DIY Antenna performance, and looking for data

After a couple weeks of messing around with DIY antennas, I’m a bit smarter and a bit more confused.

I built a total of 5 different models of antenna and compared their performance (via daily “aircraft reported” totals). All of these are basically @abcd567’s designs from various past posts

  • v1 = Quick spider - no soldering built out of a scrap of RG-6 Coax I had laying around.

  • v2 = Similar 1/4 wave spider design but made on a N-type panel jack, with 4 crimped on legs for the ground plane, using 14AWG house wire for the various conductors

  • v2.1 = v2 with the ground plane legs soldered on

  • v2.2 = v2.1 with 6 legs instead of 4

  • v3 = V-stub with 6 legs for the ground plane (soldered)

v1 was built by dimensions only, and then deployed with my first RPi on an ADBS-Exchange Blue dongle.
The rest were tuned via a NanoVNA to drive 50 Ohm Impedance and minimum SWR at 1090 MHz (usually ~1.2). I then deployed them one at a time on a second RPi/ADSB-Ex setup - basically identical to v1 - and ran them in comparison to the v1 installation.

I am in a fairly good location (I think) for plane spotting - with an unobstructed from SW to NW of the Pacific Ocean - near the coast between KSAN and KLAX.
With the v1 running, I typically get ~3000 aircraft detected/day, with a big dead time overnight (0:00 - 6:00), and some daily variation I attribute to the private pilots (roughly +/- 200) depending on the day of the week and the weather. Average max range (from graphs1090) is about 220 nm.

When I put up v2, I was expecting to see an improvement in range and aircraft count; however I really didn’t. I occasionally got a plane a bit farther away, but since it was nearly always heading closer (likely coming to LAX) the v1 station would see it eventually. In the end I would routinely get ~30 more aircraft a day (1% improvement), but that was it.

v2.1 and v2.2 gave basically identical performance - increase the ground plane leg count and soldering them on didn’t help (not that I really expected it would).

Going to v3 (V-stub) was a bit of a disappointment, in that it did improve both average max range (up to 240nm) and plane count - but only ~90 more planes than v1; so a measurable improvement, but not the significant step up I was hoping for.

Watching the performance, what I think is probably happening, is that most commercial aircraft I am seeing are generally coming towards me - there are very few that skirt the edge of my viewing area, so extending from 220nm to 240nm doesn’t buy me a lot. I suspect the difference is coming from private aviation up the coast - small planes flying out of the regional airports around LAX and north, heading out over the ocean, but low enough their signal isn’t very clear.
At this point I feel glad I didn’t sink $50 into a 5-7dB antenna to discover no appreciable improvement - for roughly the same price I got a NanoVNA and made myself smarter about the whole antenna process - which is a win even without more planes to count.

I am curious to see if I can prove the difference is private aviation, but to do that I think I need to get a dumped list of “all the aircraft I’ve identified”. Looking in the discussion archives it doesn’t seem that FA can provide that - although there were suggestions other sites might.

I’d be interested to know if anyone has a good suggestion for an easy way to list out the specific aircraft ID’d, so I can do a compare and see which ones are the “extras”.

I expect I’ll stick with the V-stub (90 more planes is better than nothing), unless someone has a suggestion for something else to try to improve range. I’m just a bit too far south to get a good look at direct transmissions from SFO/SJC planes, but maybe with the right equipment and conditions I could see over the horizon and pick a few of them up.

I’m a nearby site, and I see way more than a 90 aircraft variation day to day just due to traffic variations. I see up to 800 or 900 aircraft variation from day to day without making any changes to my setup. This is mainly general aviation traffic variations (small planes). Now I occasionally do a sudo apt update and then a reboot which reduces the counts but probably not much. So I’m thinking the variations in aircraft counts you are seeing are probably due to traffic variations rather than the antenna variations.

@jimMerk2 I would agree with that - I see identical variations between the various antennas; just with the “+30” (or “+90”) on top of it. Last weekend’s rain storms probably kept a lot of GA on the ground, and I saw that in both antennas.
Saturday I only got 2280 and 2290 on the two setups.
On Monday when it was dry, 3059 and 3099.
Today (with the V-stub) it was 3186, and 3273.

First Tweak:
Rotate the antenna to change the direction of V, 90 degrees at a time, and check performance with V in each of the 4 directions.

Seond Tweak:
Increase the width of open side of V from 45mm to 55mm. Check its performance. If performance is not improved or performance is reduced, then tune it again by nano VNA by trimming top wire, a little (say 2mm) at a time.

Curious which NanoVNA you got and where you got it. I am thinking of getting one and would like to characterize the RTL-SDR filtered LNA. I understand that these NanoVNA’s are good at characterizing passive devices such as antennas or passive filters, but there might be problems if you are measuring an active device. Reason being that they output a square wave rather than a sine wave. So I’m not sure I can use it on the filtered LNA.

@abcd567 I will try that. the bulk of my detections are to the northwest (per the coverage graph), so I pointed to “mouth” of the V in that direction (since it looked like the better gain came that way).

@jimMerk2 I bought one on Amazon:
for $60. I also got some N-SMA adapters so I could play with the ones I was building. I did put the 1090 antenna that came with the ADSB-Exchange dongle (part of the package), and it seemed pretty good - min SWR at 1090 Mhz (as you’d hope), and pretty low ~1.1

I’ve only used it for passive devices - the antennas and the cabling (to confirm my KMR400 was actually low loss - it was).


Thanks. I’ll take a look at using it to measure an amplifier.

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