Monday, February 8, 2016

40m Ham radio receiver using a NE602

I've been building a circuit I found in "Experimental methods in RF design". It's a 40m AM/SSB/CW receiver using a NE602. I've been doing some experimentation to get the receiver working, especially with the local oscillator. In the book, they recommend a toroid wound coil, but I couldn't get that to oscillate. Finally I made an air wound coil, which worked. But since the coil was wound "mid air", it picked up even the smallest vibration in the surroundings, leading to a very unstable oscillation. I solved it by shoving a roll of paper inside the coil. I also worked some on getting the antenna input filter better matched.
It receives between 6.9 and 7.4MHz, but it hasn't got a lot of selectivity, which I will try to solve somehow. Also, I want to interface the LO to a frequency counter, so I need to build a buffer amplifier to not load down the oscillator.
Here are some images of the receiver and the schematics so far:
Receiver circuit board. Antenna input, with attenuator pot seen to the left. Tuning caps on the right.
Receiver with shielding in place. Tuning knobs to the left.
Receiver diagram.

No comments:

Post a Comment