2
$\begingroup$

I built a CW receiver using NE602 for the 20m band. Unfortunately, I do not receive any CW or SSB signals, only some noise and sometimes broadcast stations.

The schematic here shows the circuit that I built. What is wrong in the oscillator and input stages of ic that can not focused on 14 - 14.35 mhz (20m amateur band)

In oscillator section as you see i used two 220pf capacitor that are in series with each other so the total capacitance is equal to 110pf . For resonance at 14 mhz with present inductor (1uH) we need a capacitor value 129pf using formulae: (C=1/39.5 * F^2 * L) so if the varactor diode can induce about 19pf , the work is done (110+19=129) the second image show the internal transistor of ne602 chip and relationship between pins 6 and 7 and the other parts of oscillator section (https://i.stack.imgur.com/e1HLp.jpg)enter image description hereenter image description here

$\endgroup$
  • 1
    $\begingroup$ Welcome to the site. You wrote that you receive only "HF". Since 20M is HF, that makes sense. Perhaps you can clarify? $\endgroup$ – mike65535 Sep 15 '18 at 13:52
  • $\begingroup$ Thank you for adding the details! :-) Perhaps someone here that's smarter (and with more time) than me will help you. $\endgroup$ – Mike Waters Sep 15 '18 at 22:29
  • $\begingroup$ Thank you for your attention. Infact these problems and abnormal behavior of circuits will cause to increase my electronic knowledge and finding good friends like you $\endgroup$ – Farshad mahmoodi Sep 16 '18 at 10:04
2
$\begingroup$

In your schematic, there is no way that the IC can get any power because:

  1. DC cannot flow through capacitors. I suggest that you look at a NE602 data sheet.

  2. There is no power being applied to pin 8.

I assume that you are receiving broadcast stations, digital transmissions, etc. Without power to the IC, it's just acting as an AM detector.

$\endgroup$
  • 1
    $\begingroup$ @Farshadmahmoodi Understood. Unless someone else sees something that I didn't, it appears that you might have to show us your entire circuit. Perhaps photos of both sides of your printed circuit board would help. $\endgroup$ – Mike Waters Sep 15 '18 at 15:57

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.