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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
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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

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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

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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
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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
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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: 413
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
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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
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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: 5
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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 Post subject: Re: FlightAware ADS-B filters now for sale worldwide
PostPosted: Tue Mar 28, 2017 9:46 pm 
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k6rtm - FlightAware user avatar

Joined: Tue Nov 18, 2014 10:18 pm
Posts: 413
Location: Silicon Valley
alleyoopie wrote:
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


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


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 Post subject: Re: FlightAware ADS-B filters now for sale worldwide
PostPosted: Thu Mar 30, 2017 5:14 pm 
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alleyoopie - FlightAware user avatar

Joined: Mon Feb 20, 2017 4:36 pm
Posts: 5
k6rtm wrote:
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 :lol:
Image


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 Post subject: Re: FlightAware ADS-B filters now for sale worldwide
PostPosted: Thu Mar 30, 2017 7:38 pm 
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k6rtm - FlightAware user avatar

Joined: Tue Nov 18, 2014 10:18 pm
Posts: 413
Location: Silicon Valley
alleyoopie wrote:
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 :lol:

Tell us more about this cheap 4-section cavity filter! Who? How much?

--bob k6rtm


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 Post subject: Re: FlightAware ADS-B filters now for sale worldwide
PostPosted: Fri Mar 31, 2017 3:20 pm 
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alleyoopie - FlightAware user avatar

Joined: Mon Feb 20, 2017 4:36 pm
Posts: 5
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)


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 Post subject: Re: FlightAware ADS-B filters now for sale worldwide
PostPosted: Fri Mar 31, 2017 6:54 pm 
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abcd567 - FlightAware user avatar

Joined: Sat Feb 15, 2014 3:08 am
Posts: 1929
Location: Toronto CYYZ
JUST A CONCEPT
A 1/4 wave monopole whip with horizontal groundplane has a curve like a bandpass filter. See below a curve for such a monopole for 400 Mhz.


Image

If two such monopoles are used, enclosed in metallic container, and one is connected to antenna and other to receiver, the signal picked by antenna will be transmitted by first monopole, and received by second monopole. There will be double the filtering effect of one monopole.

Can this be a workable filter?
How much is insertion loss?
How much is bandwidth of the pass-band?

A VNA is required to determine all these, and I dont have a VNA :(

Image


Image


Image


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 Post subject: Re: FlightAware ADS-B filters now for sale worldwide
PostPosted: Sat Apr 01, 2017 6:18 am 
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obj - FlightAware user avatar

Joined: Tue Sep 30, 2014 7:14 pm
Posts: 3323
That starts to look like a cavity filter.. The resonance within the cavity is pretty important, remember that the return loss etc usually assumes "free space" and two antennas in a metal box is anything but free space.


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 Post subject: Re: FlightAware ADS-B filters now for sale worldwide
PostPosted: Thu Apr 06, 2017 1:05 pm 
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abcd567 - FlightAware user avatar

Joined: Sat Feb 15, 2014 3:08 am
Posts: 1929
Location: Toronto CYYZ
I was browsing eBay, and came across these two 1090 MHz filters, one from Hungary, other from China.
Both are priced around $19 + shipping.
Hungarian one is simply a TAI SAW chip on a small PCB with SMA connectors.
Chinese one does not show internals, but guessing from its size and specs, it also seems to have a TAI SAW chip inside.

Their price is similar to FA external filter, but I doubt if these can perform as good as Flightaware external filter which has superior LC Ladder circuitry.

Has anyone tried these?


Hungarian Filter
(TAI SAW chip)
Image


Chinese Filter
Image
Impedanz: 50 Ohm
Mittenfrequenz : 1090 MHz
Passband : 1086 ~ 1094 MHz
In-Band-Einfügungsverlust : <3dB
Maximale Lastleistung : 10 mW (10 dBm)
Schnittstelle: SMA-M, SMA-F


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 Post subject: Re: FlightAware ADS-B filters now for sale worldwide
PostPosted: Thu Apr 06, 2017 5:02 pm 
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abcd567 - FlightAware user avatar

Joined: Sat Feb 15, 2014 3:08 am
Posts: 1929
Location: Toronto CYYZ
Price drop on the FA ADSB filters!
Now $15.50 Only!!!


Image


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 Post subject: Re: FlightAware ADS-B filters now for sale worldwide
PostPosted: Thu Apr 06, 2017 6:38 pm 
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Skibox - FlightAware user avatar

Joined: Tue Nov 17, 2015 12:33 pm
Posts: 80
abcd567 wrote:
Their price is similar to FA external filter, but I doubt if these can perform as good as Flightaware external filter which has superior LC Ladder circuitry.


Why do you think their design is superior?

The SAW filter has a narrower BW and 1.8-2 dB center loss. The FA filter seems to vary a bit, different measurements show 1.9-2.7 dB loss, and it is too wide, which is a real problem with the FA design.

So. I would say on most accounts the SAW design is superior.

/M


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