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Radio Broadcast Technical Consulting and Sales
10032 Island Drive, Brainerd, MN  56401


Technical Tips from Mark W. Persons
Collins AM RF Switch Improvement

This RF switch came into the shop for repair.  It was built by Collins Radio probably in the 1950's. 

The switch is used to connect and disconnect an RF ammeter in an antenna coupling unit at an AM broadcast transmitter site.

The large circle with four small holes around it is a 2-13/16" diameter hole for mounting a thermocouple ammeter. 

The 1/2" diameter switch suffered a failure when one of the top contact pieces wore out. (see below)           

Replacing a contact and cleaning the brass pieces made it look like this. 

The problem was that the mechanical tolerances were so difficult to maintain that another failure is very likely.

The revised version looks like this.  Beryllium-copper strips are now held in place by springs.

These springs, with their inherent inductance, are not normally a good choice in an RF circuit.

However, the actual RF contacting is done on the machined solid-brass blocks.

Springs are used to hold the 1/2" diameter control rod tight to the blocks.

Shown on the ruler is the worn-out beryllium-copper strip that needed to be replaced.

The stories go on and on.  Stop in again sometime.  I'll leave the soldering iron on for you. 
Mark W. Persons   Ham WMH      

Questions?  Email Mark Persons:  teki@mwpersons.com       

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page last edited 02/21/2016