• [SADARS] 17 Feb 2022 - A 400 Watt 80M AM transceiver by Graham G4JBD

    From SADARS via rec.radio.info Admin@21:1/5 to All on Fri Feb 18 17:11:24 2022
    XPost: uk.radio.amateur, free.uk.amateur-radio, rec.radio.amateur.equipment XPost: rec.radio.info


    17 Feb 2022 - A 400 Watt 80M AM transceiver by Graham G4JBD

    Posted: 18 Feb 2022 04:12 AM PST

    Grahams transceiver

    A boat anchor it is NOT!  This high quality transceiver for 80M runs a cool 400w in Class E and is small and light at only 3kg, including the power supply!  The original design was by Dave GW4GTE and the PCBs and parts were from Eric GW8LJJ. (www.s9plus.com)

    Graham explained the amps Switch-mode has many advantages, it is
    theoretically 100% efficient. The audio processing uses a well tailored RMS
    AGC which controls maximum modulation without the usual heavy modulation transformer. Syllabic compression tracks the users voice power. A very
    sharp, easily tailored low pass filter keeps the signal bandwidth very well controlled resulting in excellent on air audio reports.

    Graham went through each stage of the transceiver to explain how each stage operated to produce the phase width modulated signals with 100% modulation.

    The receiver part of the unit is single conversion superhet allowing a
    choice of 80m or 160m during construction.  No special tools were required during construction but Graham did admit to purchasing an illuminated free standing magnifier (£23). He did, however, use his oscilloscope to set the
    PWM and drain waveforms. His shack receivers display was used for
    monitoring modulation bandwidth. A most impressive part of this build was
    the cost, only £347 total.

    So, what to add next? CW keying and a BFO, and perhaps add a 160m matching network.

    Graham felt it would make a fine addition to the GB2RS news in AM for 80m. Graham (L) keys xmtr while Dave (centre) measures signal

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