FlightAware Discussions

New filter or LNA

My installation is the orange FA stick, “old” FA filter, then a short piece of flat coax cable, some 10-15 meters of good quality Hirschmann Koka 9TS coax cable to the rooftop where it connect to the FA antenna.
Pics here: https://www.flickr.com/photos/iemand91/48330182842/in/album-72157709763696967/
And: https://www.flickr.com/photos/iemand91/29749362000/in/album-72157675511065535/
Not extremely ideal, but it has been working fine for 3+ years.

Recently though, I’ve been think of ways I can improve it.
The best thing is to move everything to the antenna (in a waterproof box) with ethernet cable going down inside powering it with POE.
Moving the RPi to the roof could work (I haven’t needed to touch it for years) but still; it’s not really accessible there…

I’ve run the RTL_power tests; first without the FA filter and then with.
Results without the filter:


The new FA filter (this would make perfect sense to replace the old filter.
However, people have notified me of the RTL-SDR LNA which should be placed at the antenna with something (dongle or injector) powering it.

But I’ve some options:

  1. If I want to change as little as possible, I could replace the old FA filter with a new one. Costs about €30.
  2. For a little more (basically a few euros for a bias tee injector) I could place the RTL-SDR LNA at the antenna and this should provide better results than option 1. Right?
  3. Instead of a (cheap) bias tee injector; I replace my orange FA dongle with one that can provide the 5V; either the RTL-SDR V3 or Nooelec *NESDR SMArTee v2.

Those are options if I don’t want to change much of the installation. Best solution their is probably the LNA at the antenna; but would replacing the orange FA stick with one of those 2 also provide better results or is that negligible?

If I would want to change more; I could move everything to the roof. So antenna -> filter/LNA -> dongle -> RPi -> ethernet with POE. My gut says this would be the most optimal solution, but I’m not exactly a fan of moving the hardware up there. But if I would do that; would the LNA make more sense than the dark blue FA filter, since I would not be using a long piece of coax anymore? The LNA is a filter just like the FA filter, but it also meant for coax losses.
And same question here about replacing the orange FA dongle with either of those other two; would that make sense then?

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I would try just an FA Pro Plus stick and see what happens.

I thought the Pro+ stick was basically the same as the old Pro stick + 'old" filter I have now.
But comparing the specs; the Pro+ does seem to have a narrower passband range; 1,075 MHz – 1,105 MHz versus 980 – 1150 MHz on the filter I have now.
That’s pretty much the same as the new FA filter 1080-1100 MHz.
So I could (in theory) go either way; buy the new FA filter or the new Pro+ stick; they both cost (about) the same and should result in similar results.

However; I’m thinking about the RTL-SDR LNA since I have a fairly long coax run and people seem to love this thing with situations like mine. I wonder how the filter of that LNA compares to that of the Pro+ stick and/or new dark blue FA filter.
That LNA with a bias tee injector should also cost about the same as the Pro+ stick and FA filter.

And that’s all if I keep my setup the same with the long coax run. If have place the RPi + dongle/filter (+ optional LNA) + antenna in a waterproof box on the roof; I wonder if one of those 3 solutions has a benefit over the other 2.

So basically, the options I have. First hardware inside:

  1. RPi -> Prostick -> new dark blue FA filter -> coax -> antenna
  2. RPi -> Prostick Plus -> coax -> antenna
  3. RPi -> Prostick -> bias tee injector -> coax -> LNA -> antenna
  4. RPi -> RTL-SDR V3 or Nooelec *NESDR SMArTee v2 (build-in bias tee) -> coax -> LNA -> antenna

Place hardware at the antenna in waterproof box, options include:

  1. Place current hardware: RPi -> Prostick -> FA filter -> antenna
  2. RPi -> Prostick -> new dark blue FA filter -> antenna
  3. RPi -> Prostick Plus -> antenna
  4. RPi -> Prostick -> bia tee injector -> LNA -> antenna
  5. RPi -> Prostick Plus -> bias injector -> LNA -> antenna
  6. RPi -> RTL-SDR V3 or Nooelec *NESDR SMArTee v2 -> LNA -> antenna

So tons of options. I like to tweak around with things, but I don’t really wan’t to try out lots of hardware since I’m not planning on spending much € on the whole thing.
So not buy thing, try thing and buy new thing and try new thing over and over again.

Years ago I tested my setup with and without the short piece of flat coax, if I remember correctly; it didn’t result in massive differences. The 50 versus 75 ohm difference shouldn’t matter much if I’ve read things correctly.

I have the RTL-SDR Blog LNA/Filter as well.

My choice then would be: RPi, NooElec Smartee, RTL-SDR Blog LNA/Filter, FA Antenna.

I don’t get this idea that 75 ohm cable is OK in 50 ohm systems, particularly as 50 ohm and 75 ohm connectors are incompatible.

While not ideal, it’s far from a ‘show stopper’. A 50% increase in impedance does not translate into a 50% loss. As for termination, again, F connectors are rated for the frequency. Adapters can be used, or the coax re-terminated.

I used two different types of these flat cables, one was just like those flat cables for eg a raspberry pi camera, the other more like a real cable but flatter.

IIRC both did not work very well, the first „filtered“ out all signals, but then it was just starting with this and my setup pretty basic, maybe with an amp or a different sdr these would have worked better.

Thanks! I get why you would choose a dongle with build-in bias tee over a dongle with a bias tee injector (less things to break/go wrong), but any particular reason to choose the NooElec over the RTL-SDR V3? Is it the always-on bias tee of the NooElec or something else?

