FlightAware Discussions

Announcing the new 1090 MHz only bandpass filter!

#21

Ok, thank you for the clarification. I’ve bought one of the new filters but was beginning to think I had made a mistake.

#22

The UK cell phone system, like any GSM system in Europe, used from the beginning the 900MHz band, so called E-GSM.
The actual limits of that band are 880-960MHz:

In North America that band is 850 MHz, with limits 824-894 MHz.

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#23
GSM band ƒ (MHz) Uplink (MHz) (mobile to base) Downlink (MHz) (base to mobile) Regional deployments
GSM-850 850 824.2 – 848.8 869.2 – 893.8 North America (Canada & USA) Caribbean, Latin America
E-GSM-900 900 880.0 – 915.0 925.0 – 960.0 Europe, Asia-Pacific, Middle East and Africa

.

The Uplinks (signals transmitted by phones) are weak.

The Downlink (signals transmitted by Cell/Mobile Towers) are very strong and cause problem to our receivers.

.

#24

Hi thanks for info :smile:
I live close to a major city with lots of GSM mobile phone signals about, last year I upgraded to a 16 element collinear and the new blue pro stick plus and immediately saw a vast improvement.
My question is, would this new filter be any good with my existing set up.
Best regards
Paul

#25

The Pro Stick Plus does have a filter, but not for the GSM band. If you’re near a mobile tower the 1090MHz only filter will probably help you out.

#26

Another option is just a metal case for the dongle.


https://www.rtl-sdr.com/buy-rtl-sdr-dvb-t-dongles/

It is a low cost option that could be worth trying.

I use both a metal case and cavity filters in my location (The new 1090Mhz filter wasn’t available until recently). I have a dozen cell/mobile towers within a few blocks.

#27

Thanks for advice :slight_smile:
Ordered one from moonraker, went to modmypi but none in stock.
Will let you know how it performs.
Regards
Paul

#28

Quick update:
I tried the new filter for a few days with the flightstick pro plus although it looks like the message rate might have increased a little the range has dropped considerably. Might just be coincidence due to weather conditions but i’m wondering if the other pro stick without the inbuilt filter might be worth a try?
Regards
Paul

#29

If you don’t have strong interference a filter can reduce the signal level.
A colinear with as many elements as yours is already a good filter for GSM signals.

The prostick plus has its filter behind an amplifier, so changing that to one without filter is unlikely to provide an improvement.
(the critical signal level is before the amplifier)

Depending on the length of your cable run, placing a dedicated LNA near the antenna or just your whole receiver closer to the antenna might improve things.
Dedicated LNAs for most people give a little better performance compared to the prostick plus.

#30

Raise the gain level?

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#31

I have also installed the new filter this week and found I had to substantially increase the gain to optimise the tracking. (I went from 33.8 to 42.1 …). Attenuation of the 900Mhz Mobile signals was substantial. For the moment I have the filter on the receiver end of the Coax I will try it at the Antenna end soon as I suspect it may further improve the performance. I think what has improved is that I am getting more valid messages (less noise to corrupt the ADSB) and slightly more aircraft thought the range is about the same which is limited by geography.

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#32

Are you using the Pro Stick (Yellow) or Pro Stick Plus (Blue) or maybe something else?
I took my new filter out as my range dropped considerably, I get over 250 mile on a good day, I checked my coverage on heywhatsthat and I’m getting better than predicted, you know what it’s like though trying to squeeze that bit more out of the system :slight_smile:
I took note of weidehopf “If you don’t have strong interference a filter can reduce the signal level.
A colinear with as many elements as yours is already a good filter for GSM signals.” so I guess I’ll settle for what I have unless someone comes up with a better idea.
Regards
Paul

#33

I am using the blue Pro Stick Plus. My range initially dropped after inserting the filter, I ran the python “optimise-gain.py” script and it showed that the “best” gain to use (42.1 instead of the 33.8). The range plot I get is very similar to what I had previously, qty of aircraft and locations appear to have gone up at most approx 5%. There have been some additional 900 Mhz band mobile upgrades close by in recent months and I had notices a drop off of tracking performance. I did a before and after scan of the RF and it looked very similar to that post above by abcd567 on Feb 9. My range for the last couple of days is as below.

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#34

apologies previous jpg was pre filter insertion. here is the view post (with the gain increase). Outer ring is 200 nm.

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#35

Just recently got round to experimenting with gain settings.
I manually tried settings working down from 50 to 20 in increments of 1.
I found the optimum setting for me was a gain of 44 (43.9 actual) roughly about 5% improvement on -10 setting (auto)
On completion of my testing I had a browse through the forums only to find a script which would have automated the task D’oh

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#36

No answer to my question about availability of the new filter in North America. I wonder why?

Ended up ordering from the UK. While ADS-B ‘inspired’, I also ordered the RadarBox dongle.:smile:

#37

Not sure how we missed your post. My apologies for not replying to your question. We’re currently not selling the 1090 MHz only filter in the US. We were offering that specifically as a fix for GSM interference which isn’t present here.

#38

Thank you @esmathews .

Ordering from ModMyPi was painless. I like when a site allows Guest checkout and PayPal. The total cost for ordering from the UK is a bit higher, but not a show stopper.

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#39

Isn’t Canada using the 800 MHz and 900 MHz range as well for mobile phones?

#40

Looks like 850, but not 900MHz
https://www.worldtimezone.com/gsm.html