600 watt HF Linear Amplifier Project

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

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  1. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hello Ed,

    No sir, not quite yet, the LDG tuner is still acting erratic. Sometimes it will memory tune perfectly on the lower frequencies (80 and 40 meters) but if I try to tune a frequency on say 15 meters, the antenna tuner goes into protection mode plus when I do finally tune on the higher band then go back down to a previously stored frequency on the lower bands it takes several tries before the LDG matches to the antenna.

    So here are my next steps:

    1.) Try connecting a copper strap (from Georgia Copper) from the common grounding point in my shack to the earth ground below the second floor window in my ham shack. The run is probably be around 20'. Currently, there is a #10 copper wire running from my common ground point to the ground hole in a three prong power outlet under the radio workstation desktop. The theory is that by doing this I am adding to my RFI issues.

    2.) Make another common mode choke and connect itat the feed point of the Alpha-Delta antenna above my head.

    3.) Order some #31 toroids to slide over the control cable that runs between my Icom and the linear (I am beginning to suspect my problems are associated with that cable).

    We will give it a go and see what happens.

    AF6LJ likes this.
  2. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Well I spent most of the day working on the auto tuner problem and in the end I am no better off then when I started.
    The first task this morning was to disconnect the existing ground connection and temporarily run a copper ground strap from the common ground point in the ham shack, out the window, and down to the ground rod below. The length of this run was approximately 25'. Then I tested all the bands for three things.

    1.) To see if the LDG automatic antenna tuner would work properly with the linear amplifier on and in circuit.
    2.) Listen to hear if I was setting off the CO detector and If I could hear the RF hum coming from the sub-woofer in the shack.
    3.) Check to see if the TV in the workshop was still turning on.

    There was really no difference if I had the outside ground, the ground using the power receptacle's third hole, or no ground at all. Just the common grounding point for all of my equipment. In the end I reverted back to using the grounding pin hole in the power outlet to tie my common ground point to a "Ground" like I had been using all along.

    So next I turned my attention to making another common mode choke using ten #43 mix toroids and about 4' of RG-213 like so.

    While in the process of installing this choke at the feed point of my Alpha-Delta 80-40-20-10 dipole antenna I found this.



    This being the RG-213 cable that goes from the output of my existing ugly balun to the feed point of the antenna. This connector in particular is the one that plugs in to the top of the ugly balun. All of my outside coax cable connections where sealed with Coax Cable sealing tape but when I cut through the tape to check this cable I found an oxidized connection and this black tarnish on the copper center conductor and outside braiding. For a moment I though that this corroded connector was the cause of my woes but after making a new cable and testing it, the only problem that was cured was with the carbon monoxide monitor going into alarm when I transmitted on 80 and 40 meters. Nothing else changed.

    So as the sun was beginning to set I added the common mode choke that I made earlier and gave it a go.

    The LDG antenna tuner still goes into protection mode if the SWR is above 2.5 and if the amplifier is in line, and if the frequency to be tuned has not been stored in the LDG AT-1000ProII's memory. Even at that memory tuning has only about a 60% success rate on only the lower bands (80,40, and to a lesser extent 20 meters). I still have hum in the sub-woofer but it has diminished in volume and the workshop TV still turns on when I operate on 80 and 40 meters regardless if the amplifier is on or off.

    So what can I conclude from today's work? I am pretty sure that I don't have a grounding issue and my prime suspect is pointing more and more to the control cable between the linear amplifier and my transceiver. Consider this. I have the PTT signal from the transceiver doing two things via one relay within the linear amplifier. When transmit is activated on my Icom it energizes a 12 volt relay that (1.) supplies the bias voltage to the PA module and (2.) provides closure so that 120 volts AC is supplied to the antenna relay. I am now beginning to suspect that RF is getting into the cable and causing the relay to drop out as the antenna tuner is trying to do it's tuning cycle. What bothers me about this theory is when I turn down the drive to the linear to 1 watt the antenna tuner still gives me a power/high SWR error set of blinking LEDs. Which makes me think that I have more of a high SWR situation occurring other than a high power issue. Regardless "something" in or around the the linear amplifier, when it is on, is fooling the LDG antenna tuner to go into protection mode. I ordered a #31 toroid kit from Palomar to tackle this issue.

