Smoke Testing The GW3UEP 630m Transmitter


Drain (top) vs Gate (lower) on testbed Class-E GW3UEP TX

I've just completed the Muppet-styled printed circuit version of my previously breadboarded GW3UEP 630m transmitter. The earlier version was built "ugly style" in order to optimize part values and measure circuit parameters.

Testbed (Ugly-Style)
The "ugly version" performed well at 12V and during overnight beacon testing was aurally copied as far east as Kansas. Although the final version has yet to be mounted on its small 19" rack panel, along with a meter to monitor final amplifier drain current, all indications show that it too works well.

Final Version (Muppet-Style)
This version, based on the GW3UEP design, has a few small changes, the main one being the addition of a second parallel-connected FET ....described in an earlier blog.

Running the TX at 12.8VDC on the drain(s) at 2.3A produces an input power of 29W. The measured power out, after the LPF, is 23W into a 50 ohm load. This represents an efficiency of 80%. When run in the normal speed CW mode, the FETs run cool enough that they would probably not even need a heatsink but if run in any of the QRSS (long keydown periods) modes, would certainly benefit from  heatsinking.

Running the TX at a higher voltage of 22.6VDC (on the amplifier only) yields a current of 4A for an input of 90W. Measured output power is 71W for an efficiency of 79%.

Heatsinking would be required at this power level, even for normal speed CW but the finals seem to run just slightly warm. A larger heatsink or possibly a small fan as well would be required for any QRSS CW modes.

I suspect that the efficiency could be further improved yet with very fine tweaking of the output circuit L/C network but the extra few watts gained would not be significant.

At either power level, this easy-to-build transmitter would make a great "first 630m transmitter" for anyone wanting to get started on our new band.
Steve McDonald, VE7SL, is a regular contributor to AmateurRadio.com and writes from British Columbia, Canada. Contact him at v[email protected].

3 Responses to “Smoke Testing The GW3UEP 630m Transmitter”

  • Hans (BX2ABT):

    Looks very nice, Steve. Especially the inductors look very neat. What kind of material do you use as core?

    One other question: is that a burned-out capacitor in the upper left corner?

  • Steve VE7SL:

    Hello Hans….the coils are wound on 22mm PVC tubing. The cap was removed from a scrap computer monitor pcb and the black stuff was adhesive they had put on it but I never got around to cleaning off!

    Steve 73

  • Tom WA9YI:

    FB! (Meaning fine business, see below.)

    Anxious to build one of these; do you have as-built parts list and board layout available?

    (Took me a long time with the schematic to figure out that FB was a ferrite bead, but don’t see specs on it anywhere.)

    Thanks, 73

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