FlightAware Discussions

Do I Need A Filter?

The bigger the percentage of Messages > -3dbFS means that I’m getting more short range than long range planes?

Those are messages with very strong signal. It’s likely that you are receiving some messages with a signal even stronger that can’t be received anymore.

So you aim for about 5% of those messages and hope that there aren’t too many “even stronger” messages which can’t be received.

Or if you only care for planes far away you just ignore the percentage.
That could mean you don’t receive planes flying close by very well but depending on the case it can increase reception at least a bit for planes far away.
This is not guaranteed though, depending on electrical noise it might not help going higher with the gain.

Also see this thread:
Thoughts on optimizing gain

The label of this L-band Satellite Amplifier (RCA D903) says 950 - 2050 MHz

This gives an impression that this Amplifier has a built-in band-pass filter 950 - 2050 MHz

If this is true, then it is amazing. LNA+band-pass filter for $4 (I have purchased it from local electronics store for $4).

I have used it during 2013~2016.
After purchasing ProStick+FA antenna+FA Filter in 2016, I dismantled it.

I am planning to fire it up again with generic DVB-T, and conduct two scans.

  1. Scan with the amplifier.
  2. Scan without the amplifier.

If this satellite amplifier has an effective built-in band-pass filter, it will remove (or at least reduce) the interference of GSM800 Mhz band, which is very strong at my place.

I’ve got a couple of the unbranded 20dB sat amps and they certainly do not have any filtering.

One thing to be aware of with any sat amp is that they are DC pass-through. An antenna with a DC short (J-pole, CoCo with top short etc.) will not play well.

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The one I have is from a very reputable manufacturer RCA, and that is why I expect that it really cuts-off outside its specified frequency range (950~2050 Mhz). A scan and heatmap will reveal the truth.

While RCA is a reputable company, this is just an amp for a domestic sat receiver, not even for commercial applications. My guess is that the specs should be interpreted to mean the amp will provide 13~18dB in the range of 950~2050 Mhz, and the gain outside that range is simply not specified.

If something is too good to true - it probably isn’t.

I found an ebay listing showing the rear of this amp. The back panel is just a press fit and can be levered out (and popped back in).
If you get bored, do you want to open it up and see what makes it tick?
image

Knowing how it performs is subtly different to knowing why.
(I like the ‘why’).

I would have thought that the frequency range quoted was the range it was within spec. I.e. gain is as specified within this frequency range.

There is nothing to suggest there is any filtering outside that frequency range.

I await the results of the scan.

S

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Dear All,

Hi, I got the result of heatmap.py based on this document.
And
RTL-SDR Blog I purchased and connected the ADS-B Triple Filtered LNA (Bias Tee Powered) but could not receive any data.

My composition is
DVB-T Stick> Cable 15m> Connected to Flightaware Antenna.

I connected an LNA between DVB-T and cable, but nothing was detected.

I share the result of not connecting the LNA and not connecting.
I would like to make sure that I do not need an LNA and only need an FA filter.

(And when I connected my flightfeeder machine, the data was normally detected.)

Regards,

scan scan_190526

Did you enable the bias-t in the rtl-sdr v3 to provide the LNA with power?
Explained here:
https://www.rtl-sdr.com/getting-the-v3-bias-tee-to-activate-on-piaware-ads-b-images/

Did you make sure you connected the LNA the correct way?
(5V input comes from the receiver, it has small print on it to show the correct direction)

Also works for dump1090-fa installed via the package install.

You need an rtl-sdr v3 dongle otherwise it will not have a bias-t which you can enable.
(The Flightaware sticks or other dvb-t sticks don’t have a builtin bias-t and you will need an external one)

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Should I set the LNA power? Thank you.
I have not done it yet.

And I’m using a regular dvb-t stick.
If so, should I use the stick of rtl-sdr?
I made sure that others connected fa’s sticks or regular dvb-t sticks and bought them.

Thank you.

It is an amplifier. Without power it will block signals.

Option 1:
Use the rtl-sdr blog v3 stick and turn the internal bias-t on via the software:

(https://www.rtl-sdr.com/buy-rtl-sdr-dvb-t-dongles/
https://www.rtl-sdr.com/getting-the-v3-bias-tee-to-activate-on-piaware-ads-b-images/)

Option 2:
Use an external bias-t to supply the LNA with power.
(For example: https://www.ebay.de/itm/10MHz-6-GHz-Bias-Tee-Breitband-Radiofrequenz-Mikrowelle-Koaxiale-Bias-T-Stück-g9/283289518784)

It goes between the dvb-t stick and the LNA.
Needs to be supplied with +5V (you can use a single wire from the 5V on the RPi)

Mobile%20Cell%20Phone%20Frequencies%20Close%20to%201090%20and%20978%20MHz

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Can anyone help me which filter i would need?

This interference doesn’t look too strong compared to the 1090 MHz signal.

I’d say a filter is not really needed.

What kind of setup are you using (antenna, cable, dongle)?
What gain did you record the spectrum at?

Anyway i basically always recommend the rtl-sdr LNA, it almost always improves reception, regardless the interference present.
(https://www.rtl-sdr.com/new-product-rtl-sdr-blog-1090-mhz-ads-b-lna/)

Between 920 and 960 there are the typical “European” GSM signals. The dark blue FA filter would filter them out (not the light blue), but hard to say if that is necessary. Or you use a filtered preamp, those usually cost more and you need to power them, but depending on the rest of the setup, that might have the biggest impact.

Also, not sure how expensive the FA filters are nowadays, when they were sold via amazon directly from FA there were good price wise, apart from the fact the light blue even then was not ideal for Europe.

The FA filters were on sale for a short time, but i can’t find one for less than 20$ right now.

Given the fact that the rtl-sdr LNA is 30$, the choice is clear to me.
But it’s some extra complication to power them of course.

Current setup is Jetvision A3 ADS-B antenna, 15m coax and Jetvision dongle (ADS-B USB Dongle (R820T2).
I did order a new coax 5 meter, would this give any changes?
I do have a light blue FA filter, but its not connected atm$

Thanks for the quick response!

It also depends on the p&p costs of the shop in question, sometimes it is quite expensive to have something sent outside of the country the shop is based.

Your perpetual recommendations finally succeeded and just now I order one, though I dont need one: The coax length between antenna and Dongle is 1 meter only, and I have FlightAware Pro Stick, ProStick Plus, and RB24 FlightStick, and FA light-blue filter

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Reducing the coax length should improve reception.
(But it also depends on the coax quality of course. If the 15m cable was very very good quality, the improvement might be less)

Getting any sort of LNA will also improve your reception.

If you want to keep the setup simple, i would recommend either getting the Flightaware Pro Stick Plus and try that without the extra filter.

Or you could try the uputronics LNA, that’s also quite simple because it can be powered via USB.