(Editor's note - I will eventually add an index for this series. Until then, please look in the Ham Radio Online Library for previous articles in this series... de Ed, KF7VY.)
 

Figure 1 shows a simplified diagram of the transmitter section.

Each block in Figure 1 represents one or more modules in the transmitter. In my prototype, I built each module separately, then connected them together. All the transmitter modules can, of course, be built as a single unit, if you wish. The whole thing will fit nicely on about half of a Radio Shack 276-147 circuit board. I will show parts layouts for the individual modules, and you can fit them into your box any way you like. Refer to "Wanna Tinker?" #10, #12, and #13 for the Carrier Oscillator and VFO circuits. 

The 3.58 MHz signal generator, AKA QRP transmitter, you built to test the product detector can be used as the Carrier Oscillator. Some modification is required, as shown in Figure 2 (refer to "Wanna Tinker?" # 10 for the original circuit).

The next thing you need for the transmitter section of the transceiver is a MIXER. Any kind of mixer will work, but I’m going to use an NE602, as shown in Figure 3. 

As usual, I recommend using a socket for the NE602 so that resistance and voltages can be checked BEFORE plugging the IC into the circuit. Notice that the NE602 circuit is a bit different from the one used for the receiver product detector. The 3.58 MHz signal is mixed with (subtracted from) the 10.58 MHz VFO signal to produce the 7 MHz (40 meter) signal. 

Q is a 2N2222, or equivalent.

The primary of T6 is 34 turns on a T50-2 core; the secondary is 6 turns. 

T7’s primary is 15 turns on a FT23-43 core and the secondary is 7 turns. 

An additional 78L06 circuit is required to supply the NE602 TX mixer with +6VDC, regulated. I mounted mine near the mixer, but you can mount it on the voltage regulation and distribution board, if you like. 

The parts layout I used for the mixer module is shown in Figure 4.

When you have assembled the module, perform the checks shown below. DO NOT plug in the NE602, yet.

RESISTANCE CHECKS, NE602 socket:

From ground to Pin 3, zero Ohms.

From pin 4 to pin 5, (NOT to ground) no more than 0.2 Ohms.

2N2222, from ground to: 

Emitter 103 Ohms

Base 160 Ohms

Collector 1.4K 

If the resistance checks are OK, apply power and do VOLTAGE CHECKS, NE602 socket :

Pin-3 Zero volts

Pin-8 6 volts

2N2222:

Emitter 1.6 volts

Base 2.2 volts

Collector 11.5 volts

If the voltage checks are OK, you are ready to test the mixer. Remove power and gather the following items:

* TX Mixer Module

* 3.58 MHz Carrier Oscillator

* A VFO that tunes 10.58 to 10.74 MHz

* A general coverage receiver

First, be sure the 3.58 MHz oscillator is working. Apply power to the oscillator (DO NOT apply power to the other circuits, yet) and listen for the oscillator signal on your general coverage receiver.

When you know the 3.58 MHz oscillator is working, remove power and attach the output from the oscillator (C30) to Pin 6 on the NE602 socket.

Next, be sure your VFO module is working by applying power and listening for the 10.58 MHz signal on your general coverage receiver.

NOTE: When I presented the VFO in "Wanna Tinker?" #12 and #14, I anticipated a requirement for adjusting the output from the TX VFO buffer. As it turns out, little or no adjustment is required. Simply set R10 (see Figure 2 in "Wanna Tinker?" #12 and/or #14) to about mid- range. If you want, fixed resistors can be substituted for the potentiometer, as shown below.

When you know the VFO is working, leave the tuning on the VFO set to about 10.58 MHz, remove power from the VFO circuit, and attach the output from the VFO to Pin 1 on the NE602 socket.

Next, PLUG THE NE602 INTO IT’S SOCKET, attach a test lead or a couple of feet of wire to the BASE of the 2N2222. Apply power to the 3.58 MHz oscillator, the VFO, and the NE602 (DO NOT apply power to the 2N2222 circuit, yet).

Listen for a 7 MHz signal on your general coverage receiver. If your 3.58 MHz oscillator is at EXACTLY on frequency, and If your VFO is tuned to EXACTLY 10.58 MHz, then you should hear a signal at EXACTLY 7.000 MHz (I heard mine at 7.00170 MHz). You may have to tune around a bit to find the signal because your oscillators are probably NOT exactly on frequency. If you do not find the signal in the range of about 6.9 MHz to 7.1 MHz, you probably have a wiring error or a bad solder joint. NOTE: The strong signal that you hear at about 7.16 MHz is NOT what you are looking for. This 7.16 MHz signal is the second harmonic of the carrier oscillator (notice that this signal does NOT move when you tune the VFO).

When you find the 7MHz signal, record the S-meter reading. This reading could be most any value. The exact value is not important, but it will be used to compare to another value you get by doing the following …

Disconnect the test lead from the base of the 2N2222 and attach it to the output of T7, then apply power to the 2N2222 circuit. Your S-meter reading should be a few S-units higher than with the lead attached to the base. My reading went from about S-9 to about 5 dB over S-9. The exact readings are NOT important, but the output of T7 should be about 2 to 6 S-units higher than the reading at the base of the 2N2222. If there is no change, or if the reading is lower at the output of T7, you have a wiring error or a bad solder joint.

Assuming you have 7MHz output from the 2N2222 circuit, you are ready for more transmitter circuits, which I will show you next time. 

‘Til then … 73, Dick, W6BKY