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7.8MHz I.F. Amplifier

7.8MHz I.F. Amplifier

Primary winding has 18 turns, the secondary winding has 4 turns. The capacitors across the IFT primaries are 82pF. The -6db bandwidth is about 2.5KHz.
The I.F. transformer primary has 18 turns, the secondary winding has 4 turns. The capacitors across the IFT primaries are 82pF. The input/output transformer has 12 turns, tapped at 3 turns from ground. This transformer is wound on a ferrite core. The mosfets are 3SK45’s. The diodes in the product detector are 1N34’s. I use a six pole SSB filter from a scrap CB. The centre frequency is 7.8MHz. The -6db bandwidth is about 2.5KHz.

Since I built this rig, I have replaced the original IF amplifier board with a completely new unit. I used a dual-gate mosfet as the first IF amplifier and a Motorola MC1350P as the second IF amplifier. The low noise of the mosfet combined with the excellent AGC characteristics of the MC1350P results in a very good IF amp.

Article by at EI9GQ http://homepage.tinet.ie/~ei9gq/index.html



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