ADS-B DIY Antenna

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ab cd

Senior Member
OK thanks. That clears up my confusion. I can start on the Franklin now. :)
The phasing stub is actually a ½ wavelength section, collapsed over itself, so the total length of phasing stub (i.e. upper horizontal+bend+lower horizontal) is equal to ½ wavelength exactly. So the length of wire before collapsing it into hairpin should be 138mm.

For matching stub, horizontal distance from start of stub to tip of bend should be ¼ wavelength. So the total length of wire = ¼ wavelength + length in bend+ ¼ wavelength = ½ wavelength + length in bend i.e. 138mm+length in bend. That means the length of wire in matching stub is 138mm + center-to-center gap, i.e few mm more than ½ wavelength.
 
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jepolch

Active Member
The phasing stub is actually a ½ wavelength section, collapsed over itself, so the total length of phasing stub (i.e. upper horizontal+bend+lower horizontal) is equal to ½ wavelength exactly. So the length of wire before collapsing it into hairpin should be 138mm.

For matching stub, horizontal distance from start of stub to tip of bend should be ¼ wavelength. So the total length of wire = ¼ wavelength + length in bend+ ¼ wavelength = ½ wavelength + length in bend i.e. 138mm+length in bend.
Great info. And for the coax connection, do you still favor using a terminal block to connect to the matching stub, or solder directly at 55 mm from the opening?
 

ab cd

Senior Member
Great info. And for the coax connection, do you still favor using a terminal block to connect to the matching stub, or solder directly at 55 mm from the opening?
For coax connection, I prefer terminal blocks as it the flexiblity to fine tune by moving it +/- few mm. Once optimum position is found, the terminal blocks can be removed and the coax soldered directly to stub wires.

EDIT: To insert & remove terminal blocks, the matching stub should be cut at the bend, then soldered after placing/removing terminals. This will mechanically weaken the antenna, and not preferred for outdoor installation. For outdoor installation it is better to keep antenna in one piece, and solder the coax.

It is better to use terminal blocks for printed circuit board, as the terminal spacing is 5mm center to center. If electrical wiring terminal blocks are used, these normally have a center to center spacing of 10mm, resulting in stubwire spacing of 10mm, larger than stub's 6mm center to center spacing (center to center spacing=wire dia+surface to surface spacing =2mm+4mm=6mm).[/color]
 
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ab cd

Senior Member
For mine, I milled a wooden shim 4mm thick. It made it trivial to get the spacing right. Just bend the wire around the shim.
-- Doug
Last year forum member "trigger" used the same technique, and was able to make a successful Franklin. I hope Dave (trigger) will come up and provide valuable guidance from his experience.
 

jepolch

Active Member
For mine, I milled a wooden shim 4mm thick. It made it trivial to get the spacing right. Just bend the wire around the shim.
-- Doug
I've just been practicing using a 4 mm drill bit. I found that using that as a jig, the opening always comes out too big. I'll try tomorrow using a 3.5 mm and see how it comes out. When I find the right size, the bends should come out nice.
 

jepolch

Active Member
For coax connection, I prefer terminal blocks as it the flexiblity to fine tune by moving it +/- few mm. Once optimum position is found, the terminal blocks can be removed and the coax soldered directly to stub wires.

EDIT: To insert & remove terminal blocks, the matching stub should be cut at the bend, then soldered after placing/removing terminals. This will mechanically weaken the antenna, and not preferred for outdoor installation. For outdoor installation it is better to keep antenna in one piece, and solder the coax.

It is better to use terminal blocks for printed circuit board, as the terminal spacing is 5mm center to center. If electrical wiring terminal blocks are used, these normally have a center to center spacing of 10mm, resulting in stubwire spacing of 10mm, larger than stub's 6mm center to center spacing (center to center spacing=wire dia+surface to surface spacing =2mm+4mm=6mm).[/color]
I hear what you're saying about the terminal blocks. I actually don't have any, but I may get some on ebay. It occurs to me that terminal blocks are cheap, so once you're done with them you can just cut them off with wire cutters. But that still leaves the matter of getting them on. I guess you could put them over the wire before you bend it, or maybe you can just thread it around the bends? Hmmm. :rolleyes:
 

giacomo1989

Member

ab cd

Senior Member
Same here. Wind at 100km/h . 9000 families are without power and two mayor wireless carrier are down at the moment. I wanted to test my antenna in this conditions. (Someone is thinking about static charge?)

A person died cause a rock felt on his car during driving :( :( So sad. There were fences in that place but the rock jumped them.
Tragic to hear people suffering & dying due to natural catastrophes!
 

trigger

Member
Last year forum member "trigger" used the same technique, and was able to make a successful Franklin. I hope Dave (trigger) will come up and provide valuable guidance from his experience.
I built several Franklins and each new one was better than the last. Measurements MUST be accurate. It seems that any collinear must be built with mm accuracy otherwise they don't perform.
I split the terminal block down to single units and slipped them on the wire before bending. The bends I did over a 4mm drill bit like jepolch. Then I made a wooden 4mm shim and then with a pair of pliers, gently persuaded the wire parallel. I found the tap was exactly where ab cd's theory said it would be.

I mentioned elsewhere on this thread that when it rained the gaps filled up with water and altered the gain. I then moulded the stubs around a 20mm piece of pipe to make them circular with the intention of slipping the antenna into a radome. I never finished that experiment :rolleyes:.

Krain's Franklin is a thing of beauty.
 

trigger

Member
Reply is late, but better late, than never....try Yagi
You can start with the simplest first: the 3 element Yagi (pictures at left & center below). Later you can build Yagi with larger number of elements (picture at right below).
Yagi Calculator: http://www.k7mem.com/Electronic_Notebook/antennas/yagi_vhf_quick.html

Yagi-Uda Antenna

View attachment 612 . View attachment 613 . View attachment 614
There are several calculators I've found for building a Yagi and they all give slightly different measurements for the element lenghths. I've built a Yagi according to the measurements in the link above but it doesn't seem very directional so I'm wondering if the measurements are correct. The image on the left is for you Imperial folks and the other is Metric. Non-metallic boom (square conduit). elements are 1.8mm copper wire.
upload_2015-3-5_19-45-31.png
upload_2015-3-5_19-46-8.png


The driven element is a dipole, not a folded dipole
Any thoughts/comments?
 

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jepolch

Active Member
Another Franklin

By FR24 member lutorm
See his post #993 on page #100 (click here).

The Franklin is at the edge of arm on right side of the big 2-meter band j-pole.


View attachment 1270
Thanks for all the info and pictures. I didn't get started on mine today. I had to replace my router. Actually, I put my previous one back in service because my new one is acting screwy.

I just ordered a Raspberry Pi 2!
 

Sjacket99

Member
Thanks for all the info and pictures. I didn't get started on mine today. I had to replace my router. Actually, I put my previous one back in service because my new one is acting screwy.

I just ordered a Raspberry Pi 2!

Kool. I still need to get a new Pi also. I had router issues and not your having router issues. Must be the year for that.
 
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