[TenTec] Rationale for the PROC selection of the Inrad Roofing Filter

[Dave Bowker]

This is to clarify my rationale for using the PROC switch to activate the Inrad roofing filter 
modification.  For those not familiar with the history of this, I performed this modification to my 
Omni VI+ (opt 3) over 2-1/2 years ago while testing various home-designed roofing filters, and 
needed a front panel selection capability so that I could record A/B test data while still keeping 
the N1 (500 Hz) and N2 (250 Hz) filters independently selectable.



The primary requirements (for the modification of the Inrad roofing filter implementation) were: 
(1) the implementation needed to simply take the roofing filter selection off of the N1/N2 buttons, 
(2) without incurring any additional components, with a (3) minimum of effort, and (4) with minimal 
impact to other operating modes and functions.  These requirements narrowed the design to only one 
choice of front panel switch . the PROC switch, which is a "hard" switch with push-push states.



The question has been raised on the reflector as to why not use the FM or VOICE or other main keypad 
switches to select the Inrad roofing filter, switches that (appear to) have less of an impact on 
operational modes than the PROC switch.



The first reason is that ALL of the main keypad switches are "soft" switches, which are scanned by 
the microprocessor, and do not provide a permanent status of the selected state.  Use of any of the 
soft switches for this modification would require an additional PC board with buffer and latch 
circuits, contrary to requirements 1, 2 and 3, and would require removal of the Logic Board in order 
to implement the interface in hardware.   Further, use of the FM button would require a software 
change, as once the button is depressed; the radio is in the FM mode!



Use of the VOICE button on the main keypad would, in addition to the above four requirements, 
require the optional voice board to be installed, a further complication of requirements 1-4.



Dave, K1FK

Fort Kent, ME