Parasitic Suppresser

Discussion in 'Amateur Radio Amplifiers' started by KA5ROW, Jun 13, 2012.

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  1. K9FV

    K9FV Ham Member QRZ Page

    What is this? Are you referring to W8JI? SK????? I sure hope this is not the meaning.

  2. KD0CAC

    KD0CAC Ham Member QRZ Page

    "But overall the analysis method isn't that of an engineer, it's the analysis of a radio ham. Maybe that's because it's aimed at radio hams but to me it could be dealt with better with basic system analysis to model the mode of instability and also how the suppressor can be used to improve stability."

    I would like to see / read that .
  3. KM1H

    KM1H Ham Member QRZ Page

    No, sorry about the confusion, I was referring to the AMPS owner, Bill Fisher, W4AN.
  4. AG6K

    AG6K Guest

     The 100MHz Q of a 922's parasitic suppressor is c. 5.5 and a SB-220's is c. 5. With above-average gain 3-500Zs Parasitic oscillation is sometimes possible with this amount of parasitic suppressor Q. To improve VHF stability of a 922 or 220, lower VHF amplification by lowering the VHF suppressor's VHF-Q. The retrofitted 922 suppressors in the photo on:
    have a Q of c. 1.5 at 100mhz. The tradeoff is about 2% less P out at 28MHz. No further oscillation has been reported in this amplifier.
    - note 1 - when wire is coiled around a MOF resistor, arcing between the resistive film and the wire can take place -- so the wire coil is placed a safe distance from the R as in the photo above.
    - note 2 - Amps are designed by humans. Humans are not perfect - even though some seem to think they are.
  5. K9FV

    K9FV Ham Member QRZ Page

    Thanks for the clarification Carl - I felt for sure if it had been JI I'd read about it. The line "trying to launch a Mustang airborn" sure sounds like something that could happen to a real Hot Rod<:)

    73 de Ken H>
  6. WA7PRC

    WA7PRC Ham Member QRZ Page

    The answer to my question appears to be 3 days, 33 minutes. ;)
  7. AG6K

    AG6K Guest

     There is nothing special about Ni-Cr resistance wire since all it does is add ESR to an inductor. You can achieve the same Q reduction in a VHF suppressor made with a silver-plated L by increasing the L - but that exponentially increases the dissipation in R-supp. If resistors with under 15nH of L were available that would dissipate 50W there would be no need to use resistance-wire for a VHF suppressor's L. By using resistance wire for L, commonly available MOF resistors like Ohmite's OY-series can be used.
    - note 1 - The lower the VHF-Q of the VHF oscillation suppressor, the lower the VHF RL presented to the anode and the lower the VHF amplification.
    - note 2 - the name "VHF parasitic oscillation suppressor" is somewhat inaccurate since the device can not possibly suppress/absorb an in-progress parasitic oscillation, rather it reduces VHF amplification so that such an oscillation hopefully can not take place.

    “The combination of both resistance and inductance is very effective in limiting parasitic oscillations to a negligible value of current.”
    - - F. E. Handy, W1BDI 1926 Ed. The Radio Amateur's Handbook, p. 72
  8. AG6K

    AG6K Guest

     Chortle. Good description of him Carl. Ethanol-driven thinking is that way. It's based on denial of reality - a monumental human malady.
  9. AG6K

    AG6K Guest

     The old AMPS forum was designed to be Emperor JI's throne. Thanks for tipping me off back then as to it's creation Carl. As far as I know I still hold the record for getting jackbooted off of AMPS for suggesting that the emperor might be unclad from time to time.
    - Take it as a rule, censorship is poison because largely-uneducated people with a miscreant agenda want to be the Censor/Moderator/ and even his magnificence the "SuperModerator".

    "Lord, what fools these mortals be!" -- Puck.
    --From "A Midsummer Night's Dream" (Act 3, scene 2)
  10. KM1H

    KM1H Ham Member QRZ Page

    We go back a long way Rich.

    I see a bit of the emperors hatchetman attitude on here also but not as pervasive.

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