FlightAware Discussions

$10 Groudplane (Spider) Antenna

dschaper - heres some info for you re cutting the antenna - cross posted from the Flightradar forums - credit to K5TED:

*1. Radiator is pressed in to the hardline center. DO NOT ATTEMPT TO TWIST AND REMOVE IT. Trim it in place. It protrudes 81mm from the center conductor (measured with cover off) Remove the black plastic bootie and trim accordingly from the tip. (13mm for a 68mm adjusted length)

  1. Ground Radials are 84mm long and threaded into the aluminum base ring, measured observing the three to 4 threads left exposed. Remove the black plastic bootie and trim accordingly from the tip. (16mm for a 68mm adjusted length)*



Great! Thanks!

I bought three of these and have had one running on 1090 since I joined FA . You can see my stats for reference. Running indoors, in a NW facing windows about 25’ up on a RTL 820T2 dongle and Intel Compute Stick on Win10 Pro

It is not necessary to take it apart or unscrew the radials for trimming. However, I took one completely apart and got the dimensions so you don’t have to:

  1. Radiator is pressed in to the hardline center. DO NOT ATTEMPT TO TWIST AND REMOVE IT. Trim it in place. It protrudes 81mm from the center conductor (measured with cover off) Remove the black plastic bootie and trim accordingly from the tip. (13mm for a 68mm adjusted length)

  2. Ground Radials are 84mm long and threaded into the aluminum base ring, measured observing the three to 4 threads left exposed. Remove the black plastic bootie and trim accordingly from the tip. (16mm for a 68mm adjusted length)

If you insist on taking it apart to see the guts, after the three radials are unscrewed and removed, the assembly slides out of the cover. It is a bit fiddly to get the threads all lined up when putting it back together. Remember this is aluminum, so be gentle.

Antenna works somewhat better than a homebrew groundplane I made, much better than the colinear, or the Franklin I made. Go figure. I make a lot of antennas for ham radio on all bands. These are fun because the elements are small. Lots of room to experiment.

As for the cost of the antenna, it is commercial quality, though I don’t think it was designed for outdoor use, seeing that it uses a BNC, but it’s perfectly fine outdoors if you use some electrical grease or tape it up nicely.

The seller has it for “Make Offer” so I paid 8 bucks each plus shipping. It would cost me more than that in gas, time and effort to create something that is not as well made.

Most folks don’t have the machine shop to turn out an aluminum ring with threaded holes at the perfect angles, plus the threaded radials, a threaded center, the PVC hood and the tips, plus a piece of hardline with BNC connector for $12

I’m also using one of these antennas, not trimmed, since it is for 800 MHz, on a low power HDTV transmitter on ch 25.3 (835MHz) Works great.

The other one is on one of my Icom PCR-1000 receivers, listening to public service stuff.

Here’s some background info on the original design intent for this antenna mobileinfo.com/Wireless_Netw … ardis_.htm

Thank you very much for all the valuable information. I’ll be sure to refer to it when the unit gets here on Monday or Tuesday. (I did the Make an Offer also for the unit.)

All of this has inspired me to take an ARRL course staring tommorrow for my Technician Class ticket, so I’m going to have to dig out the old Physics books, lol…

We need more hams!

Regarding the antenna trimming, in case you haven’t worked with this guage aluminum, it’s not at all complicated. Simply measure back from the tip, mark it with a Sharpie, use wirecutters to squeeze some dents into the metal, less than halfway through, then use pliers to snap it off. If you squeeze all the way through with the cutters, it will splay out the tip.

Due to its easy and simple construction, dimensional tolerance & hence reproduciblity in DIY enviroment, good performance, and popularity, I have placed the Spider as first one in the list, and titled it “Easy Antenna #1” in the following threads started by me in March 2015:

Flightaware Forum - Three Easy DIY Antennas for Beginners




I now have one of these on its way to Australia (don’t ask how much though - with the way the Aussie dollar is to the $US a the moment…) - am looking forward to see how it performs against my permanent antenna.

Final plan is for this to be the antenna for my portable ADS-B rx.

I planned on a Dremmel with a cut-off wheel on it, and then de-burr the finished edges before re-capping with the booties. Now the question is do I get a second one for UAT, and what are the measurements needed for that frequency. The first one should be here tomorrow (Saturday) and I already have the BNC pigtail from my existing install. (Panel mount BNC on the antenna-of-shame that’s there now…) I ordered http://www.amazon.com/gp/product/B015J23EYW, for a second SDR for UAT.

