ADS-B DIY Antenna

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TomW

Member
Watch out on the VF with brass tubing on a stripped 50 ohm LMR400 guys,
You could treat yourself and try to make a coco with the mother of coaxials, Andrews Heliax LDF5-75 (a 75 ohm cable for a 75 ohm job),if you can get it..the 50 ohm (LDF5-50) is more popular.
No faffing with tubing as its already in the cable makeup..Here you will be in the company of the elite of coaxial cables, Andrews are always batting at the top of their game on heavy duty microwave feedlines but, a caveat..connectors will put a serious dent/ouch in your wallet.
A hardline N connector is anything between $75-$125 USD, yes thats each !
I dont trust my weak soldering skills with a connector of this expense.
I would recruit xforce,jepolch,tom or bramj..well worth the return postage !
Davis RF will have and sell this by the foot I imagine.

Off topic, To model maker extraordinaire @jepolch,
I found a very interesting page via flightaware about the demise of the Russian space shuttle program, made very sad reading..what a travesty.
http://gizmodo.com/these-are-the-sad-remains-of-the-soviet-space-shuttle-p-1710827956
"VF" ???
Sorry for the neub question
Tom
 
"VF" ???
Sorry for the neub question
Tom
Hi Tom,
Velocity Factor, each coaxial has a velocity factor, this should be taken into account when cutting coco the elements to length.
The VF value usually features in antenna element calculators.
In this case though, the intention is to change the makeup of the cable by stripping the braid and replacing it with a tube.
This will no doubt make a change to the VF and what it will be after the change I am unsure.
This would mean the possibility of incorrect element lengths due to the unknown/guessed VF.

Also LMR400 is a 50 ohm unbalanced cable, the receiver/dongle has a 75 ohm unbalanced input. Not usually an issue but cocos are a notoriously difficult antenna to master and any micro mis-measurements can cause poor performance/builder frustration.
 
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airbus340

New Member
I bought a diplexer today and trying it now, am I correct that it should be placed between the amplifier and the dongle?
I was really looking forward to try this as I read someone made a 20% improvement, here it seems to be 80% worse...
 

jepolch

Active Member
Watch out on the VF with brass tubing on a stripped 50 ohm LMR400 guys,
You could treat yourself and try to make a coco with the mother of coaxials, Andrews Heliax LDF5-75 (a 75 ohm cable for a 75 ohm job),if you can get it..the 50 ohm (LDF5-50) is more popular.
No faffing with tubing as its already in the cable makeup..Here you will be in the company of the elite of coaxial cables, Andrews are always batting at the top of their game on heavy duty microwave feedlines but, a caveat..connectors will put a serious dent/ouch in your wallet.
A hardline N connector is anything between $75-$125 USD, yes thats each !
I dont trust my weak soldering skills with a connector of this expense.
I would recruit xforce,jepolch,tom or bramj..well worth the return postage !
Davis RF will have and sell this by the foot I imagine.

Off topic, To model maker extraordinaire @jepolch,
I found a very interesting page via flightaware about the demise of the Russian space shuttle program, made very sad reading..what a travesty.
http://gizmodo.com/these-are-the-sad-remains-of-the-soviet-space-shuttle-p-1710827956
Can you give me some details on your comment about VF with the LMR-400. It's supposed to be 85% - but that's "as is" - before we strip off the jacket and braid and add the brass tubing. I wonder how to calculate the VF on "modified" LMR-400 - that is with brass tubing applied.

Yeah, I saw that site, too. It's sad, but shows that the Soviet shuttle program (like their moon landing program) was just an "arms race". They couldn't afford to compete, so they gave up. In the end, their shuttle program would have probable been an expensive debacle, like ours. The Russian Soyuz is really the hero of the space age.
 

jepolch

Active Member
Well, damn. Another $20 down the drain. I just got the LMR-400 and tried to see how it fits into the brass tube - doesn't! - at all. :mad: The foam core is about the same diameter as the outer diameter of the tube.
 

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trigger

Member
I bought a diplexer today and trying it now, am I correct that it should be placed between the amplifier and the dongle?
I was really looking forward to try this as I read someone made a 20% improvement, here it seems to be 80% worse...
I have mine antenna> amp> diplexer> length of coax> power inserter> dongle. I have a CoCo so don't need a DC blocker between the antenna and the amp.

Which diplexer did you get? Mine is in the loft so not readily accessible but from memory there are 3 ports on it labelled Sat, Ant or TV and In/Out. Make sure you connect between Sat and In/Out. The Ant/TV port will attenuate 1090Mhz :eek:
I got an improvement with mine but not 20%. I ran a few frequency scans and the diplexer chopped some of the stuff at and below ~950Mhz
 

airbus340

New Member
Thank you very much trigger!

Mine looks like you describe, 3 ports with SAT and TV on one side and on the other side it say IN/OUT.
I have antenna>amplifier>diplexer>dongle and I hooked the antenna to SAT and dongle to IN/OUT.

My antenna is indoors and I have 30 cm coax between antenna and amplifier and dongle direct into amplifier.

Before I gave up with the diplexer I started SDRSharp and with the diplexer I get a lot more noise than without it...

