Re-engineering my 1st “Shirt-pocket” transceiver

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2020-06-28 19:27:31

When the project of building a very small transceiver was accomplished 4 years ago, I still lacked lots of skills in setting up electronic circuits using SMD technology. The radio’s craftmanship  had been a defective to a certain degree (there were still lots of things to learn when using SMDs on Veroboards), the inside looked more or less “messy” and the performance was not sited in the premium league. Particularly the receiver was prone to IMD problems when signals on the band were strong. But because I liked the outer appearance of the radio a total revision of the inside had to be performed.

In the receiver I changed the NE612 into a dual gate MOSFET mixer stage because I found out that the IMD3 was causing problems in the evenings when high signal levels were present. The dual gate MOSFET mixer turned out to be more stable in respect to  high signal levels. With the Si5351 being able to produce about 3 Vpp. of rf energy the mixer could be fed with an appropriate signal level.

The MC1350 had been removed because the simplicity of the AGC that section that could also be simplified because only one type of AGC voltage had to be produced. Remember: The dual gate MOSFET and the MC1350 have reverse AGC characteristics, thus an AGC that controls both types of amplifiers has to produce two types of AGC voltage. One rising and one falling when signal levels increase in the receiver.

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