One of the things you will get to learn through Amateur Radio is the calculation for making antennas.
Speed (in metres) divided by Frequency (in Megahertz) divided by the part of antenna length of interest.
So, 300 / 978 / 4 (for 1/4 wave at 978 MHz for UAT) = 0.07668 (which is 76.68 millimetres) so cutting at 76mm will be just fine.

All the Amateur bands are often known by their (approximate full wave) metric antenna length i.e. 80 metres, 40 metres, 20 metres … 2 metres, 70 centimetres…

Buy another dongle plus an HF upconverter (Noolelec ‘ham-it-up’ or similar) hook up some random longish length of wire to the centre pin of the coax connector, throw the wire out of the window, install SDR# (SDR Sharp) and tune around 7.05MHz and 14.1MHz and 21.2MHz etc and listen to what you can hear from around the world.
You will find that morse code is still very much alive and was perhaps the first mode of digital communication and the first ‘social media’ !

I have been a ‘ham’ (in the UK) for over 30 years and still enjoy every facet of the varied hobby and wish you well on your ham journey.


I’m starting to get that, here in the States a Technician Ticket gets you CW on 80m, 40m, 15m and phone/CW on 10m. The brilliance though, in an effort to get more people into the fold the FCC removed the requirement for CW, so Technician’s can get licensed without knowing any code. Thanks for the words of encouragement though, I’m waiting for my test before I pick up my first dual-band…

Okay, the new EbaySpider has been up for about a day, and I can say that I really haven’t noticed any difference in performance. That could mean two things: The homemade antenna really actually was pretty decent and was just ugly (lol). The new antenna doesn’t add much to the equation.

Aesthetically the new EbaySpider does look orders of magnitude better than the old homemade, I guess the next step is to start considering amps and filters. I have a cellular tower a city block away, but I haven’t made any waterfall graphs to see what kind of interference it may be producing.

In general I think the cost was worth it.

How about this - not sure what to think:
ebay.co.uk/itm/Antenna-Body- … 1680134183

£20 ($29) for a piece of plastic :open_mouth: . Bring your own 15mm(!) copper tube.

Thanks for sharing all of this technical knowledge. I am working on my receiver and appreciate what I learn from this group.

If you are setting up your system for the first time then you have following options :

(1) Purchase a professional high gain antenna like Flightaware’s from Amazon.com, or Jetvision’s from jetvision.de .

(2) Purchase a low cost low gain MaxRad groundplane (Spider), and trim its elements as described in this thread.

(3) Make a DIY groundplane (Spider or Cantenna). See instructions here Three Easy DIY Antennas for Beginners

(4) Make a DIY high gain collinear antenna (Coaxial Collinear, Wire Collinear, Franklin Collinear). This is not recommended for beginners as most end up with a collinear which is worst than groundplane. You may try your luck with collinears once your system is up & running with easy & reliable groundplanes. The reason is that collinears are highly intollerant to dimensional inaccuracies caused by FLAWED DESIGN or INACCURATE CONSTRUCTION, and need test equipment to tune, which most diy makers lack.

If the length of coax cable between antenna & receiver is more than 5 meters / 15 feet, adding an amplifier becomes necessary, and boosts plane count & maximum range. Even with short coax length, amplifier does improve the plane count & maximu range. Due to high gain of amplifier, it is worth trying lower gain settings of the reciever dvb-t, say 45 instead of max or -10.

For a real life example see here:http://discussions.flightaware.com/post186711.html#p186711

Has anyone tried this antenna from Slovakia?


5/8 wavelength groundplane antenna 1090mhz.
Gain =3 dBd (=5 dBi), N connector

£15.49 + £4.70 Postage to UK

My spider is in the country… just waiting on FedEx to deliver it :unamused:

abcd - I’ve seen those antennas on eBay, just haven’t been game enough to order one …

I have one of those 5/8 wave ebay antennas in my watch list.
Maybe I will hit the ‘buy it now’ …
The seller is stanislavpalo130 and his feedback is pretty good (although nothing very constructive about actual antenna performance).
He also makes other 1090 antennas - check his other items.

My gut feel is it will be like this (but with a plastic radome)
ebay.co.uk/itm/ADSB-1090MHz- … xyoahSXp1d
also sold by Moonraker and Maplins amongst others.


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Yes, This is my feeling also.

The strict 5/8 wavelength groundplane is a high impedance antenna wich will have high SWR for 50 ohm & 75 ohms system.

Addig a coil and a small vertical section on feed side reduces the impedance & SWR, and is most common solution. In the antenna you have linked, this coil is visible. In Salovak antenna, the impedance matching arrangement is hidden inside pvc pipe, and most likely it is also a coil. It requires someone to remove the pvc pipe and see what is inside to be sure.

Yes! I believe that is the one that I have :slight_smile:


My ADS-B page is here: