Tuesday, November 26, 2013

Newsky TV28T RTL 2832U / R820T DVB-T DAB FM SDR

Sorry for not updating so often now the blog, I have time but have been without patience to write. While before coming to Ireland I wrote in English just for fun, now that I write and speak every hour of the day I get a little tired!

Back to radio...

Some time ago (in September) bought one of those new (at least for me) TV receiver dongles with the initial idea to make a simple spectrum analyzer or a standalone receiver using one of the small Linux computers boards.

What I got in the mail:

 And the cost was 19 Eur, so, excluding the computer you have a nice receiver for a small amount of money (that's always relative).

After installing in the laptot according to one of the guides (you have to use a diferent driver from the one that comes with the card) and to make the initial test, I placed on the airband for the Cork airport approach and connected around 50 cm of solder "wire" acting as antenna:

This is the screen on the Cork approach frequency

The plane was here:
 Then requested to change for tower frequency

 And prepare for landing (north wind most likely):


 There's a discrepancy in the plane reported altitude and the airpot one so I guess that someting is changed in the ADS-B system used in the plane spotter site.

It was fun! Placed the card together with the other electronic components and when I get one of those small computer boards will place it on a standalone box....

Have a nice week!


Ping said...

Hi Ricardo,

The discrepencies between various altitudes may come from different altimeter settings between the sources :
* Mode S sends "standard" barometric altitude, referenced to 1013.25hPa. This should be the value transmited through ADS-B ;
* GPS will provide geometric altitude with regard to a reference geoid ;
* When in contact with approach or tower, aircraft will set their altimeter on QNH (pressure at sea level extrapolated at a given place), making their altimeter display the geometric airport altitude compared to medium sea level when they are landed. For light aircraft and local trafic, they might also use QFE setting (pressure on the runway), making the altimeter display 0 when aircraft is landed. Mode S will in both case continue to report an altitude compared to standard 1013.25hPa setting !

On your last screencap, Flightradar24 reports 350ft altitude (and 640fpm descent speed !), the aircraft is not completely landed (maybe some delay in FR24 display). When fully landed, it will most likely have report a bit less, while Cork airport seems to be more or less (did not find the exact value form aeronautical information) 500ft. This means the actual 1013.25hPa curve was actually above the medium sea level (or the pressure at sea level was higher than average) : Cork was probably in a "high pressure" (>1018hPa) area at that moment.

My 5 cents, for what it's worth ;)

Ricardo - CT2GQV said...

Hello Ping,

Thank you for the comment, that makes sense.

73 de Ricardo, CT2GQV