best antenna

[Anmer]

Some antennas of interest ....

I'd add the TMRF-1090, now only GBP £54.00

http://www.tmrf.co.uk/product/tmrf-1090/

I reviewed this in March 2013 and it performed well compared to my more expensive Elad GP-1090.

http://radarspotting.com/forum/index....html#msg10861

[gregy]

after reading thru the complete thread ..I was motivated to jump in with the Coco challenge.
I watched with interest 1090 LDF coco

Having 1/2" Andrew superflex (FSJ4-50) available to me (not as ideal as LDF 1/LDF4) - because the superflex is a spiral outer ... makes it more difficult to cut and trim accurate)

My setup
RTL SDR dongle + minicircuits power injection (both 75ohm impedance) - both in separate diecast fully sheilded enclosures ... with heavy power supply filtering (not using PC USB power)
& heavy chokes on USB cable (DSO confirms power very clean)
ADSBscope & RTL1090 beta 3
Feeder cable LDF4-50 (50 ohm) approx 10m
All N connectors
(yes I know there is an impedance mismatch - but i have a LNA4ALL 50 ohm LNA ready to fit at antenna base - after antenna benchmarking - which along with 50ohm feeder and 50 ohm antenna ... will minimise mismatch loss at bottom end later)
antenna mounted on PVC pipe approx 3m above rooftop & overall approx 10m above ground
surrounding houses all flat roof and exact same height and design.
flat terrain in most directions - with water over approx 160 degrees (my location inland approx 400m from coast)
I have a VNWA vector network analyser available at home

Reference antenna - Diamond D130J discone (VSWR at 1090 suprisingly good)
Results 50-100nm

The antenna saga ... so far (yes i feel the coco frustration also)
FSJ has VF 0.81
1/2 wave elements adjusted for VF 0.81 (element intergap spacing less than 1 mm, inner dielectric trimmed flush with outer sheild)


CoCo #1
used the F5ANN design (but with only 4 x 1/2wave plus 1/2wave whip - not shorted)
1/4 wave phasing choke from 3/4" copper water pipe - initially directly at bottom element.
outer sheath removed from feeder cable under choke - hence used VF1 for choke calc length (unlike F5ANN design)
VNA sweep - couldnt get VSW below 3 ... with multiple combinations of choke length amd 1/2wave whip length (not shorted - because LNA not in circuit at present, i have no DC blocking from power injector - which is not so easy to remove ... hence all antennas w/o short during testing)
Results : range typically to around 150nm
peak frame rate 7100

Coco #2 (ongoing evolution of #1)
moved choke to be 1/4 wavelength BELOW the bottom element join point to coax feeder (after a lot
of internet research inc this forum ... this appears to be considered the optimum position)
... cant say i saw much change in VNA sweep results
BUT .. after removing 1/2W whip and replacing with 1/4 coax element (VF adjusted) and 1/4 whip (VF 1) ... a signifigant improvement.
VSWR still around 2 ... and still cant get it to behave like i expected when tuining it on VNA ...
however put it onto mast (same as #1 test) ... and WoW!
Results : range now reliably 200nm in multiple directions .. with detections out to 230nm
(and in many "inland" directions range doubled! to 200nm ...)
Framerate - peaked for 20 minutes at 11,000 (during exact same period 24 later under test as c/w #1 achieving 7100 fpm)

As yet I have not fitted LNA (i need to connectorise and house it into diecast and weatherproof enclusre) ... this will be the next test

Conclusions and observations (thus far)
- out to sea (200-230nm range) ... I believe Im limited by horizon/curvature of earth.. with my calcuated elevations being less than 1degree ... eg plane at 40,000ft at 220nm ... elevation is very low (improvemnt #1 to #2 was 180nm to 230nm)
However in other directions, I was previusoly constrained by signal, hence why the improved antenna performance has boosted these directions considerably (aka doubled)
I chose 4.5 element to begin with, to minimise the cumulative errors in coco ... and also because it was faster!
My location is VERY close to airport (less than 2km to control tower) but both under and at distance from some very heavy routes with high altitude planes traversing at long ranges (eg 200nm range at 40,000ft for long periods) .. hence didnt want to flatten the coco pattern too much and loose closer in performance
rigid coax (LDF/FSJ or similar) is MUCH easier to work with and get accuracy - as c/w braided coax
The antenna is self supporting, the joints are soldered and reliable, cutting and trim easier
(note i cut elements approx and then trimmed each on small bench grinder - fine wheel to get reasonable accuracy ) soldered each and checked continuity at each step.
AFter frustration with the VNA and trying to tune the coco ... ultimately just putting it to the live test ..
I was hoping for an exprience like 1090 user ... and his LDF coco sweep test - where it demonstrated expected tuning and sweep behaviour.
.. But heh i cant argue with the live results ... its certainly performing no doubt.

