[KYHAM] Repeater tone work-arounds

[William Call]

Ron AG4TY mentioned his solution of a DTMF command sequence to temporarily 
turn off a repeater's CTCSS requirement.  Good idea.  Here's some more 
possibilities.

We use CTCSS on the Murray 146.940 repeater, but have added work-arounds 
for users without tone encoding capability.  The first one works like this: 
a timer circuit provides a window of about 2 seconds after the repeater is 
unkeyed, during which a carrier-only signal can gain access.  After the 
two-second window, PL is again required to open the repeater.  So a user 
without tone can jump in during this window and answer (or call) someone.

It's not a perfect solution--a person without tone still can't open the 
repeater when it is quiet.  And distant signals from other areas can grab 
the repeater during those two-second windows.  But still, this provides 
some relief to total lockout of a tone-only repeater, while greatly 
reducing undesired keying of the repeater.  We have tried varying window 
times over the years, and two seconds seems to be the best compromise.

We have a second work-around that involves a single-tone decoder of 1477Hz, 
which triggers the repeater and opens that timer window.  This circuit 
allows a user with a good set of lips to access the repeater, by just 
whistling it up!  Or, a DTMF pad that will generate a single tone when two 
column buttons are depressed simultaneously can be used to open the 
repeater.  The "3" and "6" buttons are usually used--that column generates 
the 1477Hz tone.  The older hardware tone encoders would do this; most 
modern microprocessor-controlled radios won't produce the single common 
tone, however.

This isn't a perfect solution, either.  The decoder has to be set up to 
require a tone of some length and purity, or speech components in undesired 
signals will get through.  If the purity requirement is set too high, few 
operator's whistles will work.  And modern radios won't generate the single 
tone (but they usually provide PL anyway).  A fair amount of adjusting is 
required to get the circuit just right.

Even with the limitations of these work-arounds, they do help make the 
repeater more accessible to users with older radios, while still providing 
the desirable interference protections of tone-access.  I presume that 
these devices, a solution of many years' standing for us, would still 
satisfy the requirements of SERA for tone access on repeaters.

Hope this helps someone.

73,

Bill Call KJ4W
Murray, KY