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The following are two versions of the Mosfet single balanced mixer. The first one uses tuned circuits at the input and output. I never got this circuit to work. Details on winding the toroids were not given in the original article (W1FB's Design
Notebook, by Doug DeMaw, Page 41) and my attempts at winding some tuned toroids with the tuning capacitors as shown in the circuit never worked.
However, the second one worked perfect on the first try. It uses a broadband toroid using FT50-43 cores with 12 turns bifilar and a 5 turn link. The Mosfet source connections were modified to include the LEDs on each Mosfet for ease of circuit diagnosis. I did make some of the mixers with only one LED and tied the sources together which worked OK also. I liked the dual LEDs better because the more LEDs, the more impressive the circuit looked. |
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Never got this one to work, but this does not mean it won't. Proper construction of the tuned circuits would make this mixer have about 15 dB of gain.
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This mixer is from the January 1981 issue of QST, "Modern receiver Mixers for High Dynamic Range", by Doug DeMaw and George Collins, Page 20. The dynamic range of this mixer has varied from 85 db to 120 db, depending on what article and author your reading. In my very crude tests, I have found little to no difference between this circuit and a diode mixer. According to this article, the conversion loss of this mixer is -5 dB and the loss of diode mixers are around -8dB. |
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