Good or Bad

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by RSTORRIE, Apr 13, 2021.

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    I was bored yesterday and built me a 20m inverted V antenna to play around with. I have a ZS6BKW flat-topped at 45' that I use. The inverted V is only at about 22' in a tree for now to play with it. Ran WSPR last night and was hitting Australia and the far side of Brazil without a tuner like I do with the ZS6BKW on a tuner. But here is my question, I truly do not fully understand the MFJ-259C analyzer when it comes to R and X. I cannot get the analyzer to see 50 ohms. Here are my readings on it for the following frequency range I cut it for. Maybe somebody that knows about feed lines can give me some guidance as to whether the readings are good, or point me in a direction to get close to the 50 ohms using RG-8X. Any advice would be greatly appreciated.

    14.050.... SWR: 1.0 R=40 X=0
    14.100.... SWR: 1.0 R=41 X=0
    14.150.... SWR: 1.1 R=41 X=0
    14.175.... SWR: 1.1 R=41 X=0
    14.200.... SWR: 1.2 R=41 X=1
  2. AK5B

    AK5B Ham Member QRZ Page

    With reactance at zero or very close you have achieved perfection, basically. Be happy!
    K0UO likes this.
  3. N3PM

    N3PM Ham Member QRZ Page

    How's the 259 look connected to a 50 ohm dummy load?
    Mike N3PM
    K0UO and WB5YUZ like this.
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    It's already amazingly resonant, in fact it seems resonant over too wide a bandwidth. The X=0 usually appears at ONE frequency or a very narrow range of frequencies; however, this really doesn't matter.

    The feedpoint impedance, which in your case is almost entirely resistive, is determined by height above ground. See graphic below.

    With the antenna at 22 feet we'd normally expect it to be >50 Ohms, closer to 80-90 Ohms; however, that's for a "flat-top" dipole, not an inverted vee. If the average height (midway between the feepoint and the ends) is 14 feet, then the R would be much lower and could easily be <50 Ohms. If this is what's happening, to raise the impedance (R), you'd need to raise the antenna higher.
    K0UO likes this.


    I do not know, I am in the process of buying a dummy load. Be here this week. I already had to send the 259c in for repairs once under warranty so I can check its accuracy. Thanks for the reply!


    I will see what happens raising it, but I will have to move it somewhere else as the 22' branch is closest to the station. My tallest trees are 50' but a little ways from the house. Took a 30lb test ocean pole and 4 oz. weight to chuck it over the tops to string up the flat-top.
  7. WA4SIX

    WA4SIX Ham Member QRZ Page

    Run it as is. It'll do just fine. Just ground interaction.

  8. WB5YUZ

    WB5YUZ Ham Member QRZ Page

    Many MFJ 259 series analyzers are in need of calibration. It isn't a design fault; they're just getting old!

    Calibrating an original 259 is easy with dummy loads. The more recently the analyzer was made, the harder it is to calibrate.


    I am happy with its performance, it is holding its own against my ZS6BKW antenna on a tuner flat-topped at 45'. I was trying to find out why the ohms are reading 40-41 instead of 50 ohms. Guessing I will take a reading with the 259c on the ZS6BKW on the same frequencies to see what the ohms say using the same feed line. I know the SWR is going to be up in the 2's, if I remember correctly. Been awhile. Thanks for all the advise everybody 73'.
  10. WA4SIX

    WA4SIX Ham Member QRZ Page

    When the X=0, the antenna is "Resonant".


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