Renaissance of HF DC (Direct Conversion) receivers

First receiver I was ever built for HF was tube receiver without RF amplification called OV2 .It was working good and enable me to listen short waves and HAM bands. After that I build super heterodyne receivers but when I built DC transceiver by W7EL at the beginning of 80’s ZL2BKW version I was surprised how good DC receiver can be. With simple dipole antenna for 7MHz I worked 102 DXCC in 1985/86 with not to often work and with output power 1W (BD135 output transistor). After that I made a lot of HF and VHF DC receivers HAM and for professional use, my or other authors design. In year 2000 I made presentation in KKE club Belgrade with next subject “Renaissance of HF DC receivers”. Paper material contains 30 pages collected materials about DC receivers with schematics, useful formulas for calculation, PCBs and complete receivers made or design by author. I received in last time over 40 request for the translation original article. This is translation of original article from year 2000. Now in 2007 I have quite different point of view to the some subject and because of that I am preparing new article part 2 with direct receivers designed and tested by author. I apologize that this materials schematics and comments on them are still written on Serbian language Subject DC (direct conversion) receivers in next text DC is not often subject in amateur and professional articles and we can hard find some original designs and realizations. The older homebrew can remembered with an nostalgia DC receivers called OV1, .. or similar types .In late 60th, 70th this was the easiest way to receive HF broadcast and amateur bands. These types of receivers have relative good sensitivity. Super-regenerative process is used for the demodulation SSB/CW signals. The situation on HF bands now is quite different that it was at that time. HF bands are now crowded with enormous big number strong signals. The DR (dynamic range ) this kind of receivers is very poor and receivers are producing a lot of IMD and non existing signals in the air. Because of that this kind of receivers which still have big use specially in simple alarm, remote control receivers I will not take in consideration. In this article I shall describe receivers with next block diagram pic1. These receivers have separated LO (local oscillator called VFO or BFO) and they can be divided in 3 main categories: