Re: PiTNC9k6 and BTECH UV25X4 mobile

Brian Webster

Is the device actually on devSerial0? From the video and description of the problem I would check that setting first. In Linux I thought the first serial port was ttyS0.


If that is not the issue I would back the receive audio way down. Most times you can get away with much less than 50%, 25% from my experience works well. Too hot and the audio gets distorted and the TNC can’t decode it. Remember is trying to detect 2 different audio tones to convert to digital, too hot audio can make it difficult to distinguish the difference in the tones. I good method of tuning for receive audio is to turn the volume down to nothing, then move up until the DCD light starts to flicker when you know there are packets on the air.


Another thing to check would be the port settings on Xastir. The serial connection speeds can be different than the on air speed. The TNC and Xastir need to match. This is probably not the case for you if your transmitted packets are being decoded.


One last thing to check would be your squelch setting on the radio. I have had very bad luck using cheap Chinese radios for connected packet, mostly because the recovery time of the receiver is not fast enough compared to other radios, so what happens is the first part of the packet is not received. It’s one thing to hear a packet and see the DCD light, quite another to hear the whole packet without errors. In connected packet you can kind of hear it because you would hear a lot of retries, APRS is unconnected packet (outside of messages) so there is no error checking and acknowledgement (ack’s) packets sent. Think of APRS as UDP vs connected packet as TCPIP. One is just a broadcast protocol and if you get the packet you get it, no retries.


If you have a local connected packet network you can try not on the APRS frequency, move over to it, use the terminal window and try connecting to a local packet station and see if you are getting a lot of retries.


One other thing to consider, on some radios there are different connection points for receive audio for 1200 baud vs 9600 baud TNC’s, 9600 needs discriminator audio and 1200 baud uses regular speaker audio. If you are hooked to the discriminator audio point, 1200 baud APRS packets are likely not going to work. If you are using VOX to key the radio it is also quite possible you have that set so that the other packets are coming in before your radio has fully unkeyed. To test that just turn Vox off and set the radio to decode packets without trying to transmit.


Brian N2KGC


From: [] On Behalf Of N5XMT
Sent: Wednesday, June 17, 2020 3:50 AM
Subject: Re: [RaspberryPi-4-HamRadio] PiTNC9k6 and BTECH UV25X4 mobile


Here is a link to the quick vid I made

On Jun 17, 2020, at 00:40, "N5XMT via" < target=_blank>> wrote:

Making sure it would talk to the TNC, no radio connected.  Should ptt and dcd both come on with no input to the PiTNC?  Here is a short vid...

On Jun 16, 2020, at 23:31, Mat Murdock < mat.murdock@...> wrote:

Ok, download and flash the stand alone firmware to you tnc.  It should show up as a com port on your computer now.  Start up Winlink Express and start a packet session.  Configure you TNC settings as show below.



Try connecting to a local node.


Also, it would probably be a good idea to send a clear picture of the top of your TNC to verify everything is in order.




On Wed, Jun 17, 2020, 12:17 AM N5XMT < dacooley@...> wrote:

There are a couple nearby, and have access to 4 windows computers here! 

On Jun 16, 2020, at 22:49, Mat Murdock < mat.murdock@...> wrote:

Is there a Winlink node in your area?  Do you have access to a Windows computer?


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