Question about a wattmeter for my station

Discussion in 'General Technical Questions and Answers' started by WB6BUM, Jan 13, 2018 at 4:58 AM.

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  1. WB6BUM

    WB6BUM Ham Member QRZ Page

    About five years ago I purchased a Kenwood TS-530s with an AT-200 tuner. When I bought the unit I had a tech check it out and it was putting out an hones 100 watts.
    Lately I have noticed that when I do a dummy load tune up my old AT-200 indicates about 80 watts on 20 meters.
    I'm thinking the finals are getting tired or perhaps the old AT-200 is just not at all accurate.
    I really don't want to invest in a bird, I don't do that much tech work.
    I am wondering if the $100 MFJ watt/swr meters are that dependable? Would it be worth the investment, or should I just try to find someone in the area with a Bird?
     
  2. KA5IPF

    KA5IPF Ham Member QRZ Page

    When you tune it up is the current draw what it was in the past? How about the high voltage? Carrier control at same spot?
     
  3. WB6BUM

    WB6BUM Ham Member QRZ Page

    Clif...Yes, yes, and.....yes
     
  4. AI3V

    AI3V Ham Member QRZ Page

    My recommendation,

    You could $pend 500 dollar$ on a bird.

    Or,

    You could spend $500 on a second hand amp, or a directional antenna.

    Gue$$ which one will actually make your signal louder, or reception clearer?

    Rege, who $pent over a grand on a bird and "slugs", instead of a bigger antenna :( :(
     
    KU3X likes this.
  5. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Bird instruments are nice and I own three of the portable 43 models; handy to carry around, require no power source to operate, and their finest attribute is the well designed and machined coupler that works into the low microwave frequency region (if you have the right elements) and also down to MF (ditto), and full-scale elements available from 2.5W to 2500W are common (I think there are even some higher powered ones, which I don't have), plus the quick-change coaxial connectors are commonly available for UHF-N-BNC-DIN. So, it's "versatile," and that's the only reason to own one. "Accuracy" is not its best feature.

    The bridge in the Kenwood tuner may very well have drifted out of calibration over time; that stuff is all pretty old and anything can drift.

    Rather than buy anything new, you might find a local ham or 2-way radio shop who has a known accurate meter and borrow it for an hour or a day, compare it with the readings provided by the Kenwood tuner and see if they agree or not.

    Another tip: If you're interested in knowing only "how much power can this transmitter deliver into a 50 Ohm load?" and not measuring SWR, there are a lot of surplus dummy load/wattmeters made by Bird, Struthers-Dunn and others who made them for the military over the decades that have built-in wattmeters that are very accurate. They are not "in line" types, they're terminations, but can often be found cheaper than a Bird 43. Some use thermistors to "measure" the power applied, and although they are slow to respond compared with a diode detector, they can be accurate over an enormous frequency range and provide "RMS" equivalent power readings irrespective of waveform, so they can provide useful information even with a highly distorted signal.
     
    WB5YUZ likes this.
  6. N1OOQ

    N1OOQ Ham Member QRZ Page

    80W vs 100W is about -1 dB. More or less within the margin of error...
     
    WA7PRC likes this.
  7. K0MB

    K0MB XML Subscriber QRZ Page

    Sounds like you need to re-peak the 20m coil group.
     
  8. WA3QGD

    WA3QGD Ham Member QRZ Page

    Before doing any radio trouble shooting check your line voltage when transmitting and then when not.Check to see whats on the same circuit your transmitter is connected to and what else you might be running simultaneously .Loads on the other side of the single phase line will bump up or down the line voltage on Quickwired receptacles and may skew the readings due to either a decrease or an increase in volts on that circuit.Remember some meters are more accurate, all meters have some error and the act of inserting them change the circuit so Meters Lie especially so when not being tied to a known stable non reactive load.
     
  9. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Although he stated (perhaps erroneously) that his B+ and also loaded Ip haven't changed at all.

    When the "20m coil group" goes out of tune or has a component failure, you'd never get the loaded Ip up as high because the tubes would be starving for drive.

    If the B+ key-down hasn't changed (the Kenwood meters this), then it wouldn't be a line voltage problem, either.

    Either something in the transmission path between the tubes and the wattmeter has increased in loss, or the meter has drifted in calibration.
     
    WB5YUZ likes this.
  10. KA9JLM

    KA9JLM Ham Member QRZ Page

    Why is the magic screwdriver a fix for everything ?

    Unless you are calibrating radios a bird is overkill, And not needed.
     
    WA7PRC likes this.

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