Re: My PA0FRI active loop receiving antenna
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Very high ft is a problem with these '590 BJTs.? But we all know that.?
I'll offer a tried-and-true "most-of-the-time" solution:? Instal a 1/4 or 1/8-watt - better yet, an SMD - 22 to 68 ohm resistor in series with the collector/drain.? If you use a leaded resistor, trim the leads to "zero" length and install it as close to the ground layer as possible.? I've used this trick for decades and it tames "most" of the high ft BJTs and FETs.
In addition, you should have a spectrum analyzer or other means of verifying there is no oscillation at or below the rated ft.? Without that, you may end up with a "parametric amplifier" which can fool anyone regarding its exaggerated "performance".????
Dave - W?LEV
On Fri, Jan 31, 2025 at 12:47?PM Dhiru Kholia via <dhiru.kholia= [email protected]> wrote: Hey!
Thank you Steve, Leong and other folks.
Steve - Your skills and confidence are super inspiring - thank you for
jumping into the problem (i.e. gain drooping with original LZ1AQ
design with 2N2222s) and solving it so quickly while retaining the
usage of two PZT2222A transistors!
The usage of two PZT2222A transistors reduces the risk of PCB design
failures to a fair extent.
This is my first attempt at building the LZ1AQ amplifier. I am looking
for ideas on simplifying the circuit to its essentials and thereby
reducing the PCB size. Currently the PCB will fit inside a 100x100mm
IP65 box just fine.
Also, can this 2-Layer PCB design really work with BFU590 transistors
on it? Folks are telling me 'horror stories' of how these GHz fT
transistor devices like to oscillate.
Cheers,
Dhiru
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