FlightAware Discussions

Built my first antenna and doubled my coverage

Good and neat built. Good Soldering skill. Very crafty.
Waiting for the results.

Hi Dan - Welcome to the discussion.

Like ppauly says, do the simple thing of eliminating the coax and see if there’s something there to work on.
However, 50’ of 9913 is only about 4 dB loss (including connectors, etc.) at 1090 MHz. That’s not a lot. As someone else pointed out on another thread, ADS-B performance is not so much noise-floor-limited as it is interference-limited.

  1. If you do find some software which can provide fairly accurate estimates of received signal strength, I’d be interested in that as well…
  2. Put the receiver (as was said before) immediately after the antenna and see what your coverage looks like with and without the added coax. If the coax is really limiting you, you could see a range improvement of as much as 40%.
  3. You could have local interference impacting your receiver. Are you near cell towers or other radio transmitting towers? The added filtering in your more expensive receiver may protect you from those sources, however. Do you or your neighbors have satellite TV, and is there above ground (as opposed to buried) cable TV service? Some of that may be radiating signals (been known to happen).
  4. Everyone says the midwest is flat :smiley: but every time I drive around out there all I see is rollling hills and valleys, and lots of vegetation. Are you down in a swale or up further?
  5. Sounds like your antenna is outdoors - that’s good. Having an antenna in the attic is ok until the roofing material collects moisture, then the performance can get bad quickly.
  6. You said you had an earlier receiver. Do you know what the performance difference is between that receiver and your newer one? Was it on the same antenna at the same elevation?
  7. You say your antenna is a 1/2 wave ground plane. I’m not quite sure what that is. Is it a 1/2 wave dipole mounted vertically or is it a 1/4 wave monopole on a ground plane? Whatever it is, do you have a second antenna you can try? Perhaps one like jepolch and others have made, simple 1/4 wave ground planes? Try swapping antennas and see if there are remarkable differences.
  8. Do you notice any significant seasonal/wx changes to your station’s performance?
  9. Is your coverage pattern more or less omnidirectional? Sometime that’s hard to tell as the a/c aren’t in all directions.

There could be other questions or considerations, but those are all that I have right now.

Cheers and 73 - Jon N7UV

Thanks for the suggestions. I’m not aware of any cell phone towers near me. It’s a very residential area but that doesn’t always preclude those demons. The ½ wave ground plane is the same as the spider antenna another user built except that the elements are twice as long. All the utilities around here are underground so no interference from that and I don’t see anyone around here that satellite antennas but they could be out of sight. The reception is definitely omnidirectional. If I find any software that will measure signal strength I will achieve know.

Thanks for the comments, Dan

If you run dump1090-mutability, when you select an aircraft, signal strength in dB is displayed - that can help. I’d also do a spectrum sweep with rtl_power using a normal sdr so you get a better idea of what’s going on.

Bob k6rtm

Thanks for that information Could you explain that a little further? I’m not sure what you mean by mutability.

See this link regarding dump1090-mutability.

ads-b-flight-tracking-f21/raspbian-ubuntu-packages-for-dump1090-mutability-available-t19619.html

Hi Dan -

I’m struggling here to figure out your antenna. If I’ve misunderstood the antenna, forgive me.

The spider antennas I’ve been seeing in this topic and others are 1/4 wave antennas, and as such their feedpoint impedance is roughly close to the transmission line impedance (either 50 or 75 ohms). A 1/4 wave antenna with the radials at a 90 degree angle to the center element will have around 30 ohms feedpoint impedance; if the radials are bent further away from the center element to an obtuse angle of about 130 degrees, that will give roughly a 50-ohm feedpoint impedance; if the radials are folded back essentially on top of the insulating jacket of the feedline, that gets about a 70 ohm feedpoint impedance (however, other issues can arise from this particular configuration).

At 1090 MHz, a wavelength is 275 mm, a 1/4 wave is 69 mm. Factoring for the conductors, the electrical 1/4 wave center radiating element should be around 65 mm. Are you saying the center radiating element is twice that, or about 130 mm?

If that’s the case, the feedpoint impedance will be extremely high, and very little power will get coupled from the antenna to the feedline, which means very little signal power will get to the receiver. That antenna, if it’s twice as long as you say, should work well at 545 MHz as a quarter-wave ground plane but not well at all at 1090.

Cheers and 73 - Jon N7UV

Helo guys,

I have seen a quite big interest coming from this pages to my blog page so decide to give you just a few words that may help you building a better ADS-B reception system.

