FlightAware Discussions

RF Scan of Various Combinations of Dongles, Filter, and LNA

Noise Source Used: BG7TBL

NOTE:
Do NOT use specified 12V DC Power supply, it will fry the Noise Source in a short time.
I used 5V DC power supply, with which the Noise Sourse runs just warm, and output signal level is also not too high.

(A) FA ProSticks & Filter Combinations

Setup

Scan Results of FA Sticks (orange & blue), with and without FA Filters

Image 1 of 4 : ProStick (Orange), without FA Filter

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Image 2 of 4 : ProStick (Orange) + FA Filter

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Image 3 of 4 : ProStick Plus (Blue) without FA Filter

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Image 4 of 4 : ProStick (Blue) + FA Filter

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(A) RadarBox24 FlightSticks & Filter Combinations

Setup


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Scan Results of RadarBox24 Stick with and without FA Filter

Image 1 of 2 : FlightStick (Green), without FA Filter


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Image 2 of 2 : FlightStick (Green), + FA Filter

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( C ) RTL-SDR Tripple Filtered LNA

Setup

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Scan Results of RTL-SDR Blog’s Tripple Filtered LNA

4 Likes

Thank you for the heads up. I have this board, but have not used it yet.

Unless one needs Watts out, it appears that a number of these boards work just fine on 5V.

That’s not my experience with THIS (current) version of the board.
As highlighted, this version has 100Ω limiting resistors feeding each amp, so they are well protected.
image

This is the older version that had a reputation for running hot
image

Rather than driving the receivers directly, I’d suggest at least a 6dB attenuator or you run the risk of damaging the receivers.

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You could also use two quarter wave antennas, using the airgap for attenuation!
The neighbours will be thrilled!

Sarcasm disclaimer: This would be an illegal broad band jamming device, so don’t do this.

Oh and on a technical note, you won’t be measuring not only the filter attenuation, but antenna characteristics as well.

More seriously: Without attenuation and at the gain settings you used, the graphs seem rather pointless, you need to adjust the gain for each individual filter/dongle combination so you are able to have -3 dB or so for the strongest signal.

2 Likes

Well, I have 3 dB and 6dB attenuators lying around somewhere. I purchased and used these only once in 2016. Don’t remember where I kept these. If found, will re-scan with attenuators inserted.

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Not if you enclose the assembly inside a metallic enclosure, such as a Drink Can. :slight_smile:

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Yes, it will act as an additional filter as both whips are 69 mm (1/4 wavelength), and therefore resonant at 1090 Mhz, making it a sort of double-tuned LC circuit.

June 2015

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March 2017

1 Like

That’s basically the idea behind cavity filters. :+1:

June 2015 photos


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June 2015 - This one was fried by 12v dc power supply

From the pic looks like the one that got fried has transistors as active elements for the noise amplification. Or very low power MMIC’s.
The newer one has MMIC’s (integrated amps) with heat sinks soldered on the ground plane.

Some interesting tests there, but I don’t think they have any validity in the real world.

For a start, the drive level is not representative of a local transmitter tower - it’s more like a helicopter about to land on you roof.

Image 3/4 shows about 15dB attenuation at 970MHz - but the datasheet of a typical SAW filter shows you should expect about 35dB
image

There could be several explanations for the poor performance, but RF leakage is high on the list - There is nothing stopping RF radiating from the noise generator and nothing to stop it entering the receiver.

image

2 Likes

The board I have is dated 2016-03-06. It was improved alright, it says that it’s also a ‘nose’ source. It can be used for sniffing as well, I guess. :wink:

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Seems mine & your’s are identical.
My current one is also dated 2016-03-06
It also says :NOSE" source :slightly_smiling_face:

This is the one which I used with 5V DC adapter, for scans posted in first post of this thread.

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Looking back, we had this exact discussion a year ago. I did the measurements then, so I won’t bother doing them again, but I will repeat my findings:

Been there, done that, burned a couple of devices in the past.

For all the bad things we hear and say about switching wall warts, and they are true, when it comes to output voltage one does not normally have to worry about it being above the listed output.

It will go down on switching wall warts that claims to be 5A when they are actually 2A, but not up.

Linear wall warts can be as high as 50% above the listed output. Some will come down when the load is applied, but not all to the listed voltage.

Some devices can handle the time it takes for the voltage to settle down, others are not as tolerant.

I dont see any harm using 5V dc instead of 12v dc with this NOSE :wink: source. It is rather safer. In addition lower dc voltage generates lesser RF power, which is good for direct connection of noise source to a receiver.

1 Like