Very small Collinear antenna (~ 300 mm) ??

[Richard Lee]

I'm not all that great with theory (I'm rusty on the basic stuff too)!

When I think about the little PY4BZB antenna's design, I see the horizontal lines where the feed is connected,
as a parallel feed line/transformer that drives the driven elements..
My visualization is only of the waveforms launching from the DE as a nice sine wave that's about 275 mm long.

This old Ham HF design sure seems a lot like the tiny 1090 MHz antenna on my tower.. Have you built one yet?
http://www.hamuniverse.com/n4jaantennabook.html

Seems to be an easy way to stack two of them..
http://dg7ybn.de/Phasing/Phasing.htm#Feed_2x_50

 

[stephenkearney]

I did see a lot of discussion of the quarter wave stub for impedance transformation. The quote in my last message was about a slightly higher gain variation on the full wave dipole + quarter wave matching stub.

The horizontal stub lines have currents moving in opposite directions. Those currents create EM fields which affect each other, changing the impedance. I want to understand exactly how...

 

[Richard Lee]

My 'understanding' of the feed matching section is:
It's electrically the same thing you will find inside your antenna-tuner. An LC network/transformer.
So, maybe studying antenna-tuner theory will help in understanding how matchers made from feed-lines work..

 

[stephenkearney]

It took awhile but now I understand how the 1/4 wavelength matching section works! Here's a pretty good explanation:
http://www.allaboutcircuits.com/vol_2/chpt_14/7.html

And as mentioned earlier the PY4ZBZ fullwave has an extra 1/8 lambda added to each each arm to get a little more gain (approx. +1 dB). Also, the 1/4 wavelength matching section is shortened to accommodate the longer radiating elements.

 

[Richard Lee]

Performed a semi-side-by-side compare today. The 9dBi DPD vs the DIY very-small-collinear.. (aka FullWave).

Using both RTL1090 and modeSdec_xp w/ VRS, I watched the tracking and signal levels for 2 hours this morning.
Watching the total plane count was very informative. Since plane count includes all planes, not just those sending lat & long data.
I tried to ignore those planes in areas where there was tower blockage.
The FullWave may have some tower gain to the north, since many of the planes up north had better signal levels on the FullWave.
Tower gain might be due to the tower metal acting as a reflector element for the antenna. The level wasn't a lot higher, but I did see it higher consistently.

Because using flying aircraft as signal sources to compare these antennas can never be anywhere near as accurate as measuring stationary signal sources,
I spend a lot of time quickly A-B comparing plane signal levels on those planes in directions where both antennas have known good coverage.

I also tried about a dozen different RF gain settings (AGCs off) on the dongle. (No LNAs or filters were used).
I wanted to insure that neither ant was over-loading the dongle or decoder software (or PC CPU).
Reducing the gain didn't seem to cause one antenna to stand out over the other.

Instead of being able to compile a bunch of numerical data (that would take weeks),
I just got a good 'feel' for how well each antenna worked with the dongle.

Bottom line, these antennas work about the same. (in known good directions).
I think the FullWave sufferers from being mounted too close to the tower, (but gets greater gain to the north)
and I believe the FullWave would preform the same as the DPD, if it were mounted where the DPD is mounted.

IMHO: If the DPD is has a true 9 dBi of gain, so does the FullWave very-small-collinear..

Disclaimer: These antennas each have their own coax. Westflex 103 on the DPD and 30 year old hardline on the FullWave.
If their losses are much different my 'results' are invalid. Both antennas (and their feeds) exhibit excelent SWR levels.

 

[PaulGulliver]

Richard, in your various antenna trials have you tried the 1/4 ave ground plane as described here http://www.atouk.com/wordpress/?wpdmact=process&did=Ni5ob3RsaW5r (pdf document), if so I would be interested how it compares to other antenna you have tried.
I'm using a rather roughly made version of the ground plane, using 16swg copper wire and only 4 ground elements, the results I'm getting (with a LNA) are not too bad - see attached diagram - the aerial is loft mounted around 20-25ft above ground.

Note the rings are 50Km (around 35 miles)
The 2 dips to the North are due to external obstructions (trees) and the reduced range to the Northeast (around 150Km) is due to a hedge. Living on a housing estate there are numerous other obstructions at various distances
I was considering building a 3.5 element coaxial collinear as described here http://forum.planefinder.net/threads/ads-b-diy-antenna.23/ (about a third of the way down the 1st page) but I'm not sure if that will improve matters much - I assume a loss of signal due to obstructions can never be improved by better aerials assuming the height is fixed.
I would be interested in your thoughts.
Paul

 

[Richard Lee]

Hello Paul,
Yes, I have tested a 1/4~GP..
I had good luck with my 1/4 wave ground plane testing. http://forum.planefinder.net/threads/1-4-wave-ground-plane.156/

50 status miles per ring.

I think it might have been better, had I added a second LNA at the Dongle.

I did try using a second LNA with the Full-Wave and it added some miles..
If you can build the Full-Wave, you might find it's range is a lot better than the 1/4 wave GP ant..

