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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(B) 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

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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.

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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

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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

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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:

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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.

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RadarBox24’s 978 Mhz Flight Stick (Red)

RadarBox24’s 1090 Mhz Filter

Setup

Scan 1 of 2: DVB-T Generic Black - without Filter

Scan 2 of 2: DVB-T Generic Black + RadarBox24 Filter

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That looks very good.

See this also:

Generic DVB-T (Black), No Filter

 

Generic DVB-T (Black) + RB24 Filter (Blue)

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We’ve been doing a bunch of testing in other threads and @abcd567 kindly offered this thread to continue various testing efforts.

My plan was to get several antennas up on the roof this week and to start doing some comparisons but I soon realized that I need to get baselines on some pre-antenna components before testing any antennas. Given my high-RF interference environment I decided to start with making a few things…


From the left…

  • FA 978-1090 Filter
  • RBOX 1090 SDR. Unshielded on top, shielded on the bottom.
  • RBOX 1090 Filter, Unshielded on top, shielded on the bottom.
  • NooElec NESDR NanoV3 SDR, Shielded on top, unshielded on the bottom.
  • gtj0’s super-duper dual 3-way resistive delta shielded splitter.

Why the shielded versions??? Heh, here’s why…


That’s my ambient environment with an unshielded NESDR, 33db gain and the FA 1090 antenna on the roof.

First let’s talk about SDRs…
The following graphs were taken AT THE SAME TIME (well almost since I had to get screenshots a few seconds apart). I had 4 SDRs connected and 4 Spektrum windows open. Aso all settings were the same… sweep 24.0 - 1200.0 MHz, 200Hz bandwidth and 33db gain.

Here’s an unsheilded RBOX 1090 (with built-in 1090 filter) with a dummy 50Ω load:

and here’s the shielded RBOX:


It’s actually kinda weird because the VHF interference is gone but the UHF grew a bit.

Here’s the unshielded NESDR (no built-in filter) with the dummy load:


That’s MUCH better.

and here’s the shielded NESDR:


That’s very nice. Going forward, I’m going to use the shielded NESDRs.

Next post… RBOX 1090 Filter vs the FA 978-1090 Filter.

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