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Thread: Wacko SWR Readings

  1. #1

    Default Wacko SWR Readings

    OK, guys, here's a puzzler. Setup: TS 440S, MJF 949D antenna tuner, MJF Antenna analyzer, 84' longwire antenna + 9:1 balun fed with coax. Everything is grounded, current balun in place (loops of coax). Ready?

    Now, when I connect direct (no MFJ antenna tuner engaged), and I use the TS 440 antenna tuner, it reads like 80 SWR on the MJF 949's SWR meter while showing 1.1/1 on the TS-440 Shouldn't it be the same or at least in the same ballpark?

    So, let's make it more weird. I use the MFJ antenna tuner, tune it to 1.1:1 using the Antenna Analyzer. Then I connect it and do a "straight through" on the TS-440, ie not using the built in antenna tuner. The thing literally shuts down. Pegs the SWR meter, display goes black. Oye. Not good.

    Now, lets get more weird... I have the same set up as above, but use the TS-440's antenna tuner to match to the theoretically perfect MFJ tuner to antenna setup. Can't get less than 5:1 after a lotta cranking and straining on the part of the TS-440's tuner, during which time it hits peaks that cause it to "blank out" the screen.

    So, how do we explain all this? Thought it might be stray currents. I have everything grounded. No RFI in the shack, per my super sensitive computer speakers.

  2. #2
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    You do have the little slider below the meter on the radio set to the correct position?

    My 440's SWR meter hasn't always shown exactly what an external one does, but it's pretty close - close enough...

  3. #3

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    In paragraph 2 you state that the SWR reads higher using the MFJ analyzer compared to the SWR on the TS-440 after tuning. This makes sense if the ts-440 has an INTERNAL tuner. Tuning up with the built in tuner does nothing to the coax or antenna system when you unscrew the coax from said radio and connect it to something else (like an antenna analyzer). In that case, the antenna analyzer would see the input impedance as it is without the effects of the TS-440ís internal tuner. They should be reading different.

    If there is a mismatch at the end of a coax, the coax can transform the impedance to a new value, and this new value may not be in the tuning range of your tuner. If a coax of a half wavelength (or multiple thereof) is used to connect the antenna analyzer to the antenna (or balun), the transformation comes full circle and, aside from the effects of loss (which go up with every half wave multiple), the impedance at the coax input is the same as whatever is connected to the other end. Use a Ĺ wavelength coax to connect the antenna analyzer to the balun-antenna combination to get an accurate impedance measurement to determine the quality of match to a 50ohm coax. Shooting a TDR pulse down the coax to test the main feed line wouldn't be a bad idea either.

    An SWR reading can show a lower value than it really is when there is loss in the system. If the coax is long and lossy, the forward and reflected wave can be partially absorbed by the coax before it can get back to be measured. You can also have resistive losses in the tuner inductor and arcing of the capacitors if the impedance being matched is too low or too high. If the tuner is trying to do the impossible, the inductor could be getting hot.

    I would start by visually inspecting the transformer at the antenna and then taking an impedance measurement at that point using a half wave coax (at whatever test frequency) to the analyzer. If it is fairly matched at the antenna, perhaps the core used in building the 9:1 is saturating under the power of the TS-440.

    Well, Iím out of ideas, but it sounds like a mismatch at the antenna to me. If it is a small mismatch, the coax could still be putting the impedance in a bad range for the tuner. In that event, try adding or subtracting some coax. The tuner might like it better. Good Luck!
    Last edited by brandon lind; Tue 2nd Apr 2019 at 02:59.

  4. #4

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    What counterpoise are you using with the antenna?


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