It’s at 14 but I have one filtered LNA at the antenna, followed by 150 ft of RG6 cable and then another LNA. Without the second LNA, I was at max gain and still felt that is not optimal.
The LNA noise (1dB) is smaller than the noise of the tuner chip alone (3.5dB).
Airspy’s really need LNAs in front.
@jimMerk2 what antenna are you using? You said a +6dB (IIRC) - so I presume a commercially purchased one?
Originally, I was considering going the route of a directional (purchased) one, but the couple models I saw referenced were either out of stock, or a lot more than I wanted to pay. I made one of my own based on this post
and my performance got a lot better. I had thought about getting the unit you did (LNA from RTL-SDR), but opted to try this instead -
https://www.amazon.com/dp/B09F2ND4R6?psc=1
Since for a similar cost, I would end up with two radios (either use my RTL-SDR for a second PiAware, or else use it for something unrelated since it’s fairly generic). The ADSB Blue stick has a filter but not an LNA, but upon using it, I found I got pretty good performance. I can see pretty much to the theoretical horizon (at least west), and based on looking at FA/FR24 general data, I’m not missing planes that way.
I don’t get a lot to the east, but then I’m down the hill towards the beach in Solana, so the geography really restricts what I see to the east, regardless of my equipment. That said, I might give a better antenna a try and see if I get a bit more inland results - and so coming back to asking what you’re using, and how you like it. Would you recommend it or get it again?
Yes, it’s a store bought antenna (Amazon)
The nameplate gain is 6dBi, but that’s just theoretical. Probably no one has actually measured the antenna pattern on these things.
It highly depends on your location. I started with home made antennas and moved over to commercial ones.
Jetvision A3 is a good one, also the 1090MHz variants from Vinnant.
I have both and can’t really see a significant difference.
But on my location a very good DIY antenna would make the job as i am limited only by terrain. This cannot be changed by simply changing the antenna.
I am using a Flightaware antenna 5.5 dB, and a home made antenna of my own design, the V-Stub antenna.
Running both antennas installed indoor in same large window at a horizontal distance of 50cm (a sisde-by-side comparison), both with very short length of coax, the V-Stub performs about 80% of FA antenna.
I could not measure Gain or radiation pattern as I dont have professional equipment to do so, but I ran computer simulation on the design and it showed promising gain and radiation pattern.
(1) Side-by-Side Comparison of Flightaware and DIY V-Stub Antenna
(2) Computer Simulation Results:
2-D radiation Pattern & Gain
3-D Radiation Pattern
(3) Measurement of SWR
(4) Physical Build - Prototype
Interesting. On the pattern plot, it says 4.32 dB on the right side and 3.91 dB on the left side (in the boxes) but on the graph scale itself it looks like over 6dB. Are the dB values in the boxes dB relative to a dipole? Also, you probably mentioned this somewhere, but what software is that for the radiation plots?
Also, with all this discussion of gain adjustment, the antenna compensates somewhat when a plane is nearer. That is, the antenna gain is maximum at the horizon and decreases as the elevation increases.
The numeric figures are in dB (dipole), while graph circles are in dBi (isotropic).
dBi = dB + 2.15
Right Side Value on graph (dBi) = Right Side Numeric value (dB) + 2.15 = 4.32 +2.15 = 6.47
Left Side Value on graph (dBi) = Left Side Numeric value (dB) + 2.15 = 3.91 +2.15 = 6.06
The simulation software is 4nec2, a free of cost software 
Exactly. This is called “Donut Effect”
In the sketch below, the first is of a theoretical antenna, the second is of a 1/4 wave ground-plane antenna, the third is of a 1/2 wave dipole antenna, and the fourth is a 5/8 wave grund plane antenna
Too bad it’s Windows only.
An old tool. Not very good and not very conclusive, but worth trying.
