A visit to KSAZ with W7TFO today

Discussion in 'Amplitude Modulation' started by N6YW, Jul 18, 2019.

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  1. N6YW

    N6YW Ham Member Volunteer Moderator QRZ Page

    Most any AM station is interesting to me especially when it involves hanging with Dennis W7TFO. We met up to repair the ATU for the 3 stick array running 5 KW.

    While this is not an amateur installation, the theory and practical knowledge is the same, so read on.

    A blown input cap ( puck) spewed and hurled its silver and beeswax all over the shunt coil.
    By using an in service L/C bridge, Dennis determined that there wasn’t enough C to make that circuit stable, in other words, too much reactance at 50 ohms. By replacing the bad cap, and adding additional C in parallel, he was able to cancel out the reactance and tune the input T net coil for 50 ohms. After a few adjustments between that coil and the output coil tap corrected, the unit was ready to close the doors and see if it behaves under full power. It did. Dennis knows these things like a neurosurgeon. I loved watching and assisting and of course, enjoying the thrill of putting the station back on the air.
    The BE 5E AM transmitter is a sweet machine. And you should look them up. There’s a lot to be said for class E.
    Enjoy the pictures.
    Billy N6YW

    Attached Files:

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  2. W7TFO

    W7TFO Premium Subscriber QRZ Page

    Whoops! I'm back, you yobbos!

    That site was plagued by Africanized bees, but the owner took care of having them removed, much to our satisfaction.

    This ATU was built by Kintronic down in Tennessee. They do top notch work.

    Those 294-style caps are a bit over $1K per. Ouch, but that one has been in service since '93.

    The daytime ATU in the photos is actually two in the same cabinet, one side for 5kW day, the other for 125W night as part of the directional antenna.

    Mr. Yates is a great guy to work with, too!

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  3. AC0OB

    AC0OB Subscriber QRZ Page

    When did they drop nightime power from 390 Watts to 125 Watts?

  4. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    Very interesting read, thanks.

    In the last photo, coming off of what looks like the feed to the tower, is a helical copper (I think) tube. What is its function?

    Also, there is what appears to be a lightning discharge gap at the top, shaped like a Jacobs Ladder. Why is it so shaped ? Is it to help extinguish an arc as it moves upward?
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  5. W7TFO

    W7TFO Premium Subscriber QRZ Page

    Phil...The center (day) #2 tower runs at about 125W when in night mode. The rest goes to towers 1 & 3

    N0TZU...the 'coil' in the link from the ATU to the tower is thought to act as a surge suppressor in the event of a lightning strike. The jury is still out of it's effectiveness.

    The arc gap is pointing up, just as you said, to use natural convection to terminate an arc if one gets started.

    The non-metallic flex carries the lighting circuits.

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  6. K5UJ

    K5UJ Ham Member QRZ Page

    I took a look at that tx site with google earth and street view. Two things crossed my mind: 1. If I lived out there I'd probably be going through two bottles of sun screen every month. 2. How hard was it to plow in a ground system in that land? Looks like rock hard dry dirt that instantly turns into a mud slurry with a desert downpour. I was stationed for a year in Sierra Vista when I was in the Army.
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  7. AC0OB

    AC0OB Subscriber QRZ Page

    If I were to guess, in Pic 1 the coil at top-right with the reddish enamel coating is the lighting choke for the tower lights.

    In Pic II the Black rubber covered thing exiting from the porcelin insulator, that looks like coax, is not coax but a conduit for the wiring to the tower lights.

    The actual 580 kHz RF current is carried by the darkened copper tube wound into a large one-turn coil that feeds the tower base just above the insulator.
    Broadcast ATU for 5kW.jpeg

    Broadcast ATU for 5kW II.jpeg
    Last edited: Jul 21, 2019
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  8. W8KHK

    W8KHK Ham Member QRZ Page

    I would sure love to come out west and hang with you for a couple days, Dennis!

    Billy, I bet you were in heaven! Dennis, ya gotta love that work!
    N6YW likes this.

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