ADS-B DIY Antenna

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trigger

Member
Hi ab cd,
To properly compare two antennas, their performance should be compared WITHOUT AMPLIFIER.
The reason is that the amplifiers have AGC (automatic gain control). They increase gain for weaker input, reduces gain for strong input, giving fairly equal output & hence false impression that both are equal.
Yes, of course! I'll take the amplifier out of the circuit. I'll be back ....

Dave
 

jmcq

New Member
So, I ordered an 18v 1000mA power supply. I figure I need to add an additional 32 ohm resistor on the front end to achieve an overall 360mA. Kinda worried about heat though. Any thoughts? Logic by applying Ohms Law is 18v which produces 1A (1000mA) has 18 ohms of resistance on the circuit. By adding another 32 ohms, for a total of 50 ohms, that will result in 360mA, or what ab cd is running on his 14v power supply. I will be using the same cap and choke as ab cd.
 
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ab cd

Senior Member
So, I ordered an 18v 1000mA power supply. I figure I need to add an additional 32 ohm resistor on the front end to achieve an overall 360mA. Kinda worried about heat though. Any thoughts? Logic by applying Ohms Law is 18v which produces 1A (1000mA) has 18 ohms of resistance on the circuit. By adding another 32 ohms, for a total of 50 ohms, that will result in 360mA, or what ab cd is running on his 14v power supply. I will be using the same cap and choke as ab cd.
DO NOT ORDER 18V, as the power supply output is usually higher than rated when you draw only a fraction (40mA) from rated (1000mA) current. The actual/measured voltage may be as high as say 22 Volts. (Mine rated 14V, actual/measured 17V).

Even if you add a resistor of 32 ohms, it will reduce the voltage reaching amplifier by an amount = current drawn by Amplifier x Resistance = 40mA x 32 Ohms = 0.040 x 32 = 1.28 Volts. Then 22 Volts- 1.28 Volts = 20.7 Volts will reach your amplifier. This will overheat your amplifier, and may finally fry it.

Other alternative is to add higher resistance to drop more voltage across resistor. This will result in heating up of resistor (unless its wattage rating is high enough) and finally the resistor may fry.

CONCLUSION: Better order 14V or 15V rated Power Supply.
 
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ab cd

Senior Member
Hi ab cd,
I've made a new antenna following this design http://martybugs.net/wireless/collinear.cgi I've made the 5 loop version shown towards the bottom of the page with dimensions
λ/2 of 137mm and 3λ/4 of 206mm. The whip I guessed at 190mm. I made it from 1.5mm copper wire.

The antenna is working fine and seems comparable with my Franklin. I will be running some tests in the next couple of days. The advantages are that I don't need the power inserter above the amplifier as the antenna is not "shorted" and it should be easier to mount the antenna in a tube for outdoor use.

Have you any thoughts about the diameter of the loops? I made them by wrapping the wire around a 15mm piece of dowel. Should the circumference be a fraction of the wavelength?

Regards
Dave
I have run computer simulation on 3nec4 software. Results are shown in the images below:

Screenshot #1: Input (Wire Data)
daves-coil-type-whip-wire-data.png



Screenshot #2: Output (Gain, SWR, Pattern)
daves-coil-type-whip.png

 

trigger

Member
Hi ab cd,

The performance of the above antenna with the amplifier removed is not good! I've done a few quick back to back comparisons today and the Franklin is far superior in coverage. I've also made a new one with 22mm diameter coils and it also doesn't work as well as the Franklin.
I've sacrificed one of my early Franklins and I've folded the stubs to 22mm diameter. I'm just about to put it on test.

Thanks for the plots.
Dave
 

ab cd

Senior Member
Waiting for results of wrapped-stub Franklin. Since franklin's stub length is already 1/4 wavelength, using 22 mm dia will make end of stub in line with vertical legs. It is not necessary to use 22mm, and a larger dia should also be ok.
 

jmcq

New Member
DO NOT ORDER 18V, as the power supply output is usually higher than rated when you draw only a fraction (40mA) from rated (1000mA) current. The actual/measured voltage may be as high as say 22 Volts. (Mine rated 14V, actual/measured 17V).

Even if you add a resistor of 32 ohms, it will reduce the voltage reaching amplifier by an amount = current drawn by Amplifier x Resistance = 40mA x 32 Ohms = 0.040 x 32 = 1.28 Volts. Then 22 Volts- 1.28 Volts = 20.7 Volts will reach your amplifier. This will overheat your amplifier, and may finally fry it.