Note: For fump1090-fa Package install on Raspberry Pi OS image (bullseye). Will NOT work on Piaware SD card image.
https://github.com/abcd567a/optimize-gain
TESTED TODAY
wget https://raw.githubusercontent.com/abcd567a//main/optimize-gain-dump1090-fa.py
sudo chmod +x optimize-gain-dump1090-fa.py
sudo ./optimize-gain-dump1090-fa.py
pi@raspberrypi:~ $ sudo ./optimize-gain-dump1090-fa.py
READING AND SAVING SETTINGS BEFORE STARTING THE TEST
THESE SETTINGS WILL BE RESTORRED AT THE END OF THE TEST
RECEIVER_GAIN=36.4
ADAPTIVE_DYNAMIC_RANGE=no
test 1 of 3
gain= 49.6 messages= 18746 positions= 2629 planes= 90
gain= 48.0 messages= 17013 positions= 2432 planes= 91
gain= 44.5 messages= 16031 positions= 2258 planes= 93
gain= 43.9 messages= 18125 positions= 2400 planes= 91
gain= 43.4 messages= 18475 positions= 2298 planes= 93
gain= 42.1 messages= 18458 positions= 2399 planes= 89
gain= 40.2 messages= 17833 positions= 2287 planes= 89
gain= 38.6 messages= 17321 positions= 2224 planes= 81
gain= 37.2 messages= 18473 positions= 2465 planes= 85
gain= 36.4 messages= 17289 positions= 2102 planes= 83
gain= 33.8 messages= 16090 positions= 2036 planes= 84
gain= 32.8 messages= 14865 positions= 1803 planes= 79
gain= 29.7 messages= 13295 positions= 1680 planes= 75
gain= 28.0 messages= 12995 positions= 1543 planes= 66
gain= 25.4 messages= 12161 positions= 1264 planes= 54
gain= 22.9 messages= 9646 positions= 1085 planes= 41
gain= 20.7 messages= 9013 positions= 991 planes= 36
test 2 of 3
gain= 49.6 messages= 17771 positions= 2351 planes= 82
gain= 48.0 messages= 19599 positions= 2469 planes= 86
gain= 44.5 messages= 19379 positions= 2477 planes= 81
gain= 43.9 messages= 20103 positions= 2650 planes= 86
gain= 43.4 messages= 20868 positions= 2796 planes= 84
gain= 42.1 messages= 22237 positions= 3036 planes= 90
gain= 40.2 messages= 22126 positions= 3090 planes= 84
gain= 38.6 messages= 22027 positions= 3161 planes= 87
gain= 37.2 messages= 21639 positions= 3064 planes= 84
gain= 36.4 messages= 20089 positions= 2948 planes= 80
gain= 33.8 messages= 18686 positions= 2651 planes= 90
gain= 32.8 messages= 17945 positions= 2586 planes= 91
gain= 29.7 messages= 19250 positions= 2836 planes= 79
gain= 28.0 messages= 17576 positions= 2563 planes= 71
gain= 25.4 messages= 14231 positions= 2178 planes= 63
gain= 22.9 messages= 14611 positions= 2191 planes= 65
gain= 20.7 messages= 11427 positions= 1562 planes= 46
test 3 of 3
gain= 49.6 messages= 22275 positions= 3288 planes= 103
gain= 48.0 messages= 20902 positions= 3033 planes= 98
gain= 44.5 messages= 22114 positions= 3316 planes= 99
gain= 43.9 messages= 24955 positions= 3522 planes= 100
gain= 43.4 messages= 24323 positions= 3437 planes= 102
gain= 42.1 messages= 24931 positions= 3487 planes= 100
gain= 40.2 messages= 27125 positions= 3651 planes= 95
gain= 38.6 messages= 27294 positions= 3485 planes= 96
gain= 37.2 messages= 27335 positions= 3668 planes= 91
gain= 36.4 messages= 25482 positions= 3526 planes= 87
gain= 33.8 messages= 23086 positions= 3246 planes= 84
gain= 32.8 messages= 24540 positions= 3354 planes= 85
gain= 29.7 messages= 23214 positions= 3097 planes= 81
gain= 28.0 messages= 23596 positions= 3095 planes= 79
gain= 25.4 messages= 18757 positions= 2392 planes= 66
gain= 22.9 messages= 17210 positions= 2207 planes= 69
gain= 20.7 messages= 12712 positions= 1598 planes= 53
===Totals===
Gain, Messages, Positions, Aircraft
49.6 58792 8268 212
48.0 57514 7934 206
44.5 57524 8051 204
43.9 63183 8572 208
43.4 63666 8531 211
42.1 65626 8922 207
40.2 67084 9028 207
38.6 66642 8870 207
37.2 67447 9197 202
36.4 62860 8576 198
33.8 57862 7933 194
32.8 57350 7743 192
29.7 55759 7613 186
28.0 54167 7201 172
25.4 45149 5834 153
22.9 41467 5483 142
20.7 33152 4151 113
SETTINGS RESTORED AT END OF TEST:
RECEIVER_GAIN=36.4
ADAPTIVE_DYNAMIC_RANGE=no
pi@raspberrypi:~ $
@abcd567 the description for the V-stub picture says “Physical Build - Prototype” - did you ever make any additional modifications to go from “prototype” to “final”?
