Well the filters turned up today 
Have just installed one of them - will be interesting to see if they make any difference.
Did you get much of a difference? I am still running without a filter, only put the fa antenna in recently so so optimising that but I am curious what the filter might bring.
Not much at all if any… any insertion loss would appear to have been recovered by the fact I have the gain set to AGC in the DVB-T stick. I mustn’t have much other interference at the moment - I thought some of the 4G-LTE frequencies used by the mobile phone carriers here in Australia may have caused some issue.
Next step is to buy a Pro-Stick …
Hello Guys,
I just buy a filter and i connect to my ADS-B instalation but don`t know why there is no range increase - there is no diff between with/without filter.
I use Raspberry with Raspian.
There is any software where i can check this filter working properly?
Mayby this is a fake - i buy this filter on e-bay from someone because FlightAware don`t send to my country 
Best Regards
TaKeN
You will only see an improvement with a filter if you have strongly interfering signals nearby.
Maybe in your area there’s just not any strong interference, so the filter does nothing but add a bit of loss.
But how to check it`s working?
There is any software or something to check this Filter working or not?
You could compare a rtl_power spectrum with and without the filter in place.
I am new on forum and i just buy my Radar… can You tell me exacly what to do please?
What i must install and how to check it ?
I got a flight feeder in September. Is this filter already in the new units?
If you received a FlightFeeder model G7 (metal case) then a filter is not included and not needed (due to the design, an external filter is not needed and will prevent the FF from working properly – do not install a filter).
If you received a FlightFeeder model H8 (orange plastic case) then an external filter was included in the kit and may be used if it improves performance.
I live in dense urban area in center Poland, near 4 BTS’ and with FA filter installed I have worse reception, less frames/s and max range is decreased about 10-15%.
EDIT: Filters from 925 MHz, so there is no GSM Downlink filtering at all (declared is 980 MHz).
If the close-in energy you have is at a known fixed frequency, you can try cutting a quarter wave stub to filter out that frequency.
The bandwidth of a quarter wave stub is about 20% of the frequency.
You put a “T” fitting in the line from the antenna to your SDR, with the stub hanging off the “T.” Leave the end of the stub open. The quarter wavelength calculation needs to include the velocity factor (Vf) of the cable used (usually between 0.66 and 0.80). The traditional approach is to calculate, cut a bit long, and then go through steps of measuring performance (with one of the SDR power tools) and trimming. Plan on making a second stub as you trim too much on the first one! As an example, a quarter wave at 925 MHz with a Vf of 0.66 is around 54mm – from the centre of the main conductor to the end of the stub. A Vf of 0.8 gives a stub length of about 65mm.
Oh, use the FA filter as well: Antenna → “T” with stub → FA filter → SDR. The insertion loss of the FA filter is reasonably low.
If the stub + FA filter doesn’t do it, then you need to go to the next level – a cavity filter or a SAW. Cavity filters are bulky, expensive, and have very good performance. SAW filters are inexpensive (around $20 US on eBay sourced from Eastern Europe), have very good performance, and about 2.5 dB insertion loss. I did a number of posts on hand-assembling SAW filters for ADS-B use, and ran them in my systems until the arrival of FlightAware’s SDRs with filters built in. I still use the FA filter in front of the SDRs, as they clean up a lot of the RF crud in the area. I also have data that demonstrates putting the FA filter in front of the filtered FA SDR improves performance by a statistically significant amount. Yeah, if I didn’t waste so much damn time sleeping, a cavity filter or a stripline would be interesting to try.
Have fun, keep good data, and let us know what works and what doesn’t!
bob k6rtm
Yes, it is a well known problem, we see that a lot here also.
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The attenuation is quite high, we measured almost 3dB, so you will reduce 10% of your traffic
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The filter is wide open over the whole GSM900 downlink. It’s basically useless in close range of a BTS.
You need a better filter, or I would like to suggest FA to re-tune their filters for a non-USA version for the whole rest of the world that does NOT use UAT, but DO use GSM900…
I have found used cavity filters that does an excellent job with 0.8 db passband and >60 dB attenuation at both 960 MHz and in the 23cm band.
/M
Skibox, must agree. After couple weeks of testing on different antennas I stopped using FA filter.
I highly recommend a cavity filter. I have several of the jetvison.de versions and they work really well in my noisy environment (Like 2 aircraft without and 200 with the filter). They are not cheap so it may be above what you are prepared to pay for this hobby.
Here’s a part of the noisy RF spectrum in my area, note the very strong (-34 to -31dBm) signals between 927 and 960Mhz due to a cell phone antenna about 100yards from my home.
To extend my receiving range, I guess that only a cavity filter will be steep enough to attenuate these signals?
You might get good response with a quarter wave stub as a filter – put a “T” in the line and connect an open-ended section of the same feedline a little longer than a quarter wavelength of the midpoint of your troubles, about 945 MHz from the plot you put up, (don’t forget the velocity factor of the cable). Re-run your spectrum plot, trimming a little at a time, for best results.
bob k6rtm
Thanks for the advice Bob but I’m already using a relatively cheap Chinese cavity filter with 4 sections and obtained remarkable results.
The strongest cellular signal dropped down from -46dBm (S9+45dB) to -122dBm (S4) and my reception range got a great boost.
As things are going I may even make it into the top 100 within a couple of weeks 
http://www.aalstar.be/images/cavity_filter.jpg
Tell us more about this cheap 4-section cavity filter! Who? How much?
–bob k6rtm
Well, the cavity filter looks like a black Lego block on steroids and has 2 SMA-connectors.
Passband goes from 1086-1094MHz and the insertion loss is less than 1dB, the attenuation for the GSM900 band is about 80dB.
A first review can be found here: http://www.jonadams.com/wireless/?p=315
And another one even shows an inside peek: http://www.radioforeveryone.com/p/test-ads-b-cavity-filter.html
I know that this kind of filter could be a complete waste of money if you live in an area with a clean RF spectrum around 1090MHz, but for me it increased my reception range in all directions with about 40nm. (Prostick LNA gain at 45dB)