Step by step construction from cutting the coax sections to the correct length, soldering together then potting. Measuring the SWR and on air testing. From a New Zealand amateur radio article with the link at the end.
I built one of these antennas from RG393. (Of course I modified the dimensions accordingly) Thanks for the video it helped me to find a good way of building the elements.
Hi Simon, thanks for the compliment. I am located in Sydney and a lot of the video was shot on hot summer nights. Had to cut out the stubby of beer in the background!!
Jonny, can you please post a CLEAR copy of this PDF article? all the copies on line on the ZL sites have the key page in terrible resolution that is a copy of a copy of a copy till its useless.
Hi Jonny, that's just the DIY-Project, I was looking for. I want to build a LoRa-WAN-Antenna for Europe tuned for 868 MHz and approximately 9 dB. Buying is too expensive and I want to tune it perfectly to 868 MHz. Would you please tell me the exact measurements of the coax pieces or the way to calculate it for my own. And : What effect has the piece of copper at the bottom and in what distance it has to be soldered ? Many thanks, Ulrich from Germany
You can calculate the element length in inches using the formula 5904 divided by the desired resonant frequency of the antenna, times the velocity factor of the coaxial cable. I used RG-213 with a velocity factor of 0.66 or 66%. The copper tube is a coaxial sleeve balun to prevent RF travelling back down the coax braid. It should be 1/4 wavelength long and connected 1/4 wavelength down from where the feed line attaches to the first element. Here is a link to the original article. zl2vh.org.nz/assets/pdf/other/23-cm-band-fm-repeater-specs-rev-2014.pdf
Jonny, thanks for your answer. I just calculated a bit and recognized, that the antenna will get rather tall (90,2 cm). Would it be possible, to make the 1/2-wavelength-pieces only 1/4 in length and therefore the 1/4-pieces in to 1/8 length ? Would make the antenna only half long (45,1 cm). But what is with the frequency (868 MHz) ? Will it fit also ? What do you mean ?
Hi Ulrich, it’s a physics thing, it won’t work if it’s not a half wave length. You could make a ground plane antenna, four 45 degree sloping 1/4 wave radials and a 1/4 wave vertical. Not as much gain as the co-linear but still good.
@@Jonny10001 Thanks, I already built a ground plane antenna. Works fine, but I want more gain. Okay, then now I will start my project with your co-linear. I'm curious about the efficiency and the results.
Hi John, I used 9913 coax, about 10 meters from the antenna to the receiver. The 23cm band seems to propagate much better then most people realise. I was was able to receive the distant beacon with the antenna inside the shack when testing even though there was a brick wall in front and a metal roof above!
@@Jonny10001 Thanks very much for the reply!.. Ok I thought the coax would be something like that. I did a lot of S-Band work when there was such a thing as an Molniya orbiting AMSAT and pretty much 9913 was a min so I have some about the place. Yes 23cm interesting band, have been building a UHF tripler using a triode and can trigger a repeater with the output connected directly to a big fat dummy load, go figure. Great video thanx again
You have to scale the dimensions up by a factor of 8.4 but it then becomes to big to be practical. Have a look at helical filter designs, they suite the lower frequencies better.
The link to the original article has become unreadable. I have scanned in my copy of the plans and have uploaded as a PDF to Google Drive:-drive.google.com/drive/folders/1uTDLnGHStLtSZtjEc7XKe_ERZeFjlOXX?usp=sharing
at 7:20 you talk about "a specific distance" that you solder down here. In this video, you miss all the key dimensions that make the difference. You incorrectly make assumptions that the view has the same resources as you and that's incorrect.. You missed a teaching moment in describing what you were doing and the measurements and how you came about those measurments.
I didn’t design the antenna I built it from an online article by a ZL group which shows all dimensions in detail. My aim in the video was to show construction methods and give tips to aid completion. I don’t know why the original article has become hard to read but I have uploaded my copy to Google Drive, see link.
