ARLA/CLUSTER: Receptores WebSDR disponíveis à distancia de um" click".

[João Gonçalves Costa]

[http://tbn3.google.com/images?q=tbn:Uu7byGjavllepM:http://www.iw5edi.com/wp-content/webSDR.gif]<http://images.google.pt/imgres?imgurl=http://www.iw5edi.com/wp-content/webSDR.gif&imgrefurl=http://www.iw5edi.com/ham-radio/58/websdr-a-tunable-virtual-radio-from-holland&usg=__EwheWIHv_k9KmV9Cm3B3gfkEkhA=&h=268&w=350&sz=28&hl=pt-PT&start=15&tbnid=Uu7byGjavllepM:&tbnh=92&tbnw=120&prev=/images%3Fq%3DWebSDR%26gbv%3D2%26hl%3Dpt-PT%26sa%3DG>[http://www.pa3weg.nl/pa3weg/images/websdr/PC.JPG]
WebSDR receiver on 20m, 40m and 80m

The amateur radio club ETGD at the University of Twente provide a WebSDR HF receiver for use by Radio Amateurs and listeners around the world.

In contrast to other web-controlled receivers, this can be tuned by multiple users simultaneously, thanks to the use of Software-Defined Radio.

Tuning is done either by clicking or dragging with the mouse on the waterfall display, by typing a frequency into the text box, or by using the up/down buttons. The bandwidth can be changed by clicking the appropriate buttons, and by 'dragging" the edges of the yellow passband indication.

The present system consists of the following hardware:

* A W3DZZ trap-dipole for the 80 and 40 meter amateur radio bands, on top of the 40 m high "Hogekamp" building of the University of Twente.

* Simple bandpass filters for the 80 m, 40 m and 20 m bands.

* A quadrature mixer in which the signals are mixed with about 7080.7 kHz. This mixer is a Quadrature Sampling Detector or "Tayloe mixer", the well-known circuit with a four-position CMOS switch, which is also used in many amateur radio SDR front-ends such as the SDR-1000 and the SoftRock.

* Similar mixers operating at 3600 kHz and 14161 kHz.

* A PC with soundcards to receive and process the signals coming out of the quadrature mixers. The PC is an old Pentium-III at 1 GHz, running Linux and the WebSDR server software (written by PA3FWM).

To use the WebSDR HF radio receiver go to
http://websdr.ewi.utwente.nl:8901/

PA3FWM's Software Defined Radio page
http://wwwhome.cs.utwente.nl/~ptdeboer/ham/sdr/

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