    As for the RF hum and TV turning on look at this picture.


    That 80 meter trap is only about 15' away from the window in my ham shack an my workshop below it. Me thinks that I am bathing myself with RF.

    To be continued..

  3. RICHS

    RICHS QRZ Member

    This is probably the best looking ugly balun I have ever seen wound on what ever that cylindrical thing is???

    Attached Files:

  4. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Thank you sir.

    I must have stood in the plumbing department at our local big box hardware store for over an hour looking at PVC pipe fitting to come up with the pieces to make that balun. Once I had it all together I painted it brown so that it would basically disappear when mounted at the roofline. I think I might have mentioned this before but I a running a stealth antenna. Our HOA is somewhat restrictive when it comes to outside antennas (yet they have dishes on there roofs) and the soccer moms around here are an "interesting" lot. :confused:

  5. AF6LJ

    AF6LJ Premium Subscriber QRZ Page

    You said your ground lead from the shack to the ground rod was 25'?
    For a DC ground that would be okay, for an RF ground that is not acceptable.

    You also have a wire antenna overhead of the house which also contributes to RF getting into items within the house.
    Add your ground wire which is acting like an un-tuned element in your antenna and I can see why you have lots of RF woes....

    Just for grins.....
    disconnect all your grounding wires.
    Including the main ground you added to the station...
    All ground straps between pieces of gear.....

    Starting with the radio and the tuner only....
    give your system a full check out on all bands you will be using.
    If there are any problems fix them first before moving on.

    If you have a wattmeter you use add it in line now with a short jumper and see if anything changes, repeating the above tests on all bands. Then add your amplifier and see what changes.

    Don't expect to stay out of any audio equipment, this must be dealt with after the fact.
    The CO detector may have to be relocated...
    The TV set will have to be dealt with on its own as it and your audio gear are going to have their own susceptibility issues.
    CO detectors we already know they can be problematic.
    WA9WVX likes this.
  6. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hello Sue,

    The transceiver and LDG antenna tuner work perfectly together on all bands as long as the amplifier is shut off. Are you suggesting that I add my watt meter to the output of the antenna tuner then test the bands again? Also, I suspect that you want me to monitor the reflected power while I am testing not the forward power so much.

  7. AF6LJ

    AF6LJ Premium Subscriber QRZ Page

    That was not what I meant to suggest. ....
    The tuner should be last.
  8. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hello dear lady,

    OK, let me play this back to you. The setup would be transceiver to watt meter; output of the watt meter to the input of the auto antenna tuner then out the antenna tuner to my dipole. This test would be done with no interconnecting grounds and no chassis grounds to a common point plus all the RFI isolators removed as well. Does that sound correct?

    AF6LJ likes this.
  9. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Now that I have learned more about the RFI condition in my shack. I agree that the sub-woofer hum and TV in the workshop turning on are separate issues to be addressed, or not, at another time. The good news is my CO monitor doesn't alarm anymore when I am operating on 80 and 40 meters.

    It is too soon to tell but I think by adding the common mode choke to the feed point of my antenna I may have lowered my 80 meter noise floor by 2 S units. I need to operate on 80 meters over the next few days to see if that statement holds true.

    Sue, I also agree that running that copper ground strap out the second story window and down to the ground rod was a futile effort but several other folks insisted that I needed to have a good earth ground and that distance wasn't going to be an issue. It would cure my ills.

    Testing proved otherwise. It didn't fix anything but it didn't make it worse either.

    Today is grounds keeping day and I have other projects that need attention this week but I will report back when I have run those tests.

  10. AF6LJ

    AF6LJ Premium Subscriber QRZ Page

    Yes because sometimes ground loops can be a problem.
    WA9WVX likes this.

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