I have been anxiously looking forward to building a antenna and finally got around to it this morning. It’s really a simple 4-element colinear coaxial (coco) antenna that’s outside my window attached to a bamboo pole. I made the antenna out of RG59, because I have a bunch of it and it’s the first thing I grabbed. I’ll make my next one out of RG6. I used the design I found in the Plane Finder forum here: http://forum.planefinder.net/threads/ads-b-diy-antenna.23/page-18. Go down to post #358. I’m re-posting a copy of the picture here. You have to be a member of that forum to see the full-size picture.
I have cooked up several twitter based projects and documented them there. Just put “twitter” or “tweet” in the search bar (upper left, I think) and you will get some ideas. Post up if you make a breakthrough.
I built this 8-element coco and I’m getting lots more aircraft in the 100-150nm range. It’s located inside for now, but soon it will be outside on a mast. The plans are from ARRL here: rtl-sdr.com/ads-b-virtual-ra … rial-arrl/
I have some doubts about the collinear in the ARRL article.
Firstly, the way the segments are separated by “about 1/8”. On these frequencies there is no “about” and I would prefer no gap with a piece of insulating tape in between.
Secondly the 4,5" whip. I have seen designs with a 1/4 wave whip but that’s not 4,5". Did they meant it to be 1/2 wave but used a velocity factor where they shouldn’t ?
Lastly 4,5" suggests the length is not really critical. But by coincidence a halve wave at 1090 Mhz multiplied by the velocity factor of 0,83 is exactly 4,50". Be sure to check the type of coax you use and look up the exact velocity factor.
/paul
Thanks for the advice Paul. That antenna didn’t give really good results. I’m going to experiment with it a little before I make a new one (without gaps). I’ve already cut the whip off the top, but saw no improvement. Next I’ll probably cut it down to a 7.5 element. I’ll let you know how it goes.
There was a post elsewhere about a multiple segment collinear tested at 8, 6, 5 segments. Reported best results from 5 segment. I run a 6 segment with acceptable results.
Here’s a post of mine from another thread. Very easy to build and no need to ‘tune’ if the measurements are precise enough. I’d like to see if others get similar results.
After a bit of investigation, the interference I’m seeing with the CoCos looks like GSM at 960Mhz. The ‘cantenna’ seems to be pretty narrowly tuned to 1090Mhz and therefore provides a pretty clean signal. If I was to go back to a CoCo, I expect I’d have to filter the signal… but that seems like so much wasted effort when this simple antenna gives great results. Still working on a plan to get it on the roof.
I too built a CoCo antenna. The plans that I used were from http://www.balarad.net. His instructions were fairly clear and made sense to me. I am using an 8 element antenna with each element 114 mm in length as described on the site. The coax cable that I used was RG6 quad shielded (this made pushing the core into the shielding quite a bit easier). There is a 75 ohm resistor on the top that I am using to bridge the shielding to the core. I am not using any of the transformers, lightning protection or amplification that he is using; it’s just simply the feed line to a F to SMA converter which goes to an MCX right to the RTL-SDR dongle. The feed line is no specific length or gaps or anything like that. I am not sure if that would have an effect on the reception.
You can see my other antenna in the back which is a 1/4 wave groundplane antenna. That antenna gave me max range out to about 160 nm but there were some blind spots for some reason. I didn’t really ‘tune’ this antenna, but with a bit of work, I might be able to see about the same performance as the CoCo antenna.
Over the stock antenna that came with the dongle, I more than doubled my coverage with the CoCo. The furthest range that I see at the moment is about 170 nm. The blind spots that I saw with the groundplane antenna are a bit more filled in.
My initial goal was to see over to the other coast and into Georgia, but now I want more. My next step is to build some lightning suppression and mount it outside on the back of my 2 storey house. I would love to be able to fill in some of the gaps to the southeast so that I can maybe see more flights out of Miami/Ft Lauderdale area.
Also, I want to thank user ‘paulmerkx’ for his write ups on his blog about tuning the antenna. Your work is definitely useful.
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Here’s a post of mine from another thread. Very easy to build and no need to ‘tune’ if the measurements are precise enough. I’d like to see if others get similar results.
I was thinking of making a cantenna. Might do it today. Does a Coke can work as well as a Pepsi can?
I made the antenna out of RG59, because I have a bunch of it and it’s the first thing I grabbed. I’ll make my next one out of RG6. I used the design I found in the Plane Finder forum here: http://forum.planefinder.net/threads/ads-b-diy-antenna.23/page-18. Go down to post #358. I’m re-posting a copy of the picture here. You have to be a member of that forum to see the full-size picture.
Check out this video for a detailed explanation of how to build a coax colinear antenna. It helped me a great deal.