SWR vs Field Strength?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by W5DXP, Dec 12, 2019.

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  1. W5DXP

    W5DXP Ham Member QRZ Page

    Back in 1953, W5OLV was my Elmer. He had a Harvey Wells Bandmaster and a field strength meter. He would tune his Bandmaster for maximum field strength while dipping and loading. Like most hams at the time, he didn't have an SWR meter. I just did a little experiment and got a 0.5 dB higher field strength when my SWR was 1.4:1 than I did when my SWR was 1:1. Has anyone ever measured their SWR vs field strength?
  2. K0UO

    K0UO Platinum Subscriber Platinum Subscriber QRZ Page

    Most of the time, Lowest SWR = highest power out to the antenna and that would = the Highest field stength
  3. WL7PM

    WL7PM Ham Member QRZ Page

    Is it possible that radiated field strength is proportional to the CURRENT in the wire rather than the feedline POWER ratio, as measured by SWR metering ?
  4. K7JEM

    K7JEM Ham Member QRZ Page

    SWR is not an indicator of transmitted power, so it is entirely possible that you have more power going into the feedline with a 1.4 to 1 SWR as opposed to a 1.1:1 SWR.
  5. WG8Z

    WG8Z Ham Member QRZ Page

    In my primary operating position there is a FS meter directly in the line of sight.
    I have observed in many instances that lowest SWR does not automatically mean MAX radiated
    AI3V likes this.
  6. W1VT

    W1VT Ham Member QRZ Page

    The popular T network tune has a wide matching range but at the expense of multiple tuning settings.

    Getting the Most Out of Your T-Network Antenna Tuner
    QST January 1995, pp. 44-47
    Here's how to adjust this popular tuning circuit so it transfers maximum power to your antenna.
  7. NN4RH

    NN4RH Premium Subscriber QRZ Page

    Where are you measuring SWR? At the antenna or at the radio? And what is in between the two?
    SWL37632 likes this.
  8. AI3V

    AI3V Ham Member QRZ Page

    I have.

    Few transmitters output maximum power exactly into a 50Ω non reactive load (1:1 vswr)
    (And few antennas either!, and what about the vswr meter itself?)

    On my 432 and above rigs I simply tuned the output network for maximum "fire in the wire", while monitoring dc input current.


    P.S. now for a real eye opener,assuming a ordinary hf "antenna tuner" monitor dc input current and field strength while adjusting one of the capacitors, first for a 1.4:1 one way on the cap, then adjust that cap to 1:1, and then more in the same direction past 1:1 to 1.4:1

    P.P.S under certain conditions, a transmission line will have lower loss with a vswr greater than 1:1 than when operating in a "matched" condition!
    Last edited: Dec 13, 2019
  9. KT1F

    KT1F Ham Member QRZ Page

    What conditions would that be?

    If I have a transmission line of Z characteristic impedance, is there are formula to calculate the best load impedance for minimum line loss?

    I'd like to hear your theory of why it could be something other than Z.

    I don't think this thread and the observed behavior is about transmission line loss.
    Last edited: Dec 13, 2019
  10. KL7AJ

    KL7AJ XML Subscriber QRZ Page

    Yes, I've done it numerous times. Most solid state rigs actually put out maximum power with a load impedance of 25-30 ohms. They're designed to have a little headroom, when operated into a 50 ohm load, as well as to improve linearity.

    There are two resistive load conditions that will give you a 1:4 SWR....I believe you'll find that if you operate into 70 ohms, you'll get significantly less power than into 35 ohms.
    N0TZU, N7EKU, KK5JY and 1 other person like this.

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