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Posted: 4/11/2017 4:46:34 PM EDT
I figured that I would ask here first because 1. you guys da bess and 2. I know we have a few packet folks here.

I picked up a KAM-XL for cheap that appears like new.  I have wanted to play with 9600 packet and winlink, but our local 9600 nodes are down for a little while so it may be a bit before I can check out the 9600.  I've got some experience with packet, mostly playing with myself, winlink, APRS, and our local packet node - all 1200 baud using mainly my KPC-3+.  Radio is a Kenwood TM-v71a.  No problems up to this point.  Wanted to test out the KAM-XL, at least on 1200...

Now here's my issue:  The KAM-XL seems to do just fine TXing.  No issues on APRS, winlink, or the packet node getting heard on 5w or 50w.  RX, however is a different story.  The KAM-XL does fine with short packets from strong signals.  Weak signals (as heard audibly) are not decoded well or at all.  Short signals (ack, short data burst, etc) from the packet node (or logging in to the APRS digis) are fine, but longer bursts (i.e. responses from help, MH, or info commands) do not decode well, often times taking several retries to get the burst of data decoded.  TX on my end seems to be fine, as I don't see any repeat requests from the other station, even at low power.

Trying to replicate the situation with the KPC-3+, I get much much better decodes on weaker signals like APRS mobiles, and the "long" packets decode just fine... no repeat requests or missed packets at all.  This makes me think that it is not a radio, cable, or computer issue.

I went through the (incredibly long) manual for the KAM-XL, and have gone over all of the jumpers and set them in what I believe are the correct settings.  I have also set the TX deviation (by ear) as I don't have a proper monitor for that, but again I have no TX issues that I'm aware of.  There are no settings to adjust RX level or whatever that I can find.  No potentiometers inside the TNC.

The only other idea that I have come up with is that the TM-V71a has a software setting to adjust the TX and RX sensitivity on the packet port.  I haven't had a chance to fool with that yet, but I would think that if one Kantronics TNC worked, then the other would as well.

Any words of wisdom or suggestions?  I'd appreciate help, especially from someone with experience with this TNC.

Edit:
Figure I'd add: Only V/UHF packet so far (and only 1200 now), no HF or other modes yet.
Link Posted: 4/17/2017 3:07:53 PM EDT
[#1]
Fat lot of help you guys are
Link Posted: 4/18/2017 10:50:43 AM EDT
[#2]
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Quoted:
Fat lot of help you guys are
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My only experience with the Kamtronics line is receiving one in the mail and sticking it on the shelf with all the other projects I haven't gotten to yet.  Did you find any answers?
Link Posted: 4/18/2017 12:59:32 PM EDT
[#3]
Not yet.  Shack computer HDD crashed this weekend so I had to deal with that.  I've also got some power line noise issues that may be impacting weaker packets.  I'm still working my way through it.
Link Posted: 4/19/2017 10:00:50 AM EDT
[#4]
Sounds like it could be the level of audio out of the radio.  Got it connected to the 1200 or 9600 pin of the data jack?  I keep my PK900 connected to the 9600 pin of my FT7900, and turn on 9600 mode when needed.  Not that familiar with the KAMXL, even though I have one, haven't played with it much.  Damn things are still $400 new.    Does it have different equalizers you can select?  Sometimes a non equalized signal is better for radios with data ports, and equalized for connecting to the mic/speaker jacks.
Link Posted: 4/19/2017 10:35:39 AM EDT
[#5]
Only 1 data port on the radio, but it does have software settings to change it from 1200/9600.  I may try running 1200 at the 9600 setting to see if the change differences in pre/de emphasis makes any difference.

There is also a software setting via the PC to change the data port signal level.  I guess I have to find the time to guess-and-check my way through all of the setting combinations to see what works best, if anything.
Link Posted: 4/20/2017 7:20:14 PM EDT
[#6]
Well I guess I figured it out.  Really cranking the data port output setting up in the Kenwood software seemed to take care of the issue.  Guess this one is just less sensitive than the other TNCs I have.
Link Posted: 4/21/2017 9:58:29 AM EDT
[#7]
That could be a blessing.  Will probably have a better s/n ratio if the signal that you're sending out the data port is a higher voltage.  I know car audio systems have done this over the years.  Head units used to have a 1v pre-out, now most of them are between 4v and 8v, so noise floor is effectively lowered in comparison to the signal.
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