600 watt HF Linear Amplifier Project

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

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  1. AF6LJ

    AF6LJ Premium Subscriber QRZ Page

    The only thing a good earth ground is going to buy you is better lightning protection.
    But that is a relative statement. If you get hit there is little or nothing you can do to protect your gear, or your home for that matter....
    SWL37632 likes this.
  2. KD8UYQ

    KD8UYQ Ham Member QRZ Page


    Remember though that I placed RFI isolators between the transceiver and linear, the linear and the antenna tuner with no improvement but I like your idea about starting basic then adding things to see what changes.

    AF6LJ likes this.
  3. AF6LJ

    AF6LJ Premium Subscriber QRZ Page

    Get rid of all that stuff.
    Start from bare nothing.......
    WW1WW likes this.
  4. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Roger that. Bare bones it is then.

    AF6LJ likes this.
  5. SWL37632

    SWL37632 QRZ Member


    Kinda lost the thread here, but you mentioned that your ground line was about 20 feet long up a second story...don't remember if you detailed it out in this thread...may have missed it.

    First, agree with Sue on starting from scratch with these grounding issues.

    Back to the grounding line....if you are using a braid (flat, circular, oval ...whatever) you basically have an inductor to ground at RF. Recommend that you change it to a continuous flat copper sheet material if possible, as wide as practicable....understand the HOA aesthetic issues. If flat sheet material is not possible, soft copper tubing with as large a diameter as is acceptable in your specific case.

    Suggestion 2: last year discovered a surprise at my shack....the 120 vac lines were reversed at the duplex outlets in the room since the house was built 50 years ago....yup, neutral was wired as hot and and hot was wired as neutral.... shack equipment / pc's etc were originally connected between 2 of the outlets....ouch. If you haven't done it already, recommend that you check the wiring polarity of any outlets in use, also verify that outlets are on the same circuit breaker (phase differential issues) albeit minor in most cases, but in my case proved to be problematic.

  6. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hi Bill,

    The ground strap that I tried yesterday was indeed a length of 1" wide .030" thick solid copper ribbon. It made no improvement so I did not install the ground strap.

    Wiring is not an issue. When I retired back in 2015 I worked with the electricians to covert my daughter's bedroom into a hamshack and a electronics work station. These guys were great. They installed a sub panel in the hamshack closet and gave me four 20 amp circuits with outlets galore.

    SWL37632 and AF6LJ like this.
  7. N1OOQ

    N1OOQ Ham Member QRZ Page

    Of course 20 ft. is a substantial fraction of a wavelength on most of HF...
    SWL37632 and AF6LJ like this.
  8. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hello All,

    In my dogged pursuit to get this linear amplifier done other electronic projects have accumulated around the workshop to the point where they started to get in the way. I took this week to take a break and put the amplifier aside so that I could tackle those projects including this nifty vintage capacitor checker.

    and this Heathkit SB-630 that I bought at Hamvention this year.

    I had to make a new lens for the clock window among other things to bring the control station back to working condition. Just have to paint the cabinet and it is good to go.

    Meanwhile, on Monday I sent an email to the support folks at LDG describing what was going on with transceiver, linear, and automatic antenna tuner setup and here is what they said.


    Included here is the tuner interface document that shows how the interface works.

    We would highly recommend that you never have the amp on when tuning the AT-1000ProII. Since there are many type of amplifiers and interfaces, you may need to build an interface or sequencer that makes sure the amp is placed in standby when the tuner is tuning.

    I hopes this helps understand the tuner.


    Attached is the application note that they sent me. Testing so far has shown that the Icom IC-7300 works with the LDG auto antenna tuner on all band flawlessly every time. It's only when the amplifier is turned and in circuit that the antenna tuner fails to tune and match to the antenna.

    Looking at the application note and talking to my Elmer at the Radio Museum today we came up with a plan but it requires that I do a modification to the linear amplifier;s circuit that operates the PA module bias and antenna relay.

    Those other projects are done so hopefully I can state working on the modification to my amplifier this weekend.

    Fingers crossed.

    To be continued.... but I dearly hope, for not much longer.


    Attached Files:

  9. RICHS

    RICHS QRZ Member

    When I first read this I got a very bad feeling about how you incorporated your amp into your station. The part that I found troubling was when you said: "it won't tune when the amplifier is on line". What does this mean? Are you trying to let the tuner tune with RF coming from the output of the amp or are you getting RF to the tuner from the exciter by using the normal pass-through into and out of the amplifier???????
  10. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hello RICHS,

    Your bad feelings were well founded. I was under the mistaken impression that when I initiated a tune command from my transceiver or from the LDG tuner itself the tuner would throttle back the drive to my linear, tune and match to the antenna, then increase the drive power back to where it was before the tune botton was pushed. I now know that the interface cable only provides contact closer. What the linear amplifier or transceiver does when it sees a input signal line going to ground is completely up to the manufacturer. Apperently, if you have an Icom radio, an ALS-600, and the LDG AT-1000ProII the behavior that I described above does occur but that is because the Ametron amp knows to attenuate the drive going to it when the tune signal line goes low.

    I need to modify my antenna relay circuit so that when I push the tune button on the Icom transceiver the linear goes into standby mode until the tune cycle is done then the PTT line will become active again. That is certainly not how my amplifier is configured now.

    The light bulb went on when I received the email from LDG and read the application note.


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