Why do you say that?
Unless your amp is being saturated by strong signals, the filter should go after the amp.
@geckoVN, That is the ideal way to do it, however, in practice, it doesn’t seem to work well, at least with the amps I have used.
Also, it makes it hard to power the amp via Bias-T.
- The cavity filter RF ports are (usually) at DC ground and provide ESD protection for the LNA.
- A well-designed cavity filter’s insertion loss will be very low, well under 1dB, and putting it first won’t affect system noise figure significantly.
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Sure - not passing DC is a great limitation of cavity and interdigtal filters, and a receiver with a built in bais-T is a great convenience. But when paired, it can lead to other compromises not conducive to the best performance.
Every site has it’s own requirements.
If you have a very noisy location, then a low loss filter before the amp makes sense, but I think this should be tested rather than assumed.
nope. a good cavity filter has near to zero loss at passband and should be placed before amp. however the disadvantage placing it behind amp in practice is in most cases very small.
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I have the three pole cavity filter from Jetvision. It does not have a sticker what side is the Antenna and which one is the receiver. Does that matter? I have only tried one way.
The cavity filter is in a box up the pole, before the LNA and working like a charm.
Except for filter/amp combinations, the filter is symmetric, so no, it doesn’t matter which way you connect it.
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The text, in Dutch, states that this is Flightaware brand. Looks like a standard Uputronics SAW filter on the picture.
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That’s definitely not something we produce or sell.
Lots of people also believe the kits they get on amazon are produced by FA.
This shop seems to brand some cable as FA as well, strange business practices.
One of his wholesalers in the UK is modmypi / thepihut and they also carry uputronics/fa things.
That’s why he sells it in the Netherlands
My UPUTRONICS filtered PreAmp broke/ stopped work after 22 month (power supply is OK) … 
no warranty anymore …have to purchase a new one …
i still have some almost unused lying around - believe ceramic and saw - if you are interested p.m.
I picked up the Kuhne
KU LNA 1090-2 A TM, Selective Low Noise Amplifier
and mounted it in waterproof box under the eve about 10ft from my antenna.
It seems to work really well, or as least as well as the Uptronics ceramic filter/lna.
I opened it up and took some pictures before mounting it.
It uses bias T and has an external input as well it seems.
oh and it has the best case build of any of the adsb lnas I’ve seen.
Great tolerance on the holes, screws, etc.
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Hi, I am close to your location if you still have a ceramic.
Hi, Do you still have usused filters?
While searching for a Band Pass Filter for AIS (162 MHz) landed into this one. Has anyone tried this 1090MHz 20 dB Filtered LNA (Price US $3.06 + Shipping US $1.65)