ADS-B DIY Antenna

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DougJohnson

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Good thoughts on my poor Franklin. I'll take some measurements and microwave a piece of the rod as soon as I can, but life is coming at me right now. In a good way.
Thanks,
Doug
 
Hi Doug,
I too made a 6 element franklin,like you I retro added /soldered the extra bits from an original 4 element version.
I revisted a post earlier in this thread and made some changes to the stub spacing, mine are 10mm at the centre tuning stub and 5mm on the others using 2.5mm2 (around 14 awg) copper wire.
After much rechecking the wire to wire spacing at the stubs and moving the feeder coax routing,(again in a previous recent post in this thread) i got much better results.
Yours looks good to me, maybe try making the non tuning stubs half the spacing they are currently and as said earlier, use another non metalic antenna support medium. Mine is held together with more than liberal use of electrical tape , the support method being several taped together wooden kebab skewers....looks a total mess but I "recycled" materials available to hand. I can change its config/make adjustments quick, its light so easy moved about indoors..and although despite its looks, it works.
Keep on experimenting !
 
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ab cd

Senior Member
Good thoughts on my poor Franklin. I'll take some measurements and microwave a piece of the rod as soon as I can, but life is coming at me right now. In a good way.
Thanks,
Doug
(1) If the rod is made of metal, it will pass microwave test & still spoil the franklin's performance. Never use metallic support tied to elements of franklin.

(2) some paint may not absorb microwave, but only reflect it. Such paint will not get hot, but still spoil franklin.

To avoid trouble, best is to use non-metallic un-painted support.
 
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airbus340

New Member
Thank you for the welcome!

I dont have any pictures, will try to make some, but its just a normal Franklin. The stacked dipole is two dipoles one wavelength apart center to center.
First I tried the standard 68 mm but I read that 5/8 elements will work better so I cut the next version elements to 86 mm. And it was indeed correct, the 86 mm elements work better than 68 mm.

Today my friend came here and we built a new dipole, this time a single dipole with 86mm elements, and put it in a plastic can and put it on the roof. Amazing result, I doubled the range from indoors and it is a lot better than all other antennas that has been on my roof, including the spider.

But now it is a new problem we have to fix, it looks like my metal antenna mast hide the dipoles view completely in some directions... So next step is to change the metal mast to a plastic mast.
 

DougJohnson

New Member
(1) If the rod is made of metal, it will pass microwave test & still spoil the franklin's performance. Never use metallic support tied to elements of franklin.

(2) some paint may not absorb microwave, but only reflect it. Such paint will not get hot, but still spoil franklin.

To avoid trouble, best is to use non-metallic un-painted support.

That's why I chose the fiberglass rod. I just cut off a piece of it. It is not painted, the color is in the resin and goes all the way through. I popped it in the microwave and it does not heat. I can move the antenna to a wooden dowel, but my amplifier finally showed up so that will be the next experiment.
-- Doug
 

ab cd

Senior Member
That's why I chose the fiberglass rod. I just cut off a piece of it. It is not painted, the color is in the resin and goes all the way through. I popped it in the microwave and it does not heat. I can move the antenna to a wooden dowel, but my amplifier finally showed up so that will be the next experiment.
-- Doug
Congratulations for finally receiving the Amplifier!
Did the amplifier arrive by a sail boat or inside a bottle with a note? :D

I recommend moving Franklin to wooden dowel first experiment, and amplifier next step.
 

ab cd

Senior Member
Thank you for the welcome!

I dont have any pictures, will try to make some, but its just a normal Franklin. The stacked dipole is two dipoles one wavelength apart center to center.
First I tried the standard 68 mm but I read that 5/8 elements will work better so I cut the next version elements to 86 mm. And it was indeed correct, the 86 mm elements work better than 68 mm.

Today my friend came here and we built a new dipole, this time a single dipole with 86mm elements, and put it in a plastic can and put it on the roof. Amazing result, I doubled the range from indoors and it is a lot better than all other antennas that has been on my roof, including the spider.

But now it is a new problem we have to fix, it looks like my metal antenna mast hide the dipoles view completely in some directions... So next step is to change the metal mast to a plastic mast.
Thanks for the information. The two stacked dipoles are seperated by one wavelength vertically or horizontally? How are the two connected with one feed cable? Waiting for some pictures & sketches.

I will now try a 5/8 wavelength (86mm+86mm) dipole.

Theoretically 5/8 wavelength (86mm+86mm) dipole has advantage of higher gain and higher horizontal directivity over 1/2 wavelength (68mm+68mm) dipole. However it has disadvantage over 1/2 wavelength that it has much higher impedance than the system impedance of 75 ohms, while half wavelength has 75 ohms impedance, a perfect match to system impedance of 75 ohms.
 
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trigger

Member
I have a picture now, do I have to upload it to some other page and link it here?
Hi Airbus, you can upload the picture directly into a post.
upload_2015-3-29_12-1-8.png
 
Hi Airbus, attach the file/picture using the button below the text box "upload a file".
Then navigate to the stored image on your pc.
 

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DougJohnson

New Member
Congratulations for finally receiving the Amplifier!
Did the amplifier arrive by a sail boat or inside a bottle with a note? :D
I was walking down the street and a mailman handed it to me.

I recommend moving Franklin to wooden dowel first experiment, and amplifier next step.

Nope. The amp is easy and I've waited too long. I suspect the spider and the amp will show everything out to the horizon anyway. I did look at the Franklin and find the tap is not where I had measured the optimum. Perhaps it got moved when I put it up. The other measurements were spot on by dial caliper.

-- Doug
 
Thank you for the help!

Here is a picture of my piece of art... :D
Not looking very good compared to other antennas in this thread, but it perform great.

Hi Airbus,
It doesnt have to look good ..of it works well, good enough ! :)
I think you said earlier that the dipoles are 1/2 wavelength apart, but in the very grey matter some where ..I think perhaps 0.8 of a wavelength taken from the centre of the dipoles gave best results (this was some years ago when a friend/fellow amateur constructed one for 70cms) .
I maybe wrong though.
Perhaps ab cd could clarify.

Perhaps you could take a close up of the connections and provide some design notes so we can all try your design , I have some radio antenna construction bits in my "junk box" , I am not alone, others on this forum do have such "junkboxes" ,often stored away, stuffed full of useful stuff for a rainy day.
We like experimenting ! ;)
 
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ab cd

Senior Member
@trigger:
Hi Dave!
Nice that you finally decided to use a profile picture. Nice one. Makes it easy to spot the post.
379.png
 
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