INSTRUCTION TO CONVERT THE EXCITER HELICAL BAND PASS FILTER RFD6112A
Or buy a Micor mobile filter Z501 as the cardboard forms / slugs aren't glued in place. For ease of adjustment check Step 11.
First do this per Repeater Builders
Skip step 6 & 7 on Repeater Builders and go to step 8 below.
Step 8: Use a small screwdriver and loosen coils on the cardboard forms by pushing up and down on the form. This will make for easy removal when you remove cardboard forms.
Step 9: Use a very small wire cutter and cut the base of the cardboard form on the housing. Note, there is a step up on the housing the form sits on. Twist the cutters side to side as much as possible, until form is free from housing. Remove tube. Clean out remains of tube and epoxy. Step in casting will re-align new tube.
Step 10: Using a similar form (we had plastic), glue in place. I used a commercial hot glue gun. wd7f removed the wire coil on the form, I cut off the washer end and trimmed the slug to 1/4" as our slugs were to long. I trimmed the slug with a Allen wrench inserted up to the trim point. Using a wire cutter (small) I cut a thread or 2 at a time. Note: Have extra on hand just in case you break one.
Step 11: Drill .125 holes in cover. Measure, mark, drill out over slugs for adjustment. It was wd7f that suggested this and pointed out there would be no loss at the frequency with that hole size. Re-assemble, install cover.
Step 12: We took a HT on our transmit frequency, 1 watt, into a dummy load. The scope was connected with a "T" into the output of the filter. We keyed the HT and watched the pattern and adjusted it with our plastic hex head tool for the widest pattern we could get. One slug at a time and repeat.
Step 13: Then installed a watt meter and checked the power through the filter, and then with a RCA female union in place of the filter. We picked a union that had no or low loss. We measured 1.02 dB loss through the filter.
These were the coil forms we modified. Notice the .125 holes in the cover for each slug adjustment.
Page recreated by: David Stanford k7iou Copyright 7/01/2005 B.A.R.T. and k7iou