Other alternative is to add higher resistance to drop more voltage across resistor. This will result in heating up of resistor (unless its wattage rating is high enough) and finally the resistor may fry.

CONCLUSION: Better order 14V or 15V rated Power Supply.
I already had the 18v adapter ordered. Oh well. Here's the actual metrics/meter values on the adapter. 18.1v at 1.95A = 35.295 watts. Waaaaaay too much amperage to even try to step down prior to the connection on the amp. Reordering another DC p/s now. UPDATE: Would this one work? http://www.digitrax.com/products/power-supplies/ps14/ it is 14v and 300mA.
 
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ab cd

Senior Member
I already had the 18v adapter ordered. Oh well. Here's the actual metrics/meter values on the adapter. 18.1v at 1.95A = 35.295 watts. Waaaaaay too much amperage to even try to step down prior to the connection on the amp........
The current drawn by amplifier depends on amplifier's current rating (25mA to 40 mA), and NOT on DC Adapter's current rating (1000mA or 2000mA).
It is the NO-LOAD VOLTAGE output of adapter which is important.
To measure no-load dc voltage of adapter, connect the adapter to AC Supply, then WITHOUT CONNECTING any load on DC side, measure the output voltage across DC Pin by a VOLT METER, or MULTITESTER. If it is more than 20 Volts, then it is not suitable for 18V rated amplifier.
Measure again the DC Voltage after connecting the amplifier. It should be 0.5 to 2 volts less than the no-load dc voltage.
This reduction in voltage is caused by the amplifier current (40mA) flowing through internal resistance of the Adapter. (Voltage Drop in Volts = Load Current in Amps x Internal Resistance of Adapter in Ohms)
 

ab cd

Senior Member
Hi ab cd,

The performance of the above antenna with the amplifier removed is not good! I've done a few quick back to back comparisons today and the Franklin is far superior in coverage. I've also made a new one with 22mm diameter coils and it also doesn't work as well as the Franklin.
I've sacrificed one of my early Franklins and I've folded the stubs to 22mm diameter. I'm just about to put it on test.

Thanks for the plots.
Dave
I have run a sweep of your coiled whip antenna, varrying coil diameter.
The lowest SWR is at 22 mm dia, but even that it is so high (170) that it makes antenna hopeless even with 5dB Gain. See below the plot of SWR & GAIN with varying diameter of coil:

coil+whip-sweep-varying coil dia.png









.
 
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ab cd

Senior Member
BIG IMPROVEMENT BY ADDING EARTH PLANE
I have slightly modified your coiled-whip by making coil dia 22mm & adding an Earth Plane composed of 3 horizontal wires equally spaced (i.e. at 120 degrees with each other), and connected to each other & the Braid of Coaxial Cable. It improved antenna's performance dramatically. The simulation shows that the SWR has fallen down from a whooping 170 to a mere 2.8, a very good value, and the gain has increased from 5dB to 9.5 dB !!!!
See Screenshot of the computer simulation result of modified antenna below:


Whip+Coil+Ground Wires-R1.png


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trigger

Member
Hi ab cd,
You have been busy! I like your new avatar.

The coiled whip I've made has 4 * 206mm segments, 1* 137mm and a top segment of 190mm.

I will try it with an earth plane.

I have my folded Franklin on test at the moment. As you suggested I've made the loop diameter wider than 22mm. I'll come back with some measurements, results and photos soon.
Regards
Dave
 

ab cd

Senior Member
......I have my folded Franklin on test at the moment. As you suggested I've made the loop diameter wider than 22mm. I'll come back with some measurements, results and photos soon.
Regards
Dave

HERE ARE SIMULATION RESULTS FOR 6 ELEMENT FRANKLIN:


(A) WITH STRAIGHT FOLDS

franklin - 6 element - straight folds - all variable.png

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(B) WITH RECTANGULAR-WRAPPED FOLDS

franklin - 6 element - wrapped folds - all variable.png


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(C) WITH CIRCULAR-WRAPPED FOLDS

franklin - 6 element - circular wrapped folds.png

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jmcq

New Member
The 18v 1000mA power supply I bought is transformerless and more-than-likely switchable, even though it doesn't say it on the label. It is also quite light at right about 2.5 oz. Sooooo, I went ahead with the build on an 8.5 element coaxial collinear antenna which is shorted to braid at the top on a 1/4 wavelength. After performing continuity and voltage checks from the power supply to my newly built assembly, I hooked everything up and all is running fine. There is no heat building up on either the amp or the power supply, so it looks like I should be ok. On adsbSCOPE via ADSB#, I had 65 planes show up within the first 5 minutes using AGC on both the RTL and Tuner. I was floored, to say the least! I am letting the plot run for a couple of days to check the results, but so far I've had a couple of hits at 200km and 223km. Antenna is on a 5 metre run of cable and is at ground level hanging in my den window. Ultimately, I would like to mount the antenna at 10 metres of height for a good 360˚ pattern. Our geography is quite flat, but I do have some houses around.


[Above: Left-most cable is to DC power supply. Cable going vertical is to dongle (cheapo RealTek DVB-T 2832 mini dongle). Cable to the right goes to antenna (below).]



(Above: Cheapo RealTek 2832 dongle with MCX to Type F adapter)
 
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ab cd

Senior Member
The 18v 1000mA power supply I bought is transformerless and more-than-likely switchable, even though it doesn't say it on the label. It is also quite light at right about 2.5 oz. Sooooo, I went ahead with the build on an 8.5 element coaxial collinear antenna which is shorted to braid at the top on a 1/4 wavelength. After performing continuity and voltage checks from the power supply to my newly built assembly, I hooked everything up and all is running fine. There is no heat building up on either the amp or the power supply, so it looks like I should be ok. On adsbSCOPE via ADSB#, I had 65 planes show up within the first 5 minutes using AGC on both the RTL and Tuner. I was floored, to say the least! I am letting the plot run for a couple of days to check the results, but so far I've had a couple of hits at 200km and 223km. Antenna is on a 5 metre run of cable and is at ground level hanging in my den window. Ultimately, I would like to mount the antenna at 10 metres of height for a good 360˚ pattern. Our geography is quite flat, but I do have some houses around.


[Above: Left-most cable is to DC power supply. Cable going vertical is to dongle (cheapo RealTek DVB-T 2832 mini dongle). Cable to the right goes to antenna (below).]



(Above: Cheapo RealTek 2832 dongle with MCX to Type F adapter)
CONGRATULATIONS!
Nice setup. Good & neat soldering & cabling work.

Great coverage with antenna on ground level.
It will sure improve when you put it 10 meters above ground, over-looking above the roofs of all surrounding houses...a clear all-round view of horizon, and a maximum range of 400+ kms.
Waiting to see your coverage screenshot when you put the antenna above roof.
Nice view from your window.... you live in a nice neighborhood.

Did you measure DC Voltage of adapter by a multimeter/voltmeter after connecting amplifier?
 
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trigger

Member
Hi ab cd,
Thanks for the plots. In the third diagram above, I've also wrapped the tap into a circle. I've kept the feed point at 28mm. Could you do another calculation for that scenario. I really must have a try to do these calculations myself!

Preliminary tests of the coiled whip show the performance is less than the Franklin including with a ground plane.
Regards
Dave
 

trigger

Member
Hi jmcq,
As ab cd said, nice setup.
A question! In your screen shot from ADSBscope above, the small box to the left of the Select COM Port and Connect buttons, you are getting what looks like raw hex codes. I'm only getting a continuous "time out of range, fixed" dialogue. Any ideas why? The rest of the screen shot looks pretty much like mine.

I'm using ADSBscope with the graphing function switched on to monitor the Framerate. It's the icon just to the right of the icon to start monitoring. By attaching the different antennas, I can see how the Framerate varies.
Regards
Dave
 

jmcq

New Member
CONGRATULATIONS!
Nice setup. Good & neat soldering & cabling work.

Great coverage with antenna on ground level.
It will sure improve when you put it 10 meters above ground, over-looking above the roofs of all surrounding houses...a clear all-round view of horizon, and a maximum range of 400+ kms.
Waiting to see your coverage screenshot when you put the antenna above roof.
Nice view from your window.... you live in a nice neighborhood.

Did you measure DC Voltage of adapter by a multimeter/voltmeter after connecting amplifier?
Thanks. Yes, the voltage is 17.9 through the amp.
 

ab cd

Senior Member
Hi jmcq,
As ab cd said, nice setup.
A question! In your screen shot from ADSBscope above, the small box to the left of the Select COM Port and Connect buttons, you are getting what looks like raw hex codes. I'm only getting a continuous "time out of range, fixed" dialogue. Any ideas why? The rest of the screen shot looks pretty much like mine.

I'm using ADSBscope with the graphing function switched on to monitor the Framerate. It's the icon just to the right of the icon to start monitoring. By attaching the different antennas, I can see how the Framerate varies.
Regards
Dave
When you see "time out of range, fixed", click your mouse over it, and hex code will reappear. This happens with me frequently.
 
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