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Simple modification of the 1296 Mc parametric amplifier described in January, 1961, QST(1) will make a parametric useful on 432 Mc. A small change in the dimensions of the idler cavity, and an increase in the length of the signal cavity with a corresponding change in the coupling loops of the signal tank are all that one needs for a 432 amplifier.
After one understands the construction of the 1296 Mc parametric, he can adapt the following changes. First, the idler cavity is changed to 2.3 centimeter in length. Next, the signal tank must be changed to 9¼ inch in length by 2 inch wide and 1½ inch in depth. The center conductor is ,3/8 inch brass tubing. Heavy brass is recommended for construction of the signal tank.
The coupling loops were made with about inch of the loop wire parallel to the center conductor of the signal cavity. Provisions were also made to adjust the coupling loops. The tuning screw at the center of the signal cavity has a ¾ inch disk soldered to the end of it. There is also a ¾ inch disk soldered to the 3/8 inch center conductor. The screw and disk arrangement provides necessary signal tank tuning. The method of bypassing the half-wave signal tank center conductor at each end is the same, but the bypass plates were made larger to provide some additional capacity. The point at which, the diode couples to the half-wave signal tank has been changed to 3 centimeter instead of 0.8 centimeter. See Fig. 1.
Fig. 1. Dimensions for W8UST's 432 Mc parametric amplifier.
The same tuning procedure can be followed that is detailed for the 1296 amplifier.
Parametric amplifiers for 432 Mc using quarter-wave signal tanks and similar design in the idler and pump cavities have also been built and may he tried by others. I sincerely hope more 432-Me. amateurs will build parametric amplifiers for their receiving systems, as this should result in more reliable communication with stations over 200 miles away.
Notes
- W.O. Troetschel and H.J. Heuer, "A parametric amplifier for 1296 Mc," QST, Jan, page 13.
Gordon Sager, W8UST.