Xiegu XPA125 HF amp

Discussion in 'Amateur Radio Equipment Reviews' started by KU3X, Dec 28, 2017.

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  1. KU3X

    KU3X Ham Member QRZ Page


    At first I thought this amp had promise. It's half the price of the Elecraft KPA100. Not a bad deal for a 125 watt amp for QRP radios and the tuner is included.

    And then I read the specs. The harmonic suppression is only 39 db down. Sorry, for USA it MUST be down 43 db.

    So if you are looking for an amp for your QRP radio, this is not the way to go.

    I am not try to pick on manufactures, I am just try to keep the bands clean.

    NB3R likes this.
  2. KS2G

    KS2G Subscriber QRZ Page

    Isn't there a requirement for FCC Certification for amplifiers sold in the USA?
  3. KU3X

    KU3X Ham Member QRZ Page

    Go to Ebay and you can buy an amplifier, from China, with NO band pass filters and they generate harmonics all over the place.
    That shows you how strongly that rule is inforced.
    QST posted an article showing how the Baofeng UV-5RE does not meet FCC specs. I have a spectrum analyzer and tested one for myself.
    No Way does it meet FCC specs. I now ONLY use it for receiving ! You can buy them on Amazon. Rule enforcements? Seems to be a joke in these days.
    K4AGO likes this.
  4. KC1AIH

    KC1AIH Ham Member QRZ Page

    Does anyone know where the delay adjustment, if there is any, is? When using on SSB, all bands, two different radios, the normal space between spoken words allows the amp to drop off. I have been told, it sounds horrid on receive. Increasing the delay would do the trick. I can't seem to find a service manual for the xpa 125. Perhaps that may have an answer. KC1AIH Miriam.
  5. KF5YDR

    KF5YDR Ham Member QRZ Page

    Not for amateur gear, only commercial. I’ve heard some noise about asking the FCC to make a ruling on the importation of radios that don’t have adequate front-end filtration.
  6. KU3X

    KU3X Ham Member QRZ Page

    I never read in the FCC rules that you can build you own amp and not have to meet FCC specs. I also never read in the FCC rules that you can buy an amp from another country and not meet FCC specs.

    You are responsible for operating your station within the FCC rules and the FCC rules spells out clearly what the specs are.

    K4AGO likes this.
  7. W1VT

    W1VT Ham Member QRZ Page

    No amplifier capable of operation below 144 MHz may be constructed or modified by a non-amateur service licensee without a grant of certification from the FCC.

    There are exemptions for 97.315 (a) but they don't apply here.
  8. K6AER

    K6AER Ham Member QRZ Page

    You can build your own amplifier and run it without high pass filters and the FCC doesn't care a wit. Also tube amplifiers have no filtering at all. Just an output matching network. Does anyone think anybody will hear the difference between -39 dB and -43 dB on the harmonics. I have trouble hearing a 100 watt signal on 40 meters let alone a signal that is .5 mW.

  9. KU3X

    KU3X Ham Member QRZ Page

    We as hams are compelled to follow the FCC rules. We are kind of on the honor system and are really self policing. The rules clearly spell out that any HF amplifiers built or sold today are required to have third order harmonics to be at least 43 db down from the fundamental. If you build an HF amplifier and use only an L/C tank circuit after the tube, you will not come anywhere close to meeting the above mentioned requirement. Does that mean that you can put that amplifier on the air and not be compelled to follow the rules? NO, you are in violation of FCC rules. The FCC does not use Gestapo tactics to hunt you down because there may be an issue. They have much bigger fish to fry than keeping a very close eye on us hams. That does not mean they don’t care.

    Bottom line, the above mentioned amplifier clearly does not meet FCC compliance and it is to us, as licensed hams, not to put such garbage on the air.

    Are high pass filters needed for tube amps? They are not needed if the amplifier is built correctly.

    Tube amps don’t have any filtering? Sure they do. That’s what a properly designed tank circuit is for. You can build an L/C network to couple the plate impedance of, let's say, 2500 ohns down to a 50 ohm load but it’s a poor design for this application. Build a Pi network properly and you should easily comply. Pi-L will even do better. When I built all of my amps, I made sure I used no less than a Q of 12 for the plate circuit and I biased the tube(s) properly. My last amp used Pi-L, even better. I purchased a spectrum analyzer three years ago and the very first job I had lined up was to check the two remaining legal limit amps that I still use. Both not only easily complied with the FCC rules for third order harmonics, but also complied with IMD requirements with plenty of headroom for both tests.

    When I passed my tests, which were given in the federal court house back then, I made sure I would ALWAYS comply with FCC rules and have a lot of pride in being a ham radio operator.

    One either follows FCC rules or does not follow FCC rule. The ones that do not follow the rules create problems on the bands. One does not pick and choose which rules they want to follow.

    So where do you stand? “Are you part of the problem or part of the solution?”

    Barry G. Kery, KU3X

    Added foot note:
    Xeigu now has an updated "B" version that now complies. "I wander if they read this post?"
    Last edited: Jun 11, 2019
    KK4YPQ likes this.

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