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600 watt HF Linear Amplifier Project

Discussion in 'Homebrew and Kit Projects' started by KD8UYQ, Feb 9, 2017.

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  1. WB3BEL

    WB3BEL Ham Member QRZ Page

    I'd double check your harmonic output. Might be that you are overloading your spectrum analyzer. Add more attenuation and see if you get the same result to see if that is the case.

    But the plot you show for the 3.5 MHz harmonic at 7 MHz only shows about -47 dBc rejection of the harmonic. Marker 2 at +15.8 dBm minus marker 5 at-31.6 dBm = 47.4 dB.

    It is good practice for this to exceed the CFR 47 Part 97.307 with margin.

    43 + 10LOG(P) at 400W
    - 43+10LOG(400) = 69 dB suppression.
    If you intend to run higher power you need even more suppression.
  2. AF6LJ

    AF6LJ Ham Member QRZ Page

    Indeed; you have to be very careful when measuring harmonic output.
    You can add six DB or more to the apparent harmonic output power simply by driving your mixer too hard.
    I always leave 20 DB of headroom when I can, when measuring HF signals...

    VHF and UHF measurements a stub tuner is your friend.
  3. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Thank you both for the tip. I will recheck.

  4. KF5GOI

    KF5GOI Ham Member QRZ Page

    Hello to Ripley and Sue.
    I'm sure that a lot more folks may be following than you may expect.
    I was lucky enough to stumble across as I was checking another Forum.
    I hope to get to a point where I can follow a lot more.
    Sue, if possible I would like to get any information that is available and future info. also. If this is possible? If so I am on QRZ, KF5GOI.
    If any helpful info. towards a build, I would really appreciate it if could forward to my Email. which is, I want to build a near legal limit for my mobile. What I have with 2sc2879 transistors is bulky and the way they are going on price, availability, etc. Who knows future?
    If any of you need components, some which may not be available, let me know. You may be able to save on some $. I was lucky to have picked up some NOS components, majority still in packs. I acquired 25% of the total materials that were supposedly from old Electronic Supply, that had closed.
    Too bad I missed the whole lot. Have been happy and surprised with what I did get.
    Good Health to you All.
    Have fun.
    Paul, KF5GOI
  5. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hello Harry and Sue,

    I remeasured the harmonic performance on the 80 meter band (3.815 Mhz) checking to make sure that I was not over driving my SA. Here is a picture from the display. The power output is still 400 watts.

    3.8Mhz 80 meters.jpg

    This time I am measuring a 49 dB differential between the fundamental frequency and the 2nd order harmonic. that gives me a 6 dBs of headroom over the Part 97.307 spec

    Next I ran the power up to 520 watts and took this picture.
    3.82 80meters 520 watts.jpg

    This time the differential is 44.42 dBs. Lastly, just to make sure that I don't have an issue with my Kenwood TS-120 test transceiver I tested its output (100 watts) directly in the SA.

    3.81Mhz 80 meters.jpg

    The transceiver is copacetic. I will see what I can do to improve on the 80 meter 2nd order harmonic performance.

  6. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hi Sue,

    I have to admit that I had no idea what a stub tuner was so I did a bit of reading. Now I have a better idea as to what a stub tuner is and does but don't understand how I would use it measure harmonics with a spectrum analyzer. However, I was wondering if adjusting the turns ratio of the RG-188 coax cable around the 1:1 balun would effect the fundamental to 2nd order harmonic frequency differential at all for the lower bands. I checked 40 and 2o meters again and the ratio is 50 dB plus at those frequencies.

    7.250mHz 400 watts.jpg

    Above; 40 meters. Below; 20 meters

    14.250Mhz 400 watts.jpg

    When I made an ugly balun for my antenna I seem to remember adding a few more turns to cover 160 meters. I have three turns on the #61 torroid used for the 1:1 balun on the PA board. Could there be a coloration? I am kind of out of my element here.

  7. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    In light of my last post how about I update you all on something that I do know a little bit about. The cabinet for this amplifier project.

    Today I cut the other two panels, mounted the upper and lower aluminum bezels with 3/16" under cut flush head 4-40 screws, and tried them out on the cabinet with the blue masking tape removed.

    So the question is which of the three do you like the best?

    Smoked gray below.


    Or Dark smoked Gray?




    Keep in mind that I am going to paint the inside faces and the heads of the 4/40 screws a semigloss black to match the cabinet. All that you will see of the bezel will be the shiny edges. Also imagine 1/2" thick Walnut wood panels covering the whole right and left sides protruding so that they are flush with the aluminum bezels.

    Whatever panel is picked can easily be changed by pulling the band selector knob, removing two Allen head screws from either side panel, removing the wood panel, and sliding the Plexiglas front panel out then inserting another.

    Feel free to cast your vote.


  8. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hello Paul,

    Thank you for stopping by.
    So, my burning questions are; where are you going to store all these parts and are you married?


  9. K6LPM

    K6LPM Ham Member QRZ Page

    I vote for the dark smoked grey panel.
  10. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    We have one vote for Dark Gray.

    Thank you sir.


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