Kenwood SM-220 Scope RF attenuation

Discussion in 'General Technical Questions and Answers' started by N9SB, Oct 17, 2020.

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  1. N9SB

    N9SB Ham Member QRZ Page

    I have a Kenwood SM-220 monitor scope where I have to have the RF attenuation all the way to minimum to see much of a signal. Anything less than that and it is not much more than a horizontal line. This is with 100 watts. When I run 500 watts through it, I get a much better display with the attenuation set to minimum. Is this normal or is there something wrong in the RF attenuation chain. Thanks and 73.
  2. K0OKS

    K0OKS Premium Subscriber QRZ Page

    That sounds a little low. I usually use one tick from the bottom for 100W.

    You checked all the caps in the SM-220? The HV caps are typically decent, though I have heard of them failing, but if some of the elctrolytics were bad it could reduce the vertical deflection voltage.
  3. N6UH

    N6UH Ham Member QRZ Page

    You might want to check the HV caps in there while you have it open. They're the oil filled tube type ones. I ended up replacing them all due to leakage and low readings. It was still working kind of.
  4. N9SB

    N9SB Ham Member QRZ Page

    Thanks for the suggestions. I will look at the caps.
  5. K0OKS

    K0OKS Premium Subscriber QRZ Page

    I’m not certain, I believe that the manual has a calibration procedure, or at least voltage checks. I thought I adjusted mine after I recapped it.

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