Re: My PA0FRI active loop receiving antenna
|
I've just taken an in-depth engineering purusual of the NXP datasheet for the BFU590Q:
1)? For a BJT with an ft of 8.0 GHz, the gain sure drops off rapidly with frequency!? They don't even rate gain above 1.8 GHz.
2)? And no data is given for the noise figure.
3)? It is rated for ± 2kV for ESD.? But, believe me, that's not much.? That can easily be accumulated in the winter on a dry day or even summer on a dry day.?
The device is certainly aimed at the 900 MHz and 1.8 GHz cell bands.
Dave - W?LEV
QUOTE (from the first link):?
They don't blow up in an extroadinary fashion, but instead will draw
maybe 4x the current (from about 5mA ->20mA) in their failure
condition. They also exhibit low gain whenever they reach this
condition.
High current draw is a certain indication of parasitic oscillation!??
A useful tool in damping any parasitic oscillation (no, this is NOT "snake oil"!):? lay a finger firmly on the '590.? The current will drop immediately if there is an oscillation.? Your finger is introducing enough loss to quench any oscillation.? Be sure to do this before the device signs its own death certificate - rapidly after observing the overcurrent condition.? If current drops with the "finger test", immediately turn off power and do what you can to alleviate the oscillation (small series resistor on the collector).?
In dealing with these high ft devices, I would strongly recommend a set of pads be added to the PCB to accommodate an SM resistor between 22 and 68 ohms placed in series with the collector.? If other devices are used with lower ft's, the pads can always be loaded with a zero-ohm jumper.
In addition, these devices are extremely sensitive to ESD damage.? Be careful in handling, placing, and soldering.? Generally once they are in circuit, things are much more robust.??
Dave - W?LEV?
On Fri, Jan 31, 2025 at 8:23?PM Dhiru Kholia via <dhiru.kholia= [email protected]> wrote: Thanks for all the tips, info and help!
I have access to TinySA Ultra but I believe monitoring my power supply
for unexpected current consumption might work better to detect
oscillations.
I was reading the following page earlier today:
...
I am attaching the PCB files to this email to aid the review process.
The complete set of files is open at the following link:
Cheers,
Dhiru
--
|
