The Final Filter Shootout

FlightAware ADS-B Flight Tracking
118

anthony from uputronics who already proved to manufacture excellent hardware posted how difficult it can be to find the right filter - and your answer was ‘1/4w stub. Just to show how easy it is’ - sorry but i’m no longer interested in that kind of discussion.

119

(A) I feel plesure and satisfaction when I purchase a good quality hardware which greatly increases performance.

(B) I also feel plesure and satisfaction when I make a DIY hardware out of no-value materials, which increases performance, though much less than the improvement made by purchased hardware.

My pleasure and satisfaction level in (B) is far higher than in (A).

1 Like
120

sorry - my intention was not a thread about feelings and personal satisfaction but best filter performance and moreover not about pure guessing and theoretical datasheet comparing :slight_smile:

1 Like
121

True. The acid test is to put equipment in service under real life conditions, and find which one is the winner.

1 Like
122

here are two exemplary dump1090 stats from my two receivers i do most of my testings with. they are fairly good (within about 1% usable messages and aircraft numbers) synchronized what makes it possible to measure improvements/decline introduced by new gear:

receiver 1:

Statistics: Sat Nov 11 09:00:14 2017 CET - Sat Nov 11 10:00:14 2017 CET
Local receiver:
  8640266240 samples processed
  0 samples dropped
  0 Mode A/C messages received
  35773652 Mode-S message preambles received
    18999331 with bad message format or invalid CRC
    12157660 with unrecognized ICAO address
    4350455 accepted with correct CRC
    266206 accepted with 1-bit error repaired
  -21.0 dBFS noise power
  -10.4 dBFS mean signal power
  -0.8 dBFS peak signal power
  113576 messages with signal power above -3dBFS
Messages from network clients:
  0 Mode A/C messages received
  31410 Mode S messages received
    0 with bad message format or invalid CRC
    0 with unrecognized ICAO address
    31410 accepted with correct CRC
    0 accepted with 1-bit error repaired
4648071 total usable messages
5 surface position messages received
286095 airborne position messages received
274101 global CPR attempts with valid positions
1 global CPR attempts with bad data
  0 global CPR attempts that failed the range check
  1 global CPR attempts that failed the speed check
515 global CPR attempts with insufficient data
10733 local CPR attempts with valid positions
  0 aircraft-relative positions
  0 receiver-relative positions
1265 local CPR attempts that did not produce useful positions
  1257 local CPR attempts that failed the range check
  3 local CPR attempts that failed the speed check
0 CPR messages that look like transponder failures filtered
0 non-ES altitude messages from ES-equipped aircraft ignored
409 unique aircraft tracks
64 aircraft tracks where only one message was seen
CPU load: 28.6%
  647370 ms for demodulation
  317876 ms for reading from USB
  64711 ms for network input and background tasks

receiver 2:

Statistics: Sat Nov 11 09:00:15 2017 CET - Sat Nov 11 10:00:15 2017 CET
Local receiver:
  8640659456 samples processed
  0 samples dropped
  0 Mode A/C messages received
  34948766 Mode-S message preambles received
    18416624 with bad message format or invalid CRC
    11946759 with unrecognized ICAO address
    4318648 accepted with correct CRC
    266735 accepted with 1-bit error repaired
  -21.4 dBFS noise power
  -10.7 dBFS mean signal power
  -0.7 dBFS peak signal power
  98717 messages with signal power above -3dBFS
Messages from network clients:
  0 Mode A/C messages received
  30801 Mode S messages received
    0 with bad message format or invalid CRC
    0 with unrecognized ICAO address
    30801 accepted with correct CRC
    0 accepted with 1-bit error repaired
4616184 total usable messages
4 surface position messages received
284157 airborne position messages received
272263 global CPR attempts with valid positions
2 global CPR attempts with bad data
  1 global CPR attempts that failed the range check
  1 global CPR attempts that failed the speed check
497 global CPR attempts with insufficient data
10643 local CPR attempts with valid positions
  0 aircraft-relative positions
  0 receiver-relative positions
1253 local CPR attempts that did not produce useful positions
  1245 local CPR attempts that failed the range check
  4 local CPR attempts that failed the speed check
0 CPR messages that look like transponder failures filtered
0 non-ES altitude messages from ES-equipped aircraft ignored
408 unique aircraft tracks
67 aircraft tracks where only one message was seen
CPU load: 28.6%
  644762 ms for demodulation
  320265 ms for reading from USB
  64238 ms for network input and background tasks
123

and here is a short range-plot from vrs - just some hours both sites overlay:

range
range1180×865 1.23 MB

124

Is there a way to run the heatmap with an airspy?

125

Have a look here: GitHub - rxseger/rx_tools: rx_fm, rx_power, and rx_sdr tools for receiving data from SDRs, based on rtl_fm, rtl_power, and rtl_sdr from librtlsdr, but using the SoapySDR vendor-neutral SDR support library instead, intended to support a wider range of devices than RTL-SDR

I’ve not tried them, but they are ports of the rtl command line tools using soapySDR libraries. Airspy should be supported by that, so you might have some luck.

1 Like
126

Here are a few filter reflection shots I took sometime back using a noise gen - figured it fit in well with this thread:

FA Filter:

FlightAware
FlightAware1590×816 55.6 KB

Mini-Circuits CPB-1090C (ceramic used in Hab-Amp):

CPB-1090C
CPB-1090C1587×812 55.9 KB

Custom Cavity bought from China:

Cavity
Cavity1586×816 54.2 KB

127

Did you mean ceramic? Hab doesn’t have a cavity filter as far as I am aware.

128

I like the Custom Cavity bought from China
have you got details atall ?

129

Oops, yeah I messed up - fixed. Thx :slight_smile:

Unfortunately I lost the contact information. That said, there are lots of places you can contact through Alibaba. Search rf cavity filter and then narrow your search by minimum lot size, some go down to single, but they are very expensive, so look for ones with good ratings that will allow 5 minimum and reach out with the specs you want. From my experiences, they are all very willing to work with you on custom designs. Pricing fluctuates wildly. I think the cavities ended up being around $40/ea in a lot of 5 with shipping. I was going to get 100 or so and try to hawk them off, but I already have a job and didn’t want to waste the time and effort trying to unload cavity filters for $40/whack when FA was selling theirs for half that. Someone could easily do the same thing and make a profit of $20 or so each if they sell at $60 or so…At either rate, that’s expensive for the hobbyist.

ADD: I failed to mention, if you do get some made, make sure to get them with DC passthrough. This way you can still maintain them inline when using bias-tee setups. Mine weren’t, but the second round was going to be.

Crappy picture I just now took sitting next to an Airspy Mini for reference:

IMG_1892
IMG_18923024×4032 3.33 MB

130

Thanks for quick reply
i will go take a look
regards
john

131

I’m not sure where sysmocom ships:
sysmocom Webshop

But both filters, the one for 24 and the one for 42 Euros look solid.

132

That looks identical to the one I had made up… Mine doesn’t have any stickers or markings except for an “X780” stamped on the bottom.

133

Well i never i was looking at that 2 days ago looks well made and only .5 db losses unlike some others upto 4db LOL

134

This Filter + LNA based on PGA103 + high gain collinear antenna would be excellent.

135

Where the best place to plug a cavity filter : before the Amp beetwen the antenna cable and the amp, of after beetwen the amp and the AirspyMini ?

136

antenna → cavity filter → amp → receiver.

3 Likes
137

Thanks for your reply !

1 Like