Confused about antenna design


#1

So, I finally setup a PiAware ADS-B receiver, using most of the basic equipment listed on the page. Right now, I know my biggest limitation is the crappy antenna that came with the Dongle (I’m right under the SW corner post to ATL arrivals). I was looking at the long antenna thread and got really, really confused.

What I’m looking for in an antenna:

  • Something I can build with just a handful of tools(I have a few cheap kits) for under ~$50
  • something that can get my range and messages up significantly
  • Something I can put indoors, either in my attic or near a window
  • Something that I don’t have to physically attach to the house(it’s a rental)

I’m not very familar with electronics, in terms of building them, but I do enjoy software development. I’m just looking for fairly straight forward designs that I can follow from beginning to end, to be able to connect to the dongle. Would appreciate any assistance.


Any suggestions for improvement?
#2

Get some coax for cheap and build a colinear one. Just attach it to a piece of pvc to start with some tie wraps. Place it in some different locations for testing. Then let your imagination flow on how to mount it. Once you have the antenna tested then use the pvc to put the coax inside of.


#3

Start with a ground plane – a single vertical piece of wire and four radials sticking out from the base. That will get you started with fabrication, dealing with connectors, soldering, all the other issues. That will also help you establish a performance baseline.

Then look at other designs, like the oft-mentioned co-linear designs. The bad news is there’s art as well as science in antenna making. The good news is at these frequencies antennas are small and easy to fabricate (well, the tolerances get tight, but they’re doable). And your PiAware stats help you measure what’s happening.

Try things. Keep notes on what you try and the results you get. Check out local libraries, looking for amateur radio books on antennas. A very good, very pragmatic book is the “VHF/UHF Manual” published by the Radio Society of Great Britain (RSGB). It has wonderful sections on antennas, loaded with pragmatic information on building them. The American Radio Relay League (ARRL, the United States ham radio organization) also has books on VHF/UHF antennas.

And you can model and simulate for hours on end, but models and simulations don’t hook up to receivers and bring in signals. Cut up some wire. Bend stuff. Solder stuff. Test how well it works. Try some more.

You can also look around on sites like eBay for GSM antennas that cover the 900-950 MHz band – many of those work nicely at 1090 MHz. For $10 or so you can get a fold-over rubber-ducky style antenna with 6 to 9 dB of gain. Add a few bucks for the necessary adapters, connectors, and cable and you should have something reasonable for use inside or in the attic.

Have fun – and keep asking questions.

bob k6rtm

I’m still confused about antenna design as well!


#4

Try this simple indoor antenna: the "Cantenna"
It requires only a drink or food can, dia 65mm or more, a barrel connector, a piece of core wire of Coax cable about 90 mm, and a small piece (100mm to 150mm) of Coaxial Cable with two F-connectors.

.

DIMENSIONS

BARREL CONNECTOR & WHIP DETAILS
You can use either left one (non-solder barrel connector) OR right one (solder type panel mount bulk head)

CONSTRUCTION STEP 1
Cut the can 69mm as shown in above sketch, and drill a hole in the center of bottom.
To avoid sharp edge after cutting, cut the can about 30 mm longer than 69mm, then fold this extra 30 mm inside.
See the very first photo on top .

CONSTRUCTION STEP 2
Assemble the barrel connector & Whip to the can.
After fixing in position, trim the whip length to 69mm as shown in above sketch.
Fix F-connectors to both ends of the piece of coax (about 100mm to 150mm).
Screw one end of this piece of coax to barrel connector inside the can. Connect your feeder cable to other end using one more barrel connector.

ANOTHER EXAMPLE OF CANTENNA MADE FROM BEANS CAN (By giacomo1989)
Steel cans are harder to drill hole & cut compared to Aluminum cans


#5

The signals don’t easily pass through roof tile and glass does attenuate the signals too.

If you can find a way to get your antenna above roof level with and all around view of the sky, it will make a big difference - The simple antenna is lightweight and you may find you can fix it to a bamboo cane or something that is clipped to the rainwater spouting.

If the height to achieve is - maybe - as little as 5/6 meters - maybe you could fabricate a lightweight mast in the garden / yard to support the antenna (I’m thinking stout canes cable tied together to give height, nylon cord guy wires, screw in tent pegs - the first storm will blow it over but it would be easy to stand up again)


#6

Take a look at this thread http://discussions.flightaware.com/ads-b-flight-tracking-f21/built-my-first-antenna-and-doubled-my-coverage-t19517.html. We’ve been through a lot of designs and discussion there. As for the cantenna, I’ve made a couple and can vouch for them. Super easy and effective.


#7

Has anyone compared the CoCo and Cantenna? I’m interested to boost my ‘massive’ 10-20mile range with the stock antenna - with a home made one, but not sure which one is better?


#8

Just putting the simple supplied antenna outside will get you 75 miles if there are no trees and hills in the way.

The main restriction on the supplied antenna is that it has a very short connection lead.

Make a simple antenna aboude a ground plane (cantenna, or with the downward pointing wires on the ‘Ive improved mey reception’ posts.

The main disadvantage of the cantenna outside is water will pool in the hollow.

