Hi Ron, see below....
> In any case, the LPF drops all harmonic content 20 to 30 dB using an HP
> 8593 (100Khz to 22 Ghz) with a rubber duck antenna to it's input so it's
> seeing the leakage comming out of the cantenna, coax and rig.
> I guess I see your drift that I should be looking at a sample of the
> load.
[Steve Katz] Absolutely. You can't tell what's happening with even
a vague degree of accuracy when you don't have a direct connection. You're
dealing with the vagaries of signal propagation, antenna efficiencies, dummy
load leakage, etc. The data is meaningless. If I were to guess, I'd say
the system as you've set it up is much more efficient at VHF than at HF, and
will reveal you've got a serious harmonic problem when in reality no such
problem exists.
> The bias was extreme where no signal currents were near 12 to 15 amps.
[Steve Katz] The zero signal idling current is 75% of the peak Ic?
That is about Class A and must result in pretty lousy efficiency, not to
mention lots of thermal rise and probably an unstable amplifier (too much
gain). Re-bias for maybe 3A ZSIC and everything might get a lot better.
[Steve Katz] 73, WB2WIK/6
> ---
> Ron
>
> Steve Katz wrote:
> >
> > > Hello to all .
> > >
> > > I joined to pose a questionand also to copy mail to see what is new.
> > >
> > > I have a solid state push pull Broadbanded RF amp
> > [Steve Katz] What amplifier is that, exactly? If not
> commercially
> > made, then what's the circuit, intended frequency range, transistors
> used,
> > voltage applied? How's it biased?
> > > that I have replaced
> > > the transistors but the unit is taking off at higher power levels. I
> > > placed a LPF on the input drive to the amp as I would see the 3
> harmonic
> > > at 6 dB below the carrier! THe filter cured that. Looking at the
> > > signal from an HP analyzer
> > [Steve Katz] "From an HP analyzer?" Do you mean "on an HP
> > analyzer?" How are you decoupled to keep from overloading the analyzer?
> > What level signal are you actually looking at, e.g., the analyzer is
> seeing
> > +10dBm from a +50dBm signal, using a 20dB directional coupler and a 20dB
> pad
> > to knock down the signal...stuff like that.
> > > , I see multiple harmonics spaced about every
> > > 2 Mhz below the carrier frequency into a 50 Ohm load. On lower power
> > [Steve Katz] Sounds like it's oscillating at 2 MHz and
> modulating
> > the applied signal.
> > > levels, the closest is 20 dB down , but at higher only 10dB On an
> > > antenna , It takes off and pulls horrendus currents and drags the
> supply
> > > voltage down to 9 or 10 volts if I plase it on an antenna with a
> tuner.
> > >
> > > ?...Is it normally required to neutralize this amp when replacing the
> > > finals?
> > [Steve Katz] What are the finals? What is the circuit?
> > -WB2WIK/6
> >
> > > ?...What techniques are used to do this?
> > > ---
> > > Ron
> > >
> > > --
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> > > Administrative requests: amps-REQUEST@contesting.com
> > > Problems: owner-amps@contesting.com
> >
> > --
> > FAQ on WWW: http://www.contesting.com/FAQ/amps
> > Submissions: amps@contesting.com
> > Administrative requests: amps-REQUEST@contesting.com
> > Problems: owner-amps@contesting.com
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