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 Post subject: Re: FlightAware ADS-B filters now for sale worldwide
PostPosted: Fri Jul 15, 2016 7:20 am 
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takenek - FlightAware user avatar

Joined: Fri Jul 15, 2016 1:49 am
Posts: 3
obj wrote:
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?


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 Post subject: Re: FlightAware ADS-B filters now for sale worldwide
PostPosted: Fri Jul 15, 2016 7:23 am 
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obj - FlightAware user avatar

Joined: Tue Sep 30, 2014 7:14 pm
Posts: 3193
You could compare a rtl_power spectrum with and without the filter in place.


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 Post subject: Re: FlightAware ADS-B filters now for sale worldwide
PostPosted: Fri Jul 15, 2016 11:02 am 
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takenek - FlightAware user avatar

Joined: Fri Jul 15, 2016 1:49 am
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obj wrote:
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 ?


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 Post subject: Re: FlightAware ADS-B filters now for sale worldwide
PostPosted: Fri Oct 28, 2016 4:56 pm 
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christyzach - FlightAware user avatar

Joined: Wed Sep 28, 2016 9:19 am
Posts: 13
I got a flight feeder in September. Is this filter already in the new units?


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 Post subject: Re: FlightAware ADS-B filters now for sale worldwide
PostPosted: Mon Oct 31, 2016 8:12 am 
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ericcarlson - FlightAware user avatar

Joined: Sun Jan 01, 2006 5:00 pm
Posts: 72
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.


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 Post subject: Re: FlightAware ADS-B filters now for sale worldwide
PostPosted: Tue Jan 10, 2017 1:11 pm 
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kraviec - FlightAware user avatar

Joined: Wed Sep 07, 2016 11:10 am
Posts: 8
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).


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 Post subject: Re: FlightAware ADS-B filters now for sale worldwide
PostPosted: Thu Jan 12, 2017 8:59 pm 
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k6rtm - FlightAware user avatar

Joined: Tue Nov 18, 2014 10:18 pm
Posts: 408
Location: Silicon Valley
kraviec wrote:
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


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 Post subject: Re: FlightAware ADS-B filters now for sale worldwide
PostPosted: Fri Jan 13, 2017 10:40 pm 
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Skibox - FlightAware user avatar

Joined: Tue Nov 17, 2015 12:33 pm
Posts: 55
kraviec wrote:
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%.


Yes, it is a well known problem, we see that a lot here also.

1. The attenuation is quite high, we measured almost 3dB, so you will reduce 10% of your traffic

2. 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


Last edited by Skibox on Sat Jan 28, 2017 4:05 pm, edited 1 time in total.

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 Post subject: Re: FlightAware ADS-B filters now for sale worldwide
PostPosted: Sat Jan 28, 2017 3:12 pm 
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kraviec - FlightAware user avatar

Joined: Wed Sep 07, 2016 11:10 am
Posts: 8
Skibox, must agree. After couple weeks of testing on different antennas I stopped using FA filter.


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 Post subject: Re: FlightAware ADS-B filters now for sale worldwide
PostPosted: Sat Jan 28, 2017 4:31 pm 
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jonhawkes2030 - FlightAware user avatar

Joined: Tue Jan 05, 2016 4:15 pm
Posts: 1043
Location: NYC
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.


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 Post subject: Re: FlightAware ADS-B filters now for sale worldwide
PostPosted: Mon Feb 20, 2017 5:09 pm 
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alleyoopie - FlightAware user avatar

Joined: Mon Feb 20, 2017 4:36 pm
Posts: 1
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?

Image


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