ADS-B DIY Antenna

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ab cd

Senior Member
@ab cd: You do a lot of antenna simulations based on the spider design. You usually start the radials from the corners of the flange, right? So does your program calculate the length of the radials to include the width of the flange, or does it do it based on the length from the edge of the flange? Could you do a simulation with the radials beginning at the base of the whip and compare it to a model where the radials start at the edge of the flange? Rough sketch:
View attachment 2067

Here are two simulations you requested:

1. NO FLANGE:
http://forum.planefinder.net/threads/ads-b-diy-antenna.23/page-141#post-4242

2. WITH FLANGE:
http://forum.planefinder.net/threads/ads-b-diy-antenna.23/page-142#post-4258


models.png
 
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caius

Member
Haha, just been listening to Heathrow approach - Controller says "How is the weather looking by the Lambourne hold?" pilot responds "Er, bad".

Planes going all over the place today:

storms.PNG

Here's the edge of what they are trying to avoid. It's right over the top of one of the Heathrow holding stacks. Planes are holding quite a bit further east than normal.
 
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jepolch

Active Member
Here's the inside of the Motorola BDP-100/PI power inserter. As I thought, it's not as simple a device as we are making. I actually expected to find a PCB with surface mount components, but it's a hand soldered gaggle of components. @ab cd's design seems to perform as well as this one.

Edit: @ab cd: What size inductors are they using?
 

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jepolch

Active Member
I'm using rtlpan for the plotting which I believe is based on rtl_power on a laptop. I introduced a coax stub into the above. The stub is "tuned" to get rid of noise at ~950MHz. I have a question for the experts. Why the apparent sharpening at 1160MHz and the loss of db at 1090? Thanks.
View attachment 2076

Below is the baseline plot with nothing connected to the antenna port
View attachment 2077

Below is the plot with the Yagi only
View attachment 2078

Below is the plot with the coax stub in the chain
View attachment 2079
Nice work! Is the stub terminated or open?
 

jepolch

Active Member
Haha, just been listening to Heathrow approach - Controller says "How is the weather looking by the Lambourne hold?" pilot responds "Er, bad".

Planes going all over the place today:

View attachment 2083

Here's the edge of what they are trying to avoid. It's right over the top of one of the Heathrow holding stacks. Planes are holding quite a bit further east than normal.
Very nice colorful trails. Why are mine all black/dark blue? Is there a setting in VRS to make the trails more colorful?

Edit: Aha! Position and altitude? I never saw that setting til now. :)
 

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caius

Member
In the options menu that opens from the map, look on the aircraft tab. There is a section for aircraft trails - I have it set to position and altitude, so the colour varies with height. Blues and greens are lower altitudes and the reds and pinks are higher altitudes.
 

jepolch

Active Member
In the options menu that opens from the map, look on the aircraft tab. There is a section for aircraft trails - I have it set to position and altitude, so the colour varies with height. Blues and greens are lower altitudes and the reds and pinks are higher altitudes.
Thanks! I had just found it. Although I'm colorblind to a certain degree, I can distinguish the difference between the colors - just couldn't tell you which color is which! :eek:
 

jepolch

Active Member

ab cd

Senior Member
The connectors are for fitting together this http://www.rtl-sdr.com/rtl-sdr-tuto...ntenna-vswr-with-an-rtl-sdr-and-noise-source/

Here's my setup with a homemade Yagi. The Yagi was designed with 4NEC2 and was my first foray into the software. Thanks to ab cd for getting me enthused ;)
View attachment 2072View attachment 2075

The output from the graph looks a bit naff and I'm sure purists will scoff but hey not bad for bit of waste pipe and a few lengths of copper wire. It worked too !! 4NEC2 predicted a SWR of 1.5
View attachment 2073
View attachment 2074
Since you got the equipment, can you please do following experiment:
Wind 5 turns of one plastic insulated wire from telephone or ethernet cable, over ¼ inch (6.4mm)dia drill bit. Pull/compress the coil to adjust its length to 15 mm, then measure its frequency response. Calculations show it should give a notch (i.e. will be resonant) at 1.04 Ghz. The resonant frequency can be adjusted by compressing/expanding the coil.

Screenshot_2015-05-19-18-35-08.png
 

TomW

Member
Finished my first spider. It's made with an SO-239 fitting, F-adapter, 2.5 inch copper disk 12 gauge wire, 4 M3 stainless cap screws and nylon lock nuts and a 2 inch PVC pipe plug. My amp will attach to the F fitting. Trying to resist the urge to test it. I want to get 7 full days of un-messed-with cantenna first. Ive been out of town for 5 days.
Will wait till Tuesday, will wait till Tuesday...will....wait..
View attachment 2037 View attachment 2038
Preliminary Results are GOOD!
5-19-2015 6-22-22 PM.jpg
 

ab cd

Senior Member
Here's the inside of the Motorola BDP-100/PI power inserter. As I thought, it's not as simple a device as we are making. I actually expected to find a PCB with surface mount components, but it's a hand soldered gaggle of components. @ab cd's design seems to perform as well as this one.

Edit: @ab cd: What size inductors are they using?
Color bands on inductor are not very distinct. What I read is
1st ring: Brown
2nd ring: Blue or Gray
3rd ring: Black or Brown
4th (tolerance) ring: Silver
The uncertainity of colors as above, gives four possible values: 16 µH, 18 µH, 160 µH, or 180 µH. 10% tolerance.


inductor color code.gif
 
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jepolch

Active Member
Color bands on inductor are not very distinct. What I read is
1st ring: Brown
2nd ring: Blue or Gray
3rd ring: Black or Brown
4th (tolerance) ring: Silver
The uncertainity of colors as above, gives four possible values: 16 µH, 18 µH, 160 µH, or 180 µH. 10% tolerance.


View attachment 2091
Thanks. Any idea why their power inserter is more complex than ours? Why so many inductors and capacitors? Here's a better shot of the inductor if you're interested.
 

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TomW

Member
Great! The Copper Disc is showing it's superiority over SO239's Flange!

Which can you have used for your Cantenna?
It's a one quart tin paint can from Lowe's, about 4.25" diameter, slight rim, but does not stick up above top of so-239 on a horizontal plane. I cut it to 69mm +- vertically.
2015-05-19 20.05.02.jpg
 

ab cd

Senior Member
Thanks. Any idea why their power inserter is more complex than ours? Why so many inductors and capacitors? Here's a better shot of the inductor if you're interested.
1) In new shot, colors are distinct: brown, blue, black, silver. This gives 16 µH, 10% tolerance.

2) Motorola have designed their inserter for a wide band of frequencies 950 to 2500 mhz, hence used a pi or t blocking network. My design is simpler because I designed targeting only one frequency 1090 Mhz.
 

ab cd

Senior Member
It's a one quart tin paint can from Lowe's, about 4.25" diameter, slight rim, but does not stick up above top of so-239 on a horizontal plane. I cut it to 69mm +- vertically.
View attachment 2093
This type of can is ok for Cantenna. However its dia is somewhat large (4.25 inch=108mm). Try a similar can with slightly less dia, say around 3 to 3.5 inch.
 
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