[Amps] CB Amps or full spectrum???

[jeremy-ca]

Thats a loaded question since even some poorly designed ham amps and 
transmitters dont meet FCC regulations. The only proper way to tell the 
harmonic content is to use a spectrum analyzer.

In addition IMD from sweep tube amps can be as bad as the mid teens; 
certainly not anything I would dare to use.

Carl
KM1H


----- Original Message ----- 
From: "RAY FRIESS" <rayfrijr at msn.com>
To: <amps at contesting.com>; "Peter Voelpel" <df3kv at t-online.de>
Sent: Wednesday, October 10, 2007 12:12 PM
Subject: Re: [Amps] CB Amps or full spectrum???


So then the ones with tubes would not have the harmonic problems?

  ----- Original Message ----- 
  From: Peter Voelpel<mailto:df3kv at t-online.de>
  To: amps at contesting.com<mailto:amps at contesting.com>
  Sent: Wednesday, October 10, 2007 9:57 AM
  Subject: Re: [Amps] CB Amps or full spectrum???


  It´s no tube amp, but a 12V transistor amp where band passes are necessary

  73
  Peter

  -----Original Message-----
  From: amps-bounces at contesting.com<mailto:amps-bounces at contesting.com> 
[mailto:amps-bounces at contesting.com] On
  Behalf Of RAY FRIESS
  Sent: Mittwoch, 10. Oktober 2007 17:48
  To: Tom Rauch; chasm at texas.net<mailto:chasm at texas.net>; 
amps at contesting.com<mailto:amps at contesting.com>
  Subject: Re: [Amps] CB Amps or full spectrum???

  I wondering about your comment about filtering.  If you look at the tank
  circuit of these amps, you see a pi network that is usually no different
  than any other amp, except the coil is small turns wise because it is for 
11
  meters (and close to 10 meters as well).   So what kind of "filtering" are
  you talking about?
  If the pi network is not different than, say, a 30L-1 or an SB 200 or any
  other amp with a pi network, why would harmonics be any more of a problem
  than with other amps?
  Ray  wa7itz
    ----- Original Message -----
    From: Tom Rauch<mailto:w8ji at contesting.com<mailto:w8ji at contesting.com>>
    To: 
chasm at texas.net<mailto:chasm at texas.net<mailto:chasm at texas.net<mailto:chasm at texas.net>> 
;
  amps at contesting.com<mailto:amps at contesting.com<mailto:amps at contesting.com<mailto:amps at contesting.com>>
    Sent: Tuesday, October 09, 2007 9:42 AM
    Subject: Re: [Amps] CB Amps or full spectrum???



    There are at least four major problems with the amps, not
    two.

    1.) Filtering. They need filters to reduce harmonics.

    2.) Power output. These amps are all really ratty at rated
    power, and it has nothing to do with bias. ANY transistor,
    especially one running at 12 volts, can't be pushed anywhere
    near the saturated power or the IM goes to heck. A typical
    rule of thumb is if the amp starts to limit power at 100
    watts, the useful peak output for reasonable IMD will about
    50-75 watts.

    This is why the FT1000MP's and TS440's and such we use will
    run 150 watts or more output if someone gets inside and
    screws up the power limiting controls. Even if left alone at
    100watts, they are marginal for IM products. Bump them up
    another 20-50% and they go to heck fast. It's all part of
    the CB mentality. While a tube amp, in particular a cathode
    driven triode, can be driven to near the point of power
    limiting without objectionable IM products a bipolar
    transistor cannot.

    You might get away with a somewhat trashy 400 watt amp on a
    small inefficient mobile antenna, but not when it is 1500
    watts out and especially not on a big antenna!!! So if the
    amp runs 1000 watts carrier before it starts to get into
    heavy gain compression it's probably good for 500 - 700
    watts, depending on how clean you want it.

    This has NOTHING to do with bias, although the bias voltage
    stability under full drive can affect the IM a little bit.

    3.) Idling or low drive bias. CB amps don't usually have
    any. Replacing it or installing it for SSB service requires
    a regulated bias source that has very low source impedance.
    The idle bias sets the cross-over or low level distortion
    products. They are still harmful, but not as much as the
    full drive saturation above causes.

    4.) Transformers. CB amps often have only transformers good
    at upper HF.

    5.) Feedback. Many CB amps don't have negative feedback that
    reduces distortion and stabilizes the amp.


    73 Tom


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