Very small Collinear antenna (~ 300 mm) ??

[Richard Lee]

The 1/4 groundplane antenna that I've been using is working pretty well.
http://forum.planefinder.net/threads/1-4-wave-ground-plane.156/
But, I would like to replace it with an antenna with a bit more gain.
Just to see if the coverage can be improved, without going to a large antenna.

I found a small Collinear that looked 'size' suitable, but I have lost the URL!
I did save some the pictures..(See blow).

It looks like something that I would like to try. If I can make it robust enough to not to fall apart.
Because of it's size, relative to the 1/4 wave GP, I assume it will have a bit more gain. (Not sure how much).

It looks like the builder is using a 75 ohm feed point, and I would want to use a 50 ohm feed, with some 1/4" hardline.

Is anyone here familiar with this design? Do the dimensions look like they will work?

Edit: Found the URL! http://www.qsl.net/py4zbz/adsb.htm

 

[Richard Lee]

Yeah, http://www.qsl.net/py4zbz/adsb.htm
The patten looks good too.. 9dBi and low to the horizon.. (Calculated at 50 ohms)!
That would be a nice increase over the 1/4 wave GP..

 

[Richard Lee]

It took about a hour to find the right wire for the elements. I used the same 1/4 hard-line coax for the feed line.
I have some male N-connectors that will solder directly onto that line.
The element wire isn't really wire. It's a micro sized hard-line Coax cable, it's much lighter than solid copper.

I installed the little PY4ZBZ this evening, just before it got dark. It's been building a max-range pattern for almost 4 hours.
Not too impressed with the range yet, but I did notice that I was getting a good signal from the KBED runway.
Better than I've seen with other antennas. During taxi, the signal level was between 20 and 40..
That's pretty high for a runway that's behind some hills, out of line-of-sight.

After tuning and soldering the feed into place, I found there was a little bit of reflected power.
A small jumper across the 8mm loop reduced the reflected to a non-measurable level.

 

[Richard Lee]

Oddly, the PY4ZBZ antenna seems at times, to be outperforming the PlaneFinder system.

It seems to be a pretty good antenna so far. I'm sure it won't hold up to winter weather, or survive a bird landing on it.. "(

 

[Richard Lee]

Here's the installed antenna up at 30 feet.
The tower frame is blocking to the south, and the clear shot to the north is filtered by the trees in the woods behind the house.
Because large feed hardline is at an odd angle, the 1/4" antenna hardline feed has to be somewhat convoluted. (I'm an Amateur after all)..

50 miles per ring.
The signal levels 0-255 are plane label, under the Call-sign, alt and distance (miles).

The normal drop-out/loss of signal, usually occurs right after the RF level drops under 10 or 15.
But, with this antenna, I'm seeing a lot more drop-outs occur while the levels are a lot higher.

Check out the three planes at the bottom of this map. All have very good signal levels,
but as they approach the no-coverage line, the signal drops by about 50% very quickly.
And within a few seconds, they drop off the map.

That seems to indicate my max range limit with this antenna isn't because of low gain and weak signals at long range.. (over 100 miles).
Because the signal level drops off so rapidly (non-linear), and seems so strong, an instant before drop-out occurs, (like someone closing a door)
I believe these drop-outs are caused by blockage (hills etc), and not weak RF signals, due to long range..

Therefore, it appears that my location will not benefit very much by increasing antenna gain.
The max range here is mostly limited by blockage. Increasing max range would require increasing antenna height,
so as to clear some of the local blockage.. Which will do very little for max range with low blockage (like up the Maine coast).

 

[Richard Lee]

It looks good to the north this evening. The small collinear is reaching up to the Canadian border at Newport, the same as the DPD antenna.

The small collinear is seeing past the 200 statute mile line at Bangor Maine. The DPD 1090 Puck max range didn't reach Bangor today..
This is somewhat surprising. I wasn't real sure the actual gain of the small collinear was really 9 dBi.(edit). It just seems too small.
Besides, the large DPD antenna is only rated for 9dBi.. And, they likely made some real antenna Test Range measurements.

The DPD wasn't damaged in shipment or install, and is still performing like new (no water in the new coax etc).
I tested the return loss of the cable and antenna, it reads -16.5 dB (SWR 1.35 : 1). That's to DPD spec (SWR: 1.5:1 or Less on Center Freq).

I also did a quick test of the small collinear & it's feedline, and it's return loss is better than -20 dB. No bad connectors or water in the large hardline.

But, looking at the max range plots, I'm a bit shocked. I think the next step is to eliminate the differences in the electronics
and just compare the antennas and their feed-lines. I'll need to connect both antenna feeds to an A-B switch.
With the switched output going to the dongle, and look at the RF signal levels of individual planes at various ranges.
Just need to set it up, so I can switch antennas very quickly..

My next step is to config the AB switch and test it at 1.090 GHz. It might not work at that freq.

 

[stephenkearney]

So it's basically a full wave dipole antenna? According to this page impedance approaches infinity for full wave dipoles so some sort of impedance transformation would be needed; that's the horizontal section. I imagine that the feed point location is important for achieving 50 Ohm impedance.

Did you do return loss or VSWR measurements on this antenna?

.

 

[stephenkearney]

By the way, I don't understand the dimensions shown for the antenna. Why 150mm elements? The total length will be 150 + 150 + 8 = 308mm which is the wavelength of 975 MHz. Seems to me the antenna should be 275mm for 1090 MHz.

http://www.onlineconversion.com/frequency_wavelength.htm

.

