Thursday, February 04, 2010

HF radio (6) - RF preamp

I was building the RF input preamplifier, (same schematic of the K2 from Elecraft, except the transistor I an using is a 2n3866), and noticed that I might had wrongly changed the 2n3866 transistor pinout on the amplifier after the first mixer (SBL-1). I corrected the transistor position and now I have a much better radio, now is like it should had been all the time, it even has more gain that I expected.... now I can hear a lot and with good level. All this time I have been testing the radio with the wrong setup of this transistor.... oh whell... live and learn. Now I even have to reduce the IF amplifier gain...
Next step is to change BFO cristal oscilator for a simpler one now that I am using the NE602 as product detector.
Tested the RF preamplifier against my cristal test oscilator and (if I am correct) with the 1uV output from the oscilator I can loudly hear it...great! Let's wait to see on those contest days if I am not going to be overrun.....just in case there's the attenuator.

In the following image, from left to righ, the antena switch over relay, the attenuator relay, the preamp bypass relay and the RF preamp:














A little video. Now with much better receiving:



video

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