Re: 2N2222A vs 2N3904 sourcing

Tim Gorman

Back in March, 2018 I tried building up an amp section using an HP mmic
I have in the junk box. It worked very well on the desktop. Flat from
3Mhz to 30Mhz. No oscillation. I simply could find no way to add it
into the ubitx around Q90 (i.e. before and after) where it didn't break
into oscillation as soon as I tried to transmit.

At this point it would be easier to make up a new PA driver chain on a
replacement circuit board. Mount it on standoffs above the existing
board using coax in from Q90 and coax out to IRF510's. It's not a
project I want to take on. I would rather set the power out to 1w or
2w, have a clean signal, and use an external amplifier.

tim ab0wr

On Fri, 14 Sep 2018 15:23:49 -0700
"RCBoatGuy via Groups.Io" <> wrote:

In response to Warren's question about why the MMIC's would be
sensitive to oscillating..  

According to the datasheets, they are very sensitive to ground
loops.  The datasheet for the HP/Aligent MMIC on the 30dB board
available on Amazon was quite clear on this, and recommended using an
ultra-thin PCB (0.032 rather than 0.0625) to keep the inductance of
the ground vias down where it needed to be to avoid oscillation. 

Given that, it would be very hard to retro-fit one of these MMIC's
into an existing board designed for transistors rather than MMIC's
and not have it oscillate.


Carl, K0MWC

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