LPC5 is a RX-TX control board and Low Pass filter suitable for QRP transmitters. Basically, it allows you to connect your Q5 transmitter and external receiver to a common antenna. The LPC5 is rated at 5W and the band pass filter covers 5 bands: 80m, 60m/40m, 30m nad 20m.
The control board provides RX-TX switching and control voltage for both receiver and transmitter. It will allow you to safely use your "main radio" receiver while transmitting with Q5.
The LPC5 will take your enjoyment of homebrew QRP transmitting to the next level!
LPC5 Schematic diagram
Click Picture to Enlarge
LPC5 : BOM (BILL OF MATERIAL)
| COMPONENT TYPE | DESIGNATOR | VALUE | QTY |
| Resistor |
R1, R2, R4, R6 |
10K |
4 |
|
R3,R8, R10 |
1K |
3 |
|
R5 |
22K (47K) |
1 |
|
R7,R9 |
4.7K |
2 |
|
R11, R12 |
2.2K |
2 |
| Capacitor |
C12, C13, C17, C18, C19, C20, C22, C23 |
100nF (104) |
8 |
|
C14, C15 |
10nF (103) |
2 |
|
C16, C21 |
220uF (2) |
2 |
|
C7, C8, C10A |
330pF (331) |
3 |
|
C5, C10B |
56pF (560) |
2 |
|
C4, C19A |
220pF (221) |
2 |
|
C9B |
47pF (470) |
1 |
|
C11A |
680pF (681) |
1 |
|
C11B, C1A |
82pF (820) |
2 |
|
C2, C3, C6 |
180pF (181) |
3 |
| Diode |
D1 - D9 |
1N4148 |
9 |
| Trimmer |
TR1 |
100K (50K) |
1 |
| Relay |
K1, K2, K3 |
12V 1A |
3 |
| BNC Connector |
- |
50Ω |
3 |
| Integral Circuit |
IC1 |
HEF 4069 |
1 |
| Transistor |
T1, T2 |
BD140 |
2 |
| LED |
GREEN |
- |
1 |
|
RED |
- |
1 |
| Audio connector |
- |
3.5m |
3 |
| PCB |
LPC5 |
- |
1 |
| Toroid |
T50-2 |
Red core |
4 |
| Wire |
Enamel |
0.8mm |
1m |
| Switch |
- |
SPDT |
1 |
LPC5 Circuit Board
Assembly
Install nine 1N4148 diodes, D1-D9. Pay attention to band orientation!
Install resistors R1-R12, electrolytic capacitor C21 and green and red LED diode.
Again, pay attention to LED polarization!
Install as per photo below, flat side of LED housing is close to 2K2 resistor.
Install the following NPO capacitors:
100nf (104): C12, C13, C17, C18, C19, C20, C22, and C23.
10nF (103): C14, C15.
Electrolytic capacitor 220uF C16.
Vox delay trimmer TR1. Trimmer or variable potentiometer supplied may look different
than one shown here.
(Note: AF amp trimmer TR2 is optional, not included in kit).
Install IC1, T1, T2 and three 3.5mm audio connectors.
Pay attention to T1 and T2 orientation: align back side (heatsink side) with layout footprint line on PCB.
Connect +12V and hand key. The green LED will be on (RX mode), When key-down (TX mode) the red LED will turn on. Adjust trimmer TR1 for delay.
Now install relay K3. Again, when pressing the key down (TX mode) the red LED will turn on
and you will hear relay clicking. This completes assembly of RX/TX control.
Install the following NPO capacitors
80m LP section:
C10A 330pF [331]
C10B 56pF [560]
C9A 220pF [221]
C9B 47pF [470]
C11A 680pF [681]
C11B 82pF [820]
40m LP:
C8 330pF [331]
C7 330pF [331]
C6 180pF [181]
30m LP:
C1A 82pF [820]
C1B 33pF [330]
C5 56pF [560]
C2 180pF [181]
20m LP:
C3 180pF [181]
C4 220pF [221]
Wind four inductors L1-L4 as per photo using 0.8mm enamel wire on T50-2 core.
For toroid winding instruction see toroid winding tutorial
Strip, form and tin coil leads as per photo
Install the inductors L1-L4
Install relays K1 and K2
Finally, install the 3 BNC connectors.
This completes the assembly of Genesis LPC5 control and LP filter board.
73 and happy DXing! YU1LM and VK1AA
Addendum
1. Position of variable potentiometer TR1 PCB mount
2. Alternative RX/TX K3 relay wiring version 1
3. Alternative RX/TX K3 relay wiring version 2
Here is yet another alternative way of RX/TX switching.
In this case, on receive TX is connected to ground and during transmit,
the RX input is grounded.
Choose the alternative most suitable for your desired configuration
or the one with highest RX/TX signal separation.
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