[aprssig] Re: digi on old gear (Second Try!!)

Stephen H. Smith wa8lmf2 at aol.com
Wed Mar 5 19:41:48 EST 2008

Autoinsert of my signature lines trashed the original reply to your 
post.  Here it is again with the sig at the bottom where it should be 
and some slight changes in comments.

Chris Kantarjiev wrote:
> I just met Alan K6LSU, who would like to set up a digi at his QTH above
> Oakhurst (looking south towards Fresno, unfortunately, which means he
> may have a hard time hitting an igate ... one problem at a time).
> He's got a varied assortment of old gear: a Kantronics "KAM" TNC, a
> Toshiba Satellite laptop (Win98). He's got a Kenwood TM-731 dual-bander
> for the radio.
> I'm pretty sure that the KAM won't digi by itself

It does digipeat standalone.    For a home station first-hop fill-in 
digi, just set the alias to WIDE1-1    [Actually the KAM has the *SAME* 
digipeat firmware as the KPC3 (not plus) Ver 7.2;   i.e. highly obsolete 
for today's WIDEn-N "New Paradigm standards, but completely adequate for 
a simple home fill-in digipeater in standalone mode.  And the firmware 
rev is irrelevant when the TNC is under control of an external computer 
in KISS mode. ]

> , though it appears to implement KISS in almost all versions of the 
> firmware (according to the Kantronics website).

Yes it does do KISS.  I have a KAM with both ports running that is 
creating these maps on my webserver:

    Continental HF 30M:     http://wa8lmf.dyndns.org:14439/
    LA Area VHF:                http://wa8lmf.dyndns.org:14439/mapVHF.htm
The AGW packet engine splits the KISS data stream from the KAM into two 
virtual steams for use by two copies of UIview running on the same PC.

> What might he run? Digined, perhaps?

Or UI-View which implements a very intelligent configurable digipeater.  
(As with any PC-based digipeater application, the computer must have 
acces to the raw packets which means running the TNC in KISS mode. ) You 
could have UIview access the KAM in KISS directly,  or arbitrated by 
AGWpe which always places TNCs in KISS mode.

> He's got
> the TNC hooked up to the mic connector ... I don't know how much he
> cares about using it for voice on the local repeater, too.
> It appears, too, that there may be some problems with getting the
> unsquelched audio through that connector - does the KAM do software DCD?
Yes it does.  You have to initially run the unit in the command mode 
(i.e. not KISS) with a basic ASCII terminal like HyperTerm, to command 
DCD to soft.   There are three options:  NONE (default), SOFT, or 
EXTernal hardware detect (i.e. sense the squelch/"busy" light in the radio.

You can then let your digipeater application or AGW set the TNC to KISS 
mode.  Whatever DCD mode was selected remains active.    
The main issue is that the audio level on the Kenwood mic jacks is very 

The messiest part of dealing with the KAM is that there are *two* TNCs 
in the box (one 1200-baud VHF and one 110/300 baud HF unit).  Every 
command for things like callsigns, DCD mode, etc has to have two 
arguments, for the two sides of the unit.  For example "MYCALL  

> http://www.radiomods.co.nz/kenwood/kenwoodtm731.html seems germane...

What the notes are saying is that the audio at the mic jack is low-level 
unquelched un-de -emphasized raw discriminator audio; i.e. the perfect 
place to connect a TNC.
You *have* to connect a TNC here for 9600 baud operation.   But it's 
also an advantage to connect here for 1200 since the front panel volume 
and squelch controls won't affect how the TNC receives.  

The main dis-advantage is that the raw discriminator output is low-level 
(about 50-100 millivolts) and may need an audio pre-amp to keep the KAM 
happy.  [The KAM does have an internal jumper for selecting audio 
de-emphasis when connected directly to discriminator audio rather than a 
speaker.]  You may have to hack resistors on the KAM VHF input to raise 
the audio sensitivity, or throw together a basic op-amp audio preamp to 
boost the receive audio 5-10x so the KAM works reliably.


Stephen H. Smith    wa8lmf (at) aol.com
EchoLink Node:      14400    [Think bottom of the 2M band]
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