If full wavelength is 346mm then 3/4 is 260mm?
So it should look like: N-connector-173mm-loop-260mm-loop-250mm?
Or perhaps I have missed something fundamental here?
You’re so absolute right. How blind can a man be.
Changed the mid and top piece of the antenna with the new values and tested it with 3 lengths of cable.
Below the results.
conclusion : check, check, dubbel check before you publish something 
None… zilch… ZAP!
Hello,
I made a version of this antenna, but with slightly different dimensions found here:
I also added ground plane, as I read somewhere that that is a good idea. I used 1,6mm diameter single copper wire and 32mm PE drain pipe. I cut grooves in in the drain pipe to get the circular N chassis connector with the ground plane wires sticking out. Then cut a small piece, approx 20mm with a groove, to use as insert to hold the antenna in place, but also to strenghten. I plan to use a joint to extend the pole with the antennae cable going inside. It will be 2 meter cable in to the gateway at my loft.
Tuned the antenna by inside the PE pipe to get good VSWR at 868Mhz:
And this is the return loss (I think) using NA mode:
This all looks good to me, but I am not an expert on antennas.
When I widen the bandwidth using NA mode, I see this:
This may be harmonic, I dont know, or I have made the antenna all wrong?
It was fun making this antenna, so I decided to make the ground plane antenna:
I did this the same way as the collinear using circular chassis N and cut grooves into the PE pipe:
Tuned it in the drain pipe and got this:
VSWR
dB
Next step is to try both antennas and see how they perform using a node.
Maybe I will try the J pole as well, but from what I have read, the Ground plane or Collinear seems to be good.
Make sure your ‘drain pipes’ are RF transparent as though you have worked hard on the electrical matching & tuning many pipes you can buy in diy/plumbing supply shops can be poor RF performers due to materials used, metallic contaminants or use of recycled plastics …just a heads up!
@jeff-uk Thank you for the advice. I first made one using 32mm piping for electric wiring. I thought that would be good as it had only approx 0,5mm WT, compared to the drain pipe which is approx 1mm. Unfortunately when I cut a 10cm piece and put in the microwave it got hot, then the microwave oven died on me! The oven was over 25 year old so I guess it has done it’s job:) The drain pipe is soft, clear white PE, I belive, but I have not been able to test it as I no longer have a uW oven. On the Collinear the pipe made a big jump in resonance frequency, which makes me think it is not that good. I actually planned to use a glass fiber rod and glue to antenna to it and leave it open, perhaps spray it with plastic spray, but decided against it.
I did try this collinear antenna design as mentioned in this post. Can you confirm your design is for a 5/8 - 5/8 - 1/2 wavelength collinear antenna. I would like to know what your performance tests show. You mentioned you changed the dimensions, what lengths did you use and what is the diameter of the loop?
I found out that regular water pipes are bad for RF. However a waste pipe which is much lighter works very well. Those are quite transparent to RF.
@aizukanne
I used this drawing::
Loop dimension is slightly less than the above drawing, as it would not slide in to the 32mm PE pipe with 28mm OD on the loops. Dont think performance change much. The openings of the loops had to be increased when tuning it inside the pipe. I just received the pigtail sma to N yesterday (ebay) and will mount it on the roof this week or weekend. Unfortunately I dont have a portable node for ttn mapping and measurement, however it is on order. In the mean time I’m hoping to see nodes that are approx 20km away, problem is that there is no line of sight, so it is not that likely I will see them. I plan to test with both the GPA and collinear and post results, but it will take some time before I have them.
Thank you for the input on material for pipe, I’ve used drain pipe, so fingers crossed it will perform ok. I also thought about using a ~24mm glass fiber pipe, perhaps cut of the base of an old fishing rod, then place the antenna around it and glue it to the pipe.
I did build a co-linear from on-line plans, I wont say which one, and whilst the antenna tuned up just great on an antenna VNA, it was a dreadful ‘real world’ performer, worse that a 1/4 wave with radials reference.
There are some thoughts on simple real world antenna testing here;
Easy to do if you have a couple of Arduinos with LoRa modules handy, one used for the test transmitter another as a RSSI field strength meter.
@LoRaTracker
Thank you for the input, and the link, very interesting article you written here.
It will be interesting to see how the collinear build performs vs. the GPA. Did you figure out why the collinear did not perform well in the real world? Have you come across other omni DYI antennas that perform better then GPA? I did read some testing on the J pole that looked promising.
Nope, life is too short.
Just remember that in most countries there is a limit on the ERP ( Effective Radiated Power) and adding a high gain antenna without decreasing the output power of the transmitter is a felony.
ERP = TX power (dBm)- cable losses (dB) + antenna gain (dB).
When adding high gain antenna’s your RX coverage might increase (being able to pickup remote nodes over a longer distance) but when you follow the rules and decrease the output power your signal might won’t be able to be received by the remote node.
Maybe this is a candidate:
It is for ads-b, so the dimensions would have to be changes slightly.
Same site also has a version of the collinear:
You can tune an antenna with a simple Arduino based field strength (RSSI) meter, as described in the link I gave earlier.
Granted it can be a bit tedious, but on a nice sunny day over the local park it aint too bad.
Installed the collinear antenna above my rooftop yesterday:
I live in a valley, hence I did not have much hope of reaching nodes over the hills near town.
However this night I got a few packages from two other nodes (Meet Je Stad sensors), distance more than 10km.
Next step is to measure signal using a node appeox 2km away and switch antenna to GPA, to compare.