a71br
10-12-2008, 09:51 PM
by Lloyd Butler VK5BR
http://www.qsl.net/vk5br/VLFLFRxPhoto.jpg
(Originally published as a series in Amateur Radio, December 1989, January 1990 and July. 1990. Reprinted in Communications Quarterly, Winter 1991)
Forward
The VLF-LF receiver was developed and published in the Amateur Radio journal in three stages. The original Resistance Tuned receiver as described in stage 1 was made with a broad band front end. In the second stage, switching was added to one of the ceramic IF filters to enable reduction of bandwidth. It was ultimately realised that there was a great deal to gain by tuning the front end and taking advantage of the very narrow bandwidth which could be achieved at LF with quite moderate values of Q. In the third stage, a circuit of a front end tuner was included. Also added to the original receiver circuit was an audio filter to restrict the bandwidth of the detected audio.
More http://www.qsl.net/vk5br/VLFLFRx.htm
http://www.qsl.net/vk5br/VLFLFRxPhoto.jpg
(Originally published as a series in Amateur Radio, December 1989, January 1990 and July. 1990. Reprinted in Communications Quarterly, Winter 1991)
Forward
The VLF-LF receiver was developed and published in the Amateur Radio journal in three stages. The original Resistance Tuned receiver as described in stage 1 was made with a broad band front end. In the second stage, switching was added to one of the ceramic IF filters to enable reduction of bandwidth. It was ultimately realised that there was a great deal to gain by tuning the front end and taking advantage of the very narrow bandwidth which could be achieved at LF with quite moderate values of Q. In the third stage, a circuit of a front end tuner was included. Also added to the original receiver circuit was an audio filter to restrict the bandwidth of the detected audio.
More http://www.qsl.net/vk5br/VLFLFRx.htm