Get the antenna outside, and elevated above the clutter of rootops, etc - and you’ll be rewarded by something like 150-200 mile range.

One thing you will need is an MCX converter so you can connect your download to the dongle for example ebay.com/itm/281103060434 - what you need depends on what plugs you use on the coax.

also see rtl-sdr.com/adsb-aircraft-ra … h-rtl-sdr/

(a dipole can be made by just pulling the centre out of a length of coax, then trimming the shield (pointing downwards) and core (pointing upwards) to 68mm each)

Experiment and reap the rewards.

I’d start with something simpler than the coco.


#9

The problem, and you’ll find much discussion about this here and elsewhere, is making a proper coco. It’s tricky to get the element lengths just right. You should have the manufacturer’s specs on the coax you’re using so you can find the velocity factor, or VF. That determines the element length. Go with the cantenna or ground plane (spider) for starters. Much easier and rewarding. Here’s a cantenna with a flat top. As PeterHR said, the soda cantenna has a hollow at the top which collects water. This one is made of a dog food can and won’t hold (much) water on top.


#10

The Coco is very alluring as it is so simple and easy to make, and needs only a piece of coax, cutter pliers, stailey knife, and a measuring scale. This also applies to wirecollinears consisting of vertical limbs connected to adjuscent elements by coils.

The problem shows up only after it is built and put to use. Most builders get a performance far below what is claimed or expeted.

All Collinears are tricky to make, specially by a DIY novice. The collinear category includes Coaxial collinear (coco), the coiled whip, and Franklin dipole.

The reason being that collinears are multi element, which requires phasing elements to connect the vertical whip element. Franklin uses stubs, coiled whip uses coils, and coco uses core wire of coax to do the phasing.

The phasing elements are very sensetive to dimensions. Only a few mm error in ill-designed, or poorly built collinear can push collinear from excellent to poor category.

All antennas with one ¼ wavelength limb (68 mm for ads-b) pointing vertically upwards, connected to core wire of feed coax AND a support element connected to shield of coax, give good results compared to whip supplied with the dongle. These antennas are not very sensetive to dimensional errors. I recomend these to be used by beginners. They can try their luck with collinears at a later stage.

The supporting element connected to shield of feeder coax can be either of the following:

(1) Radials: 3, 4, 6, or 8 horizontal wires ¼ wavelength (68 mm).

(2) Disk: A sheet metal disk ¼ wavelength radius.

(3) Slanting Radials (Spider): same as (1) above, but legs bent down 45 degrees. Users reported 8 legs better than 6 or 4.

(4) Disk+Sleeve (Cantenna): A metallic can, 65 to 100mm dia, cut to height 69 mm, bottom up, with hole drilled in center for barrel connector to connect vertical up limb to the core wire of coax.

(5)Dipole: A second ¼ wavelength limb, pointing downwards. The feed coax arrives at the dipole horizontally at mid-point of dipole.


#11

This adapter will put all the weight and pull of heavy coax from antenna, on the delicate mcx female socket of DVB-T dongle and most likely damage it in due course. A better option is to use a pigtail.

http://m.ebay.com/itm/150473818169


#12

Applause! Whistles, clapping, and stomping of feet! Enthusiastic agreement!

–bob k6rtm


#13

I must have gotten lucky on my first attempt, but I did measure it down the wire about 10 times to make sure I had everything right. Simple to make.


#14

Thank you for the post mr abcd567, very comprehensive and detailed! I will definitely try the cantenna first. The added advantage of the coco seems that you can hide it/enclose it to look more attractive - over the cantenna.


#15

Me too. I made two coco’s and measured and cut meticulously. Also checked continuity after I added each element. Still, the results were disappointing both times.


#16

As they say, YMMV. I have a spider GP on the roof at home (site 2394) geographically challenged in a valley, and a 6 segment coco (site 407) on the road this week and last. The coco has been very good to me, so I think I inadvertently did something right. As someone mentioned the connecter on the dongle is delicate, and I use a pigtail (amazon.com/gp/product/B00CTJ … UTF8&psc=1) to take the strain. I am in awe of the quality and quantity of information that has been posted, and eagerly await the next installment. To anyone thinking of making their own antenna, jump right in!

Many thanks to all the contributors.


#17

You guys won’t believe the amount of work this guy has done designing and building home antenna(s) - there is a section in the FR24 forums running (probably by now) 300pages on antenna design and abcd5678 has been the major contributor there.


#18

I have done all three; coco, ground plane and the cantenna. All have been in my attic. I have had the best range and position count with the cantenna, then the ground plane and last the coco. With the cantenna, I have occasionally picked up aircraft on the ground at KORD. I am 8 NW of KORD.

Marty

https://dl.dropboxusercontent.com/u/14758318/IMG_0522.JPG

https://dl.dropboxusercontent.com/u/14758318/cantenna.jpg


#19

Forum member jepolch has built and tried 4-leg & 8-leg Spider, and reported 8-leg one gives better performance than 4-leg.

**Your Spider has 4 legs. I suggest you add 4 more legs. **


#20

You guys are going to make me build a cantenna now. Hmmm… Clean the shop or make an antenna?