I was surprised. Did not think the full-wave performance could be improved, because of all the blockage around here..
Adding more LNA gain up at the antenna would be better than the way I did it.. Down at the dongle.
At 7 meters (23 feet), this little Full-Wave design preforms like it has 9dBi of gain.

For an indoor installation, the main problem I foresee, is tweaking the match. I was able to tune mine up using SWR test gear.
I cut my 1/4 wave GP per published numbers, and was lucky. It has a good match to 50 ohms.

I assume you are working with 75 ohm cable (which is common for home ADS-B gear), so you might want to try
making an adjustable tune feed point. If you decide to build a a full-wave.
http://forum.planefinder.net/attachments/dsc03002-jpg.351/


I have tried to build coaxial collinear antennas in the past. Once for 440 Mhz and recently I tired to modify a 900 MHz coaxial collinear
to work on 1090 MHz.. http://forum.planefinder.net/threads/915-mhz-coaxial-collinear-conversion-to-1090-mhz-project.160/
It seemed like an easy project. I measured twice and cut once. Carefully spent hours cutting and soldering..
Did the best I could, but was very disappointed by the high SWR.. Nice looking, but not a usable antenna..

The only really good 1090 antenna that I've ever had great success with, is the Full-Wave very-small-collinear-antenna...

 

[PaulGulliver]

Thanks for the reply Richard, I'll have to study your post on the 1/4 GP later, I happen to be using 50 ohm cable - to me, as an ex- radio amateur, this seemed standard , I also has a supply of bnc plugs to suit the cable.
Since writing my post this morning I've come across this design http://ads-b-antenna.blogspot.co.uk/2014/04/interest-check.html and I'm just wondering if it might be worth the investment, seems idea for indoor/loft use.
Paul

 

[Richard Lee]

That PCB antenna looks good. A lot of design work went into it, or slick marketing.
If the SWR is really low, you are all set. But, if the SWR is high, it's going to hard to fix.

You do get static discharge protection, just like the Full-Wave, but the gain isn't going to be as good.

I think you should try the Full-Wave.. Easy to build and they work great..

BNC are great for 1090 Mhz. I've seen open BNC connectors used outdoors and wondered why..?.
An old Ham told me, they have a rubber gasket inside the male and if you leave them open (no tape wrap),
the water will drain out and the sun will dry them up..

 

[PaulGulliver]

Well, I'm afraid I didn't have much luck with the full wave, I took quite a bit of care in the construction, getting the dimensions as close as I could but the results were disappointing - coverage below (compare to my 1/4 GP four posts above)

I have no way of testing the aerial, I had to guess at the feed point, I couldn't see any reference in earlier posts - I opted for 18mm from the shorted stub, I think this dimension was quoted for the Franklin aerial. The feed was via a 150pf silvered mica capacitor because I had DC power on the line.
The set up for this aerial was the same as the 1/4 GP - same location, cable and LNA.
I've now gone back to the 1/4 GP and going to leave it for now and concentrate on other things like looking at the data I'm receiving - my next project is to make a RaspberryPi version of the receiving station to free up the Windows computer - that's going to be a large learning curve for me.
Paul

 

[ab cd]

Hi Richard & stephenkearney!
I saw this thread just now, and a quick brows shows it to be very interesting. Will go through it in detail when at home at my desktop. Right now I am posting this by my phone.

 

[Richard Lee]

Are you going to try one? Mine was easy to 'match' to the feed-line, since I now have my own L-band antenna tester..

It's still working very well. I can combine the radios into one display, and see when planes are heard by which antenna and radio..

The FullWave Ant is on Receiver 2, using the Dongle and one LNA.
The other receiver is the PlaneFinder 1090 Puck using the DPD antenna. (No LNA yet).

The Puck doesn't provide a signal level number, so any Signal level number in the first column,
that's on the Puck radio, is left-over from when the Dongle heard the signal. (It sometimes hears planes Before the Puck).

 

[ab cd]

Are you going to try one? Mine was easy to 'match' to the feed-line, since I now have my own L-band antenna tester..

It's still working very well. I can combine the radios into one display, and see when planes are heard by which antenna and radio..

The FullWave Ant is on Receiver 2, using the Dongle and one LNA.
The other receiver is the PlaneFinder 1090 Puck using the DPD antenna. (No LNA yet).

The Puck doesn't provide a signal level number, so any Signal level number in the first column,
that's on the Puck radio, is left-over from when the Dongle heard the signal. (It sometimes hears planes Before the Puck).
View attachment 503

View attachment 504

Very interesting & useful information. Thanks Richard.

 

[ab cd]

Can anyone guide me which is an INEXPENSIVE equipment to measure SWR/reflected power/impedance of an antenna or transmission line? Any idea about cost of such equipment? I have a very limited budget for my hobby.

 

[Richard Lee]

The cost is higher than I wanted to pay, but the return-loss results are usable for tuning 1090 antennas and filters.
I'm not sure about reading the Z of coax, but you should be able to tell if it's a clean 50 ohm or 75 ohm cable,
by feeding it into a good 50 or 75 ohm load. My main antenna test cable shows zero return loss when
I screw a 50 ohm load on the end..

The 'Tester' is described here: http://forum.planefinder.net/threads/adf4351-signal-generator.161/

Cheers,
Rich