Still to come ... complete and fit LNA - Id be very dissapointed if I didnt see an improvement, even with my low loss LDF feeder (benefit of being in the "industry" ... with discarded lengths from cell sites) ... given the LNA4ALL has a very good noise figure and excellent gain ... having it at antenna will
improve overall system noise figure & overcome the mismatch loss, feeder/connector loss, power injector inline attenuation etc
... Yes I know my setup uses some more costly items ... but Its the challenge of extracting every bit of performance from DIY - as compared to just buying off the shelf commercial.
(& yes Ive been monitoring my live ADSBscope vs flightradar feed - & Im now reliably seeing a signifigant number planes not shown on FR24) .. - i live in a part of world with very few feeders I suspect

Long post I know - but spent quite a bit of time testing and working up to this summary thus far.
SUmmary : coco would appear to feasable - but yes accuracy counts and thus more time consuming, and definitely the rigid coax with solid outer sheath makes it easier/more rerliable and accurate (but agree if you have to purchase the coax its not exactly cheap)

Oh ... and during this period - I was seduced by the work of ABCD567 .. and threw together a franklin colinear - with very poor results - perhaps i was seduced by the apparent ease of construction and didnt pay close attention to detail .... unlike my coco ... cuatiousd as result of the coco challenges as noted by many on this forum
Next step will be to make new franklin or one of the others on this forum - to use as a benchmark against my coco ...

[abcd567]

@gregy:

Franklin definately requires accuracy.

For vertical 1/2 wavelength limbs, accuracy is easy to achieve: these are all 138mm long.

It is the phasing & impedance matching stubs for which accuracy is critical, difficult to achieve, and is often neglected by DIY enthusiast.

(1) For all the phasing stubs, the TOTAL length = 138mm i.e. upper horizontal wire+bend+lower horizontal wire=138mm.

(2) For central impedance maching stub, the sum of upper horizontal wire+lower horizontal wire=138mm. The length of wire in bend is in addition to this.

(3) the spacing shown between parallel stub wires are from center of wire to center of wire. Hence a spacing of 5mm with a wire dia 2 mm means 5-2=3mm gap between surfaces of two wires.

(4) The optimum spacing of impedance matching stub's parallel wires (to achive a swr below 1.5) depends on wire dia.

Forum member Dave ("trigger") has made a Franklin very carefully and got good results. I hope Dave will give you some valuable practical tips.

[abcd567]

I have received quotation+specs from "Fujian Quanzhou Huahong Communication Co. Ltd, China" for 9 dBi (=6.8 dBd) antenna.

Good day there.
Thank you very much for your kind inquiry.
We can do supply the 1090MHz antenna.
Enclosed the specification for reference. Pls check and advise.
Below is detail quotation.

EXWORK 30USD/pcs.
10pcs total 300USD.
Freight by FEDEX (to Canada) 120USD.
Total: 420USD (for 10 pcs).

Delivery: 5-7 working days.

SPECIFICATIONS:
Chinese 9 dBi Specs.jpg

[YsMilan]

I have received quotation+specs from "Fujian Quanzhou Huahong Communication Co. Ltd, China" for 9 dBi (=6.8 dBd) antenna.

Good day there.
Thank you very much for your kind inquiry.
We can do supply the 1090MHz antenna.
Enclosed the specification for reference. Pls check and advise.
Below is detail quotation.

EXWORK 30USD/pcs.
10pcs total 300USD.
Freight by FEDEX (to Canada) 120USD.
Total: 420USD (for 10 pcs).

Delivery: 5-7 working days.

SPECIFICATIONS:
[ATTACH=CONFIG]4795[/ATTACH]

Chinese ADS-B Antenna?My antenna manufacturer：
http://item.taobao.com/item.htm?spm=..._u=n1nudufca8d
Tel：(86) 755-89985723
E-Mail:sdtxlj0925@163.com
1.png2.png
Price：150RMB=24.4USD,Detection range about 200nm
2 (1).PNG

[abcd567]

Chinese to English translation of page link given by forum member YsMilan:

http://h5.m.taobao.com/awp/core/deta..._u=n1nudufca8d

Research and design can be customized 100Mhz ---- 6G various communication antennas, according to drawing production, mold production

For more information, please call: 0755-89985723 18681562757 Liao Health QQ: 358963559
E-mail: sdtxlj0925@163.com
4G antenna, mass production, welcome to order counseling
Brand: Sheng
Category: Fiberglass Omni Antenna
Frequency Range: 1020-1150Mhz
Bandwidth: 100
Gain: 9dbi
wave debate width °: H: 12E: 10
VSWR: ≤1.5
nominal impedance -Ω: 50
Polarization: Vertical
Maximum Power W: 100
Size m: 1.2
Housing material: PVC
Weight kg: 0.5
wind strength m \ s: 60
Connector: N Female or customer specified
base: M110 big sucker, with three m 50-3 cables, connectors buyers custom.
Note: Do not big sucker base, minus 20 yuan without a big sucker base, the antenna comes with N-type female.

