Almost zero packets after installing FA Bandpass Filter

[herren]

BLUF: I purchased both FA bandpass filters and when I install either of them, my system is reporting ADS-B packet per second are reduced to almost zero.

With my current setup, I’m receiving (peak) 700-800 packets/sec and about (avg) 300-500 packets/sec. When I install the filter, I’m at 0.3-0.8 packets/sec. I tried both filters, 1090 & 1090/978, with the same effects. I’m thinking I might need to adjust gain or place filter directly after LNA, but I’m kind of confused about what’s happening. Any one have any suggestions? I can provide more information if needed.

Without filter

With filter

Setup

Before
FA 1090 Antenna → RTL-SDR 1090 LNA → cable → RTL-SDRv3 (gain 44.5)

After
FA 1090 Antenna → RTL-SDR 1090 LNA → cable → FA bandpass filter → RTL-SDRv3 (gain 44.5)

[wiedehopf]

@herren

FA 1090 Antenna → RTL-SDR 1090 LNA → cable → FA bandpass filter → RTL-SDRv3 (gain 44.5)

DC block.

No need to add it to the rtl-sdr filtered LNA anyhow.

[jonhawkes2030]

I do use a filter with the RTL-SDR LNA amp in my location, however, I have a lot of noise.

It will D/C block the LNA as @wiedehopf stated. If you want to use it, then it needs to be between the antenna and RTl-SDR LNA.

That gain looks a little high, unless the coax cable is really long. Have you tried lowering it.

[herren]

Ah, not familiar with that but after a little Google-fu and some reading I understand.

I plan on installing a couple more feeders in other locations and am trying to figure out to put together the optimal setup, hence LNAs and filters. Sounds like I should be able to use a filter in locations where I won’t be using a powered LNA.

[herren]

I followed @wiedehopf GitHub page about optimization to end up with that gain. Any lower and I started losing packets. Noise is high and I figure I’ll burn out my RTLSDR sooner than later. Coax is short, maybe 12 feet.

$ grep -sh . /run/{dump1090-fa,readsb}/stats.json | jq '.total.local | ((.accepted | add), .strong_signals, .signal, .noise)' | xargs -n4 echo | awk '{printf "\nPercentage of strong messages: %.3f\nSignal: %.1f\nNoise: %.1f\n", $(2) * 100 / $(1), $(3), $(4)}'

Percentage of strong messages: 16.382

Signal: -6.3

Noise: -21.0

[jaymot]

With the filter in the circuit between the dongle and the LNA it’s blocking the bias-T voltage. With no power that LNA acts as an open circuit and you don’t see any messages. If you have to add that filter put it between the LNA and the antenna.

[abcd567]

@herren

FA 1090 Antenna → RTL-SDR 1090 LNA → cable → FA bandpass filter → RTL-SDRv3

Change location of FA filter from above to following and it will be OK:

FA 1090 Antenna → FA bandpass filter → RTL-SDR 1090 LNA → cable → RTL-SDRv3

 

 

[wiedehopf]

@herren

Any lower and I started losing packets.

Highly doubt that. (i’d guess you’re looking at short term fluctuations too much)
16 percent … is pretty much always too much.