Collinear Antenna Help


#1

So 2 weeks into my ADS-B experience, I decided I wanted to try and build a Collinear Antenna to try and increase my range. I watched several videos and read the post on balarad.net/. I have managed to get 2 segments together but can’t seem to get the 3rd without that lovely buzz from my multimeter. I admit I don’t really have any idea what I am doing. This is all foreign to me. I am wondering if the quad core cable is giving me trouble or the straight edge knife I am stripping the coax with? Anyone had trouble with this? I’m using a RCA Digital Plus Quad Shield RG6 coax from Lowes.

Thanks,
Brian


#2

Brian, I have had similar issues using the same RG6QS cabling from Lowes using the balarad.net instructions and here is what I did:

  1. In cutting of each segment, I made sure there were no external strands which may contact the inner copper wire. I used an Exacto knife to go around the inner plastic core and made sure there were no strands which may cause a short.

  2. When joining the segments together, make sure there is electrical tape between the two segments to further provide insulation.

  3. In the assembly of any two segments, again I double checked that there were no external strands of the shield which may be in contact with the copper core wire. It is critical that no little strand of shielding create a short. Make sure there are no strands on the tape you may have accidentally picked up. They are wispy and anything can work against you.

  4. Make sure the inner copper core wires do not kink inward and touch when pushing them into the shield. I know this sounds obvious, but I did have an occurrence where this had happened when the slightest gap was inadvertently left when assembling two segments.

  5. I found it more helpful to make 4 sections of two elements, test each one and then begin to assemble the two elements together. So then I have 2 sets of four elements, which I then joined together to make 8 elements. To me It just seemed like less hablding of the entire cable, bending/stress/etc.

  6. It was helpful to me to “heat” the cable to make the wire insertion easier. I left it out in the sun on my car for 10 minutes (Las Vegas) so it got more than hot enough and pliable to insert. You can use an oven and set it on like 150 degrees for 10 or so minutes to heat the cable segments up as well. Be careful when inserting the two segments together; I have a small hole and slice in my finger where the cable pierced the plastic shell and somehow found it way into me!

  7. Maybe I did just get lucky my first time assembly.

  8. With the 8 element collinear coax I built I found dramatically improved results over the supplied base antenna with my R820T dongle. However, I did build a 1/4 wave ground plane antenna with 4 bolted radials (from directions within this forum) which outperformed the collinear. It is easier to construct and I have been having better reception. I have a few tips I can share on the quarter plane assembly as well.

I have only been doing this for a month, so have similar issues and learning day by day.

Thanks,

Brian R


#3

Hello

Be sure that the elements are the good lenght
I cut pieces of 15cm of coax and then strip 2 cm of the coax on both sides, so the element is 11cm
i used this video to build the antenna https://www.youtube.com/watch?v=TkUYdCPFXXs.
that worked for me.

A collinear antenna is not the same antenna as a gp or groundplane a collinear looks to the horizon and a groundplane also looks a bit up to space.
so a colinear can look furter then a groundplane antenna it will increase your recieving path
Dont worry about the planes above you there signal is hard to see them anyway
But a collinear must have free sight if there is a wall or tree or building that will block your signal you wont see much from that direction.
a 1090mhz signal is not able to go tru a wall
and a nice addon is a preamp that will increase your reception big way

i hope it helps you a bit to get a good antenna

(sorry for my english its not that good)

Edwin van den berg


#4

I agree with everything Brian R has said. I make a “pocket” by gently pushing the end on the multimeter lead between the outer insulation and the braid. Leave it for 5 minutes and there is space to insert the cores.

I stopped adding the insulation between the segments as I found it too fiddly. I just leave a gap of 1 - 2mm. I’m not sure if this has any effect ion the segment length but it works for me!

Good luck :wink:


#5

When I made mine, the copper wire in the center was not bonded to the insulator. (not sure if this was a defect) This enabled me to push/pull the center wire through far enough that I could just do a clean cut of all the other layers at the exact length I wanted. (111.4 for the velocity factor of my particular coax) After this cut, I pushed the wire back through and assembled the segments. Made for much cleaner cuts than trying to use a typical coax stripper.

