Re: TNC Quirks

Joshua KJ7LVZ

On Sat, May 22, 2021 at 01:21 PM, David Ranch wrote:
Hello Joshua,

Your first sentence isn't complete so I cannot tell if you ARE able to create a connection or not but I'm assuming KJ7LVZ-9 (D710 TNC) to KJ7LVZ-2 (BPQ32) works.  It's the reverse path that isn't responding.  Do you have CONOK enabled on the receiving D710 TNC?

   Here is a cheat-sheet that might help
Sorry David, the correct word is "established".  I was able to establish a connection between the TNCs one direction but not the other.  CONOK was on for both TNCs.  Thank you for the link to the cheat-sheat.  I had seen that and was using it along with the manual.  I hacked away at this for a while and realized two things. First, the handheld(s) I was using wasn't quick enough and wasn't doing a good job at receiving packets.  I moved my KISS TNC from a handheld to my TM-V71A and I stopped losing packets.  Second, the TM-D710G wasn't accepting a connection request from its own callsign, even with a different SSID.  I used my wife's callsign for one of the radios and the connection was established on the first try.  So, #1 has been solved.
2. When I am trying to write a message on the Kenwood using the W command, it's all fine and dandy until I want to exit the body using (return), (CTRL+C), (return).  All I get is new lines, the message never finishes.  The only way for me to exit the message is to restart the TNC. 

When you start the message, the TNC prompts you with:

   You terminate with either a <cr>/EX<cr> or <cr><ctrl-Z><cr>

I recommend to use "/ex" as that seems to be the common standard
The "/ex" option works.  I saw it on one of my connections and gave it a try.
#2 is solved.

3. What's the importance of PACLEN?  The TNC on the handheld defaults to 236 even though I have the config file set to 128 and the Kenwood defaults to 128.  They connect fine with different PACLENs.  I can set them the same and everything is still kosher.

PACLEN is the AX.25 payload MTU and the bigger it is, the faster your throughput *could* be assuming you have perfect RF conditions.  If you have poorer RF conditions, you might consider using something smaller like 128 bytes as well as use a smaller packet window (aka "MAXFRAME").   Generally speaking, these are some of the common settings:

   - Excellent RF conditions for UHF/VHF AX.25 - PACLEN: 255
   - Excellent RF conditions for UHF/VHF AX.25 over NETROM - PACLEN: 236

   - Decent RF conditions for UHF/VHF AX.25 - PACLEN: 128
   - Decent RF conditions for HF AX.25 - PACLEN: 64

   - Poor RF conditions for any packet: forget about it - the retries will kill any effective communications

Btw, I have another cheat sheet that takes new Packet users through the using connected and unconnected packet operations here:

PPs.  You can find ALL TNC commands in the "TNC COMMANDS LIST" section (PDF page 36) of Kenwood D710 instruction manual -


Thank you for the explanation of PACLEN.  I wasn't sure if one TNC set to a packet length of 128 would have a problem receiving a packet with more than 128 bytes.  Sound like that is not the case. 
I love manuals and already have the full Kenwood manual on my computer to reference.  I will definitely look at the "Getting Started With Packet Radio" document you sent.

Thank you for the help.  

Since I want to be able to use my TM-V71A with packet radio also and I currently have a homemade Mobilinkd style TNC connected to it for APRS, I decided to try a TNC emulator with that setup.  I use a MacBook as my laptop and that has hindered me greatly but where there is a will, there is a guy who will spend his whole weekend making a way.  I now use a Raspberry Pi Zero W running linBPQ and G8BPQ's Simple KISS configuration.  I connect to the Pi over wifi, SSH into it, start the emulator, open another SSH terminal, start a minicom terminal, and use that as my TNC interface.  It's quite a software dance but it seems to work!

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