ADS-B Site Upgrade Reconditions

I have both. The uputronics seems to be susceptible to RF overload a little more than the rtl-sdr. It is easier to power the uputronics with a USB cable.
My location requires a cavity filter for both.

Hi,

Thanks for the reply - at the moment I’m thinking if I would go ahead with the RTL version I would use a bias tee (external) as recommended by @jaymot earlier. This would be powered via USB, so it seems easy enough just to strip a USB cable and gather the relevant cables inside to power it. But the uputronics seems to be the easier option.

That’s poor coax. I would look at Messi & Paolini Hyperflex 10. Martin Lynch sells it in the UK.

Thanks for the advice, I’ll have a look later on and probably go for it.

Also, just did a scan of RF noise in my area and I think it would be a good idea to get a filter…

The 1090MHz band looks pretty poor as the antenna is inside at the moment as I’m currently doing work on the new setup and should be up and running soon.

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Sorry, but NO.
RF simply isn’t that straight forward.
It’s a beginners mistake to treat RF as DC

You need to take into account the mathematical relationship between two (or more) frequencies.
For example, a strong 364MHz signal could easily resonate a 1090MHz antenna and de-sence a receiver.

There is an old RF adage that says: " Every mixer can be an amplifier, every amplifier can be a mixer"
As we all know, the output of a mixer is four frequencies: the two fundamentals plus F1
+F2 and F1-F2
Using a simplified example: a high powered, FM station on 110MHz plus a local transmitter on 980MHz could produce 1090MHz inside your LNA and you’d never know why your system performed poorly.

Not to mention possible splatter and bleed-over from strong signals on nearby frequencies and harmonics from transmitters on completely different frequencies and bands.

 

 

If you place a good band-pass filter like Flightaware Light Blue or Dark Blue Filter or a Cavity Filter beween Antenna and Receiver (or Antenna & LNA if you are using a LNA without builtin filter), then all the FM and VHF UHF out of band frequencies will be eliminated by filter and wont reach the Receiver or LNA. This will prevent:
(1) Overloading & de-sensing of receiver or of LNA
(2) Creation of harmonics by mixing & cross-modulation of various out of band frequencies in the amplifier stages of receiver or LNA.

Please see “Scan 3 of 3” below which shows how adding a Filter Between Antenna and Receiver eliminates unwanted RF signals picked by Antenna.

Spektrum - How-to Speedily Scan RF Noise in band 24MHz ~ 1800MHz

 

The results of scans are below:

The scan 1 shows RF noise picked by antenna and processed without any filter , The scans 2 & 3 were done with filters, and show how filters remove this noise.

Scan 1 of 3 - FA Antenna + Generic DVB-T (no internal or external filter)

Thumb-Generic DVB-T

CLICK ON IMAGE TO SEE LARGER SIZE

Scan 2 of 3 - FA Antenna + ProStick Plus (Only Internal filter of ProStick Plus. No External filter)

image
CLICK ON IMAGE TO SEE LARGER SIZE

Scan 3 of 3 - FA Antenna + ProStick Plus (with internal filter) + External Filter (FA Light Blue)

imageimage
CLICK ON IMAGE TO SEE LARGER SIZE

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Hello everyone,

Thanks for the replies regarding the filter, at the moment the plan is: 1090MHz antenna (reference the picture at the start of this thread), then as short as possible coax (3D-FB) run into a waterproof box with the 1090MHz filter before the LNA which would be both in the box directly bellow the antenna, then as short as possible LMR-400 cable run indoors - which would go through a bias tee then into the FlightAware Orange SDR. Any further advice would be appreciated if anything seems in the wrong position or anything else what would improve it further. Thanks.

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There is no need of that cable to be low loss. After the LNA you can have attenuation, the resulting chain SNR will not be affected significantly.
That “better” cable expense will not yield any real benefits.

Another questionable decision. People keep being scared of “interferences” in front of a LNA. I think that’s not needed in most of the cases, and placing a filter in front of an LNA will just decrease the SNR of the chain. You can try to see what results you get.

Thanks for the advice, guess something like RG58 would do the trick. Would I still see a relative improvement in messages received and the amount of aircrafts seen even using a low quality coax after the LNA - guess that would be roughly 2/3 dB amount of loss.

Not likely at 1GHz. I used RG6. It’s an impedance miss-match, but it won’t affect too much the end result.
Note that you might need adapters at the end of the cable: F-type to SMA.

I haven’t ordered any coax yet, so should be able to get some RG6. I’ve got all the adapters needed for all the different male / female connections. Not sure if you have seen the scan I did of RF noise posted earlier, but here it is attached regarding the amount of noise being received by the antenna. I’m planning on getting a RTL-SDR 1090MHz LNA (what has no filter, unlike the uputronics LNA.)

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That scan looks “normal”, except the end portion. Also I think the antenna you used is not appropriate for higher frequencies. Your receiver stops working at about 1.5GHz, what you see after that is a mirror image created in software.
The LTE signals look impressive on the scans but remember, all the cellphones work perfectly fine tuning on those close frequencies, without interfering one with another. The LNA chips inside the ADS-B LNA filtered amps are similar in their technical capabilities and will not be overloaded. Unless you are really at less than 30’ of a cell tower. A good ADS-B antenna is tuned for 1090MHz, so it will favor that signal.

Thanks for the advice, regarding the antenna - its a AirNav ADS-B 1090 MHz (not sure if its specifically tuned at 1090MHz - anyone’s knowledge on this antenna would be useful.) I do live in a rural environment, but with very strong LTE coverage what doesn’t help. I do have a LTE tower (I think) at 533m what might be why I’m receiving the strong signals on the RF graph.

I think you are far enough from that tower so you don’t need any filters ahead of the LNA.
I am at about 300 m of several towers plus 1000 meters from an airport (SSR emitter at 1030MHz) and I don’t use a pre-filter.
Raise the antenna as much as you can above surrounding obstacles (houses).

Thanks for the advice, don’t know if its a LTE transmitter or something else, don’t have any knowledge in that area. I’m planning on raising it more before I’ve finished with the upgrade, only issue is the location isn’t ideal to the northeast - I have a line of large trees what make it impossible to get above them. Although I have line of sight out towards the North Atlantic what helps with range, I’ve attached a reference photo if you want to have a look.

This was before any upgrades, with the antenna on a mast with 30 feet of coax which went into a Orange FA stick.

My trees are surrounding me. After fall I see a bit of improvement in long range (200-250 miles) position numbers, from <50 to about 555 a day. All in all not a big deal, I have 800k positions a day.

I’ll attempt at raising it further and see if it improves my range by a couple of miles, but I think the main improvement will be the shortened coax length from the fixed connection on the antenna - also with the LNA which should boost the number of packets received with positions.

Please, please, please don’t buy 75 ohm coax. Get the right stuff for the job.

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