US: 978mhz reception - discussion (% feeding both, best antennas, filters, etc)

I have been researching ADSB-Out solutions for my plane and have come to realize that 978 is likely to get much busier after Jan 2020. The lower cost solutions available send their ADSB-Out data on 978. The majority of the US fleet stays in US and can't climb above 18,000ft, so 978 is fine.

Some examples:
https://seattleavionics.com/NavWorx.aspx
http://sarasotaavionics.com/avionics/gdl82

Some people may also opt for 978 out because you can go "anonymous" mode to hide your ICAO data that is present on 1090.

Some questions come to mind:
- What % of the US based feeders are feeding both?
- What antenna do they find the best?
- What band-pass filter did they go with, if any?
- other ?s

 

I cannot directly answer any of your questions but I can tell you that 978 MHz UAT coverage on ADS-B Exchange in the USA is very spotty at best. While there is good-to-excellent 1090 MHz coverage in most areas, it's a rare station that feeds both. Of course, FAA coverage is a different story and is generally not an issue.

I became aware of this situation when I attempted to track a friend's VariEze from Phoenix to Oshkosh last month using data from ADS-B Exchange (and other non-FAA sites). Except for a brief series of reports leaving Phoenix and a brief series approaching OSH, there was absolutely nothing in between. His coverage had also dropped when he flew somewhat north or south on local flights; there must be a single 978 MHz feeder on the east side of Phoenix.

My own ADS-B feeder is on 1090 MHz only (using an RTL-SDR receiver and a homebrew collinear antenna). I'm using Dump1090 with ModeSMixer running under Windows to feed ADS-B Exchange (via VRS) and FR24. I wish I could find a way to accommodate a second RTL-SDR receiver on the same setup but so far I've had no success running two. But if I ever did solve that problem, I would use my existing collinear antenna with a power divider (splitter) to feed both receivers.

--
Joe

 

I know that two SDRs can run on the same RPi because my Stratux unit in my plane listens to both 1090 and 978 concurrently.

I am going to pull the Stratux and make a Piaware SD for it and check it out.

I am about 90% sure that I am going to install a 978 solution in my plane as I have perfectly good transponders (Garmin GTX327) and just need ADSB-Out compliance. I am in the same boat as a lot of pilots so 978 is going to need some real attention in ADSBx over the next year or two.

 

What config file should I be editing to lock in which SDR is for which dump* daemon?

 

No such file.

---

[email protected]:/var/log$ cd /etc/default/
[email protected]:/etc/default$ ls -Fla
total 112
drwxr-xr-x 2 root root 4096 Jan 2 15:31 ./
drwxr-xr-x 80 root root 4096 Jan 2 05:24 ../
-rw-r--r-- 1 root root 221 Jan 2 15:31 beast-splitter
-rw-r--r-- 1 root root 221 Jan 2 15:31 beast-splitter.bak
-rw-r--r-- 1 root root 222 Apr 27 2014 bsdmainutils
-rw-r--r-- 1 root root 549 Aug 23 2014 crda
-rw-r--r-- 1 root root 955 Sep 5 2015 cron
-rw-r--r-- 1 root root 297 Oct 10 2016 dbus
-rw-r--r-- 1 root root 92 Apr 6 2015 devpts
-rw-r--r-- 1 root root 428 Jan 2 15:31 dump1090-fa
-rw-r--r-- 1 root root 428 Jan 2 15:31 dump1090-fa.bak
-rw-r--r-- 1 root root 84 Mar 5 2012 fake-hwclock
-rw-r--r-- 1 root root 86 Apr 6 2015 halt
-rw-r--r-- 1 root root 674 Nov 4 14:18 hwclock
-rw-r--r-- 1 root root 178 Jan 2 15:31 ifplugd
-rw-r--r-- 1 root root 178 Jan 2 05:30 ifplugd.bak
-rw-r--r-- 1 root root 52 Nov 4 14:18 locale
-rw-r--r-- 1 root root 306 Jun 21 2012 networking
-rw-r--r-- 1 root root 1756 Jun 19 2017 nss
-rw-r--r-- 1 root root 15 Aug 4 2006 ntp
-rw-r--r-- 1 root root 292 Jul 3 2017 raspberrypi-kernel
-rw-r--r-- 1 root root 620 Apr 6 2015 rcS
-rw-r--r-- 1 root root 125 Nov 4 14:27 rpi-bootconfig
-rw-r--r-- 1 root root 1768 Sep 30 2013 rsync
-rw-r--r-- 1 root root 124 Dec 14 2015 rsyslog
-rw-r--r-- 1 root root 133 Apr 14 2016 ssh
-rw-r--r-- 1 root root 1115 Apr 6 2015 tmpfs
-rw-r--r-- 1 root root 1118 May 17 2017 useradd
[email protected]:/etc/default$ more dump1090-fa
# Generated automatically by fa_config_generator
# This file will be overwritten on reboot.
DECODER_OPTIONS="--max-range 360"
NET_OPTIONS="--net --net-heartbeat 60 --net-ro-size 1000 --net-ro-interval 1 --net-http-port 0 --net-ri-port 0 --net-ro-port 30002 --net-sbs-port 30003 --net-bi-port 30004,30104"
JSON_OPTIONS="--json-location-accuracy 2"
RECEIVER_OPTIONS="--net-bo-port 30005 --fix --device-index 0 --gain -10 --ppm 0"
[email protected]:/etc/default$

