FlightAware Discussions

Poor performance with DIY antennas

Hello
I’ve recently built all three “beginners” antennas but I’m getting really poor performance from all of them. My reference antenna is just a cutoff whip from the nooelec bundle.
I’m getting about 1/3 of msg/s and about half of distance on any DIY antenna compared to the whip.
I’ve rebuilt the spider twice, used brand new coax, checked continuity and resistance using multimeter on all legs etc…

For SO239 spider, I’m using a short (20cm) UHF to male SMA adapter, for quick coax spider and cantenna, I’m using short RG6 with F connectors and F to SMA barrel adapter.


What I’m doing wrong? What else I can check/improve?

Example polar plots for quick coax spider and the whip:


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Those whips seem kinda long, have you tried shortening them?

Are you using a different SDR with the DIY antennas?
If you have lots of interference, the FA blue stick can be much worse than a regular SDR due to its LNA getting swamped.

Using an USB extension can cause voltage issues.

have you checked what max range you can get? the best antenna will not improve if you’re limited from geographical aspects.

Also any obstacles can limit it.
My device is outdoor with a well tuned antenna, however i have a blind spot with limited range caused by the roof in one direction and geographical limit in another direction

I’ve double checked all measurements on spiders and cantenna and they’re spot on (68 ±1mm) so that’s not it.
I’m testing the antennas with blue flighaware stick. I also have nooelec smart so I might try that later.
I’ve removed the usb extension, we’ll see if it helps.

Problem is, if I swap any of the antennas with the short whip without changing anything else, I’m instantly getting better results. I can pickup planes 250km away, while on any DIY I can barely reach 160KM. There’s also huge difference with msg/s (500-600 vs 300-400)

It’s like I’m missing something.

try exchanging the positions of the antennas

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Gain adjustments with each antenna, perhaps.

I played around with my device using different indoor antennas. I never had a performance decrease regarding range even if the gain was too high.

In most cases i needed to select 48.0 or 49.6 any lower number gave me a lower performance.

In my experiments, 48.0 is usually the best compromise, that’s where I’ve been for a long time now.

I’m wondering in case he is using -10. I’m known for disliking -10. :rofl:

I got much better reception with the whips quite a bit shorter.
62mm maybe, don’t remember, maybe even shorter.
Just snip off mm by mm and see how the reception is.

Maybe that adapter is the issue?
RP-SMA is always a favorite for screwing reception because of the missing pin.

Maybe your left and right window are different? :slight_smile:
It’s a mystery!

I buy my adapters on eBay so I know the quality is not the greatest, but F adapters are the ones I have to triple check every time as they are the worst of the bunch.

Can you please post the link to the web page from which you purchased the F-to-SMA adaptor?

Difference between SMA-male and RP-SMA-male: Missing Center Pin

 

F to SMA Male (has center pin)

41LmOwi1-vL.AC_SY400

 

F to RP-SMA Male (does NOT have center pin)

41A0qWMBVZL.AC_SY400

You’re right, but that should not end up in such a poor performance. I did some experiments with it. The number of messages and aircraft was impacted, but the range was quite similar

Thank you for all your suggestions for far.

I’m running cantenna atm:
I’ve removed the usb extension, moved the antenna about 10cm higher and it seems that things somewhat improved.

Opensky says the furthest plane I’ve picked was 561KM which seems odd, probably a fluke, but the covered area is now closer to what I had before (76 vs 86kkm2)

I’ll let each antenna run for 24h and then start trimming mm by mm.

Indoor antennas can be a bit of a minefield because there are so many things for signals to interact with. When I had an antenna in the loft, moving it by quite short distances had a noticeable and sometimes quite large effect on performance.

No.
You want to compare “only” the antennas (at this stage), so you did it right.

If you can make your center antenna piece remove-able, your can try different lengths real-time. It also makes it easy to go back to a longer center antenna if you cut too much off.

All I can suggest, if you have the budget, to get something like an antenna analyzer or a cheap VNA(a nanoVNA can be bought for around US$50), and learn some RF fundamentals, or get a friend knowing something about RF, with hopefully some test equipment (maybe find a local HAM-club). Probing in the dark, trying one solution after the other, without knowing why they don’t work, is the quickest way to loose interest in a hobby. Only once you

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NanoVNA got me curious but the only models I could find on amazon go up to 900MHz only:

Can’t find anything up to 1090MHz

For that price, I could just buy flightaware antenna and be done with it, but I really like tinkering:)

I’m glad I bought this $150 analyzer - it’s fun to tune each DIY antenna by changing the center antenna length which shifts the curve to the right if you make it shorter or to the left if you make it longer. Once the low point is centered at 1090MHz, I then adjust the radials up/down to get VSWR as close to 1.0 as possible (basically moves the curve up or down).

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Latest nanoVNA firmware goes up to 1500MHz. Noisy at that frequency, but cmbined with the PC-software, Nano-VNA Saver, it does quite a respectable job above 1GHz.

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