Build this Universal Gilbert Cell HF Mixer for $10.




SA612AN PDF Spec Sheet
This HF Mixer kit includes VXO circuit parts to be used with the 612 audio detector to receive 40 meter signals on 7030 KHz.
The balanced front end of the 612 mixer connects to a BN-43-2402 balun transformer for matching.
For a 50 ohm input, make the primary 2 turns and the secondary 12 turns center tapped at 6 turns. Use the 34 GA wire included in the kit.
The center tap is the mixer AGC control. See the LM386 amp kit for more info.
D1,D2 are input protection diodes; not required and not included in the kit.
L1 is used to lower the mixer's crystal freq. Using 14 turns of 27 GA wire on the black FT37-61 core will provide a tuning range of about 7026 to 7032 KHz.
More than 14 turns tend to stop the VXO from oscillating.
OUTPUT: Parts are included in the PCB bag for 2 different output circuits.
1. Single ended output; connect the 1000pF cap from pin5 of U1 to pin2 of J3
2. Balanced tuned; Install C5 (note flat side physical polarity) and C6.
For 5068 KHz output, wind a 24 turn primary and a 5 turn secondary on a red T37-2 toroid and install on the PCB.
Use the 27 GA wire (red & green)
Note: Schematic show a 7 MHz output but 5 MHZ is correct.
Note: The 34 GA wire is heat stripable while the 27 GA wire is not.

Parts List
T1 - BN-43-2402 - 12" #34 red wire
L1 - FT37-61 - 12" #27 red
OUTPUT OPTIONS:
Tuned balanced: L2 - T37-2 - 14" #27 red & 4" #27 green
Single ended: C9 - 1000p labeled "102" (not shown on PCB)
C1,C2 - 330 n
C3 - 100p
C4 - 56p
C5 - 70p
C6 - 150p
C7,C8 - 47n (labeled 473)
R1 - 100
R2 - 100k
D3 - MV2105
U1 - SA612AN or NE602AN