To be honest, I don’t know. I can’t remember what design i used on the chimney one. I am looking now to see which one I used, bear with me.
Did you put the filter in or are you still talking about it instead of trying it? 
Not done it yet, was still trying to find the picture, found another picture similar to mine, but has an extra 1/4 wave balun at the bottom that I don’t have.
Tried it, looked like it made a difference, but messages went down from 1200 a second to 800 a second, so maybe some noise was inserted, range increased a bit to just over Lille in France.
I think I am at my maximum range I can get as I have done a preliminary check on where I can receive and it coincides with the maps I got back perfectly, and without the pre-amp and filter. I am limited now by things out of my control. Oh well, I tried.
Here is my presumed line of sight estimation
Did you properly reduce the gain set in dump1090? Without that the reduction in messages is expected.
The gain seems very high compared to the competition. There is no mention of the semiconductor used.
But the biggest question mark of all is the noise figure. At these frequencies, it’s a very important spec to be left out.
I would say, go for it. One for the team. I’ll be right behind you, if it’s good. 
That’s like the one that I am using now.
The “caption” of the 1090MHz signal (active part of the antenna) is happening with the actual external shield, not with the internal core.
Only the delay links in between are using the cable as is intended to be used (1090MHz signal running inside the cable core), so those should be calculated with VF.
As a side note, I don’t think that installing whole assembly inside a PVC tube any calculations, because there is air again in between the tube and actual antenna. So the VF goes Air-PVC-Air.
Look at the eBay listing below. It includes a diagram. Not the same circuit, just one SAW filter, but it may give an indication of the semiconductor used.
The price is reasonable for what you get: antenna, amp, bias t adaptor.
Go for it. I have the Pro Stick Plus as well and a clean spectrum nearby. Despite this I bought the Uputronics SAW preamp for the extra gain and installed it at the receiver end for convenience. It gave a big increase in messages, aircraft and range. I’m very pleased with it.
After installing I saw the benefits straight away. But after some experimentation I got a slight improvement again by changing the gain in PiAware, from the default -10 (max/AGC) to 49.6 (the next one down). This is because the preamp introduced a bit of in-band noise which was drowning out some of the weaker signals, and dropping the gain a touch sorted it out.
As you can see from the photo I’m powering the preamp from a USB port on the RPi. It works no problems. I’m using the official 2.5A RPi PSU.
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I’m really confused by people running double amplifiers with max gain on the dongle. Oh well.
Gotta still ask: Have you tried for example 34 as a gain?
Max gain is the default setting, chances are some people will install a preamp and leave the settings alone. But in any case the preamp still more than compensated for any loss due to the gain being too high, here at least.
With the preamp in place I found that 49.6 gave the best result. -10 (default) was too high with distant aircraft being drowned out and 48.0 lost some range and aircraft, with lower values losing even more.
Specially when using an FA antenna outdoors, up high. I’m puzzled as well. But hey, if it works, it works!
I guess so. Should stop questioning it. I guess the flatter the gain pattern of an antenna the better you can set high gain when you don’t have low flying aircraft nearby. Still…
I think they either have all the planes far away or… a bad antenna, installed indoors that cuts down all the signals. Maybe a bad connection between elements on the cable?
I literally have the gain at 8dB after adding a preamp in front of my FA ProStick Plus with FA antenna installed outside. But I have lots of planes flying in 50-100 miles radius.
At 30dB I see the number of planes reduced at 1/4. At 50dB I see none.
One possible explanation is that some of the installations must have huge losses that are compensated by the extra high gain.
Indoor antennas, as you mentioned, but also poor connections, excessive number of adapters, long cable runs, poor quality cable, etc.
Looks like the noise figure is around 2 dB.
The RTL-SDR Blog LNA is less than 1 dB.
This is the generic LNA I purchased some time ago. I’ll solder the barrel connector to the board, and feed it with 12 VDC. I’ll also use the spare FA filter in series with the LNA. Curious to see if the location, before or after the LNA, will make a lot of difference.
Just ordered this Bias T board. Different than the one I purchased in the past, and currently use, but cheaper.
I don’t trust wide band amps. At the minimum I would put the filter in front, to cut-out any other signals. Heck, that thing can overload even from AM radio! Or your computer PS, or TV (switched mode) radiating electrical noise.
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