Thanks Steve and Sam.
I suppose I was a little vague but didn't want to go into extreme
detail.
Steve , You asked several questions so I'll expand.
The Amp is from a Ranger 2990? ...the 100 watt unit....so much for
quality but it should be useable.
I would think that the amp would be considered HF but used at or near 30
Mhz.
The "pills" (why do they call them that) run on 12 to 15 volts and the
drive is applied using a 50 ohm line. I placed the LPF in the 50 Ohm
line but I think that is wrong in that the impedance network is located
on the driver section and so the line is terminated in the input
transformer. It might be close but I get different settings when
loading the driver into 50 ohms vs the input transformer.
Both input and output are push pull. I will look again but I think
there is not a stich of filtering on the output. If there is it is just
an LC single pole.
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.
THe feedback is a cap and resistor going from the output collector to
the input transformer.
The replacments are from the same batch but I didn't ask for a matched
set. I didn't do any rise time measurments to see how close they would
be but it will be a mess taking them out.
The bias was extreme where no signal currents were near 12 to 15 amps.
That is also an area that I was playing with as it seems that it is
biased almost to class A in tha the rig only draws 16 of 17 amps. The
complaint is also that the heatsink is hot and should have a fan.
None of this is critical as I have plenty of rigs to run but it is easy
to ask a few questions to see who has done similar tasks than to
re-invent the wheel.
---
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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