1090 Mhz Preamp

@ramjet555
It seems due to TV+FM+Cell signals overloading and making deaf the RF Amp #1 chip, as there is no filter between it and antenna. Please see photo below.

1090MHz%20RF%20Low%20Noise%20Amplifier-Description%20Added

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Has anyone else had a similar experience?

Yes, I have twice faced same situation, but not with this one. It was with these two:

  1. First case was with a Satellite+TV in-line amplifier (47 Mhz to 2500 Mhz) without filter. It proved to be deaf. I solved the problem by using another amplifier (RCA D903) which was designed for Satellite L-band only (950 - 2050 Mhz). As a result, TV VHF/UHF FM and Cell signals were all rejected, being outside its pass band (950-2050 Mhz), and this amplifier performed amazingly good.

  2. The second case was Pro Stick Plus (blue). It has a 1090 mhz filter, but it is not located between antenna and rf amplifier chip (the filter is located between rf amp and tuner). As a result TV+FM+Cell signals overloaded RF amp, deafning it. Adding FA external filter between antenna and Pro Stic Plus overcame this problem.

Thanks for the reply however your amp and my amp are not the same, yours is broad band,
mine is narrow band and in a way a bit like a filter as it only amplifies the 1090 segment.

Amplifiers need to be narrow band and if you use a BROAD band amp, YES, you will need
to put a filter in front of it, that is not as necessary if you have a Narrow Band or “hi Q” LNA

Just noticed that my AMP seems to be working
I’m using RTL1090 and it has the following controls at the top.
Tuner AGC on or off. ( a slider | ) [ db indicator ] ? Test
RTL AGC on or off. Send UDP on or off
Mode S or Mode AC . Config on or off . SISEX ON or OFF

I’m unable to make any changes that seem to affect the number of transmissions or the signal strength in RTL1090

Is there or are there options in Flight Aware to be able to control gain for optimum
performance with an amplifier?

I dont see any difference between the Wide Band (20 - 3000 Mhz) and Narrow Band (1090 Mhz) units on Ebay, except that in the 1090 Mhz unit, the coupling capactors between input-amp1 and amp1-amp2 have been replaced by SAW filter chips.

It seems the RF Amp 1 & 2 in both these units are same wide band chips (20-3000 Mhz), and narrow banding in 1090 Mhz version is achived simply by adding 2 SAW filter chips.

The 20 - 3000 Mhz 35 dB Amplifier

20%20-%203000%20Mhz%2035%20dB

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1090 Mhz 38 dB amplifier
1090MHz%20RF%20Low%20Noise%20Amplifier-Description%20Added

You are correct, it amplifies before it filters.
It could be an optimum way of doing the task
as its 2 stages as you point out.

When I change the gain, I am not seeing much change in
the aircraft that I can see displayed. But that’s only an antenna 5
feet above the ground and the amplifier is at the computer, not the antenna
about 12 feet of coax a way.

@ramjet555

You can assess the presence and degree of Cell phone signals at your location (particularly the GSM 850 Mhz band), by conducting RF Scan of signals received by your antenna.

If strong cell signal exists, then adding a filter between antenna and the ebay amplifier will substantially improve performance.

The method to conduct the RF scan is given in this thread. Do this scan without the Ebay RF amplifier.

Do I Need A Filter?

hi ramjet555

a much better option is ModeSdeco [http://xdeco.org/?page_id=30#md2] for those
using Windoze, or RTL1090 by Malcolm Robb (without gui).

@ramjet555
@SoNic67

RF Scan at my location (urban) using method given in thread “Do I Need A Filter?”

Hardware:
Flightaware 26 inch Antenna + Generic DVB-T (Black), plugged into Windows Computer. NO FILTER

Strong Cell phone signals detected.

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And my spectrum, to show why I wanted those filters:

960MHz is Aeronautical Radionavigation - I am just a couple miles away from an airport.

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I downloaded Modesco and it appears to work with airspy only?
I run it a administrator and a box flashes on my screen for a few miliseconds
and then disappears.

Has anyone seen signals on 1090 come alive AFTER installing a Filter?
950mhz is 90 mhz away, and I am wondering if signals that far away in the spectrum affect the sensitivity of a FlightAware Blue Stick with a built in filter?

YES, it does in many cases, depending on relative strengths of 1090 Mhz and 850/900 Mhz signals. Please see the Message Rate graph below. It clearly shows a substantial drop in message rate when EXTERNAL Filter was removed from Blue Pro Stick Plus.

ProStick Plus - With and Without External Filter

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Thanks for posting that image.
Just goes to show that the Pro Stick Plus Filter
does not do the job it suggests.

Is it better to use a purpose built filter followed by
USB receiver? If so, is any USB receiver better than
another for 1090 Mhz ADSB?

This diagram shows the differences well.
My understanding is a “H Q” Gasfet preamp is in itself a filter.
If it makes that much a difference, I’m planning on making one
with a full length inductor just a bit shorter so it can be tuned
with a screw from the other end.

Your conclusion is not accurate.
The above test applies only for his location, and only for a given time and date. You can’t generalize from it that “Just goes to show that the Pro Stick Plus Filter does not do the job it suggests.”
It actually does the job it is called for and it’s up to everyone to experiment/decide if they need an amplifier or not or if they need more filters than others. The RF conditions of each site are vastly different, you can’t generalize like that.
My plane numbers are very varied based on the day of the week and hour, even minutes, because we are talking about real-time air traffic.

@ramjet555
As @SoNic67 has already mentioned, you cannot generalize from my results.

The need for additional filter for ProStick Plus (blue) is NOT universal, and depends on strength of Cell Phone signals, which varies considerably with location.

A large number of users have reported satisfactory performance with the built-in filter of ProStick Plus.

Determining the presence and strength of Cell signals by RF Scan do give a clue if filter is needed or not. However benefit of adding a filter at a specific location/installation can only be confirmed by installing the filter. This is a trial and error process.

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Does anyone manufacture a mast-mounted or antenna mounted LNA for 1090 MHz?

Might help increase coverage towards the horizon. I’m using a Flightaware prostick (yellow) with a 1090 flightaware filter in-line. It works ok but thinking there might be some increased coverage potential having a preamp at the antenna.

Found this one, any of you have any experience with using this model?

-G.

https://store.uputronics.com/index.php?route=product/product&path=63&product_id=101

https://shop.jetvision.de/epages/64807909.sf/en_GB/?ObjectPath=/Shops/64807909/Products/68200

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Did you adjust the gain and found out that you are maxed out and need more gain?

I have this;
https://www.amazon.com/gp/product/B01MQWOM65/ref=oh_aui_detailpage_o07_s00?ie=UTF8&psc=1

and with; https://www.amazon.com/gp/product/B010GBQXK8/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1
for my second ADSB system. My Pi Aware used the flightaware pro stick plus.

I have increased and decreased the gain and found I get best plane counts around 12-18 (not sure if that is dB or s-units). The Flightaware dongle apparently has a preamp built-in, and I am using the Flightaware 1090 filter directly attached to the dongle RF input. I have some cell towers close by, and the filter improves reception considerably. (did some RF scans with and w/o). I think the LNA would require filtering as well to be helpful.