
R3500D DIRECTION FINDING RECEIVER KITRev. AMay 24, 2015
Written by CRKITS
http://www.crkits.com
Thanks for your purchase from us. This model is the upgrade of PJ-80 – an 80-m ARDF directconversion receiver kit. It keeps the characteristics of simple, low cost, easy to build, and suitable
for the fox hunting and electronic homebrewing activities among youngsters, especially for thestudents of elementary and middle schools.

Cautions••••

The power supply is switched by the earphone plug. After use, please unplug the earphone
to switch off the power supply.
Monophonic earphone is not compatible with this receiver. Use the stereo earphone
instead as attached.
Pay close attention to differ the 3 diodes: VD1 (1N60), VD2 (FV1043) and VD3 (3V6). Theylook very similar, but the letters printed on the body of diode can easily tell.
The English manual is for your reference only. Please refer to the attached Chinese manual
for more information.

A. Main Specifications
1. Frequency coverage: no narrower than 3.5 - 3.6 MHz
2. Sensitivity: No less than 600 meters (when receives T3500B fox transmitter with verticalantenna)
3. Directivity: The minimum distance for exhibiting directivity is less than 3 meter
4. Power supply: DC 6V (4x AA size batteries)

B. Circuit Diagrams
1. Block Diagram
See the printed manual.
(Boxes from left to right: Antenna, RF amplifier V1, Beating frequency detector VD1, AF pre-amp
V2, AF power amplifier TDA2822M, earphone. The lower box: Variable beating frequency
oscillatorV3)

2. Schematic and PCB layout
See the printed manual.

C. Assembly Instruction
1. Check and solder parts on PCB
Before soldering, carefully make parts inventory based on the part list to check the quantity, value
and quality of all components. For example, check if the electrolytic capacitor is dried or leaking, orthe coils T1 (black cap) and T2 (white cap) are open, or the diodes and transistors are OK. Pay
attention to the right orientation when installing TDA2822M and its socket (see Fig. 2 on theprinted manual).

2. Fix the magnetic rod
Use the white nylon ribbon to fix the magnetic rod onto the PCB.

3. Install the vertical antenna
Insert the telescope antenna from the hole on the top right of the case, and fasten it with screw
and nut. A washer shall be put between the screw and the outside of the plastic case.

4. Cautions for installing the battery wires
Only install battery wires after all the components are soldered and checked okay. Make sure thepolarities are correct.

D. Alignment
1. DC check point(1) Voltage across the zener diode VD3: 3.4 - 4.4 volt
(2) The bias of transistor V1: The voltage across R4 shall be 0.4 - 1 volt (potentiometer RP1 set tomaximum gain position, the Ic of V1 will be 0.4 - 1 mA)
The bias of transistor V2: The voltage across R10 shall be 1.5 - 3 volt (the Ic of V2 will be 1.5 - 3 mA)
The bias of V3: The voltage across R15 shall be 2 - 2.5 volt (Ic of V3 will be 2 - 2.5 mA)
Normally you don't have to adjust the bias, because the design can cover the variance of thecomponents.

2. Alignment of the variable local oscillator(1) If you have a standard RF signal generator(a) Set potentiometer to the center position;(b) Set signal generator to 3.5 - 3.6 MHz, CW mode, higher output level. Connect the output
and the ground of the signal generate with a wire. Couple the wire to the magnetic antenna of
the receiver by winding the wire on one end of the magnetic rod for one turn;(c) Change the output frequency of the signal generator in a wider range. A beating tone shallbe heard from the earphone, this means the local oscillator is working. Set the signal
generator to 3.55 MHz, then align the cap of the coil T2 (white) until the beating tone is heardagain;(d) Turn potentiometer RP2, the signal of 3.5 MHz and 3.6 MHz all be received at two positionof RP2, which shall be near by the both extreme positions. If 3.6 MHz can not be heard but the3.5 MHz can be heard at the RP2 position near by the center, please align the cap of T2
counter clock wise; or vise versa.
(e) If the receiving coverage is too wide, replace the R13 with greater value, or vise visa.

(2) If you use 80m fox transmitter(a) Set potentiometer RP2 to the center position;(b) Turn on the fox transmitter (3.55 or 3.54 MHz). Place the receiver close to the transmitter
antenna;(c) Turn the cap of T2 until a beating tone is heard, fine tune it to make the tone nicely (about1000Hz);(d) Turn the potentiometer RP2, the signal from fox transmitters of 3.5 and 3.6 MHz shall beboth heard. If only one signal of 3.5 or 3.6 MHz can be received, please fine tune the cap of T2(see the previous section);(e) If the receiving coverage is too wide, replace R13 with a greater value, or vise versa.

3. Alignment of antenna tank
Receive a signal of 3.53 MHz from a signal generator or transmitter. Fine tune capacitor CT to peak
the tone. If no peak can be obtained, change the position of the coil on the magnetic rod, then finetune CT again.

4. Alignment of the tank in the RF amplifier
Receive a signal of 3.57 MHz from a signal generator or transmitter. Fine tune the cap of coil T1(black) to peak the tone in the earphone. If no peak can be obtained but the volume is still
increasing towards the extreme counter-clockwise position of the T2 cap, please replace capacitor
C3 with a smaller value. If no peak can be obtained but the volume is still decrease towards theextreme clockwise position of T2 cap, please replace C3 with a greater value.

5. Testing for directivity
Select an open field far away from power lines and constructions. Set a fox transmitter with avertical antenna. Stand at a point of several tens meters away. Test the "8" figure characteristic of
the receiver. (The two null points of some receiver sound little different, a clearer one shall be usedfor bearing.) Then add the vertical antenna for the cardio-pattern by pushing S1. Adjust the lengthof the telescope antenna to make better cardio-pattern, and remember which side is facing thetransmitter for higher volume. If the cario-pattern can not be heard clearly, please try to change
the value of R15, and test again. The minimum distance on which a cario-pattern can bemaintained is 3 meters.
* R3500D has a charger socket for charging rechargeable batteries. You don't have to take out thebatteries for charging. However, there is no charging or protection circuit built-in, so please makesure the charger can match the voltage, polarity and type of the rechargeable batteries.