 

Thank you sir.

I should perhaps back up and ask if the leaders of ADSBx have any appetite for 978 position reports. Being a pilot and an aircraft owner I can speak to the fact that plenty of general aviation owners are going to go with the less expensive 978 solutions. I have influence over three different aircraft and at this moment the plan is to upfit all three with the 978 solutions.

Assuming ADSBx is interested in collecting US based pleasure aircraft (smaller GA aircraft) ADSB info, you will need 978 feeders.

I am not enough of a *nix guru to lead, but I am more than happy to do testing.

Will you guys create an updated FA+ADSBx image that adds 2nd SDR support for 978?

 

Ok James, Marcin tossed on you.. ;-)

I can setup a unit and put it on your ZeroTier network if you want to play with it.

 

The latest ADSBx image supports 978... that's what I'm running. The only criticism I have is that it feeds the traffic directly to ADSBx, versus feeding it back into dump1090 where it can be sent to other feeders as well. A simple change in one script fixes this.

 

So how the 978 decoder works .. it listens to the UAT .. creates a fake ADS-B packet .. It's a bit half baked but ... it does decode aircraft and tower 'pucks'.

You'll need to use a dongle without a 1090mhx filter, so that rules out the blue FA prostick+ ... the orange one should be fine or any other SDR

If you want you can send it to your local dump1090 input port ...

Code:

#!/bin/sh
if [ -f "/tmp/adsbx-params" ]; then
        . /tmp/adsbx-params
else
        echo "DUMP978 ERR:  Configuration file does not exist."
        exit 0
fi

if [ ${UAT} = "yes" ]; then
        while true
        do
                sleep 30
                if [ -z ${UATPORT} ];then
                        UATPORT=30005
                fi
                rtl_sdr -f 978000000 -s 2083334 -d 1 -g 48 - | /home/pi/dump978/dump978 | /home/pi/dump978/uat2esnt | socat TCP:feed.adsbexchange.com:$UATPORT
        done
else
  exit 0
fi

 

The FA ADSBx image supports 978 already. Dan has feeds from 2 places locally feeding 978 to custom feeds.

 

The easiest way is to change the serial on your USB SDR to 1090 and 978 ... then tell it which one to use.

You can brick the USB SDR if you don't do it right.

 

I captured some legit 978 traffic today so I ordered another dongle, a 978 antenna and compiled dump978.exe using MinGW for use on Windows ;-)

 

There is no question the US is going to have legit 978 equip'd planes. I know of at least three planes that will get a 978 upgrade in the next 12 months. I look forward to a Piaware+ADSBx build that works well for it.

 

the 2json exe wont port easily due to sys/select not being on windows...

direct links to GitHub are spam?

 

No but either cloudflare or forum is paranoid until you have a few posts. We get hordes of spammer bots trying to register every day and post ads for prostitutes and dick pills.

 

Both images already support 978! You just need 2 SDR!