yagi - do you have experience with directional antennas?


#62

This is quite an over simplification… Beam width goes in sync with forward gain and sidelobes. The main factor is actually boomlength with a number of elements which are optimally spaced to reach a desired pattern with a desired antenna impedance. I have seen the Rothammel antennabook mentioned before, there is also the ARRL antenna handbook and for example the DK7ZB antennapages. None of this specific to ADS-B but they all contain useful information.

Simply adding or subtracting elements is not the way to go. I believe there are several antenna programs out there which can calculate optimal antenna’s for a specific frequency or band, some including the images as shown earlier. MMANA http://hamsoft.ca/pages/mmana-gal.php , various versions of NEC such as EZNEC https://www.eznec.com/ and antenna magus http://www.antennamagus.com/ come to mind. As I have not yet build any antenna’s myself (yet), I have not used any of these so do not see them as recommendations.


#64

Interesting topic.

I have a question regarding antenna gain & geometry on 1090MHz.
My location has almost flat horizon 360 degrees, and I see planes out to about 200NM.

To the west, I have pretty clear takeoff over the ocean, and frequently see 200-230NM or so with high flying planes (Trans Atlantic overhead here).

I wonder if anyone have experience with adding e.g. 10dB antenna gain, and getting signals further out (how much on a regular basis)? Or is this simply a matter of limititations by the geometry of curvature & height?

I have received longer distances via tropo ducting, but I am more interested in the average conditions of coverage.


#65

It’s mostly the case.

This is the exception to the rule at this frequency.

You are very likely near, or at the limit, but one would think that an extra 10 dB could help ‘recover’ that weak tropo ducting signal you mentioned.


#66

@LA7DFA

You can easily determine your max range set by curvature of earth, terrain, and height of antenna by method given in first post of the following thread. If it is more than what you get now, you can consider using a high gain antenna or an amplifier.

What is the Maximum Range I can Get?


#67

You are on the Flightfeeder, if the antenna is installed properly i don’t believe you can get much more range, these setups tend to be very good on their own. Actually the way it is set up you should not modify it as per flightaware.

I’m not familiar with your system, do you have a gain setting? It may be preset for noisier locations with planes closer by, so you could increase it a bit probably.

For example i believe if you were to change the antenna or install an amplifier the Flightfeeder couldn’t not receive it’s GPS anymore because the antenna is integrated with the ADS-B antenna.
Changing gain should be no problem though (otherwise they would not offer it in the user interface).


#68

FlightFeeder has the gain adjust in one of the on-screen menus (“Radio”). Initially comes set up as “Automatic”. It also has a very useful report of the radio signal message rate and errors.


#69

Flightfeeder via tropo ducting. 900 kilometers.


shortened cable up to 2 meters


#70

@LA7DFA

On 1296MHz distances up to 2661km have been covered (about 1400NM). See https://vushf.dk/iaru-reg-1-dx/ and http://vushf.dk/vushf/wp-content/plugins/IARU-DxList/ShowQso.php?Call=D44TXV&Band=1,296%20GHz&Propagation=TR&Distance=2661

Now, the problem is that tropospheric ducting takes place at relatively low altitudes, somewhere between 1500-10000ft. When planes are above the duct their signal will be reflected back upwards so you could only receive those that are “below” the relection zone in the duct & only if your own antenna is in the duct as well. In the optimal case: No gain needed, what’s in the duct can overpower most every other signal (personal experience on a lower band).


#71

Thanks for the replies guys. Yes I know I would have to ask Flightaware for approval, before changing antenna (or adding diversity antennas). But my post here was just to hear what other have experienced, using yagis.

For now I will just move the antenna slightly, so its above of my other antenna on the chimney.
Later I will get rid of the 15m long feedline, and place the receiver close to the antenna.
I cannot use preamp here, as I transmit 1kW on HF & 50MHz nearby.

JoePPi makes a good point regarding Tropo ducting. Yes the duct will be below most planes, so even when you receive planes far away, it does not mean you have good coverage at high altitude.
I remember receiving a plane and a helicopter at about 1000ft near Shetland, during my first days of operation. But it was no reception in that area at high altitudes.

I will have a look at the gain setting. Actually I live in a very quiet location, so it might be something to gain there :slight_smile:

Regarding GPS, a 1090MHz yagi, would work as a badly tuned dipole on the GPS frequency. It probably would work just fine with clear view to the sky.


#72

Most preamps have a high pass filter fitted before the amplifier anyway, at least those aimed at ADS-B. Don’t know which hardware the flightfeeder is exactly, but i suspect they have at least some sort of LNA fitted.


#73

There is a built in bandpassfilter in the unit, but filters are not infinite, so using 1kW close to the antenna will probably overload the receiver somewhat, even if its 1GHz lower. I looked at the settings on the F.A. receiver (v10) now, but it was no way to change gain settings using the screen.


#74

Modesbeast receiver + RPi.
http://wiki.modesbeast.com/Mode-S_Beast:System_Design

Major change is splitting up the total gain into two ERA-3 devices, so one of them is placed before the first filter, and so improving the total noise figure by about 3dB and the sensitivity by 3.5dB. Also the whole chain is matched, which results in a flatter passband.


#75

The orange FlightFeeder doesn’t have any filter, it has the FA Pro receiver stick. You would gain something if you use in front of it a SAW filter (or even a cavity filter).
SAW are cheap and very efficient.