Do I Need A Filter?

Pity it doesn’t have a cover, maybe just a bit of heat shrink to keep it protected in the roof space. So will this replace the need for the FA filter? Or have this in line with them both?

Range is determined by the signal to noise ratio. This is the signal you want over the signal you don’t want.

Filters removes both some of the signal you want (called the passband attenuation) and a lot of signals you don’t want (stop band attenuation). For the FA filter the passband attenuation is around 1.6dB to 2.3dB and the stop band attenuation is around 40dB. The cavity filters are usually around 0.5dB passband and 60dB stop band.

You want to have just enough filtering to remove the unwanted signals. Adding more filtering will remove more signal but will also diminish the signal you want and might lower your signal to noise ratio.

So will this replace the need for the FA filter? Or have this in line with them both?

Depending on your location and how strong signal you have will determine how much filtering you need. So try with both filter vs 1 filter and see what works better.

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I put my filter back on. Running the scan now. Likely will leave it on for a week. Then may run the analysis for gain (again). I see that the scan too says it’s “Tuner gain set to 29.70 dB” so I must have it set to AGC.

Scott

does anybody know if the following configuration is suitable / will work for the bias-t ?

cantenna → coax → FA filter → v3 dongle → RPi

thx / evangel

Looks better!

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Yes, the RF Scan sets the gain to 29.7 at start of scan. A gain of 29.7 is used as it is a median value. Too high (49.6 and AGC) or too low (less than say 15) gain during RF scan will not give results which correctly show the interfering signals.

Unfortunately the scan does not set gain back to original value at the end of the scan.

The Gain optimization scripts also leave the gain set to a low value when these complete their cycle.

In both these tests, the user should manually set gain back to the value it had before start of these tests.

By the way, have you seen this thread about mods to include (display + set) gain from SkyView dump1090-fa map / dump1090-mutability map?

Read / Set Gain from SkyView and Gmap

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Oh snap. I didn’t. Let me get a coffee and set this up.

The idea to include gain setting in SkyView/gmap originally came from @evangelyul. He thought of it, then referred to me for helping him with it. I tried to built on his idea with very limited knowledge of PHP and Bash script. Unexpectedly I succeded.

@evangelyul was actively involved in the entire development process. Please see this thread if you are interested in history of development:

https://discussions.flightaware.com/t/set-gain-from-browser/36278

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Done. Works like a charm. Now, how best to exploit it…

Yes that will work.
Be aware FA filter is a ceramic SAW element and can’t pass DC. This only matters if you want to feed an amp close to the antenna.

In that case the LNA can still be used with the following setup:
Antenna → SAW filter → LNA ------- Coax -------- Bias-tee → USB dongle → Rpi

No, The FA External Filter is NOT SAW or Ceramic type

The FA external filter is a LC ladder circuit.


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,

LC LADDER - UNBALANCED

LC%20Ladder%20-Unbalanced

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LC LADDER - BALANCED

LC%20Ladder%20-Balanced

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I stand corrected - thanks

Hi @abcd567 are you able to explain the difference in laymans terms? Oh and what a stub filter does.

Thanks Coxy

well I tried with the configuration I mentioned in my previous post and it does not work,
meaning it receives nothing. so had to reboot to make it work again.
the other thing is that even with the FA filter there is a lot of strong signals between 920-970 Mhz, at 1030 Mhz and the ADS-B at 1090 very faint.
there is also a lot of ‘echoes’ on the sides of 1090 can they be harmonic ?
here is a recent scan.(sorry dont know how to enlarge it)

@evangelyul

The GSM-900 / EGSM-900 signal is very strong. If the FA filter does not effectively remove it, then try another filter.
evangelyul-scan-920-970%20mhz

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1030 Mhz signal is weak, and should not affect ADS-B reception
evangelyul-scan-1030%20mhz

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1090 mhz is weak. Filtering out GSM-900 / EGSM-900 and then increasing gain may enhance it. Also an amplifier or a high gain antenna will improve it.
evangelyul-scan-1080-1100%20mhz

Is it possible to install Jetvision 3 Pole filter between RTL-SDR v3 with bias-t enabled and Uputronics SAW filter?
Do I need an external power source for my SAW filter?

Is it a SAW filter ONLY, or a LNA + SAW filter?
Please post link to it to enable us to see exactly what equipment you are referring to.

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Please post link to Jetvision 3 Pole filter to enable us to see exactly what equipment you are referring to.

SAW Filter + LNA - 1090MHz ADS-B Filtered Preamp
Jetvision 3 pole - https://shop.jetvision.de/epages/64807909.sf/en_GB/?ObjectPath=/Shops/64807909/Products/71010

@strobil

The user @TomMuc has used Uputronics SAW filter and Jetvision 3 Pole filter.
He can advise you better. He has posted some results here:

https://discussions.flightaware.com/t/the-final-filter-shootout/26821

https://discussions.flightaware.com/t/help-requested-with-outdoor-setup-with-poor-reception/27479/30