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:
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhVL_AhAk1FwttnA7Bj4N_3cPMUbBuJNyyfTvmEScJ-JNEOUT63ee0DmPnTH4FuvCETYLWQP3bnyLCKNVTOhgh_6Rz2F7yD8o7g4lmXiktOodJYlg457QCeobFX2p9K1Sfsc-MJkQ8Jx-NF/s400/20160208_153430.jpg) |
Receiver circuit board. Antenna input, with attenuator pot seen to the left. Tuning caps on the right. |
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiLPnYH4hB8e3fr1isSWoTfedrYN6_k96rjmA6jvFiEMBvyfIiA3P2-vtqjJIyJI6BZRYGTmJR9ngSLw9ErePB_G2Ie88LwYAE1Z0D-Zv41EE8bluGwNKVWJAF_rqChi6U5IhQNPpMenSZO/s400/20160208_153221.jpg) |
Receiver with shielding in place. Tuning knobs to the left. |
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhu-EpWnE-GWnfnCeqWL3ZoFTTCJn4BpQTqQ5v6MdE_dNlXizF4TXdw5q5uhHiUOLZoX-cchVwAGrjPVIpZNMD4Qfsw1969Ij6ZDxKwZwMEy9a7XEKeIGntSr86hSMqhG9ZmC3NzayBg_xV/s400/20160208_201303.jpg) |
Receiver diagram. |
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