To: file hagen\wpfiles\430tx\pucks

From: Jon Hagen

Date: 7-5-01

Subject: Tuning New Collectors, SN002 and SN003

As with the first new collector, these units were mounted, one at a time, in the spare section of slotted waveguide. An imperfect termination (standard WR2100 waveguide-to-coax transition with a coaxial load) was put at the open end of the slotted guide. The network analyzer was connected to the output stack of the collector, using a half-height waveguide-to-coax transition.

The reference plane at the end of this transition was calibrated using the three shorts that make up our half-height WR2100 cal kit.

The tuning puck was positioned on the side of the collector output stack at the position that best centered the circular trace in the reflection plane, produced when the collector was rolled along the slotted waveguide. The reflection coefficient at the center of the best circle indicated a return loss of about 26 dB. The best position was in the center of the waveguide, indicating that the puck needed to be taller to get an even better return loss.

A plot of return loss vs. frequency was made as follows: The imperfect termination was made "perfect" by arranging a metal bar to protrude into the waveguide slot. The position and penetration of this bar was adjust until the reflection coefficient did not change as the collector was rolled along the slotted guide. This match seemed quite good over the range 420 Mhz to 440 MHz. With the termination tuned and the analyzer calibrated at the input plane of the collector's output waveguide, the attached plot was made. The trace with the deeper return loss shows the collector before the tuning puck was installed. Installation of the puck improved the performance at and below 430 MHz.