And would you remove the long coax run in that scenario too?
The thing is; if I’m going to place the LNA at the antenna, that LNA has to be made so it can withstand the elements; aka; some kind of waterproof box.
In that case; I might as well go all the way and move all the hardware - including the RPi - up there too in that waterproof box.
To me, that seems the optimal configuration, but it’s just the fact I don’t really like the idea having the RPi all the way up there with limited access to it, even though I haven’t need to access it in 3 years.

I’ve had experience with 2 kinds of flat coax. The first was something like this and it was indeed terrible.
Then I got this, this one is MUCH better.
My memory is correct about seeing no difference with of without that piece, I talked about it in this post in December 2016.

However, after 3+ years that cable is starting to age; the white exterior is coming off although I haven’t seen worse results because of it.

I’ve used ‘that type’. It is made with a length of RG-179 inside the protective sleeve.
No reason it shouldn’t perform well.

The cable you describe above is rated as indoor use, so it won’t have any UV protection.
An “outdoor cable” will last much longer.

I like the RTL-SDR Blog v3 very much, so much so that I ordered another one this past week, but the NooElec SmarTee makes things easier and ‘cleaner’. I’m using an RTL-SDR Blog v3 stick with an eBay bias-tee power inserter and the RTL-SDR Blog LNA/filter, by the way.

I’m not a fan of putting the RPi too far away from easy access. If you install the LNA at the antenna, coax length is not a problem, and the RPi can stay close by.

You don’t need an LNA if you move everything to the roof. The LNA makes up for the loss of the long cable run and you want the LNA before the receiver (dongel). Once you do put an LNA in the losses from impedance mis-match don’t mater much. You have plenty of signal. You should lookup the spec for signal loss on your cable it will be dB/foot or dB/meter compare that to your LNA gain. If Gain is larger your in great shape to not worry about mis-matches.

I do advise against putting the RPi on the roof. About 1 out of 3 power failures I get a corrupted SD. card.

Good to know.

The Koka cable is going up to the antenna underneath the roof tiles. So that should be fine.
It only gets some sun exposure on the first part (1 meter or so outside the window) and the last part (1 meter or so on the antenna mount).

The cable that the white exterior is coming off, it the short piece of flat coax.

Just because of the always-on bias tee versus software based on?
That’s also the reason why you’re using a power inserter instead of using the V3’s build in one?

I don’t know the losses of the connectors and the short piece of flat coax, but the longer run Koka 9TS cable has a loss of 18,4dB per 100 meter at 1000Mhz. so let’s say it’s 20dB per 100 meter; I have 10-15 meter of it, so loss is around 2-3dB.

Both of you advice not to put the RPi on the roof. I think you guys may be right, even though I never experienced issues - not even with the SD cards - on several RPi’s I’ve used.

Before it do anything though; I’m planning to place the RPi at the antenna location (so direct connection RPi -> FA dongle -> FA filter -> antenna) and run a powercable to a power socket.
Just for a day to see results.

Yes, I’m not a software guy. While the software modifications are not major, I prefer to focus on the hardware side of things.

One reason is that the RTL-SDR Blog v3 can also be used to receive HF, my main interest. The software package I use for that has the bias-tee option built-in, so no software modifications needed.

The other reason is that using the stick built-in bias-tee 24/7 can cause thermal issues, and may reduce the life of the stick.

I am not feeling comfortable feeding the LNA from the source inside my dongles. Increased the heat, the power draw from USB port, I don’t know how well will fare in case of an accidental short-circuit.

I just noticed that the NooElec SmarTee price increased substantially (percentage wise) in the past few days. On Amazon Canada at least, it went from CAD$32 to $39.

At first I thought it was the exchange rate, but the FA and RadarBox items are still at the same price.

Thanks for the replies guys.
So the general view is to keep my installation as-is, place the RTL-SDR LNA at the antenna and a bias tee injector between the coax and the dongle.
So in theory I could keep the orange FA dongle and get the old FA filter out.

How does the RTL-SDR LNA filter cope with the out of band noises I have, in particular the 950MHz. GSM noise? It is on par with the new dark blue FA filter?

Oh and yes, the NooElec dongle has increased slightly on several EU Amazon sites too.

So, I assume the LNA is on par with the new dark blue FA filter for filtering out the 950MHz. GSM signals so LNA it is, getting it from here.
On your recommendation an external bias tee injector, should this or this work?
If yes, are there any benefits of using the 2nd apart from the fact it has a housing?
I can supply the bias tee with 5V from the RPi’s GPIO pins.

Since the LNA has to be placed at the antenna; I guess it needs some (waterproof) housing, me thinks it’s not great to leave it outside on it’s own.

I use the first one.

Depends on the installation. In my case, since it’s ‘airborne’ no benefit, actually it weights more.

It must be waterprofed if outdoors.

The one with the female/male connector has them on the wrong side.
So if you connect the male SMA to your SDR, the SDR will be getting the bias voltage instead of the LNA.
(it’s basically a bias-t to supply something AT the antenna if that device doesn’t have its builtin bias-t like the LNA you are using has)

If you can route via the attic and have the LNA after a short or shorter length of coax that eliminates the need for waterproofing.
Otherwise yes you need waterproofing.

Thanks guys. I haven’t ordered anything yet, but this with female SMA on both sides looks ok.

I * might * be able to place the LNA underneath the rooftiles (visible here), but otherwise will search some sort of waterproof box for it.

Meanwhile, I’m gonna look around how the filter of the LNA compares to that of the dark blue FA filter.