Do you have any guidance on how to “tune” it? I presume you were using the analyzer in the photo to tweak the length to minimize the VSWR. Once you had a length, did you solder it - or make any permanent setting?
I don’t have a VNA, but have pondered getting one - is there way to tune this effectively without one?
Would setting the upper length to 150mm and calling it a day work “reasonably well” do you think? At least resulting in better performance than a 1/4 wave/ground plane spider?
Looking back at a post you made in 2018 here:
It looks like the “1/4 wave spider with ground plane” was giving 1.31dB, so the V-Stub ought to boost performance by ~3dB relative to it. That seems enough to warrant my giving it a try to construct one - even if I can’t optimally tune it.
An additional question - the V-stub antenna seems to have 4 “ground plane legs” extended at 90 degrees to the vertical. The 1/4 wave spider I built has the legs (6 total), pointed about 45 degrees below horizontal. Aside from the question of “leg count” (which I suspect isn’t a big deal), I’d think the leg angle might matter. Is there a reason that the 1/4 spider designs suggest a downward angle, but the V-stub does not?
Here’s what I got running the gain tests python script:
===Totals===
Gain, Messages, Positions, Aircraft
49.6 120931 17456 304
48.0 122986 17495 315
44.5 124417 18137 314
43.9 125288 18548 316
43.4 127672 18548 325
42.1 131398 18783 323
40.2 132828 18972 316
38.6 130388 18738 315
37.2 134300 19320 323
36.4 135865 19803 312
33.8 132587 19235 320
32.8 131727 19208 327
29.7 134336 20108 326
28.0 133838 19663 325
25.4 130613 18983 316
22.9 129763 18844 309
20.7 125721 18670 314
SETTINGS RESTORED AT END OF TEST:
RECEIVER_GAIN=37.2
ADAPTIVE_DYNAMIC_RANGE=no
I had been using 37.2 dB, but it looks like optimum would be 29.7 dB.
Note that MLAT loses sync during these tests. Probably because dump1090-fa is continually restarted.
Well it depends what you are looking for as criteria.
If criteria is Messages, then your best setting is 36.4
If criteria is Positions, then your best setting is 29.7
If criteria is Aircraft, then your best setting is 32.8
I normally take Messages as criteria. On this basis, in script method my best setting becomes 37.2
In manual method of trial-and-error also I used Messages as the criteria, and it gave me setting 36.4
So in my case, using same criteria, the results of script and trial-and-error are close to each other.
Yes, I used Analyser to measure and tweak VSWR.
However if analyser is not available, then Messages per sec* displayed on the Skyaware map (on top of aircraft table) will serve a rough guide.
No I did not solder because
(1) It was proto type, I wanted the sliding capability available, not lost by soldering
(2) The plastic sleeve holding the two wires was tight enough to hold the pieces in position, particularly because it was indoors and not subject to wind.
Even a crude tuning is better than no tuning. As explained above, if yiu dont have VNA, use the Messages per sec reading on Skyaware map as guide to tune.
The desired impedance of antenna is 50 ohm. This is to match with receiver and coax impedances of 50 ohms.
The 1/4 ground plane has impedance as follows
- Horizontal Radials = 32 ohm
- Radials bent down to 45 deg = 50 Ohm
- Radials bent down to 90 deg ( i.e. totally vertical) = 75 ohm
For many antenna designs, the 50 ohm impedance is achieved with horizontal radials. The V-Stub antenna also achieves 50 ohm impedance with horizontal radials, so no need to bend the radials down.
I see the problem in this script that the data is provided sequential - not parallel.
So even if the script shows a certain number of aircraft, 2 minutes later it can be different even without touching the gain.
Looking at the example of jimMerk2 the number of aircraft at 43.4 is the same as at
28.0
For having 100% reliable data, you would need two identical setups side by side, both running on different gain settings and then compare
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Yeah, they get around this somewhat by doing three rounds of testing spread over an hour. It’s all you can do with one set of hardware.