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SWR reading question

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KF0FQL, Jun 8, 2021.

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  1. KF0FQL

    KF0FQL Ham Member QRZ Page

    Hi! Still learning newbie here!

    I’ve got a question about SWR readings in antennas. I purchased this https://www.amazon.com/gp/aw/d/B075H8FDDR?psc=1&ref=ppx_pop_mob_b_asin_image

    to test my homemade ground plane antenna and my whip. So I used my Baofeng HT to test. When I tested on Medium or high power at the lower side of the 2m, the readings were 2.2- not good. But when I switched to Low I got 1.5.

    I just bought a 25w mobile Anytone but I can’t test the antennas on this because the SWR meter I bought doesn’t have the right connectors.

    So my question is if I tested the antennas at 2watts and use my mobile a 25w, will the antenna not be good for that frequency? Do antennas SWR readings vary based on the type of radio?
     
  2. AA5MT

    AA5MT Ham Member QRZ Page

    Try to find a local ham who can compare it to his. A dummy load is even better if he has one. Always start with what you know and then solve for the unknowns.

    In this case, do you know if either or both of the radios are correct. Is the cable good. Does your new meter read good at high and low power. Verify everything.

    Tom
     
  3. W9IQ

    W9IQ Ham Member QRZ Page

    Ideally, changing the transmit power should not change the SWR reading provided all other test conditions are the same. Some reasons that SWR readings may change with only a change in power level are inaccuracies of the SWR meter or heating/breakdown of antenna system components. I would suspect that the change in SWR readings in your case is due to meter inaccuracies.

    Higher power radios tend to be more sensitive to high SWR. At some elevated SWR level, most of these radios will deliberately cut back power to prevent damage to the final transistors. So watch for that with your new radio.

    It is great that you are learning about SWR. It is an important metric when working with antennas. But don't become obsessed with it as it can also lead you astray. There are many other factors that come into play when trying to optimize the performance of your antenna systems.

    - Glenn W9IQ
     
  4. KF0FQL

    KF0FQL Ham Member QRZ Page

    Thank you. I primarily bought the item because I wanted to make sure that the ground plane antenna was tuned correctly, which it's not, so that led me to see how the store bought ones did. I'm not entirely sure I will be building another antenna but I wonder if it's worth to hang on to it for when I decided to purchase a new antenna. Or perhaps it's best to return the meter.. especially because I certainly don't understand why they store bought antenna was so off. Unless I am doing something incorrectly too however. For example, I tested the mag mount antenna on a cookie sheet in my house. Perhaps it might test better if attached to the vehicle? I started to think about that last night. I did take the Nagoya 771 whip outside to test it but it still was 2.3 range. I also think I need to read up on about SWR too and it's importance. I say that because I can hit repeaters just fine, even with these being so off according to the meter. So that leads me to think that like you kind of hit on, don't get hung up on it. Thanks for your help!
     
  5. KF0FQL

    KF0FQL Ham Member QRZ Page

    Thanks. Still new, and not sure about clubs quite yet, and I don't know any hams near by. Something to work on doing.
     
  6. W4HWD

    W4HWD Premium Subscriber QRZ Page

    "It is great that you are learning about SWR. It is an important metric when working with antennas."

    It's not the only "metric" though...and sometimes it's not the most important. Non-resonant multi-band doublets, for example, work very well with high (but not ridiculously high) SWR and a matchbox; in that case SWR is not as important as efficiency.
     
  7. KU4PT

    KU4PT Ham Member QRZ Page

    *****************************************************

    Due to the way the diodes work in the SWR meter they often do not give accurate measurements at low power. Unless the meter is especially calibrated for very low power, the measurements will often not be accurate below 25 watts or so. If you are using very high power for an antenna it may breakdown and change, but no matter what power below that you use the actual SWR will not change. While not likely on a store bought transceiver , the meter can show a different SWR with different radios if one of them has a high harmonic content. There is probably nothing wrong with the meter and other meters will probably act the same.

    Ralph ku4pt
     
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    There are 75 hams listed in your zip code, so you have ham neighbors you don't know yet.:)

    Lotsa radio clubs around there...


     
  9. WB5YUZ

    WB5YUZ Ham Member QRZ Page

    This depends on the type of meter. I frequently make SWR measurements with my thirty-year-old Diamond SX 200 at power levels below one Watt, with very good accuracy. It was not an expensive meter.

    This is not true, however, of the SWR measurement system in my IC 718 (I haven't made the experiment yet with my IC 7300 and probably won't bother to). The manual specifies 30 watts for an accurate reading! So it depends greatly on what kind of meter one is using.

    Using as low power as possible to make SWR measurements is a matter of common sense and common courtesy. If the manual cannot be found, experiment with lower power readings to see if they will work. With stand-alone meters, they frequently will.

    (This is also one example of why I keep a stand-alone watt meter in the shack instead of relying on the one built in to the radio.)
     

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