best antenna

[Oblivian]

Immediately after creation of FR24 thread, I realized that its title is too long, and wanted to modify it to the shorter name "Do I Need A Filter?", but the FR24 forum does not allow to change thread title once it is created.

... https://forum.flightradar24.com/thre...ignals-In-Area

[abcd567]

During the week I ran the 'do I need a filter' test .....

In October & November 2017, I created two identical threads describing method for RF Scan as listed below:

28 October 2017 - FlightRadar24 forum, Titled: Find Out Existing RF Signals (Cell/Mobile/Pager etc) In Your Area

09 November 2017 - FlightAware forum, Titled : Do I Need A Filter?

Immediately after creation of FR24 thread, I realized that its title is too long, and wanted to modify it to the shorter name "Do I Need A Filter?", but the FR24 forum does not allow to change thread title once it is created.

Few days later when I created the same thread in FlightAware forum, I used the short and handy name "Do I Need A Filter?"

[Ubbe]

About DC blocker: Or you could open up the amp, the lid is often just a very thin metal plate with press fit, and remove the power pass coil that are easily spotted as it goes from input to output and are usually the only component that are placed on the circuit board on the lid side.

Remember that those sat amplifiers could have a noise figure of 5dB and the generic 50-3000MHz $25 amplifiers from Ebay have 0.8dB or even less. You can dig up more signals 4dB down in the noise with those low noise amplifiers. It's like you had doubled the gain of your antenna.

[Stealth]

Went and bit the bullet and ordered an FA antenna and set it up last weekend replacing the old 8-element CoCo;

[ATTACH=CONFIG]9463[/ATTACH]

It's now running 'naked' (ie no amp which was in that piece of pipe you can see on the fence) into a FA Prostick+. I'm now getting regular hits 200Nm+ and yesterday set a new bench-mark of 224Nm to the NE out over the Coral Sea.

The mast consists of a 1.8m J-bracket (designed for mounting TV antennas) sitting 1.7m above the ground to which I've added an old pool cleaner pole which adds another 3.8m on with the antenna clearing the house roof-line.

During the week I ran the 'do I need a filter' test and there's spikes from the not-too-far distance GSM tower
[ATTACH=CONFIG]9465[/ATTACH]
so I've ordered a filter from Hungary via eBay and it should be here in a week or so. I'll test it locating it up top of the antenna and also just before the Prostick to see if there's any discernible difference.

Good to hear its worked well for you. It still leaves some room to experiment, so win-win!

[petercr]

Went and bit the bullet and ordered an FA antenna and set it up last weekend replacing the old 8-element CoCo;

Antenna.png

It's now running 'naked' (ie no amp which was in that piece of pipe you can see on the fence) into a FA Prostick+. I'm now getting regular hits 200Nm+ and yesterday set a new bench-mark of 224Nm to the NE out over the Coral Sea.

The mast consists of a 1.8m J-bracket (designed for mounting TV antennas) sitting 1.7m above the ground to which I've added an old pool cleaner pole which adds another 3.8m on with the antenna clearing the house roof-line.

During the week I ran the 'do I need a filter' test and there's large spikes from the not-too-far distance GSM tower (about 1km away slightly to the right of that tree)
1090Mhz waterfall and spectrum.jpg
so I've ordered a filter from Hungary via eBay and it should be here in a week or so.
https://www.ebay.com.au/itm/ADSB-Fil...53.m1438.l2649
I'll test it locating it up top of the antenna and also just before the Prostick to see if there's any discernible difference.

[Stealth]

@abcd567

Maybe I didn't convey in that post that I'm on top of the basics.

The point of the post was to relate how dramatic the effect of signal overload can be. It wasn't just a reduction in displayed aircraft or range, it was a drop from seeing numerous aircraft, some beyond 175nm to seeing virtually nothing. Virtually nothing was just one aircraft within about 15nm. It was way more dramatic an effect than I would have imagined.

Some additional learning points from this scenario were:

+ Don't assume an antenna is going to work well solely based on reflected power reading i.e. VSWR, however its a good sign that it will work to some degree
+ Range should not be used as the sole indication of antenna effectiveness, look at message rate and the number of 'hits' over a significant period of time
+ Finally, don't ever take something at face value, check it out

My 'fall back' and the 3 element co-linear I mentioned previously are shown below (original graphics as downloaded, not my actual versions).

