So leave them tuned as-is?
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You can try tuning them in place but itās not certain how successful that can be.
Try mounting them further apart even if you have to bend two radials downwards to accommodate the side of the box.
It also looks like you canāt really close the front of the box right now or is that just the angle of view?
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The box lid is about 3/4" deep. I may experiment with temporarily removing the 978 antenna to see if the 1090 reception improves.
Tuning plays no direct role in the antenna gain. Gain is a function of the antenna design. A ground plane antenna, which is what the QuickSpider is, does not have a lot of gain to begin with, compared to the isotropic model.
Always tune for lowest SWR. One can have all the theoretical antenna gain in the world, but an impedance mismatch will detract from the modeled gain.
As I mentioned before, the proximity of the two antennas are likely to cause interaction. Tuning each antenna individually, and outside of the box, will not ensure proper in-place tuning.
Whatās the expected range of an unobstructed 1/4 wave ground plane 1090MHz antenna? With my current configuration, Iām picking up most FA traffic out to 50-70nm.
Iām running an LNA and that improves range quite a bit.
Reaching up to my terrain obstruction, so iāve seen planes 220 nmi out, but thatās only possible in a small portion of the sky without much high altitude traffic. 180 nmi is not a problem with the LNA.
Without the amplifier using a similar antenna inside the attic if i remember correctly the range would still be 100 nmi.
So unobstructed with a good rtl-sdr chip like the v3, iāll say 120 nmi should be possible.
Using a filtered LNA tremendously increases range.
Are you running -10 as gain?
You shouldnāt run anything else with a quarter wave antenna and no amplification.
Not exactly what you asked for, but my indoor garage mounted FA antenna, receives up to 150 nm in the unobstructed direction.
Iām running the gain @ 49 for the 1090 & 978 SDRs which is close to max (-10) setting. I wasnāt sure whether -10 caused AGC issues with ADS-B data so I changed the SDR gains from -10 to 49. Sounds like that was unnecessary.
I do have inbound DFW traffic flying overhead at about 12,000 feet - Iām assuming those planes arenāt impacting my range.
I was surprised to see 1 aircraft at 167nm yesterday. Iāll occasionally see a few at 90-115nm.
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I got 200 nm in most directions, and 250 nm in the best direction
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Having the antenna in the box and not completely above the building is gonna reduce range.
Normally AGC will just dial up the highest gain and due to a driver quirk that is around 6dB more than a gain of 49.6.
There are cases where AGC will reduce gain, but if that happens you have massive noise problems usually.
I did and 1090 reception did improve significantly - probably 40% more aircraft and range extended from 70nm to 100nm.
I also tried another box with the 2 antennas farther apart (almost 3") - was able to tune both in the box to that VSWR 1.4 range but aircraft tracking didnāt improve. I may try mounting them against the opposite walls with 2 radials straight down and the other 2 at 45 degrees.
Iām also experimenting with 1 antenna feeding a mini-circuits splitter to see if it will do better than 2 antennas farther apart.
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Rough rule of thumb is that you want them at least 1/4 of a wavelength apart (and ideally a lot more).
If that mounting bracket is conductive thatāll be contributing to the problem.
(Essentially all the antenna design stuff assumes that thereās no other conductors in the near field - if there are other conductors, the design needs to take that into account as theyāll act as parasitic components - e.g. this is how a yagi works)
1/4 WL at 978 MHz = 76 mm
1/4 WL at 1090 MHz = 69 mm
Photo below:
Left mag-mount for 978 MHz
Right mag-mount for 1090 MHz
Mag-mount spacing: 4 inches (100 mm), centre-to-centre
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pi@raspberrypi:~ $ sudo systemctl status piaware
ā piaware.service - FlightAware ADS-B uploader
Loaded: loaded (/lib/systemd/system/piaware.service; enabled; vendor preset: enabled)
Active: active (running) since Sun 2019-06-09 16:44:16 EDT; 1 day 18h ago
Docs: https://flightaware.com/adsb/piaware/
Main PID: 493 (piaware)
CGroup: /system.slice/piaware.service
āā 493 /usr/bin/piaware -p /run/piaware/piaware.pid -plainlog -statusfile /run/piaware/status.json
āā 1335 /usr/lib/piaware/helpers/faup1090 --net-bo-ipaddr localhost --net-bo-port 30005 --stdout --lat 43.xxx
āā 2643 /usr/lib/piaware/helpers/fa-mlat-client --input-connect localhost:30005 --input-type dump1090 --resul
āā27060 /usr/lib/piaware/helpers/faup978 --connect localhost:30978
Jun 11 11:10:34 raspberrypi piaware[493]: mlat-client(2643): Receiver status: connected
Jun 11 11:10:34 raspberrypi piaware[493]: mlat-client(2643): Server status: synchronized with 145 nearby receivers
Jun 11 11:10:34 raspberrypi piaware[493]: mlat-client(2643): Receiver: 280.2 msg/s received 99.2 msg/s processed
Jun 11 11:10:34 raspberrypi piaware[493]: mlat-client(2643): Server: 0.2 kB/s from server 0.0kB/s TCP to server
Jun 11 11:10:34 raspberrypi piaware[493]: mlat-client(2643): Results: 99.2 positions/minute
Jun 11 11:10:34 raspberrypi piaware[493]: mlat-client(2643): Aircraft: 10 of 25 Mode S, 25 of 35 ADS-B used
Jun 11 11:13:59 raspberrypi piaware[493]: 440028 msgs recv'd from dump1090-mutabi (1342 in last 5m); 439678 msgs sent to
Jun 11 11:14:00 raspberrypi piaware[493]: 131 msgs recv'd from dump978-fa (0 in last 5m); 131 msgs sent to FlightAware
Jun 11 11:18:59 raspberrypi piaware[493]: 441312 msgs recv'd from dump1090-mutabi (1284 in last 5m); 440962 msgs sent to
Jun 11 11:19:00 raspberrypi piaware[493]: 131 msgs recv'd from dump978-fa (0 in last 5m); 131 msgs sent to FlightAware
pi@raspberrypi:~ $
The mounting bracket is not conductive - itās 3D printed PLA.
Is your test run confirming both antennas have the same reception whether they are far apart or 100mm apart?
Never cared to compare with different spacings. Just followed the principle spacing > 1/4 WL.
Cannot move mag-mounts up to the edge of cookie-can, else ground-plane at one side will be zero.
Get bigger tin of cookies.
Bonus, more cookies to eat 
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Assuming all the cookies are gone, you could use the bottom of the cookie can - just remember to empty out the crumbs before you flip it over 
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Ok, found a toffee-can lid, and placed with separation of about 12 inches (30 cm). Watched for 25 minutes (14:10 to 14:35) no noticeable improvement.
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Cookie can lids generally have a better receptionā¦ 
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