Getting the best results!

[foxhunter]

Sure, but still chance of incorrect measurement.

At the end it doesn’t matter if you have a result with 325, 327 or 317 aircraft in the script. That’s no evidence about proper gain setting, just a clue about the right path.

I would rely more on that > 3dBFS thing and the range provided by the graphs. Everything in between should be fine.

[craigtrex600]

Hi, would you run this code at a certain time of day or anytime?

[SDMark]

@abcd567

The desired impedance of antenna is 50 ohm. This is to match with receiver and coax impedances of 50 ohms.

I’ve got my antenna on the roof and have connected it down into the house using about 25 feet of RG-6 (75 Ohm) TV/Cable coax, and then I have a TypeF/SMA adapter to connect to the ADSB Dongle. Based on other posts here (and elsewhere on web) it seemed like the impedance mismatch when the cable reached dongle and changed from 75 Ohm to 50 Ohm wasn’t a big concern - as long as it’s in a Rx situation (for Tx the reflected energy is large enough to cause issues). It didn’t occur to me there’s also a potential for a mismatch at the start of the cable, where the antenna plugs in.

@abcd567

The 1/4 ground plane has impedance as follows

• Horizontal Radials = 32 ohm
• Radials bent down to 45 deg = 50 Ohm
• Radials bent down to 90 deg ( i.e. totally vertical) = 75 ohm

So given my current set up, I think it would make (technical) sense to have the antenna impedance match the 75 Ohm cable, and I should bend the radials down to 90 degrees. However, I’m not sure it it make practical sense to do that - it loses the ground plane (doesn’t it?) and if one 50-75 Ohm interface isn’t a huge deal, would two make a big difference?

@abcd567 how are you calculating the antenna impedance - is that coming out of 4nec2?

Finally - I feel like this very interesting, valuable thread has morphed into about 3 or 4 conversations. Is there some method or protocol to “fork” it? I almost “replied” here by starting a new thread (“Antenna Impedance and Gain Predictions”, or some such) and linking back to the last relevant post in this thread, but I wasn’t sure if that “good form” or not for the forum.

[abcd567]

@SDMark

I’ve got my antenna on the roof and have connected it down into the house using about 25 feet of RG-6 (75 Ohm) TV/Cable coax, and then I have a TypeF/SMA adapter to connect to the ADSB Dongle. Based on other posts here (and elsewhere on web) it seemed like the impedance mismatch when the cable reached dongle and changed from 75 Ohm to 50 Ohm wasn’t a big concern - as long as it’s in a Rx situation (for Tx the reflected energy is large enough to cause issues). It didn’t occur to me there’s also a potential for a mismatch at the start of the cable, where the antenna plugs in.

Your views are logical and practical.

You may like to brows following post:

Spider Antenna - How Tilt of Radials Affects Impedance and SWR

 

[foxhunter]

@craigtrex600

Hi, would you run this code at a certain time of day or anytime?

If you really want to use that script, you would need to run this on different times of the day.

[jimMerk2]

Also, as I mentioned earlier, if you are feeding FlightAware while running the tests, the MLAT sync will be lost. Maybe should stop piaware while running the tests?
sudo systemctl stop piaware

[geckoVN]

@SDMark

I should bend the radials down to 90 degrees. However, I’m not sure it it make practical sense to do that - it loses the ground plane (doesn’t it?)

A 1/4 with a ground-plane is a mono-pole antenna, but becomes a di-pole with the ground radials folded down.
(this is not a bad thing)

[foxhunter]

Stopping piaware is not required for package installs. But it will run into an error that no data are processed.

[jimMerk2]

No, I meant while the script is running, should you stop piaware? The script does a restart of dump1090-fa after each gain change. This causes problems for the mlat-client.