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weak reception in ADS-B using upconverter

Posted: Tue Jan 15, 2019 11:41 pm
by zytorx
Hi guys.
I enjoy a lot receiving and decoding ADS-B.
My equipment:
Raspberry PI 2, RTL-SDR Dongle, and a 1090 bandpass filter.
I receive a lot of aircraft data using dump1090.
Now the problem.
I bought a metal box (RTL-SDR + upconverter), it works very good on HDSDR picking signals.
But, when I use it as an ADS-B receiver it DOES NOT PICK as many aircrafts as the dongle does using same antenna.

Please if anybody knows what's wrong using a RTL-SDR + upconverter as an ADS-B receiver.
Also when calibrating with KALibrate software, the dongle picks several GSM frequencies , and the upconverter using same antenna, only picks one frequency.
it seems the upconverter has a weak reception. I don't know.

thanks for your comments.

Re: weak reception in ADS-B using upconverter

Posted: Wed Jan 16, 2019 12:21 pm
by Evap1
Hi,
Top limit for an upconverter is around 30 MHz.
It shifts 0 to 30MHz to around 120 MHz using the RTL & other dongles.
ADS-B is 1090 MHz so the dongle is always going to be better
at this frequency.
Evap1

Re: weak reception in ADS-B using upconverter

Posted: Wed Jan 16, 2019 10:14 pm
by zytorx
thanks Evap1 for your comments.
the RTL-SDR+UPCONVERTER tunes HF,VHF, and UHF. the frequency range is the same as the dongle in VHF/UHF.
when tuned to an active aviation frequency (VHF band, AM mode on HDSDR software)it performs very well receiving such signals.
maybe, i think , for data reception as ADS-B , and some other modes it doesn't work accurately.

any other comments are well recived.

thank you.

Re: weak reception in ADS-B using upconverter

Posted: Thu Jan 17, 2019 12:05 am
by rtlsdrblog
Those units probably have some losses in the upper frequency ranges. They're not designed particularly carefully.

Re: weak reception in ADS-B using upconverter

Posted: Thu Jan 17, 2019 12:33 am
by Evap1
Hi,
You are getting breakthrough/bleed-over of VHF/UHF signals with the Upconverter inline.
The Upconverter is not receiving these signals in it's own right it is passing these at a lower strength level.
Hence the weaker/less signals.
Most have an upper limit 30 MHz or 60 MHz.
Evap1

Re: weak reception in ADS-B using upconverter

Posted: Fri Jan 18, 2019 3:39 am
by snn47
the dongle picks several GSM frequencies , and the upconverter using same antenna, only picks one frequency.
Another possibility is that the receiver is not within it's dynamic range where it is able to process strong signals any more, thus creating additional intermodulation (IM) products. If you have a 10 or 20 dB attenuater add it in line all signals should get weaker by 10 or 20 dB. Those that are missing or have not been attenuated by 10 or 20 dB are IM-products.

Re: weak reception in ADS-B using upconverter

Posted: Sat Jan 19, 2019 7:09 pm
by zytorx
Many thanks for your comments ! :)