Do I Need A Filter?

Here is the FlightAware Pro Stick Plus + FlightAware external antenna + Uputronics 1090Mhz SAW filtered preamp. You can see what a great job the preamp does of removing comms and mobile signals and boosting ADS-B.

Click the image once to open, and a second time to zoom to normal size, then scroll left and right to view the comparisons at different frequencies.

You can see that the Pro Stick Plus does a good job of filtering but still picks up a fair bit of unwanted stuff, and the filtered preamp nicely takes care of that.

I’m in the UK. You can see digital TV, comms and GSM signals present without the preamp.

1 Like

Very interesting to see the comparison between having or not having the uputronics 1090 SAW filter preamp.
I guess that I really need to buy that filter+lna to further improve my ADSB reception. Seems to be a winning combination! That SAW filter really made a significant difference in out-of-band signals.

We should not also forget that FA antenna has not only low VSWR in ADSB band… https://www.rtl-sdr.com/wp-content/uploads/2016/03/FightAwareAntenna.png - which gives a harder job to the dongle.

1 Like

Indeed, I think the filtered preamp works brilliantly with this antenna, allowing you to get the most from the high gain where it’s wanted and keeping it in check everywhere else.

The upper scan is ProStickPlus only
The lower scan is ProStickPlus + Uptronics

The lower scan is combined effect of two filters, one in ProStickPlus, other on Uptronics. Attributing all credit of combined effort to uptronics only is not fair.

A fair comparison is:

ProStickPlus+FA antenna
VS
Generic DVB-T+Uptronics+FA antenna

.

I’m not doing any such thing. I’m showing that the Pro Stick Plus’s filter does a good job but allows some stuff through, and I’m showing the effect that the Uputronics has on top of the Pro Stick Plus for anyone who already has the latter and is considering buying the former. Clearly the Uputronics filtered preamp makes a big difference. This is mirrored by the improvement in positions and aircraft seen after adding it.

This post is about filters:

SWEEP/SCAN BY NOISE GENERATOR

That is great but what is the effect on your message rate, the number of aircraft you can see and range?

The filter and amplifiers are certainly having an effect but how does it translate into better stats for your receiver?

It is very difficult to see the effect of a change as the traffic is continually changing. I run two separate systems with one kept unchanged as a reference and the other used for experimenting in improving performance. Looking at the Skyview pages side by side in real time gives me a good and quick indication of the actual effect of a change in amplifier, filter, antenna and Gain.

If you don’t have two complete systems a comparison with a nearby station over a 24 hr period from 0000UTC is useful but a lot slower.

S.

The Uputronics increased the number of my messages, aircraft seen and range over a period of a couple of days, compared with previous days and the same days the previous week. Chatting with the designer he also said that he has never had anyone yet tell him the LNA doesn’t increase the number of messages.

Was that on 11/4 when you had a quite significant jump in stats?

S.

Up to the 28th was without the preamp, from the 28th to the 9th was with the preamp, from the 10th (the part you mention) was changing to the external antenna indoors. Averaging from 20th-26th and from 3rd-9th (to avoid the UK Easter bank holiday weekend and some network admin here) and comparing there’s around a 20% improvement in reported positions and a 12% improvement in reported aircraft.

1 Like

I missed that the antenna was moved outdoors. I was looking at the wrong data. :slight_smile:

The numbers of positions and aircraft reported has gone up. Has the range increased also?

Whilst your plots show the out of band signals have significantly decreased, the inband noise seems to have gone up considerably. It is possible that the signals you want are now overloading the dongle receiver.

Have you tried dropping the dongle gain by about 20 or 30 dB?

S.

I didn’t move the antenna outdoors. I switched from the mini mag mount antenna indoors to the 26 inch external antenna indoors.

Yes, the range increased when I added the preamp. It looks like the 1090MHz signal to noise ratio has improved overall, taken across all signals now received. I’ve not played with the gain setting yet because I’m changing one thing at a time. I will play with it in due course and report on any improvements which may assist others with this combination.

Hi abcd. I ran the gain Optimize-Gain script already and collected that data. I actually ran it 3 times and selected a gain that seemed reasonably good across all 3 tests. I say “reasonably good” because there was a lot of variation in the results. Solely using the Message Counts as a metric I went with 42.1. The peak message counts seemed to be associated with gains between 38.6 and 43.9. Any further thoughts appreciated.

@roadfun
As you have already tweaked Gain, go for next step and purchase a Filter.

While playing around with rtl_power earlier it occured to me that the visual effect you mention is partly down to the increased gain being used in the command at the start of this thread. Setting that to auto, as it would be in normal dump1090 use, shows something more realistic and all other parts of the band are black, versus the Band V and GSM signals present previously after the Pro Stick Plus is done filtering.

scan0

I’ve written a script which takes the rtl_power command and cycles it through all of the gains supported by the Pro Stick Plus and records an image for each one. This should allow a gain to be eyeballed and selected which gives maximum detail at 1090MHz while avoiding the noise around it at higher gains. I suspect it will be a much quicker way to home in on the optimum gain setting for a given installation, allowing the gain to be set as high as it needs to be but not needlessly higher. I’m testing it and will followup with more info.

2 Likes

The RF scan will show strength of GSM and 1090Mhz signals in dB, if the RF Scan is done using software rtlpan.exe (dongle plugged into Windows computer), as described in:

OPTION-2

.
EDIT:
The rtlpan graph also shows the noise floor. In the graph below it is -35 dBFS
.
Scan below is at my urban residence (Toronto, Canada). The GSM850 and E-GSM900 signals are very strong.
.

I ran this previously with a rtl-sdr V3, plugged into my computer USB port, with a little antennae and it ran well I have just tried this, as a prelim in trying the new script re using a visual test for gain. On both scripts, I get this error:

Using device 0: Generic RTL2832U
Found Rafael Micro R820T tuner
Tuner gain set to 1.40 dB.
Exact sample rate is: 2790696.209609 Hz
[R82XX] PLL not locked!
Using a Prostick plus into my PI3 B+

Disregard, I see above this “[R82XX] PLL not locked!” would be a standard response, I will let it run and see what happens

Jeff

disregard all above, the script worked perfectly ( wait till it is finished before posting it doesn’t …lol :wink: )

Hi all

Do i need a filter ohhh yesss i think so
i have done the test on main setup 57m to antenna
flightaware pro stick coax 10m to loft
bias tee triple filter LNA
sdr-rtl v3 dongle into rpi3
ethernet from loft to the router
result


Screenshot_269
Screenshot_267
Screenshot_266

Screenshot_265

1 Like

Test 2
8 segment coco antenna 1090 outside window 2m coax to
ndsr smart dongle
flightaware filter 1090 mode s
windows pc / rtlpan
test without FA filter


test with FA filter

1 Like