150_x_150 colinear.jpg

5-8th.jpg

[abcd567]

@Stealth

I suspect your "fall-back antenna" is a low gain simple antenna like the mag-mount Whip (supplied with dvb-t), or Spider or Cantenna. These simple antennas pick comparatively less cell/mobile signals, and the 1090 mhz signal is not "drowned" into the strong cell/mobile signals.



Below is the RF Scan of signals at my location showing strong Cell Phone signals.

The scan was done using OPTION-2 (DVB-T plugged into Windows computer) of following thread:

Find Out Existing RF Signals (Cell/Mobile/Pager etc) In Your Area

[Stealth]

Playing with antennas is the best part of this pursuit. Last week I was about to build my third co-co in recent times, first two were duds. No matter what I did with them the analyzer kept showing a low VSWR everywhere but 1090. So for a change I built a three element co-linear using coax screen and built on a 6mm fiberglass rod, three simple coils and all was ready to go. Analyzer showed around 1.6 VSWR. Down with the mast, up with the antenna. Rush indoors to see results.......nothing, blank screen.

Back to the fall-back antenna and a re-think. Decided to get a FA antenna express mailed, just to give me a commercial benchmark. Arrived today, wait for the wind to die down and up it goes. Expecting glorious signals, hurry inside. One measly signal within 20 nm, nothing else.

Much head scratching, try a few changes on the gain settings and two or three signals close in. I wonder, so drag out the bandpass filter and insert. Bingo! Signals flooding in and at a very decent rate. The FA antenna had brought enough signal in to completely overload the FA Pro-stick Plus.

Now I wonder if my co-linear from last week was good after all and I had the same issue........

I should mention that the 'fall-back' antenna had been receiving quite well, worst was out to 100nm best out to 200nm + in some directions.

[abcd567]

CONGRATULATIONS!

[petercr]

Looks like the new antenna is working based on the last 7 days...
new antenna.png
(and today is only just 4hrs old based on GMT)

max range last night was 145Nm

[abcd567]

Great to know you already have experiance in DIY antennas by helping your dad, an amateur radio enthusiast.

Yes, DIY is cheaper for sure . This is in addition to the fun and satisfaction it gives.

[petercr]

Hi Peter
Good that you have decided to make a DIY dc blocker.
DIY is fun.

My Dad was an amateur radio enthusiast from the time he got out of the RAF at the end of WWII until he died (about 20yrs ago) and I fondly remember helping build a number of his antennas so this does bring back some memories...

(and DIY is often cheaper )

[abcd567]

Hi Peter
Good that you have decided to make a DIY dc blocker.
DIY is fun.

A 100pF capacitor is ok. The 200pF is not critical, but preferable.

The impedance added in RF path by 200pF capacitor is 0.73 ohms. As the 100pF has half the capacitance, its impedance is double i.e. 2x0.73 = 1.46 ohms. Both these values are low enough to be acceptable.

As the prices of 100pF and 200pF are nearly same, I preferred to use 200pF to get slightly lower impedance at no extra cost.

X_C = 1/(2 x pi x f x C) = 1 / (2 x 3.141 x 1090 x 10⁶ x 200 x 10^-12)
= 0.730 ohms

[petercr]

Hi abcd, (having read this far I feel I sort of know you)

Voltages on both F-connectors are correct (about 17V on the amp side as it's no-load without the amp connected) and 0V on the TV side. I have a spare 2-way splitter that I've gutted and there's a hobbyist electronics store 10mins down the road where I can get 220pf ceramic caps for less than a dollar so I might make a power blocker as well as an extra precaution...

(or I can put 2x100pf in parallel if 200pf important - caps come in a pack of 2pc so no problem either way)

[abcd567]

@petercr

1. There are two output ports in power inserter, one for TV, other for Amplifier.
   In the powered-up condition, when measured with a multimeter:
   • The terminal for TV MUST have zero DC voltage to protect TV (or the DVB-T dongle)
   • The terminal for Amplifier MUST have full DC voltage (say 14V DC or similar).
     Zero DC at this terminal means no power supply to amplifier and the Amplifier wont amplify. It will rather attenuate.
   
   
   Power Injector - DC Voltages.png
   
   
2. Test continuity of your antenna between core and shield at feed point by a multi tester. If it shows open circuit, then DC Blocker is not necessary. However even with open-circuit antenna, it is safer and desirable to have DC Blocker so as to protect your power insereter and amplifier from damage in case of accidental short circuit.