[App_rpt-users] DMK URI COS Level / Kenwood TKR-850

[David McGough]

Hi Guys,

Kevin is correct about the URI's--they can be a bit ticklish when used in
an active-low configuration; I have personally experienced these issues!
.....And, that's why I recommended a COS active-high configuration, 
including a COS pull-down resistor (any convenient value from 10K to 27K 
or so should be fine) to insure COS turns off.

I can post a schematic if needed, but, the COS wiring is simple: COS/TOR
output from the TKR repeater goes to pin 8 on the URI and a pull-down
resistor goes from URI pin 8 to ground.  Then, set the TKR for COS-high
signaling, and set carrierfrom=usb in the AllStar config file
(usbradio.conf or simpleusb.conf).  This combination works 100% on all
eight version 2 TKR-750/850 I've got installed currently. I fully expect
it'll work properly on version 1 hardware, too--I just haven't personally 
tried it.


73, David KB4FXC




On Sat, 9 May 2015, Kevin Custer wrote:

> On 5/9/2015 1:49 PM, John wrote:
> > Is the 0-5 Volt COS swing on a Kenwood TKR-850 sufficient to switch 
> > the COS on a DMK URI? Can't seem to get my system to repeat. I'm out 
> > in the 'boondocks' with very few parts and a long way from a Radio 
> > Shack. Just hoping I don't need to buffer the COS somehow to get it to 
> > switch.
> 
> All FOB's, including the URI, but the exception of a RIM, require a 
> logic signal capable of sinking to near ground potential on the COS and 
> CTCSS inputs (active low).  No matter if you choose a upright logic or 
> inverted (in software) the hardware needs to provide a signal that goes 
> nearly to ground.  In other words, it needs to sink to ground 
> potential.  Many radios provide a voltage when the logic state is valid 
> (active high), these don't interface to a FOB or URI well.  A pull-down 
> resistor can help in these situations, but it's best to use the right 
> type of logic circuitry to feed these logic inputs.
> 
> Since the CM119 IC is internally pulled up, changing its logic state 
> requires a ground.  This was originally done by mechanical switches in a 
> FOB, but must now be done with transistors or whatever logic is 
> available from the radio.  Protection diodes on these inputs help to 
> complicate the situation because they have a voltage drop.  The hardware 
> inputs of the CM119 require that the voltage drop to about 1V or less to 
> become valid.  While Schottky diodes keep this to a minimum (because 
> their voltage drop is about 2/3 that of a silicon diode), you still need 
> a solid pull to ground logic signal for a valid COS or CTCSS signal for 
> a URI or simple FOB.
> 
> Some radios are difficult to properly interface the COS and CTCSS logic 
> to a FOB or URI.  I have a board that I designed just for the occasion:
> http://www.repeater-builder.com/w3kkc/products/squelch/sc50.html
> 
> My suggestion is to use a NPN transistor or FET to invert the active 
> high TKR-850 logic for a solid pull to ground.  A 2N2222 or 2N7000 can 
> work well.
> 
> Kevin
>