digipi APRS with CTS pin to control tx of aprs , how to please !

[Serge Berube]

I am looking to control the transmission of aprs traffic when we are using the local 2m  repeater in the same site  transmitting at 145.41,  rx at 144810 mhz. Is there a way to disable the aprs tx , with a signal applied on the cm108 or on a gpio pin of the raspberry pi ? I am using a raspberry pi 3 B+ for the job... Any help will be very appreciated.

Best regards, Serge ve2abc

[Craig]

Hi Serge,

I would leverage a fet (transistor) to disable the ptt wire coming out of the cm108, you might need
two to invert the logic.



cool,
-craig
KM6LYW

On 3/29/26 5:24 PM, Serge Berube wrote:

I am looking to control the transmission of aprs traffic when we are using the local 2m  repeater in the same site  transmitting at 145.41,  rx at 144810 mhz. Is there a way to disable the aprs tx , with a signal applied on the cm108 or on a gpio pin of the raspberry pi ? I am using a raspberry pi 3 B+ for the job... Any help will be very appreciated.

Best regards, Serge ve2abc

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[Serge Berube]

Thanks for the idea , but the issue is not to stop the aprs transmission , this could be done with a signal from the  local vhf repeater whenever it is transmitting or receiving , which is the same. What i am looking for is a way to tell the digipi  software to wait for transmissions until the vhf rrepeater in off the air so that the aprs transmitter will not desensitise the vhf receiver.  it should be named a RTS   request to transmit pin  that will permit the digipi to buffer his messages until this pin is asserted  at the end of traffic on the vhf repeater with a kingd of CTS  signal " Clear to send "

Thanks for help,  , Serge VE2ABC

[Craig]

yah, that's what I gathered, it's an interesting idea.  At this point there's no way
to signal the software to suspend.   You might ask the question on the direwolf
github/mailing list.   Direwolf will suspend if it hears an afsk carrier to avoid
collisions, but I don't know if your vhf repeater can trick that.

-craig
KM6LYW

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[Doug Reed, N0NAS.]

I'd try to avoid that solution. APRS transmissions are intended to be "time sensitive" and ephemeral. Delivery is not guaranteed and the "new paradigm" specifically wants all digipeater retransmissions to occur immediately after the original transmission ends. This was intended to cut down on the packet storms that used to occur when multiple WIDE digis wanted to send their copy of the packet and were being polite about it. And think about position packets. A person driving around sends position packets and if you "store" those packets for delayed transmission, you are jumping his track back to an old position. The only real loss would be a message transmission, but there we are back to ephemeral and delivery not guaranteed. 

73, Doug Reed, N0NAS.