Do I Need A Filter?

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

I use both (Uputronics SAW filter and Jetvision 3 Pole filter.) with RTL-SDR, airspy and radarcape. They all work really well.

Taking another look at the FA filter, the FA filter is far more complex than the ladder diagrams (mathematically, at least).

I’m reasonably confident saying the FA filter is a series pair of 4th order Chebyshev filters, one being low-pass and the other high-pass (to give a sharp band-pass response).

Because the high-pass ‘half’ is capacitivly coupled, the filter won’t pass DC.

you are right ! I tried the config mentioned in my previous post, with bias-t on and it did not work. 0 msgs/sec and dump1090 failure message. as soon as I removed the FA filter, it started working with an increase in message rate.

Your diagram doesn’t show anything that needs power, so it shouldn’t matter.
Do you have a pre-amp in your antenna feed?

no I don’t. was just curious to try it.
the other pi has a home-made bias-t and an in-line amp and the difference is significant.

cantenna → in-line amp 1-2ghz → bias-t → nooelec dongle
the in-line amp requires 10-15vdc and i use one cord from the PC power supply to feed it 12vdc

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Did it work with the FA filter in place and the the Bias-T removed?

yes it did, and with increased message rate, but lower than v3 / biast OFF - FA filter combo.

filter-fa-v3-1

ca. 500msgs/sec | ca. 350msgs/sec but also WED less traffic

Careful with bias tee ON feeding the antenna. Any short and the RTL input may be damaged.

Apologies again FA.

Trying lowering the gain setting when using the amp. It may be too high and overloading the dongle.

@Dxista @jonhawkes2030

well it looks ok to me…or not ?

and gain 38.6, after re-optimization.

stats-10-11

Let me see how many posting I have made on this topic, before the FA robot tells me shut up.:joy:

Four…I think I’m ok then.:grin:

The CPU is not working as hard, good. The temperature is lower, good. Both ADSB tracks and SNR seem to be the same, but you have more room for stronger signals now, before the RTL overloads, which is good.

1 Like

I think you can increase the gain a little more. It should peak around the red like.

thank you both guys. :smile:

Hi
Have you got link for new graphs your using im still on the old frames
many thanks
john