@volpoon
I fully agree with you that collinears have higher gain and a better radiation pattern than a quarter wave ground plane.
I also agree with you that there is no harm in trying to make a DIY Coco. It costs almost nothing, and does not require too much effort.
The only point of disagreement is rate of success.
What percentage of Novice collinear makers succeed in making a collinear which is much better than a quarterwave groundplane?
My experiance tells “only few”.
Image 1 of 3 - Simulation results of 8 element Coco
The way settle the matter of how likely amateur antenna experimenters are to meet with success is for a few folk to have a go at building one. Otherwise we have a guy who say it is unlikely to work, and one who says if you take reasonable care it will work fine. Of course as any electronics kit supplier knows, give twenty men each a bag of components and a soldering iron and some will make grotesque mistakes in building the simplest kit. The warning to take care over whisker shorts at the ends of each element AND watching the video, AND taking proper account of the central insulation regarding velocity factor and element length makes success probable.
I built a very clumsy (no soldering, screws to long, thin copper wire, not one leg really straight or of perfect length) spider antenna with a SO-239 as its base and used it to replace a 30cm coiled wire antenna.
To my surprise, it nevertheless works well with a Nooelec-TV dongle, where it increases the number of planes seen by 30% and more, and puts it almost on the same level as a Flightaware stick with filter and 30cm coiled wire antenna.
However, attached (almost directly) to the Flightaware stick with filter, the spider leads to no improvement at all, it actually seems leads to less planes seen?
Is there any conclusion to be drawn from this, apart from that I am not well suited to patiently building things out of copper wires? Do I have to change gain settings? Rebuild the antenna closer to configuration?
The coiled antenna is supposed to work up to 862Mhz, I think.
It seems that having either the right antenna for 1090Mhz or having a receiver that amplifies and has a 1090Mhz filter leads to better results, but the combination of both has no further effect. Maybe I am already at the limit of what I can do from this location?
I’ll try and see if a change in gain settings changes this.
Spider need not be elegant looking like a fashion model.
As long as its wire lengths are fairly accurate (+/- 5%) and wires are fairly (not perfectly) straight, and angle of radial bent-down are nearly (not exactly) 45 degrees, it performs very good.
Spider is dimensionally very tolerant, and that is why it is a success even when built by a novice. Same applies to Cantenna.
But yes, in the end it is not that difficult to make, and it clearly has led to improved results with the standard RTL-dongle, so I guess it is worth the trouble.
BTW I tried changing the gain settings, but so far without any success.
Not yet, but I had seen that, it looks fairly easy to build and you basically just need a coax cable.
A quick additional observation, I tried the spider + Pro Stick without the filter, my impression is that this has increased the maximum range, I am seeing planes that are further away that I did non see before.
The total number, however, still eems to a bit lower than the other combination of NooElec stick + spider and the Pro Stick + Filter + coiled antenna, but maybe that’s just due to changes in traffic patterns.
The best part about this antenna is it’s deafness to frequencies that are out of band for ADSB. It’s easy to make so that it’s got a good SWR (about 1.5) at 1090 band and it all but completely attenuates anything below about 900. MUCH easier to build right than a Colinear Coaxial with better bandpass characteristics.
This helps to keep the receiver from dropping it’s AGC when it gets bombarded with extraneous noise.
EDIT: Can’t recommend this design enough for a simple and reliable antenna that you WILL probably make correctly on the first try. If you’re trying for maximum gain - Yeah, build a COCO. Just be prepared for a “learning experience” or two.
Build one of these FIRST so you have a decent antenna to fall back on while you troubleshoot your quad or eight element coco.
I’ve got a half decent external aerial on the way which will go up nearly 30ft in the air but wanted something temporary just so I could get a feel for things.
So I knocked up a spider with six legs and hung it from my curtain rail with cable ties.
It’s working remarkably well considering it’s thrown together and indoors. I’ve been a radio ham for over thirty years so I shouldn’t be surprised when a resonant aerial works so well but these things still amaze me. I’m getting reports up to and slightly over 200 miles with that.
I came across a very EZ, accurate and SAFE way to cut the can for a cantenna.
Cut a small piece of wood the height desired.
Place a razor knife across the top of the wood
Grasp the can by the top, away from knife and hold agains the knife blade
Turn can until it first is scored, then cut.
I am wondering where to position my antenna in the attic.
I just moved it there from a windows facing westwards, it now it sits in the middle of the attic, ca 1,50 from the top of the roof, pretty much in the center of the whole building, which is rectangular. The reason for this is that on either side is a relatively small windows. This way, I thought, it can “look out” of both of the windows.
Now get a lot more positions and planes from the East, but I am wondering if it might make more sense to
a) put it as close as possible to the top of the roof, even if that means that there is no line of sight out of the windows
b) put it away from the windows, closer to the gable, so it is close to the outer walls/roof on three sides?
I could try this out and maybe I will, but I also would like to have a better theoretical understanding why one of the locations is better than the other.
Open the window. use a hot-glue-gun, or a clamp, or whatever to position it OUTSIDE the window.
Then, get a hunk of foam rubber, and close the window on that to keep the rain out, etc. (this is assuming you’re unwilling or unable to drill a hole in the window frame…)
Then, if you want to get REALLY fancy, get another pi, and another rtl-sdr, and put another antenna on the outside of the window on the OTHER side of the house… I know, I know, shear insanity.
Ok, so after two weeks of testing with both the pro-stick with filter and without and the pro-stick plus, I can conclude that, with gain settings at auto, the cantenna does not appear to need a filter, at least not in my relatively rural area.
Thanks for the suggestions, it seems people are opting to mounting the antenna as high as possible and as close to walls.
My assumption was that the signal travels more easily through glas than wood and clay, so a position closer to a window is better.
However, being closer to the windows to the east increases the distance to the window and roof to the west, so fewer signals are picked up from this direction.
I’ll try to move closer to the top, closer to the walls, but at a greater distance to the windows that are basically on the same level as the floor and see what happens.
Outside is no option at the moment, I haven’t got the right antenna for that. Several Pi would be, a have a small collection of them…