 

[Richard Lee]

I did have to move the feed point up a bit to get 50 ohms. Didn't get zero reflected.. But after adding a small shorting jumper,
there was no measurable reflected power. The return loss is -20 dB or greater.

I didn't understand the 150 mm elements either, but the gain plot, 50 ohm impedance & SWR data persuaded me to try building one..
Plus, the builder, PY4BZB posted a max-range chart showing a 250 mile reach.. I was impressed.
http://www.qsl.net/py4zbz/adsb.htm#e

I am impressed with the performance.


Here's a well matched 1/4 ground plane. Compare it to the PY4BZB below.

 

[Richard Lee]

The very small antenna just surprised me again.
Just tracked a plane coming over the Canada border. The 1/4GP never got close.. I have heavy tree blockage to the north..
It seems to be preforming extremely well. Maybe someone can plug in the model info and see why it's even working.
Here's the modeling link.. http://www.qsl.net/py4zbz/ADSB/1090col2d.maa

Here is Roland's translated write-up:

Collinear Antenna elements 2 1/2 MHz waveform 1090
And decided to test this antenna design, which is a collinear elements 2 1/2 wave or a full-wave dipole fed by an impedance transformer by a line made of 1/4 wave, just like the antenna J . to J The difference is that instead of only one active 1/2 wave element, the two elements are fed by the next half wave points, in phase opposition, which, to a distant observer corresponds to two dipoles Half wave fed in phase. Can be considered to be a double-J, or a twin antenna Zeppelin!

Here's a link to a J-Pole antenna that's 220 mm long.. http://www.lll.lu/~edward/edward/adsb/antenna/ADSBantenna.html

 

[stephenkearney]

I created a model in 4NEC2 and it seemed to work okay. Then I installed the MMANA GAL antenna modeling software so I could use the original model file. Looks like a nice antenna and easy to make too!

 

[Richard Lee]

That's great. I just got a reply from Roland. I had asked him how he knew 150mm element size would work.

Hello Rich,
The 150mm were obtained after several simulations with MMANA program,
until a 50+j0 ohms impedance! With an exact halfwave on 1090, is reactive!
73 de Roland.

~~~

What gain figure did your two models display?


Edit:
In a post above, I mistakenly typed 10dBi, when the gain Roland posted was actually 9.01 dBi.
Dyslexia is my name middle. (I just found the error and corrected it).

 

[stephenkearney]

I did run the Optimize function in MMANA GAL and it confirmed the dimensions.

MMANA GAL shows 5.14 dB gain and 4NEC2 has it at just under 5 dB.


EDIT: In MMANA GAL it's 5.14 dBi in free space. It's 9 dBi when 7 meters above real ground.
.

 

[Richard Lee]

Thanks for your work. I've been really curious about this antenna..

Mine is about 9 meters above the lawn. Maybe I'm getting 9.01 dBi ??

I find it interesting that gain could go that much (almost 4db), just by installing the antenna at 7 meters..
Since you have the MMANA warmed up, can you run it at 9 Meters for me? Please..

Thanks,
Rich

 

[stephenkearney]

The 'height' drop-down control has 10m but not 9. At 10m the app claims 10.47 dBi gain.

 

[stephenkearney]

Hmm. It just occurred to me that this antenna is a 1 5/8 lambda dipole. That's a good wavelength multiple for dipoles, isn't it?

 

[Richard Lee]

Shouldn't be too hard to build a combiner for 1090. How many were you thinking of stacking?
Just a pair could make around 12 dBi of gain.

I can't believe the performance from such a small antenna.
Just changed the LNA to see if I could get better range.. It's adding miles to my max range lines.

Before now, tracking a plane over the Canadian border was pretty rare. Today, I logged eight planes over the border!

 

[Richard Lee]

I think it's 9 planes now..

Here's a before and after of the ebay LNA (kit form). There is considerable difference in max range. 50 mile rings.
http://s46.photobucket.com/user/Xringer/media/1090MHz/ebayLNA_zps65fea360.jpg.html

 

[Richard Lee]

How much LNA gain is enough?

The extra LNA seems to have added a little range. The signal level readings are 2 to 4 times higher than normal.

Never tracked a plane over the NYC area before..


Never saw planes so far over the Canadian border before..

 

[stephenkearney]

You're getting fantastic range! I'll never get anything close to that because our house is in a valley.

I've been doing some research on the 'full wave' antenna. I think it's what is mentioned on this page:

Even with a 1000 - 2000 ohm impedance (typical for HF wire
antennas), the antenna is easily matched with a quarter wave
shorted stub of open wire line. The position of the shorting bar and
the coax tap point on the stub are adjusted for minimum SWR.
A similar vertical antenna for 2m has appeared in many ARRL books
over the years, using copper tubing and elbows for the antenna and
the matching stub. (You can get an extra 1dB of gain by extending
the wires to 5/8 wave on each side, and shortening the matching
stub accordingly.)

5/8 wave for 1090 MHz is 172mm. I believe the 150mm dimension is the result of the usual reduction to make it resonant (needed for velocity factor?).

The section between the end of the stub (where it's mounted to the pole) and the feedpoint isn't really needed although it provides a convenient mechanical connection.

BTW the models in 4NEC2 and MMANA GAL match pretty well except the programs show different phase relationships for the antenna currents. In MMANA GAL the phases are perfectly opposed which makes me wonder if it's accurate.

I'd really like to fully understand and be able to visualize how the stub changes the impedance. I get that it's capacitance and inductance between the currents moving in opposite directions in the horizontal stub elements. But that's about as far as my understanding goes.