I checked all segments for shorts before assembling them, and checked for continuity after combining each segment.

Cheers!
LitterBug


#6

I decided one Sunday morning to put together a coaxial collinear antenna from scraps I had laying around. Decided on 8 elements, cut everything up and assembled on picnic table. Found some heat shrink tubing which fit nicely over the cable pieces and some left over silicon caulk. I applied the caulk between each segment junction, slid ~ 2" sections of the heat shrink over each connection and heated w/gun to shrink (displacing some of the silicon out the ends of heat shrink at each junction). Added a 56 ohm resister at the top (closest I could find). Antenna and down lead was all done w/RG-6 SAT coax. Then enclosed everything inside some 1" scrap PVC (capped at top). Mounted the PVC to my fence 4x4 post (top approx 15’ AGL), and began pulling in more than 3x hits over the little antenna stuck up at the same height. Here in S.FL I wanted to keep the element junctions sealed from the high humidity, this seemed like an inexpensive way to accomplish that. Will have to see how it holds up over time (but it’s all inside the PVC).

If you live in an urban area or near a cell tower, do not underestimate the value of a band pass filter. My first one was made out of copper foil tape stuck down to a piece of plastic (solder quickly + carefully). That alone doubled the daily number of hits (+ at no cost).


#7

Ken,

Great write-up many thanks. Did you check the antenna worked before you shrink wrapped it and put it in the PVC? :open_mouth: :open_mouth:

Could you elaborate on the band pass filter? Drawings/pictures would be very helpful to us all.


#8

Take a look at this (rather lengthy) thread which includes filters. :slight_smile:
ads-b-flight-tracking-f21/built-my-first-antenna-and-doubled-my-coverage-t19517-425.html


#9

Hi triggers,
I use a satellite TV diplexer as a sub 900 mhz filter, this increased my adsb msg rate

A few of us on the plane finder forum use them hooked up to 1/4 wave spider antennas to good effect, here is a practical example with photos.

forum.planefinder.net/threads/ad … #post-4491

The diplexer is a simple, cheap and useful station addition.
Different makes and types have differing insertion values.For ADSB just make sure you use the “sat” side only.
They normally have power pass in this direction so you can add powered amplifier later if you want to

You could use the diplexer as a filter in the feedline to your coaxial co linear (coco).

Hope this helps.

Mike

flickr.com/photos/45436646@N08/


#10

Hi Radiostationx and joeywiley,
Thanks for the links. I already have a diplexer in the chain as well as an amplifier and homemade power inserter. I tried coax stubs to reduce some interference at 950Mhz but it also cut my number of planes :unamused: I’ve taken them out again.

I was intrigued by the use of a piece of copper tape stuck to a bit of plastic.


#11

Yeah, I did check for continuity as I was putting each segment together (between the shield and inner conductor) just to make sure there was no unexpected short. Then along the length (end to end) to make sure there was good conduction along the way. The resistor at the very end makes for a quick/easy check anytime there might be a problem, just read the resistance from the F connector, if it’s close to the resister then all is well w/the antenna.

Sorry, but I didn’t think to take any pictures, and my filter is now potted in epoxy. But mine was modeled after the one here:
rtl-sdr.com/homemade-ads-b-filter/
This design was initially to be etched onto a Cu clad board, but I haven’t done that since i was a kid, and the foil worked really well.
I didn’t have (couldn’t find) all the connectors, and soldered the coax directly to the Cu foil. It took no more than an hour or so to complete, then sunk it into epoxy a few weeks later while I had mixed up a batch to pot another project.

Here’s another idea: Aluminum foil tape is readily available at most hardware stores. Of course the main problem is soldering to the Al, but the stuff I picked up at HD had adhesive that was relatively conductive (not enough to pass any real current, but fine for antenna mockup/testing). Of course, I’m not sure how that would hold up being cooked in the sun day after day, but makes for a quick and easy way to play w/design ideas. As for electrical connections, just use some small screws.