EXC/RX/AF- 01. RX Audio Amplifier

The Receiver Audio amplifier is built off the LM386 IC.

R57 is marked as 220K on the schematic by mistake. It should be 22K.

Components :

1. 10 Ohms - 2
2. 220 Ohms -  1
3. 22K Ohms - 1
4. 3.3K Ohms - 1
5. 4.7K Ohms - 2
6. 10K Potentiometer - 1
7. .1uF (100nF) - 1
8. 0001uF (1nF) - 1
9. 1uF (Tantalum) - 2
10. 10uF (Tantalum)-1
11. 22nF - 1
12. 220uF (electrolytic) - 1
13. 47uF (Tantalum) - 1
14. 1N4148 - 1
15. 2N3904 - 2
16. LM386 - 1
17. 2 Pin Conn - 1
18. 3 Pin Conn - 1

Install all passives first, followed by the diode, transistors and the IC.

Solder the connectors for the speakers and the Vol. Control. Refer to the schematic for the correct wiring! Center pin of the PCB connector does NOT attach to the Wiper! Short SJ5 on the PCB as we haven't built the AGC yet.

Solder wires to the Ground and V+ (Rx).

Double check your board for shorts, slivers etc, and apply power to the board. Carefully touch pin 3 with tweezers. There should be a buzzing/squealing sound on the speaker. The same buzz should be heard on the potentiometer center (Wiper) pin.

If all is working well, you should see these voltages

1. Pin 6 of LM386 : 
2. Collector Q18 :
3. Collector Q19 :

I used a mix of 1206 and 0805 SMD resistors and capacitors throughout the build. As you can see, there arent any tantalum capacitors! Shelfkey and Sunrom were out of stock when I ordered the parts!

A word of warning to those embarking on this build: Watch those connectors! Even though I got the pin pitch right, the plastic shell of the connectors were a pain as they kept budging against the next conenctor. I had to loose the plastic shell of the AF gain control connector so that I could insert the speaker connector properly in place! A dry fit would have saved me the headache!

Phase One : Bitx Exciter

The Bitx Exciter comprises of an SSB receiver and an SSB generator on an single PCB.

We will deal with the receiver section first.

The receiver section is split down into 7 sections:

1. Audio amplifier - Completed and Tested 28/05/2017
2. BFO mixer
3. Post IF amplifier
4. IF crystal filter 
5. Pre IF amplifier
6. VFO mixer
7. RF amplifier

On completion of the receiver section, we will move to the SSB generator section.

The SSB generator section is divided into  sections:

1. Microphone amplifier
2. Post IF amplifier
3. Pre IF amplifier
4. RF predriver amplifier 

Since the design is bidirectional, sections 2,3,and 4 of the SSB generator are the same as sections 3,5, and 7!

This is what makes the BITX one of the most widely replicated transceiver circuit in the world!

Start Here ...

This is my attempt at documenting the BITX V4 designed by 2E0ZHN. 

My objective is to build the a multiband( or at least dual band BITX for 40 and 20M) with atleast 10W+ power out on the HF bands.

As with any major project, the assembly will be split into sections and subsections to simplify troubleshooting.

This build will be split into 4 phases:

1. Bitx V4 Exciter (with 10Mhz IF)
2. Si 5351 VFO+BFO (Arduino based)
3. Linear Amplifier ( Driver+Power amplifier+Filters)
4. Boxing up and Final Touches

I will update this post as I progress in my build.