Specs for the diplexer: 40–2300 MHz (950–2300/40–862 MHz).
 

jepolch

Active Member
Well, more bad antenna news. I spent some hot time up on the roof the last couple of days. I put up a coco that I had made months ago, but it had never been up to the roof. It did OK, but not as good as the hybrid cantenna (cantenna with the can split into eight sections like a spider). So I decided I would go back to what has always worked best for me. I took a 8-legged spider that had been on the roof a while back. I trimmed the legs so the total length from the whip to the tip of the radial measured 69 mm. That made the legs about 53 or 56 mm, depending if they were in the middle of the SO-239 plate or on the corners. I thought this had to be good. I got back into the house and found it was only seeing a couple of aircraft, compared to my other spider that was getting about 90! I went back to the coco which I still had up there and it's getting about half the number of aircraft as my "good" spider. I have no idea why the shortened spider is doing so poorly. Here's a look at my ads-b "trident" while I still had the hybrid cantenna installed.
 

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jepolch

Active Member
I found a great price on K&S 5/16" brass tubing at http://hobbylinc.com - $16 for four 36" sections. I found a single section on Amazon for $22 (including shipping)! So now I'll be able to make the metal coco. I wrote to the guy who published the plans for the antenna and asked him how he calculated the velocity factor for the coax with the brass covering, but haven't gotten a response. The plans are for a 2.4 Ghz antenna, but I will lengthen the sections (like Bram did) for 1.09 Ghz. http://www.nodomainname.co.uk/Omnicolinear/2-4collinear.htm
 

ab cd

Senior Member
@trigger :
Good News: The Noise Generator, DC 12V Adapter, and MCX to F adapter arrived from China.
Bad news: The noise generator becomes extremely hot when in use. Also the output dB seems to be low and very non-linear with frequency. How your noise generator behaves?

I connected noise generator directly to DVB-T dongle and plotted curve from 900 MHz to 1200 MHz. Then inserted my own design, the "Double Whip Filter" between noise generator and the DVB-T dongle, and there was enhancement at 1090 MHz & reduction in other frequencies (as compared to direct connection).

Since the noise generator seems to be defective, I cannot say for sure if "Double Whip Filter" is a success or a failure. The insertion loss seems to be about 2.5 dB.

The Double Whip Filter is nothing more than two 1/4 wavelength whips (69mm each), placed side by side at a distance of about 1" (25cm) from each other, mounted on a metallic plate to provide continuity of shield (I have mounted it inside a drink can to provide shielding as well, but can is not essential, metallic plate is).

The distance between whips is not critical, and can be adjusted to fine tune the filter.

DSC03658-R.JPG DSC03657-R.JPG DSC03656-R.JPG Filter tested by Noise Gen 2.PNG Double Whip Mounting Plate.PNG
 
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trigger

Member
@trigger :
Good News: The Noise Generator, DC 12V Adapter, and MCX to F adapter arrived from China.
Bad news: The noise generator becomes extremely hot when in use. Also the output dB seems to be low and very non-linear with frequency. How your noise generator behaves?

I connected noise generator directly to DVB-T dongle and plotted curve from 900 MHz to 1200 MHz. Then inserted my own design, the "Double Whip Filter" between noise generator and the DVB-T dongle, and there was enhancement at 1090 MHz & reduction in other frequencies (as compared to direct connection).

Since the noise generator seems to be defective, I cannot say for sure if "Double Whip Filter" is a success or a failure. The insertion loss seems to be about 2.5 dB.

The Double Whip Filter is nothing more than two 1/4 wavelength whips (69mm each), placed side by side at a distance of about 1" (25cm) from each other, mounted on a metallic plate to provide continuity of shield (I have mounted it inside a drink can to provide shielding as well, but can is not essential, metallic plate is).

The distance between whips is not critical, and can be adjusted to fine tune the filter.

View attachment 2230 View attachment 2232 View attachment 2231 View attachment 2236 View attachment 2229
Hi ab cd,
Yes, my noise generator also gets very hot. There is a note on the original post "Finally a quick warning: be careful when handling the circuit board after it has been powered for some time as some of the components can get very hot." http://www.rtl-sdr.com/rtl-sdr-tutorial-measuring-filter-characteristics-and-antenna-vswr-with-an-rtl-sdr-and-noise-source/
I've been busy with beekeeping over the last few weeks so haven't paid much attention to ADS-B. As it is raining here this morning, I'll repeat your first experiment and post my results later.
 

trigger

Member
Do you have SDR# on your laptop? I just took a look across 900 - 1200 Mhz with the noise source attached to the dongle. I get a lot of noise ~40db
 

jepolch

Active Member
Hi ab cd,
Yes, my noise generator also gets very hot. There is a note on the original post "Finally a quick warning: be careful when handling the circuit board after it has been powered for some time as some of the components can get very hot." http://www.rtl-sdr.com/rtl-sdr-tutorial-measuring-filter-characteristics-and-antenna-vswr-with-an-rtl-sdr-and-noise-source/
I've been busy with beekeeping over the last few weeks so haven't paid much attention to ADS-B. As it is raining here this morning, I'll repeat your first experiment and post my results later.
Hey Trigger, I did some beekeeping a week ago! I was in Ohio taking care of my sister's house while she was on vacation. I went into her shed to get the "bee suit" and didn't see any pants, so I wore my shorts. I moved very slowly and didn't get stung. Later I talked to my sister who told me "there aren't any pants, we wear blue jeans".
 

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