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pgxl question

AB7R
AB7R Member ✭✭
in Power Genius XL Amplifier

I understand using the pgxl at 120vac is limited to about 700w. Does that limit apply to all modes like cw, ft8 and rtty? Or do I need to derate power further?

Tthanks

Greg

Tagged:

Answers

  • Flexed
    Flexed Member ✭✭

    If I recall correctly, you shouldn’t run more than 400 watts on digital with that setup, but I might be mistaken. One thing is certain: there’s a difference in power recommendations between voice and digital on that setup.

  • John KB4DU
    John KB4DU Member ✭✭✭✭

    Digital modes may have a substantially higher duty cycle than voice. Voice is about 30% average power during transmit compared to full carrier. WSJT could have a 50% duty cycle 15 second listen, 15 second transmit.

    400 watts compared to 700 watts is less than 3dB (I/2 S-unit) difference.

  • Mike-VA3MW
    Mike-VA3MW Administrator, FlexRadio Employee, Community Manager, Super Elmer, Moderator admin

    You can run the PGXL at 100% power for your line voltage if you need to. The PGXL has significant sensors in it to reduce power due to SWR issues or Temperature issues.

    4O3A claims 100% duty cycle. Given you are running at 1/2 power at most at 120VAC you won't come close to over hearing anything

    73

  • Flexed
    Flexed Member ✭✭

    AB7B: check bold part below.

    From the search results I already pulled, there’s a known issue specific to digital modes:


    Users running FT8 have reported power jumping up and down — for example, running 900W and suddenly dropping to 500-700W or even 0W with no SWR warning. One identified cause was transmitting too close to the TX passband limits (below 300Hz or above 2600Hz audio), and widening the bandwidth to 100Hz low / 3200Hz high on the Flex eliminated the fluctuations.
    Beyond that, digital modes like FT8 are 100% duty cycle — the amp is transmitting a constant-level tone continuously.

    This is where MEffA becomes relevant:
    MEffA (Maximum Efficiency Algorithm) is specifically designed for constant-level signals like CW, RTTY, FM, and FT8-type modes. It works by decreasing the drain voltage on the amplifier devices, moving it closer to higher-efficiency Class C operation.


    So for your digital operations, the practical takeaways are:
    ∙ Enable MEffA for FT8/digital — it’s the right mode for constant-tone signals and reduces heat stress.
    ∙ Watch your TX passband in SmartSDR — keep audio frequencies within the 100Hz–3200Hz window.
    ∙ Running 240V helps significantly with sustained digital duty cycle efficiency.​​​​​​​​​​​​​​​​

  • Flexed
    Flexed Member ✭✭

    So from official sources, the hard ceiling on 120V is ~750W regardless of mode. Since the PGXL’s thermal protection manages itself, running FT8 at that ceiling is possible — but staying conservative at 500–600W for sustained digital sessions on 120V is the prudent real-world limit.

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