[gregy]

hello 1090 mhz

do you have any details on measurements from your tests on your LDF coco.
i note your friend had professional test equipment,
do you have any of the VNA measurement data?
VSWR? bandwidth? impedance etc
looking to see if it gives me any clues on mine.

thx

[trigger]

Hi gregy,
I have made a few Franklins and found them to be superior to any of the CoCos I've made. I first made this one. I then made another but added an extra couple of vertical segments and stubs. The diameter of the wire I used was 1.5mm. As with any antenna, accuracy is king.

Later models used the spec as in this post http://forum.flightradar24.com/threa...ll=1#post56957 with the slightly longer matching stub.

[abcd567]

Hi gregy,
I have made a few Franklins and found them to be superior to any of the CoCos I've made............ As with any antenna, accuracy is king...........

True. The tuning / impedance matching deviates considerably with relatively little inaccuracy. This is true for all antenas: franklin, coco, coil loaded, strip, plain dipoles (any length) etc.

Only in case of 1/2 wavelength dipole, it is relatively easy to achieve required accuracy. Even some amount of inaccuracy wont change impedance appreciably from 75 ohms, hence SWR will also not change appreciably.

Two simple and easy to achieve requirements for 1/2 wavelength dipole are:

(1) Each limb is 1/4 wavelength (i.e. 68 mm at 1090 Mhz).
(2) The gap between the ends of limbs at central feed point should be as small as practically possible.

I ran two simulations:
(a) with 0.5mm gap, result gain=2.2 dBi & SWR=1.0
(b) with 2mm gap, result gain=1.7 dBi, SWR=1.2

(I use a gap of about 2mm, as it is practically very difficult in DIY situation to make a gap less than that).

[gregy]

thanks for both your responses im motivated to give the franklin (another) try
and this time be DIY pedantic in construction.
either way i want something to benchmark the coco against, im obsesive to determine if i have yet maxxed
out my range ... given physical constraints of my antenna height and terrain.

a couple of questions for you both
1) wire available to me are
brass rod dia 2.6mm
copper wire dia 1.6mm
(have tried but cant get 2mm copper)
id prefer using the brass - given its greater mechanical benefit for supporting antenna shape etc
i note you have given dimensions for "2mm wire" and that phasing and matching stub dimensions are quite critical.
Q; which to use? and how should i adjust the gap accordingly?
2) i believe your dimensions are for 75ohm,
Q; what dimensions of antenna would change for optimising to 50ohm?
if its only the feeder connection on stub - then no problem - i have a VNA and hence can adjust position on matchung stub to minimise VSWR)
(im using LNA and feeder both 50ohm... hence wish to also ensure minimal mismatch at antenna to 50ohm,
and leave the mismatch loss to occur at 75ohm power injector/ SDR at bottom of feeder - after LNA gain where impact
should be minimal)

i appreciate your encouragement and help... and in due course will post my VNA test/tuning experience with franklin,
and also range plots of coco (4.5) vs franklin

[abcd567]

thanks for both your responses im motivated to give the franklin (another) try............a couple of questions for you both..............

I will re-model the franklin for both of your wire sizes of 1.6mm & 2.6mm dia (2 models) with 50 ohm impedance match, and run the simulation to optimize dimensions, then post the results. I plan to do it this weekend.

[gregy]

brilliant! and very much appreciated.

[abcd567]

Hi gregy
How sharp can you bend 2.6mm dia brass rod? I mean if you bend a piece of brass wire in the shape of letter U, how much mimimum gap you can achieve without cracking or kinking the wire at the bend?

[gregy]

good question, will try tonight when home from office, (opp time zone to you)
i have gas torch for heating - so presumably can also heat a little to reduce tendency to tear the brass on tight bend.
... will post outcome of some differnet radius U bends.. i will try for an internal gap of 3mm.. but this may be ambitious.
(would give distance of 5.6mm between centre of brass dia 2.6 wire .. eg 3+1.3+1.3 )
aka will try 3/3.5/4mm drills as a mandrel for U bends

[abcd567]

Neat U-Bend & L-Bends (and a neat soldering job)