Illegal high power HF amplifiers

Discussion in 'Amateur Radio Amplifiers' started by N8FVJ, May 20, 2019.

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  1. LU6PSG

    LU6PSG Ham Member QRZ Page

    It is a subject that deserves its own thread, not easy to explain briefly as there is a lot of electrical background fundamentals to bring to the discussion. But kilowatt class Push Pull briad band topologies, with sort of classical AB configuration on low voltage (50V) will never be linear enough due to strain inductances almost impossible to compensate over such a broad frequency range (30MHz is almost 17 times 1.8MHz).

    So I see only 3 possible ways to overcome this limitation:

    1-Predistortion... some SDR radios have this feature and IMD is VASTLY improved, reaching tube-like IMD performance or even better.

    2-High voltage devices operating on higher impedances, so strain reactances do not represent a big deal when compared to load impedance. Say.. an LDMOS operating at 200-250V. In this way, the amp can remain AB linear untuned along the whole HF spectum, and also output matching is nearly 1:1

    3-EER: Envelope Elimination and Restoration. This requires some signal processing tecnhiques that an SDR can do. The circuit becomes more complex. Manfred Mornhinweg is one of the few (if not the only one) developing an amp using EER: http://ludens.cl/Electron/SDR/redpitayasdr.html
     
  2. AF5XF

    AF5XF Ham Member QRZ Page

    as an amateur operator it's not illegal to have a "large amp" rated at say 20000w output.

    it's just illegal to run it at that level.

    I prefer to oversize anything that i work on, repair, or build. if it needs a 1/2w component a 1w or 2w component is better so long as it fits in the available space.

    same thing applies to filament transformers and tubes particularly on tube dissipation.

    however most hams wouldn't have the money to buy these oversized components anyway.

    in short, i don't have a problem with an amp made of a pair of 4-1000s.
     
    KB8KCO, PU2OZT and N3RYB like this.
  3. AG5CK

    AG5CK Premium Subscriber QRZ Page

    Oversizing the filament supply is ok as long as you have a way limit inrush current.
     
    PU2OZT likes this.
  4. AF5XF

    AF5XF Ham Member QRZ Page

    when you're working on an amp that big, inrush limiting is a routine operation. IMO
     
  5. WA8ZYT

    WA8ZYT Ham Member QRZ Page

    I was on an early morning ragchew on 80 meters this morning. Stations were in Texas, me in Florida, Tennessee and Ohio. Ohio station reported me as being the loudest. Most stations running 1500 watts, me 600 to an inverted V at 55'.
     
  6. AF5XF

    AF5XF Ham Member QRZ Page

    true, however many hams apparently overdrive them with resulting splatter and IMD 5kc below the lower sideband envelope and 5kc above the carrier frequency for a total of 13kc of splatter
     
    PU2OZT likes this.
  7. WA4SIX

    WA4SIX Ham Member QRZ Page

    There are a couple FB pages& websites pretty dedicated to developing clean amps.


    Ed
     
  8. KF5CCN

    KF5CCN Ham Member QRZ Page

    I am with you on this one. I worked in broadcast engineering and had two Harris TVD-35H transmitters running in parallel. They were actually 50 kW transmitters derated to 35 kW by omitting driver amps. They had 8984 tubes for a final and weighed in at about 60 pounds. Cost for a brand new tube was $25,000 in the early 1990s.
    Soooo yes 1500 Watts ain't squat. And I agree that many hams are power hungry ex-CBers who are power hungry, I have known a few.
     
  9. GNUUSER

    GNUUSER QRZ Member

    true but what you have to consider here is commercial levels of licensing, governmental levels and amateur radio are completely different animals.
    commercial licensing levels are paid for by commercial concerns and you get what you pay for. while governmental/ military can be considered as unrestricted.
    while 1500 watts is considered hi power its what we are restricted to! (and even less depending on your license level)
    and yes you often do get some people who will try to push the envelope a bit.( especially when contesting)
    i like qrp because there is a challenge to it and its quite rewarding to make a distance contact, but sometimes annoying when a powerful signal overrides your message because someone either didn't hear your signal or did so purposely (and yes that does happen when conflicting attitudes get involved)
     
  10. PA0IVA

    PA0IVA Ham Member QRZ Page

    This sound like men with big linear amps en small ... I run 100watt max en make connections around the globe
     

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