high swr with amp on

Discussion in 'Amateur Radio Amplifiers' started by KU7I, Aug 6, 2019.

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  1. KU7I

    KU7I Ham Member QRZ Page

    Interesting thing happening. Running a 2kw outboard tuner to my vertical antennas. When I tune the vswr down to 1:1 with the radio only at 100 watts and then enable my Kenwood TL922A I adjust accordingly for max power out into the dummy load. Switch over to the antenna and after a second or two of tweaking I adjust again for flat swr at a KW out of the amp, no problem. When I use my solid state amp however I show a significant reflected power that requires extensive tweaking of the outboard tuner. 1:1 is never achieved as it is with either the rig by itself or when running the Knwd TL922. It gets worse with the solid state amp as I go lower in freq. Thoughts? Lane Ku7i
    WC5P likes this.
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    My first guess is the SS amp has a harmonic or spurious output problem. If the amp is creating junk outside the band you're tuned for, you'll never achieve a good match to a real antenna -- however, even if it's harmonic or spurious-laden, the SWR into a very good dummy load should still be 1:1.

    Have you tried that?
    WG7X, K7TRF and KK4RSV like this.
  3. K7TRF

    K7TRF Premium Subscriber QRZ Page

    What's the specific make and model of the solid state amp and what does it have for band specific lowpass or bandpass filtering on its output?
  4. AI3V

    AI3V Ham Member QRZ Page

    A single harmonic 20 db down from the fundamental- if totally reflected- will show a vswr of. 1.2:1

  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    And an out-of-band spur will never let you adjust a tuner for an SWR of 1:1 unless you're using a dummy load.

    There are also some SS amps out there that were really "CB" amps (or whatever) by design and don't include bandswitched low pass filters; their harmonics can be way stronger than -20 dBc. I tested one here a few years ago that if driven a bit hard (into compression) had 3x harmonics that were stronger than -10 dBc. That's powerful stuff.
  6. KL7AJ

    KL7AJ XML Subscriber QRZ Page

    Yep..I fully concur. Especially since almost all SWR meters are more sensitive to higher frequencies, so any squirrelly harmonics or parasitics will show a high SWR.
    AI3V likes this.

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