ADS-B DIY Antenna

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ab cd

Senior Member
An interesting site HeyWhatsThat.com

Here is plot of my range based on terrain, from "HeyWhatsThat.com".
The blue plot is for 40,000 feet high planes. The yellow plot is for 30,000 feet high planes.

I have superimposed on it my measured maximum range (by adsbScop). It is in thin black color lines.
There are sharp drops in measured range in various directions, which are due to surrounding tall buildings.

The plot by "HeyWhatsThat.com" is almost circular, and does not show any sharp drops in any direction.
This indicates that "HeyWhatsThat.com" site only takes into account the natural geographic terrain, and ignores any man-made tall structures.

HeyWhatsThat-1.gif

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ab cd

Senior Member
TWO PIONEERS ...
Hertz and Marconi-1.png



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And a third one, though not as prominent as above two...
Charles Samuel Franklin.jpg
 
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Richard Lee

Member
That HeyWhatsThat site is very interesting! My dream of hearing them down to the runway at JFK isn't looking too good..
But, my estimated reach into Canada is about what I expected to see. (When the new coax and receiver get here).. :)

upload_2014-5-5_0-10-26.png
 

ab cd

Senior Member
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The image below shows Radiation Patterns for collinear antennas, 1-element to 8-elements.
Source: Radio Antenna Engineering by Edmund A. Laport, former Chief Engineer RCA.

Collinear Patterns.png

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Richard Lee

Member
Those two interesting antennas remind me a little of the old Ringo Ranger that I took out of service a few years ago..
CC%20ARX-2B%20Ringo%20Ranger%20+%20Hz1F.jpg

That 2m Ringo lasted about 20 years, before I replaced it with a 3-bander (6m, 2 m & 70cm) inside a fiberglass radome. (Don't know what's inside it)..

The problem with that wire collinear, at 1080 MHz, the mechanical strength isn't real good. Wind and ice loading will bend it over.
Unless you make it out of brass and braze the joints. It needs to be inside a radome.. And that might affect it's operation somewhat.

The SWR plot numbers and bandwidth is very impressive. I wonder if that -20dB return loss would be possible at 50 ohms?

Still, it is a thing of beauty. Eye candy for the antenna fan.. :)
 

trigger

Member
Our police would have a field day with that car. "Me! on a mobile phone, I don't think so !!"
He must have a truck battery in there somewhere to power that lot.
 

ab cd

Senior Member
It takes all kinds.. Love that Alinco handheld :)

Those BNC 3-female 'T' connectors just reminded me that I want to make some 1/4 wave Coax filters for ACARS on 131.55 MHz.
I want to try out Plane Plotter's ACARS decoder, but the noise level on VHF here is awful.. Might be from power lines.?.

http://dl4xav.sysve.de/coax.filter/coax-filter.html

Thanks for the link. Now I understand what a "notch" filter is.

Practically speaking, the filter stub gives same result as a High Q Series LC Circuit, tuned to unwanted frequency.
Both short-circuit the unwanted frequency.

220px-Series_LC_Circuit.svg.png
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Zseries.gif
 

Richard Lee

Member
IMG00006.GIF

I would hope to see a bandpass effect similar to this, from a 1/4 wave shorted-end 'filter' section.
The shorted-end 1/4~ coax filter, looks like a parallel resonate tank circuit. http://sub.allaboutcircuits.com/images/02096.png
Once I get the length cut right (for 130.55 MHz, I think), I can add more sections with more 'T' adapters.
Which should increase the attenuation above and below 130.55 MHz..

I think much of the noise I'm hearing is broadband coming from power-lines etc.
Most of that is vertically polarized and reaches up higher than the 2m band..
But, there are also many local VHF RF signals near the 2.3m band that may
be interfering with the ACARS signals. http://www.rtl-sdr.com/rtl-sdr-radio-scanner-tutorial-receiving-airplane-data-with-acars/

I also have an old military surplus dual cavity tunable filter for the 100 Mhz range.
I may be able to change it's tune with a hacksaw.. :)
 
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ab cd

Senior Member
IMG00006.GIF

I would hope to see a bandpass effect similar to this, from a 1/4 wave shorted-end 'filter' section.
The shorted-end 1/4~ coax filter, looks like a parallel resonate tank circuit. http://sub.allaboutcircuits.com/images/02096.png
Once I get the length cut right (for 130.55 MHz, I think), I can add more sections with more 'T' adapters.
Which should increase the attenuation above and below 130.55 MHz..

I think much of the noise I'm hearing is broadband coming from power-lines etc.
Most of that is vertically polarized and reaches up higher than the 2m band..
But, there are also many local VHF RF signals near the 2.3m band that may
be interfering with the ACARS signals. http://www.rtl-sdr.com/rtl-sdr-radio-scanner-tutorial-receiving-airplane-data-with-acars/

I also have an old military surplus dual cavity tunable filter for the 100 Mhz range.
I may be able to change it's tune with a hacksaw.. :)

Thanks Richard for your very useful post. Changing tune by hacksaw looks funny, but it is a reality & a practical DIY method.
 

Richard Lee

Member
If I find it's an easy hack, I won't use a hacksaw, I have a nice band-saw in my little shop.

It already works a little, if tuned all the way to the stop at 120 MHZ.

P1010966s_zps6dd4dbf0.jpg



Maybe I'll only have to take off a few mm..
 

Richard Lee

Member
P1010971_zps15feec3e.jpg


It's nice inside. The gold looks good. I don't think this is going to be easy as just cutting the tubes shorter.
Those long rods will have to be shorted and the ends drilled and tapped.
I might have to solder a small shorting bar across the ends of those coupling loops. (to move the freq up).

P1010973.jpg
 

ab cd

Senior Member
P1010971_zps15feec3e.jpg


It's nice inside. The gold looks good. I don't think this is going to be easy as just cutting the tubes shorter.
Those long rods will have to be shorted and the ends drilled and tapped.
I might have to solder a small shorting bar across the ends of those coupling loops. (to move the freq up).

View attachment 295
Wow! This looks more like a Mechanical equipment, rather than an Electronic equipment. It's parts are shining, like parts of a good quality old mechanical clock with pendulum, the one which my grandfather had.
 

Richard Lee

Member
They used a lot of gold plated stuff in the old days..
I think the P1 Input link (L1), the cavity coupling links (L3 & L4) and the Output link to P2 (L6) are cut for about 110 MHz.
It's designed for 100 to 121 MHz, and hacking the internals is too much work right now.

I have some RG214 coax and some N-connectors that I can used to make a 1/4~ shorted-end coax filter. I'll give that a shot next.

This video
shows what the old R8500 can do. This guy has such a low noise floor and strong signals, he can use the Squelch in AM mode!
I really would like to see Plane Plotter displaying some ACARS packets..
 

ab cd

Senior Member
My screen grab of Virtual Radar Server (after 18 hrs run).
Receiver range plotting on VRS done using Franklin 4-element antenna with matching stub, shown below.
VRS-receiver range-18hr grab.png

Franklin 4-element with matching stub.
Franklin 4 element quarter-wave matching stub.png
Note: I am also using an in-Line amplifier (RCA D903, Gain 13-18 dB, Freq Range:950-2050 MHz, Max Output 110dBµV, Power pass DC 14-18V 25-40mA)

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