SWR Reading discrepancies

Discussion in 'General Technical Questions and Answers' started by K5EMG, Oct 6, 2020.

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  1. K5EMG

    K5EMG XML Subscriber QRZ Page

    I have this weird problem, I connected a new EFHW antenna, EFHW-8010-2K-Plus, to my Icom IC-7300. When measuring the SWR, the IC-7300 SWR meter indicates a low SWR, but my Daiwa meter indicates high SWR, but when my IC-7300 SWR meter shows high SWR, infinite, the Daiwa meter shows very low SWR, around 0.5. If I add a tuner things get more crazy but still the same pattern. IC-7300 SWR meter high, Daiwa low, IC-7300 meter SWR reding low, Daiwa reading very high.

    I use a MyAntennas EFHW-8010-2K-Plus antenna without my tuner. IC-7300 -> Daiwa 501 Meter -> Antenna. Antenna is over my roof in a inverted sloper configuration, transformer higher that the wire’s end.

    With my Chamaleon CHA III, any of those problems disappear and both SWR meters show almost the same readings.

    Thanks for your help!
     
  2. KI4POT

    KI4POT Ham Member QRZ Page

    Possibly common mode currents causing problems with the two devices. I had the exact opposite problem with an EFHW kit I was putting together (low SWR on analyzer, high on rig). A choke on the feed line fixed it.

    Chris
     
    Last edited: Oct 6, 2020
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  3. AA5MT

    AA5MT Ham Member QRZ Page

    This is a problem you see once in a while. Put it into a dummy load and see if it is still off. When in doubt, use the radio meter as it is closer to the final.

    I've seen this on MFJ meters. The fix is easy, but getting to it is more difficult. Most swr meters are voltage based, and are cheaper to make. The problem is that the voltage reference point changes along the feedline. Most MFJ meters are calibrated at about 3 feet. Multiple meters scattered down the feedline will show different values.

    To reset yours, find a variable capacitor(or coil) near the pickup coil in the meter. Use an insulated tool to adjust it for a null. Now your meters will agree(until you change the connecting coax length).

    Tom
     
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  4. K5EMG

    K5EMG XML Subscriber QRZ Page

    The problem is that the Radio - Daiwa meter combo works well when using my other Chamaleon antenna instead, same feed same placement, I just switched ununs and antenna wire, and that’s what’s is confusing me.

    As for a little more info, the antenna placement is over my roof at 5 feet high from the shingles , feed going to my shack over the roof too, about 50 feet or less. A counterpoised system made of several cable wiring running in 360 deg over my roof shingles. Feed coax connected to ground before entering my shack (a room in the house).

    Let me add a picture of my install: Page1.jpg

    Another picture: 7E309F4D-29BB-4572-9365-2B9ACF346E74.jpeg
     
    Last edited: Oct 6, 2020
  5. NM7G

    NM7G Ham Member QRZ Page

    1.0 is the lowest (best) SWR possible. Something amiss, perhaps a typo.
    It sounds much like what I'd expect if your meter(s) case is hot with RF. A very easyway to tell at QRP (repeat....at QRP only) is to touch the case while transmitting and watching the SWR display. If touching makes it wiggle/vary, the case is radiating RF.
     
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  6. K2XT

    K2XT Premium Subscriber QRZ Page

    One other thing to keep in mind however, which has been reported previously, is that the 7300 does not give accurate swr readings at low power levels. It needs some minimum amount of power for the diode detector(s) to activate.
     
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  7. K5EMG

    K5EMG XML Subscriber QRZ Page

    Sorry, instead SWR I wrote the return power in %.
     
  8. AA5MT

    AA5MT Ham Member QRZ Page

    Also, make sure both meters are on the radio side of the tuner. If it's on the antenna side, you will see differences.

    Tom
     

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