FlightAware Discussions

ADS-B LNA external usb lead

I’m interested in doing away with seperate biastee for my triplefilter amp pic below
biastee in airspy not able to power it fully so hoping some one can point to the connections it will use i will connect via wired usb lead

Screenshot_406

Not sure that is possible, if you could power it externally, most likely there would be some solder pads marked +5V and GND somewhere. I have opened the box, there are not any on the other side, either.

Thanks for you input
Iv’e just found this info
if you are confident with soldering SMT components, then there are also pads and a 0 Ohm resistor slot on the PCB to install an LDO and power the LNA directly.

Thats from the product release page? Maybe ask them which components to use?

This should get you going
I can read the chip is an AVAGO, but can’t manage the number. Without a regulator, you’d want to know the voltage limits.

image

I don’t understand why you would do that.

You risk reduced performance or even the device not working for no reason.

And if you do it you might want an inductor to make sure no power supply ripple passes into the LNA.

On mine, the writing has been removed, so maybe they are using different ones?

The inductor I marked acts as a low pass filter (or DC path) for a bias-T feeding the coax lower down the feeder. If you are going to feed the amp directly, the inductors provides a DC path from the amp back down coax.
Most dongles (not having a bias-T built in) have a pair of protection diodes across the input. This will provide a short circuit to the ‘direct fed amp’ - the amp won’t work and one of the diodes will eventually burn out.
If the dongle does have a bias-T, the supply from the amp will be applied to a reg. or switch of some sort.

@ wiedehopf, did you notice the two pics are rotated 180° with respect to each other?

Something I just picked up on - the PCB has the lands for a SOT223 voltage regulator.
It’s not a common pinout, but Microchip MCP1702 or MCP1826-s will both fit.

image

That’s on purpose according to the product page:

Finally, if you are confident with soldering SMT components, then there are also pads and a 0 Ohm resistor slot on the PCB to install an LDO and power the LNA directly.

An LDO is obviously the preferred solution :slight_smile:
I just used a inductor and external bias-t that should push the 5V of the supply down to around 4.5 V.
With all the inductance in series i figured the ripple would be sufficiently eliminated.
Anyway amplitude modulation or something like this in the kHz region shouldn’t be a problem in regards to the 1090 MHz signal.

My intention was to use another inductor to avoid getting any high frequency noise into the housing via the DC + connection.
Removing that inductor seems wise indeed :slight_smile:

RTFM - who’d-a-thought!

Scrolling down the comments, Admin states the amp is an MGA-13116