There a several things that are more important than the others and may save your radio from damage.
The first one is antenna. If you are building your antenna, then the rule: simple is better is to follow.
If you do not have the proper instruments to measure the antenna you do not know if antenna is working for the designed frequency or not. 1GHz is quite high frequency and depending on the design 1mm can make a big difference.

Use the antennas that are DC grounded. This way you can save your equipment from the ESD. If you do not have such antenna, use the old trick and make a quarter wave coaxial stub. It will act as a filter and at the same time it will ground your live antenna.

Not only that the LNAs or receivers are suffering from the ESD problems but also the SAW filters!
So better to cure that problem before you experinece the damage.

The next very important thing is filtering the RF signal going to the radio.
There are many filters available, some good, some better some not so good. The filter can help you depending the area where you live and the blockers that you have close to you.
Today it is very easy to make a good filter. Even tuning should not be a big problem and you can do it with the equipment you already have in hands and some free software.

At the end, just to confirm that we will not make a dedicated LNA4ADSB due to mentioned stencil and related costs, but mentioned LTCC filters can be inserted to the present LNA board with a bit of patience and making small modification.
I have done it for some higher frequencies (2.4GHz). It works and it should work also for ADS-B

Adam

Adam,

Welcome! And thanks for sharing your wisdom. I’m planning to make a 1/4 wave coaxial stub for my feed line. Do you recommend an open or shorted stub? Thanks.

Shorted stub is what we need.
This way you will short the live end antenna to the ground and route the statics to ground.
Double benefit, grounded antenna and a kind of bandpass filter.

Adam

Jon, the center element and the radials are all half a wave of 1090 MHZ. The length the was determined by an online calculator.

The radials are perpendicular to the center element. Bad assumption on my part. Being we are in the middle of winter in Wisconsin, that probably will not be changed soon.

It sounds like this is the likely reason my antenna has lousy performance.
I’m really interested in the ¼ wave stub do you know were I can find some simple advice on making one?
Thanks, Dan

What you need to do for the shorted quarter wavelength stub is first decide the type of the coax to have the velocity factor.
Then calculate the quarter lambda length and multiply this number with the velocity factor.
Do not forget to short one side of the coax.

When making the stub, take care and calculate also the connector if you have one (using T )
Check this page to have the idea what is going on.
mwpersons.com/FM-exciter-filter.html

Adam

Thanks for the great information! :smiley: Do you recommend shorting the end of the stub using a resistor, or just connect the center element to the braid?

Someone has used a hairpin stub as ESD & filter with this groundplane antenna.

Done by a master – with a VNA, or a very good bridge!

bob k6rtm

As mentioned, for such an approach a good knowledge and proper instruments are required.
The dimensions are quite critical to follow and who knows if the author make another same antenna what will be the result.

Using the shorted coax is far more flexible approach. The response is not so sharp, and making the error of 1mm will not result debacle. What we can see on the presented antenna with the hairpin, the dimensions are in tenth of mm. This is vey critical.

Adam

I can confirm that the LNA4All is very sensitive to static. I have probably destroyed 2 units due to that on my open coco.
Both units have been seen working for a brief time but for some reason at some time (which is hard to tell when swapping things around) both ended in silence. Current & voltages are still fine.
Will order a new chip and try the stub from above as a final try.
/paul

Hello,

if you have the consumption 60mA cca, then the unit should be OK.
Check the SMA cable jumpers.
Common problem is using heavy cables on the unit resulting the crack on the PCB 50ohm trace (input/output).

Adam

Adam, you’re a hero !!
Indeed the centre pin of the BNC connector had come loose although not obviously visible. most probably caused by swapping around. Must upgrade the whole stuff to SMA sometime soon (and should have ordered the board with SMA mounted 8)) .
And as for the improvement with just a quick snapshot on my test indoor antenna:


                   no amp       LNA4all + filter
aircraft            34                  58
max distance        90 nm             113 nm
messages/s          240                345

So the amp really works. But, as discussed here often before: without a filter adding the preamp will hugely degrade the performance. Even turning down RTL gain does not help.

Thanks again!! Here’s the artwork:


The second picture shows the outside regulator circuit, an extra protection for overloading or supply mistakes.
/paul

Since we’re in the experimental mode i would like to add another one.
My indoor test antenna is behind the window (out of HR++ high efficiency glass). Well, that might be highly efficient to keep the heat inside but it will also keep the radio signals outside. To see how much, i performed a quick comparison:

The antenna is a directional double quad. Just trying that one on my second receiver to see what some more directivity could bring.
So getting the antenna outside is well worth the trouble!
/paul