Way less aircraft with ceramic filter

I just attached an Uputronics ceramic filter to my FA ProStick+, with the USB plugged in to my Pi to power the filter, and my number of aircraft went down from 50+ to 4.

I didn’t get much chance to play with it, but thought I’d check if there was something I could be doing wrong? Is it maybe a faulty filter?

Too much signal. Lower the gain setting and it will work much better.
See @abcd567 posts on optimising the gain setting.
You are using two amplifiers. (It is like trying to understand someone when they are yelling at your with a loud speaker from 3 feet/metres away)

Uputronics sells external amp+filters.

The amplifier needs power or will not pass much of the signal. Amp are not passive devices.
Connect a 5V USB power supply and it should work much better.

I’ve connected it to an external USB power supply and also to the Pi USB, still no difference. I could try and tweak the gain settings… any recommendations?

And yes sorry it is an amp+filter… bad terminology on my part!

Tried every one of those gain settings and it just got worse - from 60 aircraft down to 0.

Starting to think it’s a faulty unit, but I may try a spectrum scan first to try and verify it!

Both - tried two separate external power supplies and none of them made any difference.

Just had a thought - a previous scan showed a pretty strong signal around 923mhz. Is it possible that the ceramic filters pass band is wide enough that the amp may be amplifying the 923mhz signal and overloading the receiver?

The plot is on their website

-40db or better around 900Mhz.

I use several, however, my area is so noisy, I have to use a cavity filter too.

Ensure you have the cables the correct way around.

I’m actually replacing the FA filter with this, as the FA filter doesn’t touch the 923mhz frequency and it’s quite strong. I was actually more interested in the preamp but figured the filter could help as well, and I see this particular filter and preamp combo referenced here quite a lot!

Cables are definitely the right way round as far as I know… ANT to antenna and RX to the receiver. It does occasionally pick up some aircraft, but far less than without it in place.

Ok, so… I opened it up and the PCB was marked with RF IN, but that socket was labelled RX on the case. The RF OUT side was labelled ANT on the case.

If RF IN and RF OUT are what I think they are… was it maybe in the case the wrong way? I’m assuming RF IN is the antenna side and RF OUT is the reveiver side.

Can’t test it for another 45 mins or so but I’ll update when I do!

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Ok, yup. So the PCB was the wrong way around, the ANT side was actually the RX side and vice versa. Swapped it round, now getting +10 aircraft and +200ish messages per second.

Thanks for all your help!

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The antenna side is the one WITHOUT the USB port.
The dongle/receiver side is the one with the USB port.

I have to check one of mine that didn’t work well(Not used for 1090Mhz).


For reference I have a Pi 3, Pi 2.5A PSU and I power the Pro Stick Plus and a Uputronics bandpass filtered preamp from the USB ports on the Pi no problem. No need for a separate preamp PSU but make sure you’re using a proper 2.5A PSU for the Pi.

With gain set to to auto the Uputronics bandpass filter still increases messages and aircraft counts, according to my experience and lots of user feedback from the preamp’s designer. Gain tweaks may help extract even more from it down the road.

Uputronics recently changed their labelling by rotating the label 180 degrees and changing it from ANT and OUT (which is seen on many images online) to ANT and RX. This also makes the arrows line up properly with the SMA connectors. If you’ve seen the filter online it’s easy to connect it with the label the same way up and not notice that’s now the wrong way around. The unit itself, and its layout, hasn’t changed, only the label.


I found a gain of 32.8 or 33.8 worked best when I was running this setup.