A 30 Mtr Direct Conversion Receiver for QRSS

Posted on Feb 6, 2014

The schematic for the crystal bandpass filter/amplifier board appears below (left) withimages of the assembled and boxed unit appearing below center andright. The signal frequency bandpass filter isconstructed over a ground plane and housed in its own enclosure measuring 75 x 75 x 50 mm. The separate enclosure ensures freedom from unwanted signal

A 30 Mtr Direct Conversion Receiver for QRSS
Click here to download the full size of the above Circuit.

"leakage" around the filter. The crystal bandpass filter module also includes a small R. F. amplifier of modest gain to compensate for the small loss in the crystal filter. The module is fitted with phono sockets for Antenna I/P and R. F. O/P. The R. F. O/P of the filter/amplifier module is connected to the antenna I/P of the QRSS DC receiver. The current drawn by this module is about 35 mA @ 12. 5 Volts which includes the L. E. D. `s. The direct conversion receiver and filter/amplifier modules together provide a very effective QRSS receiver, a further improvement can be made with the addition of the A. F. Buffer Amplifier/A. F. Filter described below. Note: (Added 25/10/06) The unit about to be described was added to the DC-RX in an attempt to further improve the performance though I have to admit the improvement was hardly noticeable except under conditions of heavy QRM when signals close to the QRSS sub band would confuse or desensitize Argo. Since this unit was built I have had some time to evaluate it more fully and would suggest that usingop-amps with a lower noise figurewould give improved performance. My feeling is that the A. F. filter is a worth while optional extra for those times when QRM is a problem. The A. F. Buffer Amplifier/A. F. Filter module was added to the receiver to ensure that the software A. G. C. in Argo was not "confused" by unwanted signals which appear in the audio passband of the DC-RX. These...

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