Welcome to the first qrp-tech synchronous buildathon.

This page started on Mar 3, 2016.

This page last updated on Jun 30, 2016.



Phase 10. Mar 3, 2016.

We now have a working receiver. We need to start building on the transmitter to complete the transceiver. The transmiiter depends upon a uP based keyer and some additional keying circuitry in order to operate. So, we will begin by building the keyer.

  • Keyer and Keying Circuit.

    This section does not depend upon the band we are going to use, so let's just build away.

    Locate and install the following in the order shown here. Again, I remind you this set of instructions is for 1W transceivers with serial numbers greater than 500. Previous to this, the kits had different numbering schemes and parts numbering, so you have to be careful and follow the instructions for the right version number(s).

    OK. Once again time to power up the transceiver. This time measure the voltage at pin 8 of U9 (U9-8). It should be around 5.0V. I measured 5.01V with my trusty dusty Harbor Freight free digital multimeter (DMM).

    Power down the transceiver. Now insert U9, the ATtiny45 uP into socket U9.

    Now power up the transceiver again. Turn down the volume on the powered speakers, if you are using them as the keyer volume is loud. You should hear 1W be output by the keyer on power up. Because we do not have a speed pot hooked up, there is the possibility that the keyer is set at 5WPM. Slooooow. :-)

    Use a piece of INSULATED wire a few cm in length with 1mm stripped off the ends. Use this to set the keyer into the command mode. One touch between the top pin and the bottom pin on J4. Then immediately touch the wire between the dit and ground on the paddles header J5. Then the keyer should output the letter S for straight key mode. Now, the wire can be used to key the transmitter continuously by putting it into the two bottom pads of J5. Try this. Here is a video showing how I did it.

  • Keyer Circuit test phase.

    Now install the following components.

    OK. Please do the following carefully. Power up the transceiver. Put keyer in straight key mode. Key transmitter with the insulated wire. While the transmitter is on, measure the voltage at pin 8 of U2 (U2-8). This should read in the neighborhood of 8.0V. Unkey the transmitter and measure the voltage at pin 8 again. It should now be reading 0.0V or very close as the capacitor discharges (C19).

    What we have shown is that 12V is applied to the 8V regulator by the keying circuit when the keyer is operational. We need this to insure that we are not wasting our time in the checking of the transmitter sections later on. The +12V is keyed on and off to U2, Q5, Q3 and Q2 during transmit. Neat stuff, for sure.


    Phase 11. First Transmit Mixer. Mar 7, 2016.

    Now we get to start in on building the complete transmitter contained in the transceiver. Continuing with the build and test technique, we will build the first tranmit mixer. This consists of a mixer, the NE602A, and its local crystal oscillator built into the IC and using X2 (6.000MHz) to combine with the VXO output to get a 14.0 MHz signal generated.

  • First Transmit Mixer Circuit. Remember, this diagram for another band.

    Assuming that you do not have an RF probe or O'scope, how would you test to determine if the circuit is operating properly? Well, you have a complete receiver working, so let's use it. Build the mixer and then watch the video to see how to test it. I made this procedure up over 25 years ago on other transceivers for tutorial purposes and will use it here.

    Install the following components onto the transceiver PCB.

    In order to test, you will need your speaker system, a dual lever paddle, a 10cm insulated wire or Arduino prototyping cable (male-to-male) and the power supply. Follow the instructions in the following video carefully.

    Send me photos of your build for the gallery page.

  • Test operation of the first transmit mixer.


    Phase 12. Transmit Band Pass Filter (BPF) and first driver stage. Mar 8, 2016.

    Install the following components. Double check on winding instructions on the KitsAndParts.com web page for the 20m build.

    Now carefully connect everything and power up. You will hear the 1W from the keyer. If you now key the rig, you will hear a tone in the speaker/headphones. This is due to the transmitter RF being higher in amplitude. Again, assuming you have the sidetone off in the keyer (V4 of the uP keyer software). See the video below on what I get. Enjoy. We are nearly through with all the parts on the PCB. Wow. Good job.

  • Test operation of the first transmit band pass filter and driver stage.


    Phase 13. Second driver stage. Mar 8, 2016.

    Install the following parts.

    Connect everything and power up. Put a test lead from the right pad of C10 to the ANT input pad. Key the transmitter and you should hear your tone in the speaker. By varying the R5 drive level pot, with full CCW as a null, you can vary the level. It may seem that after the 1/2 way point the level remains constant and that might be the case. Not enough to detect.


    Phase 14. Third driver stage. Mar 9, 2016.

    Install the following parts.

    If, at this point, you power up the transceiver again and run the keying test, you may not hear a signal at all until you use the test wire from the right center pad of Q1 to the ANT pad. This means there is little signal leakage from the built circuits. Seems counterintuitive, but it is correct. You are almost through.


    Phase 15. Final RF Power Amplifier Stage. Mar 9, 2016.

    Let me warn you right here and now. After this section the transceiver will be complete except for the experimentation of what value to use for C_x. Never ever. I mean never ever after this point power up the transceiver without it being in an enclosure and hooked up to a 50 ohm dummy load like that at QRPGuys.com for $10 or similar OR a 20m tuned antenna. Other transceivers will destroy the final PA transistor if keyed while not having anything connected to the ANT connector or a short at the output. The 1W will handle it, but I am paranoid enough to never ever power it up without a dummy load or antenna connected. Just my advice here to prevent problems that you may have to diagnose.

    Install the following parts.

    Congratulations. You are through installing parts except for C_x, which is not provided with the kit. I am going to experiment with the value to use AFTER I put the transceiver in a case.

    Hold the board up to a light behind it. Look for empty holes for missing parts. You should see nothing installed at C3 and C51. Also R_x near U5. Also the jumpers that don't have anything in them. I am going to remove all the 0.1" headers from mine to install wires directly to controls and connectors on the enclosure. I will make a separate web page for enclosure suggestions. This is where you get to be original and create one of a kind. Great job by the way. Send me photos of your work.