Poor Performance / Low Gain w/ FA ProStick/Filter/26" Ant.


#1

All,

I have installed a PiAware (Dump1090-Mutibility) with the Flight Aware ProStick / 1090MHz Band-pass Filter / 1090MHz ADS-B Antenna - 66cm / 26in. The antenna is connected to the filter via an eight meter TrendNet Reverse SMA to N-Type cable (TEW-L208) (50 Ohm connector). Filter & ProStick are connected directly.

The performance isn’t what I expect - although some statistics are somewhat better than the NooElec + cheap-o antenna it replaced, overall signal strength is low, few aircraft are captured and the maximum distance is somewhere around 50 nm.

The FA system is mounted on a pole 15’ AGL; the NooElec system was sitting on a tin can on a first floor window.

The system is located only 10 miles W of KDFW, so I would expect to see hundreds of aircraft for hundreds of miles, not the fewer than 20 very close aircraft I currently see.

I have assumed the cable is the problem and have a simple N to SMA connector arriving tomorrow so I can test that theory. However, I have a few questions:

  1. If it is the cable, what cable do I need? It needs to be at least 25 feet so I can get it up the pole.
  2. Could it be something else? If so, what?

Here are stats and graphs & thanks for your help:

Is the small number of accepted packets typical?


Statistics: Wed Jun 29 21:17:04 2016 UTC - Wed Jun 29 22:17:04 2016 UTC
Local receiver:
  4012769280 samples processed
  0 samples dropped
  0 Mode A/C messages received
  22188865 Mode-S message preambles received
    13565084 with bad message format or invalid CRC
    8612389 with unrecognized ICAO address
    10837 accepted with correct CRC
    555 accepted with 1-bit error repaired
  -35.4 dBFS noise power
  -22.6 dBFS mean signal power
  -9.5 dBFS peak signal power
  0 messages with signal power above -3dBFS
Messages from network clients:
  0 Mode A/C messages received
  495 Mode S messages received
    0 with bad message format or invalid CRC
    0 with unrecognized ICAO address
    495 accepted with correct CRC
    0 accepted with 1-bit error repaired
11887 total usable messages
6 surface position messages received
786 airborne position messages received
691 global CPR attempts with valid positions
0 global CPR attempts with bad data
  0 global CPR attempts that failed the range check
  0 global CPR attempts that failed the speed check
0 global CPR attempts with insufficient data
87 local CPR attempts with valid positions
  67 aircraft-relative positions
  20 receiver-relative positions
14 local CPR attempts that did not produce useful positions
  8 local CPR attempts that failed the range check
  0 local CPR attempts that failed the speed check
0 CPR messages that look like transponder failures filtered
4657 non-ES altitude messages from ES-equipped aircraft ignored
83 unique aircraft tracks
40 aircraft tracks where only one message was seen
0 HTTP requests
CPU load: 9.0%
  227688 ms for demodulation
  88868 ms for reading from USB
  6853 ms for network input and background tasks


You can see where the antenna / modulator systems were replaced around 24z on Tuesday. Signal strength drops, more single packets are picked up , but overall aircraft tracked remained the same or dropped.

https://dl.dropboxusercontent.com/u/235001/Screenshot%202016-06-29%2017.22.00.png


#2

TrendNet Reverse SMA to N-Type cable (TEW-L208)

There’s your problem. Reverse SMA is wrong. Use just a normal SMA connector. Your antenna disconnected with that cable.


#3

Ah!

Thanks!


#4

The SMA-male has center pin. The reverse SMA (RP-SMA) male does not have a center pin, it has a hole. The center wire connection is open because of missing pin. A temporary workaround is to cut a short piece of center wire of coax and insert in hole of RP-SMA male. This piece of wire will act as the missing pin, and connection will be established.


#5

Interesting and thanks for the pix. I’m sure there’s an “interesting” story on why there are regular and reverse versions of this connector…

I ordered LMR-400 Coaxial Antenna Cable Line with N Male & SMA Male Connectors and it will arrive in the morning.


#6

Oh, You ordered a new LMR400 with proper connectors!

You could have saved that money by the simple workaround of inserting a short piece of coax core wire into hole of RP-SMA male connector of your “eight meter TrendNet Reverse SMA to N-Type cable (TEW-L208)”.

Alternatively you could have purchased an adapter RP-SMA Female to SMA Male, a much cheaper solution.


#7

Agree - but additional connectors add places for things to go wrong later as they age. Since it’s going to be difficult to get back to the installation in the future, it’s worth it to me to reduce that risk with the right cable.


#8

Antenna arrived.

While sitting on the desk, it’s tracking 110 planes. Nice!

Current dB is 0.7dB, which I assume is high. I have the FA filter, so I guess I’ll leave it for awhile and see what happens.