External Antennas and no improvement?

FlightAware ADS-B Flight Tracking
1

Two quarter wave spider antennas -eight legs- 1090 (69mm) and 768 (77mm) mounted 20’ above ground. Approx 24” apart. Rg6 coax for 978. Superbat from coax for the 1090.

Nooelec Nano three SDRs.

I live <20nm from KDTW. DIRECTLY ON THE APPR/DEP routes for rwy 4/22.

This should all kinds of lit up and I see max 20 airborne aircraft at a time…

Best message rate was around 100-120. Lingers much lower.

Any thoughts?

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pi**@749pi:~ $ sudo piaware-status**

PiAware master process (piaware) is running with pid 517.
PiAware ADS-B client (faup1090) is running with pid 663.
PiAware ADS-B UAT client (faup978) is running with pid 13335.
PiAware mlat client (fa-mlat-client) is running with pid 758.
Local ADS-B receiver (dump1090-fa) is running with pid 485.
Local ADS-B UAT receiver (dump978-fa) is running with pid 13258.

dump1090-fa (pid 485) is listening for ES connections on port 30005.
dump978-fa (pid 13258) is listening for UAT connections on port 30978.
faup1090 is connected to the ADS-B receiver.
faup978 is connected to the ADS-B UAT receiver.
piaware is connected to FlightAware.

dump978 is producing data on localhost:30978.
dump1090 is producing data on localhost:30005.
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Tried -10 to AGC to 30 on gain. -10 seems best.

————
pi@749pi:~ $ awk “$(cat /run/dump1090*/stats.json| grep total | sed ‘s/.accepted":[([0-9]).strong_signals":([0-9]).*/BEGIN {printf “\nPercentage of strong messages: %.3f \n” , \2 * 100 / \1}/’)”

Percentage of strong messages: 1.560

The about the best I’ve seen.
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pi@749pi:~ $ sudo systemctl status dump1090-fa -l
● dump1090-fa.service - dump1090 ADS-B receiver (FlightAware customization)
Loaded: loaded (/lib/systemd/system/dump1090-fa.service; enabled; vendor pr>
Active: active (running) since Tue 2023-11-21 11:10:06 EST; 2h 34min ago
Docs: PiAware - ADS-B and MLAT Receiver - FlightAware
Main PID: 485 (dump1090-fa)
Tasks: 3 (limit: 2086)
CPU: 57min 18.600s
CGroup: /system.slice/dump1090-fa.service
└─485 /usr/bin/dump1090-fa --quiet --device-type rtlsdr --device-in>

Nov 21 11:10:06 749pi systemd[1]: Started dump1090 ADS-B receiver (FlightAware c>
Nov 21 11:10:07 749pi dump1090-fa[485]: Tue Nov 21 11:10:07 2023 EST dump1090-f>
Nov 21 11:10:07 749pi dump1090-fa[485]: rtlsdr: using device #0: Generic RTL2832>
Nov 21 11:10:07 749pi dump1090-fa[485]: Found Rafael Micro R820T tuner
Nov 21 11:10:08 749pi dump1090-fa[485]: rtlsdr: tuner gain set to about 58.6 dB >
Nov 21 11:10:08 749pi dump1090-fa[485]: adaptive: using 50% duty cycle
Nov 21 11:10:08 749pi dump1090-fa[485]: adaptive: enabled adaptive gain control >
Nov 21 11:10:08 749pi dump1090-fa[485]: adaptive: enabled dynamic range control,>
Nov 21 11:10:08 749pi dump1090-fa[485]: Allocating 4 zero-copy buffers
Nov 21 11:10:18 749pi dump1090-fa[485]: adaptive: reached upper gain limit, halt>
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2

What is the impedance rating of your RG6 coax? What is the Superbat that is connecting the 1090 antenna? Is that a splitter you are using to feed both antennas? 20 feet above the ground is pretty good but is it near to any metal objects or line of sight obstructions?

3

Two separate coaxes. The rg6 is connected to 978mhz normal . Roof extends behind it about 15’ higher. I think the rg6 is 75 ohms or so. The rg174 is 50 ohms.

No other obstructions for about 200 degrees forward. Mounted on a PVC “T” which is about five feet high at the T. The pvc is clamp to metal base. Zip ties hold the coaxes together.

Only roof mounted the antennas today. PVC was strapped on an aluminum ladder until this morning.

IMG_2002
IMG_20023024×4032 629 KB

1 Like
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IMG_2003
IMG_20031080×2266 306 KB

Rg174 from Amazon.

5

I’m not an expert by any means but RG174 has some high attenuation loss. At 33ft of RG174 you are looking at 16.5dB of loss. If you don’t have a LNA you could be losing a lot of signal across that line. RG-58 on the other hand has only 6.4db of loss at that length. These numbers don’t include any loss from connectors or filters.

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6

I did not think it was that bad! Maybe I’ll switch antennas.

It didn’t seem so bad the other day. But it’s worth a try and new coax if necessary. If I gotta climb on the roof. Maybe I’ll go all the way up to the chimney.

1 Like
7

An old rule on coax, smaller diameter means more signal loss. Larger coax has larger conductors with more surface area to carry the signals. Thicker more consistent insulation helps to maintain line impedance. This is not about DC resistance, rather how UHF frequencies at 987 and 1090 GHz are conducted through the cable to minimize losses. Sadly, bigger and better means more expensive too.

Have fun learning more, and keep improving yourselves and your systems. At some point, you may be the best producer in your local area. All because you refused to just do the minimal required.

3 Likes
8

RG6 is also 75 Ohms, and ADS-B is meant to work with cable that is 50 Ohms impedance. So that’s working against you a bit.

I’m not familiar with RG174, but from what I see on Wikipedia it looks like its attenuation is more than 3 times that of LMR240!

Your cabling is working against you in both instances!

You may want to consider changing your cables out to LMR240 or, since you’re going out 10 meters, LMR400. I just replaced a 10m (33ft) LMR240 cable with a 15m (50ft) LMR400 due to the LMR240 being damaged by weather. I think it’s actually KMR400, which is a lower-cost substitute with about 10% greater attenuation, but the Amazon seller claims it’s LMR.

You can still use the RG6, as it’s the ideal cable for an over-the-air TV antenna (or a satellite dish, if you prefer). You can attach that to sit about a foot or two below the PVC crossbar to avoid interference with your ADS-B.

4 Likes
9

I would go with something like LMR400 at 1090 MHz. Your antennas from what I can see are likely just fine. There is better … but being reasonable LMR400 is a pretty good option.

Just an FYI … I just installed a 2nd ADS-B setup and went from a temp install of 8 ft of RG58 low loss cable to LMR400 and I am getting more planes now. Every dB counts.

You have 4x as much cable and what you have above is probably one of the worst options out there for ADS-B. It is sad but sellers do this often … selling products that are ill suited to the task.

3 Likes
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  1. Where did you find schematics for spider antennas ?

  2. RG6 is bad cable choice for such frequency band. It might be good for VHF, but for anything above 150 MHz it has high attenuation loss, and very bad SWR.

  3. Preamp N/N mounted in the same pipe as the spiders, might help, but with such cable there is risk of just getting the same results.
    Teseq LNA 6901 Low Noise Amplifier 9 kHz to 1 GHz

  4. What is total cable length and how did you hook up 2 antennas to the cable (schematics) ?