[arm-allstar] Testing AllStar installation on RP3

Doug Crompton wa3dsp at gmail.com
Fri Sep 7 13:13:44 EDT 2018


I found this on the TR7950.  I assume thats what you meant.


It doesn't tell you anything about COS though.  If the light on the front
panel follows squelch it would probably work. The issue is that using just
squelch can be problematic especially if you have noise in the area. It
would trigger COS and if you were connected to other nodes it would show up

That being said COS is keyed through a Schottky diode which point out TO
the radio. Thus no radio voltage would go to the FOB and cause damage. So
make sure the FOB you are using has that diode. Most all do. So you need to
pickup a COS signal from some place that is 0 volts as a low and goes to
some high voltage (above 2V).  It does not matter if it goes high on RX
signal or low as you can set that with cosfrom=usb for a high signal on key
or =usbinvert for a low signal. Going low is preferred but not required.

I would probably take the voltage on the indicator and go through about a
4.7K to the base of an NPN transistor like a 2N3904. Ground the emitter and
the collector could be another 4.7K to 12V. Take COS from the collector. It
will go low on signal.

Her eis a link to the service manual if you don't already have it -


Let me know how it works out.

*73 Doug*


*http://www.crompton.com/hamradio <http://www.crompton.com/hamradio>*

On Fri, Sep 7, 2018 at 12:58 PM "Tom Corcoran via ARM-allstar" <
arm-allstar at hamvoip.org> wrote:

> Hello Doug,
> I agree with your suggestion to Rich. In fact, if you are planning to use
> node primarily to monitor, I find the radio-free configuration is great.
> On a related point, I have a URI/RPi and I’d like to use an old KW 7950 as
> an ALLSTAR node. Not sure where/how to find COS point on the 7950. Advice?
> There is squelch light on front panel. Is there some way I can use it?
> Tnx ... Tom VE3NY
> Thomas F. Corcoran, P.Eng, MBA, ICD.D
> Chair, Health Professions Regulatory Advisory Council (HPRAC)
> Chairman
> NexgenRx Inc.
> 185 the West Mall
> Suite 600
> Toronto, Ontario, M9C 5L5
> Tel: +1 416 695 3393 X804
> Cell: +1 416 602 0946
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