Greetings! I've been monitoring ADS-B for a few years and have built many home-brew antennas. Some worked very poorly while others worked acceptably. After reading some of the forums on FA regarding Franklin antennas for ADS-B, I built some to the specs that were posted there. They all worked, but not as well as they should. Also as an amateur radio addict, I had experience building antennas for HAM bands, but had never ventured into antennas for frequencies this high. So I went back to the drawing board with the Franklin design, and have come up with one that performs better than the commercial FA antenna. The good news is most folks can build this antenna from junk box parts so cost is very small. At most, you may need to buy a couple connectors (N and SMA). Anyway, using basic formulas based on signals traveling at the speed of light, and taking into account the velocity factor of materials used, I discovered that the specs given on the FA sight were slightly off. The attached diagram is to build a 6-element Franklin for 1090 MHz. If you're familiar with the specs posted on FA and other sites, you will notice that the elements on this antenna are slightly shorter. That's because the copper wire used has a velocity factor of about 95-97%, and previously posted specs did not take that into account. I currently use this 6-element Franklin to feed ADSBx, and have found repeatedly this antenna out-performing the commercial FA antenna! Good luck and have fun! ~A
I forgot to mention in the first message: mount this antenna to a NON-CONDUCTIVE pole. Smaller diameter PVC plumbing pipe is what I use. 1/2" or 12mm ID PVC pipe works well. Also, the picture shows the feedlline being held away from the antenna for a short distance. This is important to avoid unwanted RF coupling back onto the shield of the coax feed. I used nylon zip ties to hold the antenna to the mount pole. ~A
Hello abcd4567, Thanks for sharing that, it has nicely fallen into my antenna quandary at this moment in time, my first thought was what is the pole made from and have just the thing, It is a pole from a redundant VHF/UHF antenna, I found the plumbing pipes are a bit soft and tend to bend especially in the summer. Thanks again, most enlightening. Cheers. Colin
Hi, Firstly I would like to offer my condolences to the Friends and Family of the USAF Air Force Pilot lost today. Not a nice way to start a message but life goes on, people keep telling me anyway, tell that to his Wife and kids. I have a short update on my roof antenna and am now considering it finished and ready to go out on the roof, I have spent the last few days tuning the antenna (that's building a antenna talk for sliding the the cable wires up and down the antenna wire a couple of mm's at a time before soldering them into position). I have had a few problems one being having too many plugins on the Pi and having it's voltage starved, I cured that with a powered USB hub. I was surprised in the effect it had on the signals being received, or not as the case may be. At best with the antenna leaning against my window was about 10 - 15 a/c, I moved it outside onto the front path and the signals shot up to around 30 (the most I received for weeks), outstripping the loft antenna that I use for uploading by almost twice as many. I'm open to any questions (as long as they are not too technical). I would also like to thank MartyS and abcd4567 for their original mails without which this one wouldn't have been made and am now looking forward to it being on the roof. Regards. Colin
Hi all, Well, I didn't expect that, this morning I put my home made Franklin antenna on the roof (attached it to my Discone scanner antenna), I thought the scanner antenna might have interfered with it but no. Not only have my a/c quantity more than doubled but it has also added 50 nm + to my distance to over 200 nm. I was going to put the Franklin antenna away and a little higher than the Discone but I didn't have the parts handy so I used the Discone mount and as the Franklin is on a fibre glass pole I put it there for added strength but now I shall get the parts to enable my first thoughts on a mounting system, and move it away. MartyS and abcd4567 I can't thank you enough it's made a huge difference for me and my hobby and now I actually feel like I am giving something back for the first time. Anybody else thinking of making a antenna, go for it, it does't cost big bucks and the engineering of this one anyway does't have to be spot on, I've just proven that. Think I may go for a Mk2 and make some jigs to be more accurate. Thanks again guys. Colin Happy Hunting
Congratulations Colin on the successful antenna build! Did you build it to the specs I posted, or some other specs? Just curious. Since posting the initial specs for the 6 element Franklin, I have since built an 8 element one and now have it in the air by the house about 25 feet (8 meters) above the ground. It works great! Generally, it has pulled in more signals and slightly greater distance too. The effort seems to been worth it! If anyone is interested in building it, just use the same specs as the 6 element except add two more. Simple as that! ~
Hello abcd4567, Thanks, I built it exactly to your specification and am well chuffed with it, it's more than doubled my local area pickup and added about 50nm on my distance, I did see a drawing where the centre element had a 1cm spacing but I decided not to mix and match and to stick with the one design, My next project is to build a small jig so I can take the 'oh that'll do' out of the making of it and be more accurate with my measurements for when I build the Mk2, which looks like it's going to be an eight element Franklin now. I must get my Mk1 away from the scanner antenna though, which again is on the to do list, I don't think the Wife would appreciate a 25ft pole in her precious garden though, I have one naked gable end and a chimney stack to play with, I'll sneak it up there when she's at work Thanks again and thanks for posting your design. Best Regards. Colin
Hi abcd4567, How this design is different from your (I assume it was you) experiments a few years back (planefinder ads-b-diy-antenna.23 post-333)? Right now I'm running 10-element coax collinear antenna and curious if this design could improve my results. Regards, Vlad
Hi @abcd4567 Thanks for sharing this (and all your other designs) I built a couple of 4-elem Franklins following the "original" instructions found elsewhere (elem length of 138mm (67+4+67), with a slightly wider coupling/impedance stub of 143mm (69+5+69)), of which the first one wasn't too good, but the seconds one (built to better precision using un-insulated wire) works quite OK; on a no-name dongle it picks up 70-75% of what the Blue FA stick on the FA antenna does, sitting a few m from each other). Before doing the Franklin(s), I had built a coco antenna out of coax, and from initial testing it looked to perform quite well, but the mechanical construction was not good so I removed it again for the Franklin. I also tried a Cantenna, but that performed worse than my initial "supplied antenna with additional GP". Based on the success with the Franklin, I tried to build the 8 elem version of the one here. I built two, the later one again being more precise (I made a "model" by sawing tracks in a piece of wood and used that to form the elements) -- but none of them were good. They seems to perform some 8-10 dB worse than my 4 elem. I'm sure it's partly my inability to make it precise, but I'm wondering if there could be something else too. 8 elem is of course less tolerant -- would you suggest that I try to cut it down to 6 elem and test that? Or could it be the coupling that needs to be better adjusted? Or would it make sense to try to open the stub (i.e. making it look almost like two dipoles)? Rgds, -- Per.
For what it's worth, I built a 6 element Franklin type antenna to abcd4567's design and was astonished at the extra range and a/c quantity, and I must confess it wasn't what you would call precise so I think there is a bit of leeway in that area. If the Open Sky polar map is to be believed on some days I am getting over 400km just had a look again and it is around 360km today, not sure what that is in mph. but it's way over what I was getting. I still intend to build another but this time more precise and did think of going for the 8 element but I'm torn between the 8 and 6, height seems to be as important as anything as I'm sure you know. abcd4567 did say he was going to build an 8 element and I see he has done it and pleased with it, so, 8 or 6 that is the question, going to build some sort of former first though this time round. Thanks again abcd4567 for sharing this with us, couldn't be more chuffed with mine. Regards.
abcd4567, Have you posted the lengths for a 978 antenna? I looked for them but have not found it. Thanks.
Have you or anyone tried to build this using printed circuit boards? It seems to me that it could be very precise that way. I'm willing to try, if there is some guidance on trace width.
