So i build an 8 leg spider antenna and it worked really nice!
I got 3 times more range than with the standard antenna comming with the dongle and more than twice as much planes!
Though i haven’t placed the antenna outside yet, but that’s the next step for me 
Any experience with antenna splitters like this ?
images.biltema.com/PAXToImageSer … 20_l_1.jpg
(I have 4 trackers and hope to reduce the antenna farm down to one single antenna)
The obvious thing to watch out for with splitters is that you’re splitting the input power N ways, so for a 4-way splitter you’ll get 6dB attenuation + whatever insertion loss the splitter itself adds.
You will also want a splitter with good isolation as the dongles are noisy (I don’t know what the isolation of the one you pictured is)
As obj mentions, isolation among receivers is important. Mini Circuits publishes these numbers for its splitter/combiners. I’d have to put together a special 75 Ohm setup for my network analyzer to measure port-to-port isolation on a cable/sat 75 Ohm device.
Interference among SDRs will raise the noise floor, or throw spurs on top of signals you’re looking for. Not good.
bob k6rtm
If by trackers you mean software listening to dump1090 and sending data to websites like FA ??
Why not run them all on the same Pi? A Pi3 will handle quite the load these days…
Otherwise I am guessing they are all separate devices like dongle/mode-s beast/etc …?
thanks for info, it is 4 sep. devices running software from different sites
I don’t have any data on it so I will give it a try (8$) and see if my receive are get smaller since I have the reference from one receiver
Are they proprietary devices or just different raspberry pi’s etc?
Had some great range and results from the standard antenna that came with the USB receiver (shortened the aerial down to the recommended length). I am considering placing a single unit outside elevated with a Cantenna attached but needed to be sure of better results so what better time than to test from indoors first on both my units.
Only on day 2 and seeing a huge increase in both reports received and aircraft seen. Range has also slightly improved but I guess when moved outdoors and elevated higher should see much better distance results.
Left hand side the old results, Right hand side new results.
https://farm2.staticflickr.com/1714/26438580321_cdb53306dc_b.jpgCantenna Improvements by Jason Nicholls, on Flickr
I only had one MCX to F Connector pigtail so had to hack and chop one of the original antennas that came with the USB receiver. Its not pretty but works and does the job so far!
I have tried this antenna. It gave me poorer result than the whip antenna (supplied with dvb-t dongle) cut to 67 mm length.
https://farm2.staticflickr.com/1636/26633481376_b8cb396c38.jpg
Thanks for the heads-up!The results do look promising on the hourly chart.
Before
I’ll try trimming another antenna to 69 mm and see if it makes any difference.
After trying your other antenna for 69mm, try it by cutting it to 52mm as shown below. This is because about 15mm of antenna length is hidden inside the base, and length of antenna with 67mm upper removeable part is actually 67+15=85mm. Cutting it to 52 mm makes actual antenna length 52+15=67mm
69mm Whip
53’ish mm
Comparison with Site : 20363
https://vgy.me/Mqf349.png
flightaware.com/adsb/stats/user … tats-20363
https://vgy.me/qTyQL0.png
I think having a proper ground plane makes a big difference as compared to the precise length of the antenna whip.
@abcd567 Would the size of the ground plane (can size or material) make any difference.
The material of can should not make any difference as long as it conducts electricity. Any metal (steel, iron, copper, brass, aluminum, etc) is ok. The iron/steel has the advantage that the magnetic base of antenna clings to it and keeps antenna upright and prevents it from falling.
The one thing I have tried & know is that the 70 mm dia Can gives better result than 55 mm dia Can which gives better results than 25 mm dia Can.
Please try groundplane of several larger & smaller dia, observe the results, and post here for benefit of others.
My 65mm x 72mm can gives better results than 75mm x 110mm one.
Just a quick question: Does the outside unit of air conditioner makes a ground plane as the metal can does? It’s metal and grounded, I guess it should act as a ground plane?
I use a 4-wire spider with a metal lamp shade sitting on top.
Photo please.
Does placing the metal lamp shade improve Spider’s peformance?
When I checked, I kept height of cans same (70mm) for all the 3 diameters I have tried. The only variable in this case was diameter of can.
You have varied two parameters (dia of can, height of can) at the same time, so it is not clear that which of the two ( dia or height) has affected the performance.
Cut the taller can so that it’s height is same as height of the shorter can. This way the only variable will be diameter of can. Later you can try affect of can height by comparing several cans of same dia, cut to different heights.
I would also suggest trying different diam/heights where diam+height is held constant, as I think there is something going on involving distance from the feedpoint to the end edge of the can.
Alan
